阅读说明：本技术 一种医用超声换能器电声转换效率的测量方法 (Method for measuring electro-acoustic conversion efficiency of medical ultrasonic transducer ) 是由 李益民 王霄 于 2021-08-23 设计创作，主要内容包括：本发明公开了一种医用超声换能器电声转换效率的测量方法,分别利用电功率计与干涉法来测试大功率下超声换能器的输入电功率和输出声功率,再根据两者的比值来算出电声转换效率的大小。与现有技术相比,具有设计简单、结构紧凑、测量精度高、适用范围广等优点,能很好的满足压电陶瓷换能器的需求,很适合用于测试超声换能器的电声转换效率。(The invention discloses a method for measuring the electro-acoustic conversion efficiency of a medical ultrasonic transducer, which is characterized in that an electric power meter and an interference method are respectively used for testing the input electric power and the output sound power of the ultrasonic transducer under high power, and the electro-acoustic conversion efficiency is calculated according to the ratio of the input electric power and the output sound power. Compared with the prior art, the piezoelectric ceramic transducer has the advantages of simple design, compact structure, high measurement precision, wide application range and the like, can well meet the requirements of the piezoelectric ceramic transducer, and is very suitable for testing the electroacoustic conversion efficiency of the ultrasonic transducer.)

1. A method for measuring the electro-acoustic conversion efficiency of a medical ultrasonic transducer is characterized by comprising an ultrasonic generator, an electric power meter, an ultrasonic transducer and a laser interferometer, and comprises the following steps:

s1: the output end of the ultrasonic generator is connected with the electric power meter, the output end of the electric power meter is connected with the ultrasonic transducer, and the input electric power P of the ultrasonic transducer is measured by the electric power meter_e；

S2: the laser interferometer measures the number N of interference fringes of the ultrasonic transducer in a half vibration period, the linear resolution of the laser interferometer is less than or equal to 0.01um, the surface displacement amplitude A of the ultrasonic transducer is calculated,in the formula: λ is the wavelength of light wave, and n is the refractive index of air;

s3: the vibration velocity v of the ultrasonic transducer is calculated by:(ii) a In the formula: w is the angular frequency, f is the resonant frequency;

s4: calculating the super byRadiation acoustic resistance R of acoustic transducer_s：

In the formula: ρ is air density, c is air sound velocity, k is wave number, k =2 π f/c, and a is the radius of the ultrasonic transducer;

s5: calculating the radiated sound power P of the ultrasonic transducer by_s：；

S6: the electro-acoustic conversion efficiency η of the ultrasonic transducer is calculated by: eta = P_s/P_e。

2. The medical ultrasonic transducer electroacoustic conversion efficiency measuring method according to claim 1, further comprising, before step S1:

assembling an ultrasonic transducer: firstly, gluing the polarized piezoelectric ceramic piece subjected to surface treatment, the silver-plated electrode piece, the front metal cover plate and the rear metal cover plate by using epoxy resin, then fixing the components together by using bolts, enabling the coaxiality to be within 0.02mm, and finally carrying out aging treatment to obtain the ultrasonic transducer to be measured.

3. The medical ultrasonic transducer electroacoustic conversion efficiency measuring method according to claim 2, wherein the surface treatment comprises:

and grinding and precisely polishing the surface of the piezoelectric ceramic plate to ensure that the roughness Ra is less than or equal to 500 nm.

4. The medical ultrasonic transducer electroacoustic conversion efficiency measuring method according to claim 2, wherein the aging process includes:

and placing the ultrasonic transducer in a heat treatment furnace, and keeping the temperature at 90-110 ℃ for 12-24 h.

5. The medical ultrasonic transducer electroacoustic conversion efficiency measuring method as claimed in any one of claims 1 to 4, wherein the ultrasonic generator is configured to generate a driving signal having a frequency of 50KHz to 60KHz for supplying power of 20 to 50 w.

6. The method for measuring the electroacoustic conversion efficiency of a medical ultrasonic transducer according to any one of claims 1 to 4, wherein the bandwidth of the electrometer is 50 kHz-100 kHz, and the power error is limited to ± 0.1%.

