阅读说明：本技术 一种柔性超声波传感器及其动脉血压检测方法 (Flexible ultrasonic sensor and arterial blood pressure detection method thereof ) 是由 张甲 孙毅 于 2019-11-29 设计创作，主要内容包括：本发明是一种柔性超声波传感器及其动脉血压检测方法。所述传感器包括柔性封装层、上层导电粘结层、下层导电粘结层、上电极、下电极、声匹配层和四个并排的压电层；通过柔性封装层封装上电极、下电极、导电粘结层、压电层和声匹配层；所述上电极和下电极的正方形端露出柔性封装层封装层外,所述上电极和下电极的长方形端在柔性封装层内。本发明可以对人体血压精准、快速、实时的检测,并且具备良好的皮肤贴敷性和可延展性。(The invention discloses a flexible ultrasonic sensor and an arterial blood pressure detection method thereof. The sensor comprises a flexible packaging layer, an upper conductive bonding layer, a lower conductive bonding layer, an upper electrode, a lower electrode, an acoustic matching layer and four piezoelectric layers which are arranged side by side; the upper electrode, the lower electrode, the conductive bonding layer, the piezoelectric layer and the acoustic matching layer are packaged through the flexible packaging layer; the square ends of the upper electrode and the lower electrode are exposed out of the flexible packaging layer, and the rectangular ends of the upper electrode and the lower electrode are arranged in the flexible packaging layer. The invention can accurately, quickly and real-timely detect the blood pressure of a human body and has good skin application property and extensibility.)

1. A flexible ultrasonic sensor is characterized in that: the sensor comprises a flexible packaging layer, an upper conductive bonding layer, a lower conductive bonding layer, an upper electrode, a lower electrode, an acoustic matching layer and a plurality of piezoelectric layers;

the upper electrode, the lower electrode, the upper conductive bonding layer, the lower conductive bonding layer, the piezoelectric layer and the acoustic matching layer are packaged through the flexible packaging layer; the upper electrode and the lower electrode are arranged in parallel, a plurality of piezoelectric layers are arranged in parallel gaps between the upper electrode and the lower electrode, the piezoelectric layers are connected with one sides of the upper electrode and the lower electrode through an upper conductive bonding layer and a lower conductive bonding layer, and the other side of the lower electrode is connected with an acoustic matching layer;

the upper electrode and the lower electrode respectively comprise a first square part, a second rectangular part and a third rectangular part, one end of the first square part of the upper electrode and one end of the first rectangular part of the lower electrode pass through one end of the second rectangular part, the other end of the second rectangular part is connected with one end of the third rectangular part, the width of the first square part is larger than that of the third rectangular part, and the width of the third rectangular part is larger than that of the second rectangular part;

the first square parts of the upper electrode and the lower electrode are arranged outside the flexible packaging layer, the third rectangular part is arranged inside the flexible packaging layer, and the other end of the second rectangular part is packaged in the flexible packaging layer.

2. A flexible ultrasonic transducer according to claim 1, wherein: four parallel piezoelectric layers are arranged in a parallel gap between the upper electrode and the lower electrode, and the four parallel piezoelectric layers are filled through a flexible packaging layer.

3. A flexible ultrasonic transducer according to claim 1, wherein: the piezoelectric layer is made of rectangular piezoelectric ceramic plates which are arranged in an array mode.

4. A flexible ultrasonic transducer according to claim 3, wherein: the upper electrode and the lower electrode adopt an island-bridge type snake-shaped interconnection structure, and the upper electrode and the lower electrode are provided with island elements with the same number as the rectangular piezoelectric ceramic pieces arranged in an array mode.

5. A flexible ultrasonic transducer according to claim 1, wherein: the upper conductive bonding layer and the lower conductive bonding layer are made of epoxy resin conductive adhesive or low-temperature tin soldering agent, and the upper conductive bonding layer and the lower conductive bonding layer are printed on the surface of the piezoelectric layer by using a steel mesh with laser holes.

6. A flexible ultrasonic transducer according to claim 1, wherein: the flexible packaging layer is prepared from polydimethylsiloxane and a curing agent in a ratio of 10:1, the polydimethylsiloxane and the curing agent are uniformly stirred and vacuumized for 30min by using a vacuum drier to discharge air bubbles in the solution, and the flexible packaging layer is placed in a 60 ℃ oven to be heated for 12h for curing when in use.

