阅读说明：本技术 超声换能器 (Ultrasonic transducer ) 是由 尼古拉斯·克里斯·查加雷斯 埃里克·M.·里德 卡奇克·卡沙菲安 于 2019-07-31 设计创作，主要内容包括：提供了一种超声换能器及其设计和制造方法。该超声换能器包括压电复合材料层,该压电复合材料层用于与样品声学通信,并且具有至少部分经解耦的声阻抗和电阻抗特性。压电复合材料层包括各自由压电材料制成的间隔的压电区域的阵列、位于相邻的间隔的压电区域之间的包括聚合物基体的填充材料和与聚合物基体接触的非压电材料。在一些实施方案中,超声换能器包括在压电复合材料层上延伸的电绝缘非压电复合材料层,用于使压电复合材料层与样品电绝缘,该电绝缘非压电复合材料层与压电复合材料层和样品声学匹配。(An ultrasonic transducer and methods of designing and manufacturing the same are provided. The ultrasonic transducer includes a piezoelectric composite layer for acoustic communication with a sample and having at least partially decoupled acoustic and electrical impedance characteristics. The piezoelectric composite layer includes an array of spaced piezoelectric regions each made of a piezoelectric material, a filler material including a polymer matrix between adjacent spaced piezoelectric regions, and a non-piezoelectric material in contact with the polymer matrix. In some embodiments, the ultrasonic transducer includes an electrically insulating non-piezoelectric composite layer extending over the piezoelectric composite layer for electrically insulating the piezoelectric composite layer from the sample, the electrically insulating non-piezoelectric composite layer being acoustically matched to the piezoelectric composite layer and the sample.)

1. An ultrasonic transducer comprising:

a piezoelectric composite layer for acoustic communication with a sample and having at least partially decoupled acoustic impedance and electrical impedance characteristics, the piezoelectric composite layer comprising:

an array of spaced piezoelectric regions, each of the spaced piezoelectric regions being made of a piezoelectric material having a first acoustic impedance and a first relative permittivity;

a filler material between adjacent spaced piezoelectric regions, the filler material comprising a polymer matrix having a second acoustic impedance and a second relative permittivity, the second acoustic impedance being less than the first acoustic impedance and the second relative permittivity being less than the first relative permittivity; and

a non-piezoelectric material in contact with the polymer matrix, the non-piezoelectric material having a third acoustic impedance and a third relative permittivity, the third acoustic impedance being greater than the second acoustic impedance and the third relative permittivity being less than the first relative permittivity; and

one or more electrodes in electrical communication with the piezoelectric composite layer.

2. The ultrasonic transducer of claim 1, wherein:

the piezoelectric composite material layer is used for generating a detection sound signal towards the sample; and is

The one or more electrodes are operable to send a probing electrical signal to the piezoelectric composite layer to generate the probing acoustic signal.

3. The ultrasonic transducer according to claim 1 or 2 wherein said piezoelectric composite layer is adapted to receive a sample acoustic signal emanating from said sample, thereby generating a sample electrical signal towards said one or more electrodes, said sample electrical signal being representative of said sample acoustic signal.

4. The ultrasonic transducer according to any one of claims 1 to 3 wherein said polymer matrix is made of epoxy.

5. The ultrasonic transducer according to any one of claims 1 to 4 wherein said non-piezoelectric material is hafnium oxide powder.

6. The ultrasonic transducer according to any one of claims 1 to 5 further comprising one or more electrically insulating regions between adjacent spaced piezoelectric regions, said one or more electrically insulating regions being in contact with said filler material.

7. The ultrasonic transducer of claim 6, wherein said one or more electrically insulating regions have a fourth acoustic impedance and a fourth relative permittivity, said fourth acoustic impedance being close to said first acoustic impedance, and said fourth relative permittivity being less than said first relative permittivity.

8. The ultrasonic transducer according to claim 6 or 7 wherein said one or more electrically insulating regions are made of ceramic.

9. The ultrasonic transducer according to claim 6 or 7 wherein said one or more electrically insulating regions are made of glass.

10. The ultrasonic transducer according to any one of claims 6 to 9 wherein said one or more electrically insulating regions have an elongated shape.

11. The ultrasonic transducer according to any one of claims 6 to 9 wherein said one or more electrically insulating regions define a rod-shaped electrically insulating region.

12. The ultrasonic transducer according to any one of claims 6 to 9 wherein said one or more electrically insulating regions define a columnar electrically insulating region.

13. The ultrasonic transducer according to any one of claims 6 to 9 wherein said one or more electrically insulating regions are spherical.

14. The ultrasonic transducer according to any one of claims 1 to 13 wherein said non-piezoelectric material is embedded in said polymer matrix.

15. The ultrasonic transducer of any one of claims 1 to 14, wherein:

the piezoelectric material is continuous in one direction; and is

The filler material is continuous in three directions.

16. The ultrasonic transducer of any one of claims 1 to 14, wherein:

the piezoelectric material is continuous in two directions; and is

The filler material is continuous in two directions.

17. The ultrasonic transducer according to any one of claims 1 to 16 wherein said piezoelectric material is selected from the group consisting of ferroelectric materials, single crystal ferroelectric materials, lead-free ferroelectric materials and piezoelectric polymer materials.

18. The ultrasonic transducer of claim 17, wherein said piezoelectric material is lead zirconate titanate (PZT).

19. The ultrasonic transducer according to any one of claims 1 to 18 wherein said acoustic impedance characteristic is in the range of about 15MR to about 30 MR.

20. The ultrasonic transducer according to any one of claims 1 to 19 wherein said first acoustic impedance is in the range of about 30MR to about 40 MR.

21. The ultrasonic transducer according to any one of claims 1 to 20 wherein said third acoustic impedance is in the range of about 7MR to about 8 MR.

22. The ultrasonic transducer of any one of claims 1 to 21, wherein said piezoelectric composite layer is acoustically matched to said sample and electrically insulated from said sample.

23. The ultrasonic transducer of any one of claims 1 to 22, further comprising a backing layer in electrical communication with said one or more electrodes.

24. The ultrasonic transducer of claim 23, wherein the backing layer is a dematching layer.

25. The ultrasonic transducer of any one of claims 1 to 24, further comprising a ground electrode.

26. The ultrasonic transducer of claim 25, wherein said ground electrode is configured as a heat sink.

27. The ultrasonic transducer of any one of claims 1 to 26, wherein an acoustic path is defined between said piezoelectric composite layer and said sample, said ultrasonic transducer further comprising a near-lossless acoustic matching layer located between said piezoelectric composite layer and said sample along said acoustic path.

28. The ultrasonic transducer of any one of claims 1 to 27, further comprising an abrasion resistant layer acoustically matched to the piezoelectric composite layer.

29. The ultrasonic transducer according to any one of claims 1 to 28 wherein said piezoelectric composite layer has a thickness of about 2400 microns.

30. The ultrasonic transducer according to any one of claims 1 to 29 wherein each spaced piezoelectric region is spaced from each other by 200 microns and has a square cross-section that is 1000 microns by 1000 microns.

31. The ultrasonic transducer according to any one of claims 1 to 30 wherein said piezoelectric composite layer has a piezoelectric volume fraction of about 70% to about 80%.

32. The ultrasonic transducer according to any one of claims 1 to 31 further comprising an electrically insulating housing for housing said piezoelectric composite layer therein.

33. An ultrasonic transducer for emitting an acoustic signal towards a target, the ultrasonic transducer comprising:

a piezoelectric composite layer having at least partially decoupled acoustic and electrical impedance characteristics, the piezoelectric composite layer comprising:

an array of spaced piezoelectric regions, each of the spaced piezoelectric regions being made of a piezoelectric material having a first acoustic impedance and a first relative permittivity;

a filler material between adjacent spaced piezoelectric regions, the filler material comprising a polymer matrix having a second acoustic impedance and a second relative permittivity, the second acoustic impedance being less than the first acoustic impedance and the second relative permittivity being less than the first relative permittivity; and

a non-piezoelectric material in contact with the polymer matrix, the non-piezoelectric material having a third acoustic impedance and a third relative permittivity, the third acoustic impedance being greater than the second acoustic impedance and the third relative permittivity being less than the first relative permittivity; and

one or more electrodes in electrical communication with the piezoelectric composite layer, the one or more electrodes operable to send an electrical signal to the piezoelectric composite layer to generate the acoustic signal toward the target.

34. The ultrasonic transducer of claim 33, wherein said polymer matrix is made of epoxy.

35. The ultrasonic transducer of claim 33 or 34, wherein the non-piezoelectric material is hafnium oxide powder.

36. The ultrasonic transducer of any one of claims 33 to 35, further comprising one or more electrically insulating regions between adjacent spaced piezoelectric regions, said one or more electrically insulating regions being in contact with said filler material.

37. The ultrasonic transducer of claim 36, wherein said one or more electrically insulating regions have a fourth acoustic impedance and a fourth relative permittivity, said fourth acoustic impedance being close to said first acoustic impedance, and said fourth relative permittivity being less than said first relative permittivity.

38. The ultrasonic transducer of claim 36 or 37, wherein said one or more electrically insulating regions are made of ceramic.

39. The ultrasonic transducer of claim 36 or 37, wherein said one or more electrically insulating regions are made of glass.

40. The ultrasonic transducer of any one of claims 36 to 39, wherein said one or more electrically insulating regions have an elongated shape.

41. The ultrasonic transducer of any one of claims 36 to 39, wherein said one or more electrically insulating regions define a rod-shaped electrically insulating region.

42. The ultrasonic transducer of any one of claims 36 to 39, wherein said one or more electrically insulating regions define a columnar electrically insulating region.

43. The ultrasonic transducer of any one of claims 36 to 39, wherein said one or more electrically insulating regions are spherical.

44. The ultrasonic transducer of any one of claims 33 to 43, wherein said non-piezoelectric material is embedded in said polymer matrix.