7. The medical ultrasonic transducer electroacoustic conversion efficiency measuring method as set forth in any one of claims 1 to 4, wherein the piezoelectric ceramic is one of PZT4 and PZT 8.

8. The method for measuring electro-acoustic conversion efficiency of a medical ultrasonic transducer according to claim 4, wherein the electrode sheet is one of pure copper, bronze and beryllium bronze.

9. The method for measuring electroacoustic conversion efficiency of a medical ultrasonic transducer according to claim 4, wherein the front metal cover plate is one of aluminum alloy 7075, aluminum alloy 7175 and aluminum alloy 7475.

10. The method of measuring electroacoustic conversion efficiency of a medical ultrasonic transducer according to claim 4, wherein the back metal cover plate is one of 304L stainless steel, 310L stainless steel, and 316L stainless steel.

Technical Field

The invention relates to a method for measuring the electro-acoustic conversion efficiency, in particular to a method for measuring the electro-acoustic conversion efficiency of a medical ultrasonic transducer.

Background

Ultrasonic waves refer to sound waves with frequency more than 20KHz, and have been widely used in a variety of medical fields such as ultrasonic knife surgery, ultrasonic atomization, B-ultrasonic examination, ultrasonic pharmacy and the like due to good directivity and strong penetrating power. Compared with the traditional operation, the ultrasonic scalpel operation has the advantages of high cutting precision, small wound range, good blood coagulation effect, clearer visual field, greatly shortened operation time, quick postoperative recovery and the like, and brings great benefits to doctors and patients.

The ultrasonic scalpel device mainly comprises a high-frequency power source and an ultrasonic vibration system. The ultrasonic vibration system in turn comprises three parts: ultrasonic transducer, supersound amplitude transformer, supersound sword tool bit. Among them, the ultrasonic transducer is a device for energy conversion, which can convert an oscillating electric signal generated by an ultrasonic generator into a mechanical vibration signal, that is, convert an electric energy into a mechanical energy (acoustic energy). The ultrasonic transducer is a key part of a vibration system, and the performance of the ultrasonic transducer, such as the electro-acoustic conversion efficiency, directly affects the effect of ultrasonic treatment. Regarding the test of the performance of the ultrasonic transducer, at present, the test is basically limited to the test under the condition of a small signal, and commonly used methods include an admittance and impedance circle method, a transmission line method, a power curve method, and the like. However, most of the power ultrasonic transducers work under a relatively large input signal, and regarding the high-power performance test of the ultrasonic transducers, due to the nonlinearity of the transducers and the complexity of a vibration system, such as waveform distortion, load change and the like, no universal test method exists at home and abroad so far, and unified international and national standards are lacked, so that a unified standard is lacked for the evaluation of some power ultrasonic technologies, and the performance of high-power ultrasonic equipment, such as an ultrasonic scalpel, a cleaning machine, a welding machine and the like, cannot be measured.

Japanese academy proposed a high frequency electric power meter method for measuring the vibration performance of a high power ultrasonic transducer in the 70 s [ Mori E, Ito K. Measurement of the acoustic output power of an ultrasonic high power transducer using an electric high frequency wave meter [ C ]. Proc. Ultrasonics Intern.81, Brightton,1981: 307-312 ]. The method can measure the radiation sound power and the electro-acoustic efficiency of the transducer under the high-power state, however, the method has some fatal defects, and the application of the method in practical application is limited. First, in order to measure the dielectric loss power of a transducer, two transducers with identical performance are required, which is difficult to achieve in practice. Second, in order to obtain the dielectric and mechanical power loss of the transducer, the dependence of the dielectric and mechanical power loss of the transducer on the terminal voltage and vibration speed of the transducer must be measured in advance. For the above reasons, this method has not yet been widely used in practice.

Disclosure of Invention

The invention provides a method for measuring the electro-acoustic conversion efficiency of a medical ultrasonic transducer, which aims to solve the defects in the prior art, utilizes an electric power meter and an interference method to test the electro-acoustic conversion efficiency of the ultrasonic transducer under high power, has the characteristics of simple design, compact structure, high measurement precision, wide application range and the like, and overcomes the defects in the prior art.