45. The ultrasonic transducer of any one of claims 33 to 44, wherein:

the piezoelectric material is continuous in one direction; and is

The filler material is continuous in three directions.

46. The ultrasonic transducer of any one of claims 33 to 44, wherein:

the piezoelectric material is continuous in two directions; and is

The filler material is continuous in two directions.

47. The ultrasonic transducer according to any one of claims 33 to 46 wherein said piezoelectric material is selected from the group consisting of ferroelectric materials, single crystal ferroelectric materials, lead-free ferroelectric materials and piezoelectric polymer materials.

48. The ultrasonic transducer according to claim 47 wherein said piezoelectric material is lead zirconate titanate (PZT).

49. The ultrasonic transducer according to any one of claims 33 to 48 wherein said acoustic impedance characteristic is in the range of about 15MR to about 30 MR.

50. The ultrasonic transducer of any one of claims 33 to 49, wherein said first acoustic impedance is in the range of about 30MR to about 40 MR.

51. The ultrasonic transducer of any one of claims 33 to 50, wherein said third acoustic impedance is in the range of about 7MR to about 8 MR.

52. The ultrasonic transducer of any one of claims 33 to 51, wherein said piezoelectric composite layer is acoustically matched to said sample and electrically insulated from said sample.

53. The ultrasonic transducer of any one of claims 33 to 52, further comprising a backing layer in electrical communication with said one or more electrodes.

54. The ultrasonic transducer of claim 53, wherein said backing layer is a dematching layer.

55. The ultrasonic transducer of any one of claims 33 to 54, further comprising a ground electrode.

56. The ultrasonic transducer of claim 55, wherein said ground electrode is configured as a heat sink.

57. The ultrasonic transducer of any one of claims 33 to 56, wherein an acoustic path is defined between said piezoelectric composite layer and said sample, said ultrasonic transducer further comprising a near-lossless acoustic matching layer located between said piezoelectric composite layer and said sample along said acoustic path.

58. The ultrasonic transducer of any one of claims 33 to 57, further comprising an abrasion resistant layer acoustically matched to the piezoelectric composite layer.

59. The ultrasonic transducer of any one of claims 33 to 58, wherein said piezoelectric composite layer has a thickness of about 2400 microns.

60. The ultrasonic transducer according to any one of claims 33 to 59 wherein each spaced piezoelectric region is spaced from each other by 200 microns and has a square cross-section that is 1000 microns by 1000 microns.

61. The ultrasonic transducer according to any one of claims 33 to 60 wherein said piezoelectric composite layer has a piezoelectric volume fraction of about 70% to about 80%.

62. The ultrasonic transducer according to any one of claims 33 to 61 further comprising an electrically insulating housing for housing said piezoelectric composite layer therein.

63. An ultrasonic transducer comprising:

a piezoelectric composite layer for acoustic communication with a sample and having at least partially decoupled acoustic and electrical impedance characteristics, the piezoelectric composite layer comprising:

an array of spaced piezoelectric regions, each spaced piezoelectric region being made of a piezoelectric material;

a filler material located between adjacent spaced piezoelectric regions, the filler material comprising a polymer matrix; and

a non-piezoelectric material in contact with the polymer matrix;

an electrically insulating non-piezoelectric composite layer extending over the piezoelectric composite layer for electrically insulating the piezoelectric composite layer from the sample, the electrically insulating non-piezoelectric composite layer being acoustically matched to the piezoelectric composite layer and the sample; and

one or more electrodes in electrical communication with the piezoelectric composite layer.

64. The ultrasonic transducer of claim 63, wherein said electrically insulating non-piezoelectric composite layer comprises a region of high acoustic impedance electrically insulating material in contact with a second polymer matrix filled with a high density electrically insulating powder.

65. The ultrasonic transducer of claim 63, wherein said electrically insulating non-piezoelectric composite layer comprises an electrically insulating ceramic region in contact with a second polymer matrix filled with a high density electrically insulating ceramic powder.

66. The ultrasonic transducer of claim 63, wherein said electrically insulating non-piezoelectric composite layer comprises an electrically insulating glass region in contact with a second polymer matrix filled with a high density electrically insulating ceramic powder.

67. The ultrasonic transducer of any one of claims 63 to 66, wherein said electrically insulating non-piezoelectric composite layer is in a 13 configuration.

68. The ultrasonic transducer of any one of claims 63 to 66, wherein said electrically insulating non-piezoelectric composite layer is in a 22 configuration.

69. The ultrasonic transducer of any one of claims 63 to 68, wherein:

the piezoelectric composite material layer is used for generating a detection sound signal towards the sample; and is

The one or more electrodes are operable to send a probing electrical signal to the piezoelectric composite layer to generate the probing acoustic signal.

70. The ultrasonic transducer according to any one of claims 63 to 69 wherein said piezoelectric composite layer is adapted to receive a sample acoustic signal emanating from said sample thereby generating a sample electrical signal towards said one or more electrodes, said sample electrical signal being representative of said sample acoustic signal.

71. The ultrasonic transducer according to any one of claims 63 to 70 wherein said polymer matrix is made of epoxy.

72. The ultrasonic transducer of any one of claims 63 to 71, wherein the non-piezoelectric material is hafnium oxide powder.

73. The ultrasonic transducer of any one of claims 63 to 72, further comprising one or more electrically insulating regions between adjacent spaced piezoelectric regions, said one or more electrically insulating regions being in contact with said filler material.

74. The ultrasonic transducer of claim 73, wherein said one or more electrically insulating regions have a fourth acoustic impedance and a fourth relative permittivity, said fourth acoustic impedance being close to said first acoustic impedance, and said fourth relative permittivity being less than said first relative permittivity.

75. The ultrasonic transducer of claim 73 or 74, wherein said one or more electrically insulating regions are made of ceramic.

76. The ultrasonic transducer of claim 73 or 74, wherein said one or more electrically insulating regions are made of glass.

77. The ultrasonic transducer of any one of claims 73 to 76, wherein said one or more electrically insulating regions have an elongated shape.

78. The ultrasonic transducer of any one of claims 73 to 76, wherein the one or more electrically insulating regions define a rod-shaped electrically insulating region.

79. The ultrasonic transducer of any one of claims 73 to 76, wherein said one or more electrically insulating regions define a columnar electrically insulating region.

80. The ultrasonic transducer of any one of claims 73 to 76, wherein said one or more electrically insulating regions are spherical.

81. The ultrasonic transducer of any one of claims 63 to 80, wherein said non-piezoelectric material is embedded in said polymer matrix.

82. The ultrasonic transducer of any one of claims 63 to 81, wherein:

the piezoelectric material is continuous in one direction; and is

The filler material is continuous in three directions.

83. The ultrasonic transducer of any one of claims 63 to 81, wherein:

the piezoelectric material is continuous in two directions; and is

The filler material is continuous in two directions.

84. The ultrasonic transducer according to any one of claims 63 to 83 wherein said piezoelectric material is selected from the group consisting of ferroelectric material, single crystal ferroelectric material, lead-free ferroelectric material and piezoelectric polymer material.

85. The ultrasonic transducer of claim 84, wherein said piezoelectric material is lead zirconate titanate (PZT).

86. The ultrasonic transducer according to any one of claims 63 to 85 wherein said acoustic impedance characteristic is in the range of about 15MR to about 30 MR.

87. The ultrasonic transducer of any one of claims 63 to 86, wherein said first acoustic impedance is in the range of about 30MR to about 40 MR.

88. The ultrasonic transducer of any one of claims 63 to 87, wherein the third acoustic impedance is in the range of about 7MR to about 8 MR.

89. The ultrasonic transducer of any one of claims 63 to 88, wherein the piezoelectric composite layer is acoustically matched to the sample and electrically insulated from the sample.

90. The ultrasonic transducer of any one of claims 63 to 89, further comprising a backing layer in electrical communication with said one or more electrodes.

91. The ultrasonic transducer of claim 90, wherein the backing layer is a dematching layer.

92. The ultrasonic transducer of any one of claims 63 to 91, further comprising a ground electrode.

93. The ultrasonic transducer of claim 92, wherein said ground electrode is configured as a heat sink.

94. The ultrasonic transducer of any one of claims 63 to 93, wherein an acoustic path is defined between said piezoelectric composite layer and said sample, said ultrasonic transducer further comprising a near-lossless acoustic matching layer located between said piezoelectric composite layer and said sample along said acoustic path.

95. The ultrasonic transducer of any one of claims 63 to 94, further comprising an abrasion resistant layer acoustically matched to the piezoelectric composite layer.

96. The ultrasonic transducer of any one of claims 63 to 95, wherein said piezoelectric composite layer has a thickness of about 2400 microns.

97. The ultrasonic transducer of any one of claims 63 to 96, wherein each spaced piezoelectric region is spaced 200 microns from each other and has a square cross-section that is 1000 microns by 1000 microns.

98. The ultrasonic transducer of any one of claims 63 to 97, wherein said piezoelectric composite layer has a piezoelectric volume fraction of about 70% to about 80%.

99. The ultrasonic transducer of any one of claims 63 to 98, further comprising an electrically insulating housing for housing said piezoelectric composite layer therein.

Technical Field

The technical field relates generally to the field of acoustic energy, and more particularly to an ultrasonic transducer, related devices, apparatus methods, and techniques.

Background

The transmission of acoustic energy to and from the ultrasonic transducer is at least partially affected by acoustic impedance mismatches, e.g., differences in acoustic impedance between the material (e.g., piezoelectric ceramic) contained in the ultrasonic transducer and the material acoustically coupled to the ultrasonic transducer. In general, when the acoustic impedances of the ultrasonic transducer and the material match, the energy transfer between each other is improved.

It is generally known to those skilled in the art that impedance matching techniques exist for improving the transmission efficiency of acoustic waves across different materials. Such impedance matching techniques typically involve a tradeoff between bandwidth and efficiency, and have a degree of complexity. When large bandwidths are required, the design of the ultrasound transducer, including the matching system, can be more complex. Such complexity significantly increases the cost of the ultrasound transducer. Designing and implementing ultrasound transducers with large bandwidths remains a challenge, so the solutions known in the art remain fundamentally limited bandwidths.

Various materials are sometimes required to be acoustically coupled to the ultrasound transducer. Such materials can be used in many industrial and medical applications. Common examples include, but are not limited to, biological tissues (e.g., human and animal bodies), organic materials (e.g., wood and polymers), inorganic materials (e.g., metals), composite materials (e.g., carbon composites), and ceramics. The acoustic impedance of such materials ranges from about 1 Megarayl (MR) to over 60 MR.

Materials acoustically coupled with ultrasound transducers can be divided into four categories: materials with acoustic impedance higher than that of piezoelectric material (referred to herein as "first class"), materials with acoustic impedance close to that of piezoelectric material (referred to herein as "second class"), materials with acoustic impedance lower than that of piezoelectric material (referred to herein as "third class"), and biological materials with acoustic impedance much lower than that of most piezoelectric materials (referred to herein as "fourth class").

Examples of materials of the first category are, for example, but not limited to, tungsten, molybdenum, nickel and gold. The acoustic impedance of these materials exceeds about 45 MR. Examples of materials of the second category are, for example, but not limited to, brass, silver, zirconium, and cast iron. The acoustic impedance of these materials is between about 30MR and about 40 MR. Examples of materials of the third class are, for example, but not limited to, magnesium, aluminum, indium, titanium, and tin. These materials have acoustic impedances in the range of about 10MR to about 30 MR. Examples of materials of the fourth category are for example, but not limited to, fat, muscle or organs. The acoustic impedance of these materials is typically between about 1.2MR and about 1.8 MR. Bone is another example of a fourth class of materials and may have an acoustic impedance between about 5MR and about 8 MR. It should be noted, however, that this value may vary widely.

There remains a need for techniques, apparatuses, devices and methods that can alleviate or mitigate the problems in the prior art.

Disclosure of Invention

According to one aspect, there is provided an ultrasonic transducer comprising a piezoelectric composite layer for acoustic communication with a sample and having at least partially decoupled acoustic and electrical impedance characteristics; and one or more electrodes in electrical communication with the piezoelectric composite layer, the piezoelectric composite layer comprising an array of spaced piezoelectric regions, each spaced piezoelectric region being made of a piezoelectric material having a first acoustic impedance and a first relative dielectric constant; a filler material located between adjacent spaced piezoelectric regions, the filler material comprising a polymer matrix having a second acoustic impedance and a second relative permittivity, the second acoustic impedance being less than the first acoustic impedance and the second relative permittivity being less than the first relative permittivity; and a non-piezoelectric material in contact with the polymer matrix, the non-piezoelectric material having a third acoustic impedance and a third relative permittivity, the third acoustic impedance being greater than the second acoustic impedance and the third relative permittivity being less than the first relative permittivity.

In some embodiments, the piezoelectric composite layer is used to generate a probe acoustic signal towards the sample; and the one or more electrodes are operable to transmit a probing electrical signal to the piezoelectric composite layer to generate a probing acoustic signal.

In some embodiments, the piezoelectric composite layer is configured to receive a sample acoustic signal emanating from the sample, thereby generating an electrical sample signal towards the one or more electrodes, the electrical sample signal being representative of the sample acoustic signal.

In some embodiments, the polymer matrix is made of an epoxy resin.

In some embodiments, the non-piezoelectric material is hafnium oxide powder.

In some embodiments, the ultrasound transducer further comprises one or more electrically insulating regions located between adjacent spaced piezoelectric regions, the one or more electrically insulating regions being in contact with the filler material.

In some embodiments, the one or more electrically insulating regions have a fourth acoustic impedance and a fourth relative permittivity, the fourth acoustic impedance being proximate to the first acoustic impedance, and the fourth relative permittivity being less than the first relative permittivity.

In some embodiments, one or more electrically insulating regions are made of ceramic.

In some embodiments, one or more electrically insulating regions are made of glass.

In some embodiments, the one or more electrically insulating regions have an elongated shape.

In some embodiments, the one or more electrically insulating regions define a rod-shaped electrically insulating region.

In some embodiments, the one or more electrically insulating regions define a columnar electrically insulating region.

In some embodiments, the ultrasound transducer further comprises one or more electrically insulating regions, which are spherical.

In some embodiments, the non-piezoelectric material is embedded in a polymer matrix.

In some embodiments, the piezoelectric material is continuous in one direction; and the filler material is continuous in three directions.

In some embodiments, the piezoelectric material is continuous in two directions; and the filling material is continuous in both directions.

In some embodiments, the piezoelectric material is selected from the group consisting of ferroelectric materials, single crystal ferroelectric materials, lead-free ferroelectric materials, and piezoelectric polymer materials.

In some embodiments, the piezoelectric material is lead zirconate titanate (PZT).

In some embodiments, the acoustic impedance characteristic is in the range of about 15MR to about 30 MR.

In some embodiments, the first acoustic impedance is in the range of about 30MR to about 40 MR.

In some embodiments, the third acoustic impedance is in a range of about 7MR to about 8 MR.

In some embodiments, the piezoelectric composite layer is acoustically matched to the sample and electrically insulated from the sample.

In some embodiments, the ultrasound transducer further comprises a backing layer in electrical communication with the one or more electrodes.

In some embodiments, the backing layer is a dematching layer.

In some embodiments, the ultrasound transducer further comprises a ground electrode.

In some embodiments, the ground electrode is configured as a heat sink.

In some embodiments, an acoustic path is defined between the piezoelectric composite layer and the sample, and the ultrasound transducer further comprises a near-lossless acoustic matching layer located between the piezoelectric composite layer and the sample along the acoustic path.

In some embodiments, the ultrasound transducer further comprises an abrasion resistant layer acoustically matched to the piezoelectric composite layer.

In some embodiments, the piezoelectric composite layer has a thickness of about 2400 microns.

In some embodiments, the individual spaced piezoelectric regions are spaced 200 microns apart from each other and have a square cross-section that is 1000 microns by 1000 microns.

In some embodiments, the piezoelectric composite layer has a piezoelectric volume fraction of about 70% to about 80%.

In some embodiments, the ultrasound transducer further comprises an electrically insulating housing for housing the piezoelectric composite layer therein.

According to another aspect, there is provided an ultrasonic transducer for emitting an acoustic signal towards a target, the ultrasonic transducer comprising a piezoelectric composite layer having at least partially decoupled acoustic and electrical impedance characteristics; and one or more electrodes in electrical communication with the piezoelectric composite layer, the one or more electrodes operable to transmit an electrical signal to the piezoelectric composite layer to generate an acoustic signal toward a target, the piezoelectric composite layer comprising: an array of spaced piezoelectric regions, each of the spaced piezoelectric regions being made of a piezoelectric material having a first acoustic impedance and a first relative permittivity; a filler material located between adjacent spaced piezoelectric regions, the filler material comprising a polymer matrix having a second acoustic impedance and a second relative permittivity, the second acoustic impedance being less than the first acoustic impedance and the second relative permittivity being less than the first relative permittivity; and a non-piezoelectric material in contact with the polymer matrix, the non-piezoelectric material having a third acoustic impedance and a third relative permittivity, the third acoustic impedance being greater than the second acoustic impedance and the third relative permittivity being less than the first relative permittivity.

In some embodiments, the polymer matrix is made of an epoxy resin.

In some embodiments, the non-piezoelectric material is hafnium oxide powder.

In some embodiments, the ultrasound transducer further comprises one or more electrically insulating regions located between adjacent spaced piezoelectric regions, the one or more electrically insulating regions being in contact with the filler material.

In some embodiments, the one or more electrically insulating regions have a fourth acoustic impedance and a fourth relative permittivity, the fourth acoustic impedance being proximate to the first acoustic impedance, and the fourth relative permittivity being less than the first relative permittivity.

In some embodiments, one or more electrically insulating regions are made of ceramic.

In some embodiments, one or more electrically insulating regions are made of glass.

In some embodiments, the one or more electrically insulating regions have an elongated shape.

In some embodiments, the one or more electrically insulating regions define a rod-shaped electrically insulating region.

In some embodiments, the one or more electrically insulating regions define a columnar electrically insulating region.

In some embodiments, one or more electrically insulating regions are spherical.

In some embodiments, the non-piezoelectric material is embedded in a polymer matrix.

In some embodiments, the piezoelectric material is continuous in one direction; and the filler material is continuous in three directions.

In some embodiments, the piezoelectric material is continuous in two directions; and the filling material is continuous in both directions.

In some embodiments, the piezoelectric material is selected from the group consisting of ferroelectric materials, single crystal ferroelectric materials, lead-free ferroelectric materials, and piezoelectric polymer materials.

In some embodiments, the piezoelectric material is lead zirconate titanate (PZT).

In some embodiments, the acoustic impedance characteristic is in the range of about 15MR to about 30 MR.

In some embodiments, the first acoustic impedance is in the range of about 30MR to about 40 MR.

In some embodiments, the third acoustic impedance is in a range of about 7MR to about 8 MR.

In some embodiments, the piezoelectric composite layer is acoustically matched to the sample and electrically insulated from the sample.

In some embodiments, the ultrasound transducer further comprises a backing layer in electrical communication with the one or more electrodes.

In some embodiments, the backing layer is a dematching layer.

In some embodiments, the ultrasound transducer further comprises a ground electrode.

In some embodiments, the ground electrode is configured as a heat sink.

In some embodiments, an acoustic path is defined between the piezoelectric composite layer and the sample, and the ultrasound transducer further comprises a near-lossless acoustic matching layer located between the piezoelectric composite layer and the sample along the acoustic path.

In some embodiments, the ultrasound transducer further comprises an abrasion resistant layer acoustically matched to the piezoelectric composite layer.