In order to achieve the purpose, the invention adopts the following technical scheme:

the invention discloses a method for measuring the electro-acoustic conversion efficiency of a medical ultrasonic transducer, which is characterized by comprising an ultrasonic generator, an electrometer, an ultrasonic transducer and a laser interferometer. The method comprises the following steps:

s1: the output end of the ultrasonic generator is connected with the electric power meter, the output end of the electric power meter is connected with the ultrasonic transducer, and the input electric power P of the ultrasonic transducer is measured by the electric power meter_e；

S2: the laser interferometer measures the number N of interference fringes of the ultrasonic transducer in a half vibration period, the linear resolution of the laser interferometer is less than or equal to 0.01um, the surface displacement amplitude A of the ultrasonic transducer is calculated,in the formula: λ is the wavelength of light wave, and n is the refractive index of air;

s3: the vibration velocity v of the ultrasonic transducer is calculated by:(ii) a In the formula: w is the angular frequency, f is the resonant frequency;

s4: calculating the radiation acoustic resistance R of the ultrasonic transducer by_s：

In the formula: ρ is air density, c is air sound velocity, k is wave number, k =2 π f/c, and a is the radius of the ultrasonic transducer;

s5: calculating the radiated sound power P of the ultrasonic transducer by_s：；

S6: the electro-acoustic conversion efficiency η of the ultrasonic transducer is calculated by: eta = P_s/P_e。

Preferably, the method for measuring the electroacoustic conversion efficiency of the medical ultrasonic transducer according to the present invention further includes, before step S1:

assembling an ultrasonic transducer: firstly, gluing the polarized piezoelectric ceramic piece subjected to surface treatment, the silver-plated electrode piece, the front metal cover plate and the rear metal cover plate by using epoxy resin, then fixing the components together by using bolts, enabling the coaxiality to be within 0.02mm, and finally carrying out aging treatment to obtain the ultrasonic transducer to be measured.

As a preferable scheme, the invention provides a method for measuring the electroacoustic conversion efficiency of a medical ultrasonic transducer, which is characterized in that the surface treatment comprises the following steps:

and grinding and precisely polishing the surface of the piezoelectric ceramic plate to ensure that the roughness Ra is less than or equal to 500 nm.

As a preferable scheme, the method for measuring the electroacoustic conversion efficiency of the medical ultrasonic transducer is characterized in that the aging treatment comprises the following steps:

and placing the ultrasonic transducer in a heat treatment furnace, and keeping the temperature at 90-110 ℃ for 12-24 h.

The invention discloses an electroacoustic conversion efficiency measuring method of a medical ultrasonic transducer, which is characterized in that an ultrasonic generator is used for generating a driving signal with the frequency of 50 KHz-60 KHz and supplying power of 20-50 w.

The method for measuring the electroacoustic conversion efficiency of the medical ultrasonic transducer is characterized in that the bandwidth of the electric power meter is 50 kHz-100 kHz, and the power error is limited to +/-0.1%.

Preferably, the method for measuring the electro-acoustic conversion efficiency of the medical ultrasonic transducer is characterized in that the piezoelectric ceramic is one of PZT4 and PZT 8.

The invention discloses an electroacoustic conversion efficiency measuring method of a medical ultrasonic transducer, which is characterized in that the electrode plate is one of pure copper, bronze and beryllium bronze.

Preferably, the method for measuring the electro-acoustic conversion efficiency of the medical ultrasonic transducer is characterized in that the front metal cover plate is one of aluminum alloy 7075, aluminum alloy 7175 and aluminum alloy 7475.

Preferably, the method for measuring the electro-acoustic conversion efficiency of the medical ultrasonic transducer is characterized in that the rear metal cover plate is one of 304L stainless steel, 310L stainless steel and 316L stainless steel.