In some embodiments, the piezoelectric composite layer has a thickness of about 2400 microns.

In some embodiments, the individual spaced piezoelectric regions are spaced 200 microns apart from each other and have a square cross-section that is 1000 microns by 1000 microns.

In some embodiments, the piezoelectric composite layer has a piezoelectric volume fraction of about 70% to about 80%.

In some embodiments, the ultrasound transducer further comprises an electrically insulating housing for housing the piezoelectric composite layer therein.

According to another aspect, there is provided an ultrasonic transducer comprising a piezoelectric composite layer for acoustic communication with a sample and having at least partially decoupled acoustic and electrical impedance characteristics; an electrically insulating non-piezoelectric composite layer extending over the piezoelectric composite layer for electrically insulating the piezoelectric composite layer from the sample, the electrically insulating non-piezoelectric composite layer being acoustically matched to the piezoelectric composite layer and the sample; and one or more electrodes in electrical communication with the piezoelectric composite layer, the piezoelectric composite layer comprising: an array of spaced piezoelectric regions, each of the spaced piezoelectric regions being made of a piezoelectric material; a filler material located between adjacent spaced piezoelectric regions, the filler material comprising a polymer matrix; and a non-piezoelectric material in contact with the polymer matrix.

In some embodiments, the electrically insulating non-piezoelectric composite layer comprises a region of high acoustic impedance electrically insulating material in contact with a second polymer matrix filled with a high density electrically insulating powder.

In some embodiments, the electrically insulating non-piezoelectric composite layer comprises an electrically insulating ceramic region in contact with a second polymer matrix filled with a high density electrically insulating ceramic powder.

In some embodiments, the electrically insulating non-piezoelectric composite layer comprises an electrically insulating glass region in contact with a second polymer matrix filled with a high density electrically insulating ceramic powder.

In some embodiments, the electrically insulating non-piezoelectric composite layer is in a 13 configuration.

In some embodiments, the electrically insulating non-piezoelectric composite layer is in a 22 configuration.

In some embodiments, the piezoelectric composite layer is used to generate a probe acoustic signal towards the sample; and the one or more electrodes are operable to transmit a probing electrical signal to the piezoelectric composite layer to generate a probing acoustic signal.

In some embodiments, the piezoelectric composite layer is configured to receive a sample acoustic signal emanating from the sample, thereby generating an electrical sample signal towards the one or more electrodes, the electrical sample signal being representative of the sample acoustic signal.

In some embodiments, the polymer matrix is made of an epoxy resin.

In some embodiments, the non-piezoelectric material is hafnium oxide powder.

In some embodiments, the ultrasound transducer further comprises one or more electrically insulating regions located between adjacent spaced piezoelectric regions, the one or more electrically insulating regions being in contact with the filler material.

In some embodiments, the one or more electrically insulating regions have a fourth acoustic impedance and a fourth relative permittivity, the fourth acoustic impedance being proximate to the first acoustic impedance, and the fourth relative permittivity being less than the first relative permittivity.

In some embodiments, one or more electrically insulating regions are made of ceramic.

In some embodiments, one or more electrically insulating regions are made of glass.

In some embodiments, the one or more electrically insulating regions have an elongated shape.

In some embodiments, the one or more electrically insulating regions define a rod-shaped electrically insulating region.

In some embodiments, the one or more electrically insulating regions define a columnar electrically insulating region.

In some embodiments, one or more electrically insulating regions are spherical.

In some embodiments, the non-piezoelectric material is embedded in a polymer matrix.

In some embodiments, the piezoelectric material is continuous in one direction; and the filler material is continuous in three directions.

In some embodiments, the piezoelectric material is continuous in two directions; and the filling material is continuous in both directions.

In some embodiments, the piezoelectric material is selected from the group consisting of ferroelectric materials, single crystal ferroelectric materials, lead-free ferroelectric materials, and piezoelectric polymer materials.

In some embodiments, the piezoelectric material is lead zirconate titanate (PZT).

In some embodiments, the acoustic impedance characteristic is in the range of about 15MR to about 30 MR.

In some embodiments, the first acoustic impedance is in the range of about 30MR to about 40 MR.

In some embodiments, the third acoustic impedance is in a range of about 7MR to about 8 MR.

In some embodiments, the piezoelectric composite layer is acoustically matched to the sample and electrically insulated from the sample.

In some embodiments, the ultrasound transducer further comprises a backing layer in electrical communication with the one or more electrodes.

In some embodiments, the backing layer is a dematching layer.

In some embodiments, the ultrasound transducer further comprises a ground electrode.

In some embodiments, the ground electrode is configured as a heat sink.

In some embodiments, an acoustic path is defined between the piezoelectric composite layer and the sample, and the ultrasound transducer further comprises a near-lossless acoustic matching layer located between the piezoelectric composite layer and the sample along the acoustic path.

In some embodiments, the ultrasound transducer further comprises an abrasion resistant layer acoustically matched to the piezoelectric composite layer.

In some embodiments, the piezoelectric composite layer has a thickness of about 2400 microns.

In some embodiments, the individual spaced piezoelectric regions are spaced 200 microns apart from each other and have a square cross-section that is 1000 microns by 1000 microns.

In some embodiments, the piezoelectric composite layer has a piezoelectric volume fraction of about 70% to about 80%.

In some embodiments, the ultrasound transducer further comprises an electrically insulating housing for housing the piezoelectric composite layer therein.

Other embodiments are provided below.

According to another aspect, techniques, apparatus, devices, and methods are provided for independently adjusting the electrical and acoustic impedance of a piezoelectric composite. The apparatus and method that allows electrical and acoustic impedance decoupling of a piezo-composite device may be implemented by combining three (3) materials, rather than the traditional piezo-composite of two (2) materials. In addition to the use of a generally relatively low acoustic impedance notch (kerf) filler and piezoelectric material, decoupling of the acoustic impedance and electrical impedance manipulation of the composite material is provided by the use of a high acoustic impedance material, such as a non-piezoelectric ceramic. In some embodiments, the non-piezoelectric ceramic is alumina.

In accordance with another aspect, an ultrasonic transducer is provided for use with a target material having an acoustic impedance in a range of about 15MR to about 30 MR. The ultrasonic transducer includes a complete acoustic path extending from the piezoelectric element to the target material or Device Under Test (DUT). An ultrasonic transducer includes a piezoelectric layer incorporating a piezoelectric element, a ground electrode, a thermal management layer, an electrically insulating layer, and an outer wear resistant surface that can adapt to the acoustic impedance of a target material to be sonicated (insonate). The provided ultrasound transducer does not require the use of an acoustic impedance matching layer, so that the solution has the same efficiency at all frequencies below the upper cut-off frequency. The upper cutoff frequency is limited only by the composite design parameters needed to achieve effective performance of the composite component, resulting in a practical bandwidth from near DC to the upper cutoff frequency, which is at least several times the design center frequency of the device.

In accordance with another aspect, an ultrasonic transducer is provided for use with a material having an acoustic impedance in the range of about 15MR to about 30 MR. The ultrasound transducer includes an acoustically matched composite material. Since ultrasound transducers do not use a matching layer, the bandwidth of an ultrasound transducer is limited only by the inherent bandwidth imposed by the design and selection of materials, including piezoelectric elements.

In some embodiments, the ultrasound transducer includes a heat resistant backing layer that may also be configured as a heat sink proximal to the piezoelectric layer. In some embodiments, the backing layer may also serve as a dematching layer.

In some embodiments, the ultrasound transducer includes a high acoustic impedance kerf filling design. The high acoustic impedance kerf-filling design allows the piezoelectric element to be adapted to a variety of materials with acoustic impedances in the range of 15 to 30 MR. Materials with acoustic impedances in the range of about 15MR to about 30MR include, but are not limited to, titanium, aluminum, tin, lead, zirconium, some ceramics, and composites. For a group of materials with acoustic impedances of about 15MR to 30MR, ultrasonic transducers provide a way to efficiently couple ultra-wideband ultrasound into these materials.

In some embodiments, the ultrasonic transducer includes a layer of piezoelectric composite material designed to match the acoustic impedance of the DUT, and a layer of non-piezoelectric electrically insulating composite material designed to match the acoustic impedance of the DUT. A non-piezoelectric layer is interposed between the piezoelectric composite layer and the DUT. The non-piezoelectric composite layer provides an effective wide bandwidth acoustic path from the piezoelectric composite transducer element of the DUT while providing electrical isolation between the transducer and the DUT.

In some embodiments, the electrical impedance and the acoustic impedance of the ultrasound transducer may be independently configured, or at least partially decoupled. The electrical impedance, acoustic impedance, or both may be configured by using a hybrid non-piezoelectric/piezoelectric composite construction.

In some embodiments, the ultrasound transducer may be configured as a single element, a non-slotted annular array, a slotted linear array, a non-slotted 2D matrix array, or a slotted 2D matrix array.

According to another aspect, a method of fabricating a piezoelectric layer having an adapted acoustic impedance is provided.

Other features and advantages of the present description will become more apparent upon reading the following description of non-limiting embodiments, given by way of example only with reference to the accompanying drawings.

Drawings

Fig. 1 illustrates a cross-sectional view of an ultrasound transducer according to one embodiment.

Fig. 2 illustrates a cross-sectional view of an ultrasound transducer according to another embodiment.

Figure 3 illustrates a top view of a piezoelectric composite layer for an ultrasound transducer according to one embodiment.

Fig. 4 shows a top view of a piezoelectric composite layer for an ultrasound transducer according to another embodiment.

Figure 5A depicts a perspective view of an ultrasound transducer according to one embodiment.

Figure 5B depicts an exploded cross-sectional view of the ultrasound transducer in figure 5A.