Principles and advantages

Transducers made using the piezoelectric effect are called piezoelectric ultrasonic transducers. The piezoelectric effect is classified into a positive piezoelectric effect and an inverse piezoelectric effect, and the piezoelectric effect is reversible. The direct piezoelectric effect refers to that when a piezoelectric material (such as piezoelectric ceramic) is deformed under the action of an external force, electric charges appear on the surface of the piezoelectric material, that is, force is generated to generate electricity or mechanical energy is converted into electric energy. The inverse piezoelectric effect refers to that a piezoelectric material (such as piezoelectric ceramic) is deformed by an external electric field, i.e., an electric force or an electric energy is converted into a mechanical energy (acoustic energy).

The inventors found in the research that the electro-acoustic conversion efficiency η of the piezoelectric ultrasonic transducer can be expressed by the ratio of the input electric power to the output acoustic power. The practical working condition of the ultrasonic transducer can be simulated by using the high power (20-50 w) given by the ultrasonic generator, and the input electric power P of the ultrasonic transducer under the working condition is obtained by using a high-precision (the power error is limited to +/-0.1%) electric power meter_e. Output acoustic power P_sCan be determined by interferometry. One laser beam is divided into two beams by a beam splitter, wherein one beam can directly reach the photoelectric detector, and the other beam is firstly incident to the vibration surface of the transducer and then reflected back to the photoelectric detector. The two lasers form a set of interference fringes with a width h on the detection plane, and the output photocurrent I of the detector at X can be expressed as:

（1）

the photo-current signal I output by the photo-detector is a frequency modulated signal whose instantaneous frequency is directly proportional to the instantaneous vibration velocity of the transducer surface and when the transducer surface displacement changes by a factor of λ/2n, the output signal of the photo-detector changes by a period equal to the movement of a stripe across the detector. The number N of interference fringes of the transducer during a half vibration cycle can then be measured by recording the photocurrent signal I. And calculating the surface displacement amplitude A of the ultrasonic transducer, wherein the expression is as follows:

（2）

in the formula: λ is the wavelength of light wave, and n is the refractive index of air.

The relation between the vibration speed v and the amplitude A of the ultrasonic transducer is as follows:

（3）

for an ultrasonic transducer, the radiation acoustic resistance R is equivalent to a radius a_sCan be approximated as:

（4）

in the formula: ρ is the air density, c is the air sound velocity, k is the wave number, k =2 π f/c, and a is the radius of the ultrasound transducer.

The radiation sound power P of the ultrasonic transducer can be determined by the formulas (3) and (4)_s：

（5）

Finally, the electro-acoustic conversion efficiency η of the ultrasonic transducer is calculated by: eta = P_s/P_e。

Through a large number of experiments, the invention discovers that the measurement result and the precision of the electroacoustic conversion efficiency eta are influenced by the following aspects: 1) the coaxiality of all the components is different, and the difference of the coaxiality influences the collection and distribution of mechanical energy, so that the electro-acoustic conversion efficiency of the piezoelectric ceramic is changed; 2) the smoother the surface of the part, the less the mechanical loss generated between interfaces, and the more favorable the improvement of the electroacoustic conversion efficiency; 3) the necessity of ageing treatment, it has been found experimentally that the results of the electro-acoustic conversion efficiency vary greatly when a number of measurements are made on an unaged transducer, because the transducer requires a relatively long time to even out the distribution of the electric domains so that the transducer's state is stable. Therefore, the process of electric domain uniform distribution is accelerated through artificial aging, and the method is suitable for batch production and is more beneficial to obtaining stable electroacoustic conversion efficiency; 4) the measurement accuracy of the electric power meter and the laser interferometer, and the accuracy degree of the reading of the electric power meter and the laser interferometer directly influence the accuracy of the electro-acoustic conversion efficiency, so that the electric power meter with the measurement accuracy of +/-0.1% is selected. Under the control of the process parameters, the test method can ensure that the measurement result is reliable and has high precision.

Compared with the prior art, the invention has the following advantages:

1) the structure is simple. Only one electric power meter needs to be connected between the ultrasonic transducer and the generator;

2) the measurement precision is high. The measurement precision can be controlled to be 1 percent, which is 3-4 times of that of the existing production technology;

3) the application range is wide. Can meet the requirements of any piezoelectric ceramic transducer.