Detailed Description

In the following description, like features in the drawings have been given like reference numerals, and some elements may not be indicated on some drawings if they have been identified in one or more previous drawings in order not to unduly limit the drawings. It should also be understood herein that the elements of the drawings are not necessarily drawn to scale, with emphasis instead being placed upon clearly illustrating the elements and structures of the present embodiments. The terms "a", "an" and "an" are defined herein to mean "at least one", that is, the terms do not exclude a plurality of elements unless otherwise indicated. It is also noted that terms such as "substantially," "generally," and "about" that modify a value, condition, or characteristic of an exemplary embodiment are understood to mean that the value, condition, or characteristic is defined within a suitable operationally acceptable tolerance of the exemplary embodiment for its intended use.

In this specification, the terms "connected," "coupled," and variations and derivatives thereof refer to any connection or coupling, either direct or indirect, between two or more elements. The connections or couplings between the elements may be acoustic, mechanical, physical, optical, operational, electrical, wireless, or a combination thereof.

It will be appreciated that for convenience and clarity, terms are used herein to describe the position or orientation of one element relative to another element and, unless otherwise indicated, such terms should be employed in the context of the drawings and should not be construed as limiting. It will be understood that spatially relative terms (e.g., "outer" and "inner", "peripheral" and "central", and "top" and "bottom") are intended to encompass different positions and orientations of use or operation in this embodiment, in addition to the positions and orientations illustrated in the figures.

General summary of the general principles

There are many methods and materials available for producing electromechanical acoustic transducers. Some examples include piezoelectric crystals, ferroelectric ceramics, ferroelectric single crystals, ferroelectric polymers, Capacitive Micromachined Ultrasonic Transducers (CMUTs), Piezoelectric Micromachined Ultrasonic Transducers (PMUTs), and dynamic coil-based systems.

A large class of relatively high performance piezoelectric materials is known as ferroelectric materials. Ferroelectric materials are the most commonly used piezoelectric materials in acoustic transducers, such as ultrasonic transducers. Ferroelectric materials typically have acoustic impedance characteristics in the range of about 30MR to about 40 MR. For example, a range of formulations commonly referred to as lead zirconate titanate (PZT), one of the most common ferroelectric ceramics, typically has an acoustic impedance in the range of about 33MR to about 35 MR. Another class of relatively high performance piezoelectric materials are single crystal ferroelectric materials, which include, but are not limited to, lithium niobate (PMN-PT or PIN-PMN-PT). The single crystal ferroelectric materials have acoustic impedances in the range of about 30MR to about 35 MR. Yet another category includes emerging lead-free ferroelectric materials such as, for example and without limitation, (K)_0.5Na_0.5)NbO₃(KNN) and (K)_0.48Na_0.52)_0.96Li_0.04Nb_0.85Ta_0.15O₃(KNLNT). The acoustic impedance of these materials is about 31MR, slightly lower than most variants of PZT. Yet another example class of piezoelectric materials includes piezoelectric polymers such as PVDF and copolymers such as P (VDF-TrFE). These polymer-based ferroelectric materials have much lower electromechanical efficiencies than relaxor-based single crystals and ceramics, however, they have very low acoustic impedances and unique properties that are generally well suited for implementation as receivers in immersion-based systems.

Despite the many potential piezoelectric materials, PZT and related relaxor-based ferroelectric materials remain the dominant class due to their performance superior to most other materials, thereby bringing other piezoelectric materials into small application areas. Therefore, most transducers rely on piezoelectric materials with very similar acoustic impedances that fall within a small range of about 33MR to about 38 MR. Whether by reducing matching requirements or increasing overall transmission efficiency and bandwidth, ultrasonic transducers based on piezoelectric materials with acoustic impedances that closely match the material being sonicated can improve the efficiency of the system. Some piezoelectric materials are sufficiently acoustically matched to some materials. However, many materials that do not have suitable acoustically matched transducer materials need to be sonicated, ultrasonically inspected, and/or tested.

The acoustic impedance of a piezoelectric material can be reduced while potentially increasing the electromechanical efficiency of the piezoelectric material by creating a composite of the piezoelectric material and another, typically lower acoustic impedance material that acts as a filler and forms a supporting matrix surrounding the piezoelectric material in one of a number of ways. However, it should be understood that there is a trade-off between acoustic efficiency, electrical impedance, and acoustic impedance when manufacturing piezoelectric composites.

The composite materials commonly used in ultrasound transducers are typically in a 13 or 22 configuration, where the first number indicates the number of directions the piezoelectric material continues throughout the structure and the second number indicates the number of directions the filler material continues throughout the structure. Some examples of methods of creating composite piezoelectric materials include cutting, etching, molding, or random packing of piezoelectric material, and filling or bonding other materials, such as elastomers, epoxies, polymers, or gases interspersed between piezoelectric posts or beams to form a composite material.

Examples of composite materials in the 13 configuration include cut and filled composite materials with square cross-section posts, and cuts filled with materials with lower acoustic impedance. Such a composite material can utilize rod mode resonance in the piezoelectric column, thereby making it possible to obtain a more efficient electromechanical coupling coefficient, which is dependent on k of the piezoelectric material₃₃The less efficient k of limiting the performance of the characteristic (typically 0.7 for PZT), rather than limiting the plate mode vibration (more typical in simple longitudinal disc or plate-based transducers)_t(typically 0.5 for PZT). It is noted that, based on many design parameters of the composite geometry and the material properties of the piezoelectric material and the filler material, the acoustic impedance of the composite material may be reduced compared to a pure piezoelectric material that falls somewhere between the piezoelectric material and the matrix filler. Therefore, the matching difficulty of the material with lower acoustic impedance is reduced, and higher signal-to-noise ratio is realized.

In the biomedical field, much work has emerged in the development of composite transducers, and focus has been on developing efficient composites designed to be compatible with biological tissues. Thus, many commercially available composite materials and transducers are optimized to have the lowest possible combination of acoustic impedances while achieving the highest possible electromechanical efficiency for biological tissue and/or water immersion applications. The acoustic impedance of such composite materials is typically in the range of 8MR to 16 MR. However, many practical applications require that acoustic energy emanate from and be efficiently transmitted towards ultrasonic transducers coupled to materials whose acoustic impedance does not sufficiently match these piezoelectric materials. That is, the piezoelectric materials described above may not be suitable for other types of materials that are sonicated. For example, materials having acoustic impedances between about 15MR and 30MR are particularly difficult to match with piezoelectric composites due to the lack of ideal materials for conventional acoustic stack designs.

In these cases, various techniques are known to overcome the acoustic discontinuity inherent between the piezoelectric material and the medium. For example, a common method of matching the acoustic impedance of a piezoelectric material to a desired medium is to use an 1/4 wave matching layer. Another example is the use of a spring-mass matching layer system applied at high frequencies. Yet another example is the design of a horn structure. Such acoustic impedance matching techniques may be applied to piezoelectric transducer designs to facilitate efficient transmission of acoustic radiation from the transducer to the medium being sonicated, and typically operate in a reciprocating manner. However, there is still a common denominator for all acoustic impedance matching methods, that is, they have a limited effective bandwidth. Outside this bandwidth, their effectiveness can drop rapidly and unwanted artifacts can be created when operating at a location sufficiently far from the intended center frequency.

While acoustic impedance matching in transducer design is important, in many practical applications it is also necessary to electrically insulate the piezoelectric transducer assembly from the material being sonicated. In these cases, an electrically insulating layer must also be included in the transducer stack. For example, in the field of non-destructive testing (NDT), etc., it is sometimes desirable to electrically isolate an ultrasonic transducer from electrically sensitive components, devices, or structures while matching the acoustic impedance of the transducer to the material or object being scanned. This is particularly important in medical applications. Indeed, electrically isolating the transducer assembly from the human body (the media being sonicated) is important to help prevent injury to the patient. For example, in medical diagnostic ultrasound (and other medical ultrasound applications including, but not limited to, therapeutic applications such as HIFU), for efficiency reasons, the acoustic impedance of the transducer should match that of the living tissue, while also being electrically isolated from the patient. In other medical devices that use acoustic energy for acoustic ablation or mechanical enhancement of surgical tools, it is also desirable, for example for efficiency reasons, to match the acoustic impedance of the transducer to the medium (biological tissue or in some cases a component of the acoustic medical device) while electrically isolating the transducer from the patient.

In many cases, when the acoustic impedance of the target material is below about 10MR, the designer is readily able to obtain a mature technique to address the need to acoustically match the transducer to the target while electrically isolating it.

In medical diagnostic ultrasound, a typical solution for an ultrasound transducer in contact with a patient is to select a lens or covering material, such as silicone or polyurethane, that is sufficiently matched to the living tissue, for example, that they can all be designed to have an acoustic impedance that closely matches that of the tissue (about 1.5MR), while still functioning as an effective lens and electrical insulation material. Another common practice is to use an acoustically matched electrically insulating matching layer. These matching materials include various glasses, polymers, elastomers, powder-loaded polymers, and epoxies. For example, ceramic powder loaded epoxies, such as, for example, alumina powder filled epoxies, can form various matching layers while maintaining excellent electrical resistivity required for electrical isolation. However, powder-loaded composite materials (such as powder-loaded epoxies, silicones, and polymers) typically exhibit higher attenuation than homogeneous materials, and may not be able to make an appropriate compromise between the design parameters of the matching layer (such as thickness) and the acceptable loss of the acoustic path of the device and the required electrical isolation.

In addition, the manufacture of powder-loaded composites is limited when high volume fractions of powder and polymer are achieved. For example, above about 12MR, the common practice of powder loading with epoxy to increase acoustic impedance is not practical. In addition, the design of epoxy filled porous sintered materials is costly and difficult to control accurately. They may also be lossy if not completely filled. This is especially true for electrically insulating matching layers above 15MR and below 30 MR.

It is noted that the use of matching layers in ultrasound transducer designs is problematic when a broadband transducer is required, since broadband performance requires multiple matching layer solutions. Designing a broadband ultrasound transducer for coupling in a 10MR to 30MR target is difficult. These challenges are further complicated when it is desired to electrically isolate the transducer from the target material.

Applying existing solutions with a high degree of efficacy is increasingly difficult when the target material has an acoustic impedance in the range of about 15MR to about 30 MR. This is because there is relatively little electrically insulating material that can act as a conventional matching layer (which can satisfy the acoustic, thermal, and electrical properties of the target material with acoustic impedances in the range of about 15MR to about 30 MR).

There is a need in the art, such as, for example and without limitation, NDT and medical device development, for an ultrasonic transducer capable of transmitting high power, broadband acoustic pulses to materials having acoustic impedances in the range of about 15MR to about 30 MR. An electrically insulating layer having substantially similar (or nearly the same) acoustic impedance as the target material and the piezoelectric layer is also needed. Currently, piezo-composite designs and existing solutions do not allow for changing the acoustic impedance of the piezo-composite without affecting its electrical impedance (and vice versa).

It has been found that the electrical and acoustic impedances can be independently manipulated (i.e., at least partially decoupled) by introducing high acoustic impedance non-piezoelectric materials into the piezoelectric composite design in addition to the conventional materials used to make the piezoelectric composite, in contrast to typical methods that typically incorporate low acoustic impedance kerf-filling materials used in conventional piezoelectric composite designs.

Ultrasonic transducer

Turning now to the drawings, various embodiments of ultrasound transducers will now be described. Fig. 1 and 2 show two embodiments of an ultrasound transducer 100 comprising a piezoelectric composite layer 102.

The piezoelectric composite layer 102 is used to acoustically communicate with a sample or target material. The piezoelectric composite layer 102 has at least partially decoupled acoustic and electrical impedance characteristics, i.e., the combination of materials included in the piezoelectric layer 102 allows partial decoupling of electrical impedance from acoustic impedance. The piezoelectric composite layer 102 is typically made of at least three materials. As shown in fig. 3 and 4, the piezoelectric layer 102 includes an array of spaced piezoelectric regions 10, a filler material 12, and a non-piezoelectric material 15. Each spaced piezoelectric region 10 is made of a piezoelectric material having a first acoustic impedance and a first relative dielectric constant. A filler material 12 is located between adjacent spaced piezoelectric regions 10 and includes a polymer matrix 13 having a second acoustic impedance and a second dielectric constant. The second acoustic impedance is less than the first acoustic impedance and the second relative permittivity is less than the first relative permittivity. The non-piezoelectric material 15 is in contact with the polymer matrix and has a third acoustic impedance and a third relative permittivity. The third acoustic impedance is greater than the second acoustic impedance, and the third relative permittivity is less than the first relative permittivity. In some embodiments, the non-piezoelectric material 15 is embedded in a polymer matrix. Referring back to fig. 1 and 2, the ultrasonic transducer 100 includes one or more electrodes 112 in electrical communication with the piezoelectric composite layer 102.

Referring now to fig. 1 and 2, cross-sectional views of one embodiment of an ultrasonic transducer 100 are provided. As shown, the ultrasound transducer 100 has an acoustic stack design (i.e., multiple layers) that includes a cut and filled piezoelectric composite element/layer 102 that is acoustically matched to a target material 104. In some embodiments, which will be described in more detail below, the ultrasonic transducer 100 may be electrically isolated from the target material 104. The piezo-composite element 102 has a proximal surface 106 and a distal surface 108 opposite an ultrasonic signal source 110. An acoustic path extends between the piezoelectric composite layers 102 through the target material 104.

In some embodiments, as shown in fig. 3 and 4, the piezoelectric composite layer 102 may be made of a ferroelectric piezoelectric material such as, for example, but not limited to, PZT. In the illustrated variant, the piezoelectric regions 10 form columns or beams 130 and are spaced from one another in a typical manner for 13 or 22 composite materials, which means that the piezoelectric material 10 is continuous in one direction and the filler material 12 is continuous in three directions, or the piezoelectric material 10 is continuous in two directions and the filler material 12 is continuous in two directions.

This embodiment enables a significant increase in the electrical impedance of the piezoelectric composite while maintaining the desired acoustic impedance. In fig. 4, the space provided between adjacent piezoelectric regions 10 is a notch 128. The cutout 128 is filled with epoxy 12. In some embodiments, the epoxy resin 12 comprises an HFO powder filled matrix material.

It is noted that although the piezoelectric regions 10 are shown as squares, they may have any shape, such as, for example, but not limited to, triangular, cylindrical, or hexagonal.

In some embodiments, it is desirable to reduce the volume fraction of the piezoelectric material (e.g., PZT fraction) in the piezoelectric composite layer 102 to achieve better, improved, or more desirable electrical impedance requirements for the transducer. However, a higher acoustic impedance requirement for the ultrasonic transducer 10 indicates that a higher volume fraction of PZT is desired. In such embodiments, the matrix material filled with HFO powder is insufficient to achieve the desired properties. In these cases, as shown in fig. 4, the HFO powder filled matrix material may be replaced or partially replaced with a non-piezoelectric material such as, for example, but not limited to, an alumina rod. Such materials allow for higher acoustic impedance in the piezoelectric composite layer 102 while reducing the effective relative permittivity. In another embodiment, other relatively high acoustic impedance materials may be used.

In some embodiments, the cut-outs 128 are filled with the alumina rods 14. Alumina typically has an acoustic impedance of about 35MR and a dielectric constant of about 10. In the embodiment shown in fig. 4, the bar is sized to fill approximately 70% of the width of the cut 128, with the remaining 30% of the cut to be filled being filled with epoxy 12. It should be understood that different filler materials and different epoxy materials, as well as other proportions, may be used to achieve the desired acoustic and/or electrical impedance characteristics, depending, among other things, on the target material being sonicated.

It is noted that the non-piezoelectric material 15 need not be limited to an alumina rod. For example, but not limited to, the alumina rod may be replaced by alumina balls mixed into the HFO epoxy, or by a kerf (cut) of composite material made of HFO epoxy containing alumina balls. It is also noted that similar results may be obtained by adjusting the proportions (i.e., volume fractions) of cuts, fillers, and epoxy, such that the electrical and acoustic impedance of the piezoelectric composite layer 102 can be independently adjusted to match desired acoustic and/or electrical properties (e.g., of the target material). It should be understood that the proportions of the materials forming the piezoelectric composite layer 102 may vary widely depending on the desired result. The result of this design is that the composite piezoelectric material can be designed, tuned, and adapted to have a greater range of electrical impedance for a given size while maintaining the desired acoustic impedance. The added third material, i.e. the non-piezoelectric material 15, preferably has a high acoustic impedance, i.e. an acoustic impedance similar or comparable to (if possible) that of the piezoelectric material, and the relative permittivity of the third material is much lower than that of the piezoelectric material. In this way, the layer of piezoelectric composite material 102 can be designed or tuned to have a desired acoustic impedance and a desired dielectric constant, such that neither acoustic impedance matching techniques nor electrical impedance matching circuits are required.

As previously described, the ultrasound transducer 100 includes one or more electrodes, such as signal electrodes 112, as shown in fig. 1 and 2. In some embodiments, the piezoelectric composite layer 102 is used to generate a probing acoustic signal towards the sample 104, and an electrode (e.g., signal electrode 112) is operable to send a probing electrical signal to the piezoelectric composite layer 102, thereby generating the probing acoustic signal. In some embodiments, the piezoelectric composite layer 102 is also configured to receive a sample acoustic signal emitted from the sample 104, thereby generating a sample electrical signal toward one or more electrodes (e.g., signal electrode 112), the sample electrical signal being representative of the sample acoustic signal. As such, the ultrasound transducer 100 may be used to transmit and/or receive ultrasound.

In some embodiments, such as shown in fig. 1 and 2, the electrodes 112 are located on the proximal surface 106 of the piezoelectric composite layer 102. The electrode 112 may have a conductive backing layer 114 on a proximal surface 116 of the signal electrode 112. In still other embodiments, the backing layer may be electrically insulating. The backing layer 114 may be operatively or electrically connected to the signal electrode 112. In one embodiment, the backing layer 114 is made of titanium and may have a thickness of about 200 microns. Backing layer 114 may be made of a material with acoustic impedance high enough to also act as a dematching layer. Typically, such a dematching function requires that the backing layer have an acoustic impedance at least twice that of the piezoelectric material, thereby providing higher bandwidth and sensitivity. For example, the dematching layer 114 may be made of, for example, but not limited to, molybdenum, tungsten, or tungsten carbide.

In some embodiments, the piezoelectric material is selected from the group consisting of ferroelectric materials, single crystal ferroelectric materials, lead-free ferroelectric materials, and piezoelectric polymer materials. For example, as previously described, the piezoelectric material may be lead zirconate titanate (PZT).

In some embodiments, the polymer matrix is made of an epoxy resin and the non-piezoelectric material is hafnium oxide powder.

The ultrasonic transducer 100 may also be provided with one or more electrically insulating regions between adjacent spaced piezoelectric regions 10, the one or more electrically insulating regions being in contact with the filler material 12. The electrically insulating region has a fourth acoustic impedance and a fourth relative permittivity. In some embodiments, the fourth acoustic impedance is close to the first acoustic impedance, and the fourth relative permittivity is less than the first relative permittivity. For example, but not limited to, the electrically insulating region may be made of ceramic or glass. The shape of the electrically insulating region may vary. They may have, for example, but not limited to, an elongated shape, define a rod-like electrically insulating region, define, or may be spherical.