In summary, the invention utilizes the power meter and the interference method to test the electro-acoustic conversion efficiency of the ultrasonic transducer under high power, has the advantages of simple design, compact structure, high measurement precision, wide application range and the like, solves the problems of complex structure, inconvenient operation, low precision and the like in the prior art, can well meet the requirements of the piezoelectric ceramic transducer, and is very suitable for testing the electro-acoustic conversion efficiency of the ultrasonic transducer.

Drawings

Fig. 1 is a circuit diagram of an electroacoustic conversion efficiency measuring method of a medical ultrasonic transducer.

Fig. 2 is a schematic view of a medical ultrasound transducer.

Detailed Description

The process of the present invention is further illustrated below with reference to two examples.

The input electric power and the output sound power of the ultrasonic transducer under high power are tested by using an electric power meter and an interference method, and the size of the electroacoustic conversion efficiency is calculated according to the ratio of the input electric power and the output sound power.

Example 1:

a method for measuring the electro-acoustic conversion efficiency of a medical ultrasonic transducer comprises the following steps:

A. assembling of the ultrasonic transducer: gluing a polarized PZT4 piezoelectric ceramic plate (1) with the roughness Ra of 400nm, a silver-plated pure copper electrode plate (2), a front cover plate aluminum alloy 7075 (3) and a rear cover plate 304L stainless steel (4) by using epoxy resin, fixing the parts together by using bolts (5), controlling the coaxiality to be 0.02mm as shown in figure 2, and finally carrying out heat preservation at 90 ℃ for 24h and aging treatment to obtain the ultrasonic transducer to be tested;

B. the output end of the ultrasonic generator is connected with the electric power meter, the output end of the electric power meter is connected with the ultrasonic transducer, the ultrasonic generator provides a sine signal with the frequency of 55KHz, and the input electric power P of the ultrasonic transducer is measured by the electric power meter_eIs 30 w;

C. the number N of interference fringes of the transducer in a half vibration period is measured by a laser interferometer to be 31.5, and the surface displacement amplitude A of the ultrasonic transducer is calculated to be 9.45 um; further calculating the vibration speed v to be 3.29 m/s; radiation acoustic resistance R of ultrasonic transducer_sIs 1.2 omega.

D. Finally, the radiated sound power P of the ultrasonic transducer is calculated_sAt 13w, the electroacoustic conversion efficiency η was 0.43.

Example 2:

a method for measuring the electro-acoustic conversion efficiency of a medical ultrasonic transducer comprises the following steps:

A. assembling of the ultrasonic transducer: gluing the polarized PZT8 piezoelectric ceramic sheet with the roughness Ra of 450nm, the silver-plated bronze electrode sheet, the front cover plate aluminum alloy 7075 and the rear cover plate 304L stainless steel by using epoxy resin, fixing the parts together by using bolts, controlling the coaxiality to be 0.015mm, and finally carrying out heat preservation at 110 ℃ for 12h and aging treatment to obtain the ultrasonic transducer to be tested;

B. the output end of the ultrasonic generator is connected with an electric power meter, the output end of the electric power meter is connected with an ultrasonic transducer, the ultrasonic generator provides a sinusoidal signal with the frequency of 50KHz, and the sinusoidal signal is utilizedThe electric power meter measures the input electric power P of the ultrasonic transducer_eIs 48 w;

C. the number N of interference fringes of the transducer in a half vibration period is measured by a laser interferometer to be 38.7, and the surface displacement amplitude A of the ultrasonic transducer is calculated to be 11.61 um; further calculating the vibration speed v to be 3.65 m/s; radiation acoustic resistance R of ultrasonic transducer_sIs 1.42 omega.

D. Finally, the radiated sound power P of the ultrasonic transducer is calculated_s19w, and the electroacoustic conversion efficiency η is 0.4.

The above-described embodiments are merely exemplary embodiments of the present invention, which should not be construed as limiting the scope of the invention, but rather as indicating any equivalent variations, modifications, substitutions and combinations of parts within the spirit and scope of the invention.