Turning now to the materials used in ultrasonic transducers, it should be understood that the use of different volume fractions of filler powder and/or different filler powder in the matrix material will allow the filler to have different acoustic impedances. For example, it will be understood by those skilled in the art that powder-loaded epoxy materials having acoustic impedances of about 3MR to about 10MR can be practically obtained by mixing epotek 301 epoxy and HFO powder in varying volume fractions. In one embodiment, the filler material 12 is designed to have an acoustic impedance of about 7MR to about 8 MR. It should also be understood that the piezo-composite layer 102 will exhibit different characteristics than a non-composite piezo-material. For example, a non-composite piezoelectric material may have a relatively high Q factor, making it inherently a relatively low bandwidth material. However, in this embodiment, forming a 13 PZT piezoelectric composite using a lower resistance matrix material provides higher bandwidth and efficiency than a simple PZT plate based element. In addition, 13 composite PZT also exhibits a lower dielectric constant than pure PZT, thereby allowing for more practical electrical impedance through a large single element design. It should be understood that other piezoelectric materials may be used in other embodiments without departing from the scope of the present description. Such piezoelectric materials include, but are not limited to, lithium niobate, various PZT-based materials (e.g., PZT 8 or PZT5H), ferroelectric relaxor-based ceramics and relaxor-based single crystals (e.g., PMN-PT), quartz, and other piezoelectric materials having suitable characteristics for the desired application, such as higher bandwidth, higher sensitivity, or lower cost. Thus, the use of powder-loaded kerf fillers of relatively high acoustic impedance between piezoelectric posts allows for a more adequate tradeoff between acoustic impedance, electrical impedance, and post aspect ratio at increased degrees of freedom when compared to existing piezoelectric composites that are typically constructed using fillers in the 1MR to 3MR range, for example, but not limited to, when one wishes to match a piezoelectric composite transducer to a material with relatively high acoustic impedance, such as, for example, titanium or zirconium. In some cases, a higher acoustic impedance kerf filler may result in reduced acoustic isolation between the posts, thereby reducing the electromechanical coupling coefficient of the composite. However, the proposed trade-off may be considered acceptable in view of improved acoustic matching and bandwidth of the resulting acoustic path from the composite material to the target material or DUT. Using a matrix material filled with HFO powder, a relatively low volume fraction of piezoelectric material (e.g., 73% PZT volume/volume) may be used to achieve an average acoustic impedance of 27.4 MR. By comparison, for a typical 3MR unfilled epoxy, approximately 78% is required for existing piezoelectric composites. The lower volume fraction of piezoelectric material in the piezoelectric composite layer 102 allows for higher electrical impedance without sacrificing acoustic matching. In addition, this 73% volume fraction makes the cut more efficient, allows for larger blades to be used, simplifies the manufacturing process, and enhances the freedom of the designer to optimize the aspect ratio of the post to achieve optimal rod mode resonance. Another benefit of using a powder loaded matrix in the composite is the ability to change the powder loaded epoxy matrix to fine tune the acoustic impedance of the piezoelectric composite without changing the size of the posts and cutting. Such changes in post design and post size and associated cutting are known to be costly.

Turning now to the acoustic impedance of the ultrasonic transducer 100, in some embodiments, the acoustic impedance characteristic of the piezoelectric composite layer 102 is in the range of about 15MR to about 30 MR. As has been previously determined, this impedance characteristic is a combination of the impedances of each of the materials forming the piezoelectric composite layer 102. In this regard, in some embodiments, the first acoustic impedance is in the range of about 30MR to about 40MR and the third acoustic impedance is in the range of about 7MR to about 8 MR. It is noted that the piezoelectric composite layer is acoustically matched to the sample, and in some embodiments, may be electrically insulated from the sample by including an electrically insulating non-piezoelectric composite layer 122.

In some embodiments, the ultrasound transducer 100 further includes a backing layer 114 in electrical communication with the one or more electrodes 112. In some cases, the backing layer may serve as a dematching layer.

The ultrasound transducer may include a ground electrode 118 as shown in fig. 1 and 2. A ground electrode 118 is located on the distal surface 108 of the piezoelectric composite element 102. In some embodiments, the ground electrode 118 may also serve as a heat sink to spread the heat generated by the ultrasound transducer 100. It should be noted that the ground electrode 118 need not be used as a heat sink.

An acoustic path is defined between the piezoelectric composite layer 102 and the sample or target material 104. In some embodiments, the ultrasonic transducer 100 further comprises a near-lossless acoustic matching layer 120 located along the acoustic path between the piezoelectric composite layer 102 and the sample 104. A near-lossless acoustic matching layer 120 is positioned adjacent to and in contact with the distal surface of the ground electrode 118. The near lossless acoustic matching layer 120 is electrically conductive and has a substantially low thermal impedance. When an ultrasonic transducer is used to sonicate titanium, the acoustic matching layer 120 may be made of titanium. It is noted that acoustic matching layer 120 is optional and, in some embodiments, may serve as a heat sink as well as a mechanical support layer. The mechanical support reinforces the ground plane, which is also beneficial during the manufacturing of the ultrasound transducer 100. There may generally be no acoustic matching layer 120, but in fact, all layers in the ultrasound transducer 100 are acoustically matched. The acoustic matching layer 120 is an effective heat sink that may not typically be included in an acoustic design just next to the piezoelectric element 102. Typically, it is desirable that the material of the acoustic matching layer be the same as the material of the DUT. That is, the transducer 100 is designed to be the same material as it is matched. However, when the DUT is titanium, another sufficiently matched material having the desired characteristics may be selected, such as, but not limited to, zinc as the material of the acoustic matching layer 120, which is relatively better thermal conductivity than titanium, but nearly as acoustic impedance as titanium. In an acoustically matched stack, this may pose little design challenge, since both the thickness of the layers and the properties other than acoustic impedance can be easily accommodated in the design.

In some embodiments, the ultrasound transducer 100 further comprises an abrasion resistant layer 124. The abrasion resistant layer 124 is acoustically matched to the piezoelectric composite layer 102. The abrasion resistant layer 124 may be acoustically matched to other layers of the ultrasound transducer 100. In some embodiments, the wear layer 124 is in acoustic contact with the distal surface of the electrically insulating ceramic composite layer 122. The wear layer 124 may be the same material as the DUT, especially if the material is nearly as lossless as many metals. For example, in one embodiment designed to have titanium sonicated, the wear layer 124 is made of titanium 3mm thick. In this embodiment, the wear layer 124 serves to electrically isolate the transducer signal and ground, thereby allowing the transducer assembly to be electrically isolated from the DUT.

In some embodiments, a heat resistant and mechanical grounding structure is provided to support and help cool the piezoelectric composite layer 102. In one non-limiting embodiment, the piezoelectric composite layer 102 is adhered to a 3mm thick titanium disk, thereby establishing a thermal cooling path to the electrical ground conductor and establishing the ground electrode. The substrate may also serve as a mechanical support to aid in the fabrication of the piezoelectric composite and stack. In some embodiments, the conductive pads may be selected to match the target material and/or acoustic impedance or target material for a wide range of applications of the ultrasonic transducer 100 (covering acoustic impedances in the range from about 10MR to over 30 MR). In some cases, when the target material 104 is electrically conductive, e.g., when the target material is a metal, the disk may actually be the same material as the target material. A low loss wear plate may then be bonded to the distal surface of the electrically insulating layer to provide additional mechanical support for the insulating layer, as well as excellent moisture resistance. Typically, the wear plate may be made of the target material itself, and in the case of the exemplary embodiment, 3mm thick titanium is selected.

In some embodiments, the piezoelectric composite layer 102 has a thickness of about 2400 microns. It is noted that prior art ultrasonic transducers typically have limitations on the thickness of each layer provided. Because all layers of the ultrasonic transducer 100 have the same acoustic impedance, there is no limit or a reduced limit to the thickness of the layers. These layers may be thicker or thinner, depending on the application requirements. In an embodiment, the acoustic matching layer 120 is thicker to provide sufficient mass to act as a heat sink. Thus, the transducer layer at the distal end of the piezoelectric layer 102 can be made to any thickness so long as the acoustic impedances of the layers at the distal end of the piezoelectric layer are matched or nearly matched. Such a configuration makes it possible to optimize other properties of the distal layer independent of the thickness of the layer. In one embodiment, the matching layer 120 may be thickened for mechanical robustness with less impact on acoustic performance, or may be thinned to reduce cost without impacting acoustic performance. Also, the layers of the ultrasound transducer 100 adjacent and proximal to the piezoelectric layer 102 should have suitable thickness and material to enhance the output efficiency of the transducer 100.

In some embodiments, the individual spaced piezoelectric regions 10 are spaced 200 microns apart from each other and have a square cross-section that is 1000 microns by 1000 microns. The piezoelectric composite layer 102 may have different piezoelectric volume fractions depending on the target material 104. In some embodiments, the piezoelectric composite layer 102 has a piezoelectric volume fraction of about 70% to about 80%.

The ultrasound transducer 100 or components thereof may be housed in an electrically insulating housing.

An RF electrical connector 138 may also be provided. The RF electrical connector 138 is operatively connected to the electrode 112 via an electrical connection (e.g., a wire). This provides an electrical connection to the ultrasound signal source 110.

In some embodiments, copper (Cu) ground and thermal loops 132 are also provided. The Cu ground and thermal loops 132 provide a housing that at least partially houses the Cu cover 132, backing and/or dematching layer 114, electrodes 112, piezoelectric composite layer 102, and ground 118. It should be understood that the Cu ground and thermal circuit 132 may have any suitable shape for receiving the above-described items. In the embodiment shown in the figures, the Cu ground return path and the thermal return path 132 are annular in shape. The copper of the copper cap 134 may be used to conduct heat and/or electricity. In some embodiments, Cu cap 134, Cu ground and thermal return 132, dematching/backing layer 114, electrodes 112, PZT composite 102, and ground 118 can be press fit together to form a single unit. The ground 118 may optionally include a knurled edge to ensure good thermal and electrical contact with the Cu ground and thermal loops 132.

As previously mentioned, the techniques, devices, apparatuses, and methods described in this specification can be implemented to generate and transmit ultrasound ("transmission mode"), detect and receive ultrasound ("detection mode"), or both. In some embodiments, ultrasound transducers according to the present disclosure may also be used to deliver acoustic energy for other purposes, such as, for example and without limitation, transducers designed to drive medical shockwave therapy systems. In some embodiments, the ultrasound transducer 100 is used to emit an acoustic signal towards a target. In these embodiments, the ultrasound transducer further includes a layer of piezoelectric composite material 102 having at least partially decoupled acoustic and electrical impedance characteristics. The piezoelectric composite layer 102 includes an array of spaced piezoelectric regions 10, a filler material, and a non-piezoelectric material 15. Each spaced piezoelectric region 10 is made of a piezoelectric material having a first acoustic impedance and a first relative dielectric constant. A filler material 12 is located between adjacent spaced piezoelectric regions 10 and includes a polymer matrix 13 having a second acoustic impedance and a second dielectric constant. The non-piezoelectric material 15 is in contact with the polymer matrix 13 and has a third acoustic impedance and a third relative permittivity. The second acoustic impedance is less than the first acoustic impedance (of the piezoelectric material) and the second relative permittivity is less than the first relative permittivity, and the third acoustic impedance is greater than the second acoustic impedance and the third relative permittivity is less than the first relative permittivity. The ultrasound transducer according to this embodiment further comprises one or more electrodes 112 in electrical communication with the piezoelectric composite layer 102. The electrodes 112 are operable to send electrical signals to the piezoelectric composite layer 102, thereby generating acoustic signals toward a target.

As previously mentioned, it is sometimes useful to electrically insulate the ultrasound transducer 100 from the material being sonicated, for example and without limitation, in the case of medical applications or when the material being sonicated is susceptible to electrical damage. Such an embodiment of the ultrasonic transducer 100 may be similar to embodiments already described previously, and includes a layer of piezoelectric composite material 102 for acoustic communication with a sample 104 and having at least partially decoupled acoustic and electrical impedance characteristics. The piezoelectric composite layer 102 according to this embodiment includes an array of spaced piezoelectric regions 10 (where each spaced piezoelectric region 10 is made of a piezoelectric material), a filler material 12 located between adjacent spaced piezoelectric regions 10 (where the filler material 12 includes a polymer matrix 13), and a non-piezoelectric material 15 in contact with the polymer matrix 13. As shown in fig. 1 and 2, the ultrasonic transducer 100 according to this embodiment further includes an electrically insulating ceramic composite layer 122 extending over or in contact with the piezoelectric composite layer 102 for electrically insulating the piezoelectric composite layer 102 from the sample 104. Electrically insulating ceramic composite layer 122 is acoustically matched to piezoelectric composite layer 102 and sample 104. In some embodiments, the electrodes 112 are in electrical communication with the piezoelectric composite layer 102.

In some embodiments, electrically insulating ceramic composite layer 122 is acoustically matched and is a cut and filled electrically insulating ceramic composite layer 122. The ceramic composite layer 122 may be located on and/or in mechanical contact with the distal surface of the non-destructive acoustic layer 120 as described above. It is noted that the insulating layer 122 is generally not lossless, and the thickness is a compromise between electrical insulation and acceptable acoustic loss. In one non-limiting embodiment, the electrically insulating layer 122 has a thickness of 1.4mm, a pitch of 950 μm, pillars of 750 μm and cutouts of 200 μm. The kerf-filling material for the electrically insulating layer 122 may be HFO epoxy. In another non-limiting embodiment, the electrically insulating layer 122 comprises a base ceramic made of alumina. In yet another non-limiting embodiment, the base ceramic may be any other ceramic having an acoustic impedance in excess of about 30 MR. It will be appreciated that in the context of this embodiment, a general problem to be solved is the lack of an electrically insulating material having an acoustic impedance of about 15MR to 30 MR. The use of an electrically insulating layer 122 solves this general problem, since only the degree of isolation and acceptable acoustic losses are considered with respect to the thickness of the layer. It should be noted that as the thickness of electrically insulating layer 122 varies, there is no significant effect on the device bandwidth or frequency response. In some embodiments, the ultrasound transducer 100 includes an electrically insulating housing 136 for housing the ultrasound transducer.

In some embodiments, the ultrasound transducer 100 further includes an acoustically matching insulating layer 122 positioned adjacent to and in contact with the distal end of the ground electrode layer 118. Layer 122 may be made of a solid insulating material or composite material and should exhibit the desired acoustic impedance and acceptable acoustic loss, as well as have sufficient dielectric strength and permittivity to achieve the desired electrical isolation of the device. In one embodiment, the insulating layer comprises a 13 composite layer of alumina and HFO filled epoxy to achieve an acoustic impedance of about 27MR to acoustically match titanium. It will be appreciated that the matching insulating layer 122 is not a matching layer, but is itself adapted in a manner similar to the layer of piezoelectric composite material so that it has substantially the same acoustic impedance as the target material. The matching insulating layer 122 is inherently broadband and has a flat frequency transmission coefficient that is below the upper cutoff frequency determined by the size and spacing of the pillars, which is typical of acoustic composites. The thickness of the electrically insulating layer is independent of frequency and is only a design factor as it relates to managing acceptable attenuation and acceptable leakage current.

Examples of the implementation

Different possible embodiments of the ultrasound transducer will now be described.

In one embodiment, the ultrasound transducer 100 is a single element transducer. The single element transducer may have the following characteristics: a 50mm single element acoustic bore, an electrical impedance of 50Ohm magnitude at the center frequency, a broadband frequency response (6 dB fractional bandwidth of about 100% unidirectional), a center frequency of about 0.6MHz, and an acoustic resistance matched to titanium (about 27.4MR +/-about 0.5 MR). In addition to these characteristics, the present embodiment also exhibits high power handling and heat dissipation characteristics due to the inclusion of a relatively thick thermally conductive layer, thereby enhancing both the electrical effectiveness of the ground electrode, but primarily the thermal effectiveness of the ground electrode. For example, if the DUT is metallic, such as titanium, the layer may be made of the same material as the DUT material. This inclusion is possible because the entire portion of the acoustic stack is adjacent the far side of the piezoelectric element and includes a piezoelectric composite element having the same acoustic impedance as the DUT material. In this embodiment, the piezoelectric composite layer 102 may be a 13 composite of PZT and the filler material 12 may be made of HFO powder loaded epoxy designed to have an acoustic impedance very close to about 27.4MR, resulting in an acoustic match to titanium. It should be appreciated that this is relatively low acoustic impedance (approximately 34.5MR) compared to non-composite PZT, and much higher (typically between 8MR and 16 MR) than typical polymer-filled PZT piezoelectric composites. In this embodiment, PZT is selected because it has both efficiency and heat resistance. HFO powder loaded epoxy is selected as a matrix material for filling the cut-outs in the PZT sheet to create the composite material. The HFO powder-loaded epoxy has a relatively high acoustic impedance of about 7MR to about 8MR to closely match the acoustic impedance of the resulting 13-composite material to that of titanium. In this embodiment, the piezoelectric composite layer 102 has 1000 μm by 1000 μm PZT pillars (with a square cross section) that occur at a pitch of 1200 microns and are regularly spaced by 200 micron cuts. The thickness of the composite piezoelectric element/layer 102 was 2400 μm.

In another embodiment, an electrically isolated transducer is provided that has a broadband and low loss coupling mechanism to the intended acoustic load medium, the center frequency and frequency response can be optimized almost entirely by optimizing the piezoelectric composite layer and designing the backing and/or dematching layer. No matching is required on the far side of the piezoelectric composite and an almost perfectly flat frequency response of the acoustic stack is achieved at all frequencies below the effective cut-off frequency determined by the chosen pillar size and spacing of the piezoelectric composite and ceramic composite elements. This embodiment allows the design of ultrasonic transducers with a unidirectional fractional bandwidth in excess of 140% without any distal facet matching layer as long as they are used with the specified target media. There are many different metals and other conductive loads that can benefit from ultrasonic transducers that adapt their respective acoustic impedances, such as, for example, but not limited to, titanium and its alloys, tin, aluminum and many aluminum alloys, zinc, zirconium, lead, and other alloys having acoustic impedances of about 15MR to about 30 MR. In addition, non-metallic materials having acoustic impedances within the above-described ranges may also benefit from this embodiment to closely match their respective acoustic impedances.

Method of producing a composite material

A method for manufacturing an embodiment of the ultrasound transducer 100 that has been previously described is also provided. In one embodiment, the manufactured ultrasonic transducer 100 is designed to operate at a center frequency of about 600 kHz. The method includes the step of slitting a PZT plate having a thickness of about 2600 μm. The cuts are made by parallel slits. In one embodiment, this step results in about 1.7mm center-to-center 700 μm cuts, leaving about 1mm of uncut material between the cuts. The method further comprises the following steps: an alumina rod (e.g., having a width of about 400 μm) is provided to fit into the cut-out, and a 150 μm cut-out is filled with epoxy (e.g., powder loaded epoxy and allowed to cure) strips glued into place on both sides of the alumina. The method also includes the step of slitting the sheet at 90 degrees relative to the first set of slits to define similar slits (center-to-center spacing of about 1.7mm, slits of about 700 μm). The slit can then be filled with a similar 400 μm wide alumina rod and the slit filled with powder loaded epoxy. The resulting piezoelectric composite layer has an acoustic impedance equivalent to 82% PZT composite and can be acoustically matched, for example and without limitation, to titanium. However, the electrical impedance of this composite is close to that found in 59% PZT composites.

Several alternative embodiments and examples have been described and illustrated herein. The above-described embodiments are intended to be exemplary only. Those skilled in the art will appreciate the features of the various embodiments and the possible combinations and permutations of parts. One skilled in the art will further appreciate that any embodiment can be provided in any combination with other embodiments disclosed herein. The present examples and embodiments, therefore, are to be considered in all respects as illustrative and not restrictive. Thus, while particular embodiments have been shown and described, further modifications may be devised without departing significantly from the scope defined in the present specification.