7. An arterial blood pressure detection method based on a flexible ultrasonic sensor according to claim 1, characterized in that: the method comprises the following steps:

step 1: attaching a flexible ultrasonic sensor to the surface of the skin of a human body, wherein the flexible ultrasonic sensor generates high-frequency ultrasonic waves under the excitation action, the high-frequency ultrasonic waves are transmitted in the human body, and echo signals in the human body are received through the flexible ultrasonic sensor;

step 2: determining the sound pressure reflectivity of the ultrasonic wave at the interface between the blood vessel and the blood at different moments according to the acoustic impedance of the wall of the blood vessel of the human body and the acoustic impedance of the blood of the human body;

and step 3: acquiring echo signals in a human body, wherein the echo signals in the human body comprise echo signals of a front wall and a rear wall of a blood vessel, determining a time-varying image of the depths of a front wall boundary and a rear wall boundary of the artery blood vessel according to the echo signals in the human body, and performing difference processing on the time-varying image of the depths of the front wall boundary and the rear wall boundary of the artery blood vessel of the human body to obtain a time-varying image of the section diameter of the blood vessel of the human body;

and 4, step 4: and determining the relationship between the arterial blood pressure of the human body and the diameter of the cross section of the blood vessel to obtain a human arterial pressure waveform diagram.

8. The method for detecting arterial blood pressure according to claim 7, wherein: the step 2 specifically comprises the following steps:

step 2.1: determining an optimal matching layer for the body tissue based on the acoustic impedance of the body vessel wall and the acoustic impedance of the body bloodThe acoustic impedance z of the best matching layer of human tissue is expressed by_Matching：

Wherein z is₁Acoustic impedance of the wall of a human blood vessel, z₂The acoustic impedance of human blood;

step 2.2: determining the sound pressure reflectivity of the ultrasonic wave at the interface between the blood vessel and the blood at different moments, and expressing the sound pressure reflectivity by the following formula:

wherein, R is the sound pressure reflectivity of the ultrasonic wave at the interface between the blood vessel and the blood at different moments.

9. The method for detecting arterial blood pressure according to claim 7, wherein: the step 3 specifically comprises the following steps:

step 3.1: acquiring echo signals in a human body, wherein the echo signals in the human body comprise echo signals of the front wall and the rear wall of a blood vessel, the ultrasonic signals can generate echo signals when reaching the front wall of the blood vessel, and at the time t, the flexible ultrasonic sensor receives the ultrasonic echo signals and outputs pulse electric signals of the echo signals;

step 3.2: determining a time-varying image of the depth of the boundary of the anterior wall of the artery blood vessel and the boundary of the posterior wall of the artery blood vessel according to the echo signals in the human body; determining the distances from the front wall of the blood vessel to the skin surface layer at different moments according to the propagation average speed of the ultrasonic waves in the human body, and expressing the distances by the following formula:

wherein, X_iFor the anterior wall distance of the blood vessel at different momentsDistance of the skin surface layer, t_iFor the moment when the flexible ultrasonic sensor receives the echo signal, T_iC is the average sound velocity of the ultrasonic wave propagating in the human tissue at the moment when the flexible ultrasonic wave sensor transmits the ultrasonic wave, and c is 1540 m/s;

step 3.3: and 3.2, analyzing and calculating each group of ultrasonic emission signals and ultrasonic echo signals to obtain the distance between the front wall and the back wall of the blood vessel in a plurality of cardiac cycles and the skin surface layer, and drawing depth images of the front wall and the back wall of the blood vessel in the tissues in the plurality of cardiac cycles.

10. The method for detecting arterial blood pressure according to claim 7, wherein: the step 4 specifically comprises the following steps:

determining the relation between the human blood pressure value and the cross-sectional area of the human blood vessel at any moment according to the intrinsic functional relation between the diameter of the human blood vessel and the blood pressure of the human body, and expressing the relation between the human arterial blood pressure value and the cross-sectional area of the human blood vessel at any moment by the following formula:

wherein p (t) is the arterial blood pressure value of the human body at any time, p₁Is diastolic blood pressure, A₁The cross-sectional area of the vessel corresponding to the diastolic pressure, A₂Is the cross-sectional area of the heart during systole, p₂The systolic pressure is the systolic pressure, and d is the diameter of a human blood vessel;

and outputting a human arterial pressure oscillogram according to the relation between the human arterial blood pressure value and the cross-sectional area of the human blood vessel at any moment.

Technical Field

The invention relates to the technical field of ultrasonic sensors, in particular to a flexible ultrasonic sensor and an arterial blood pressure detection method thereof.

Background

The prevention and treatment of cardiovascular and cerebrovascular diseases are major problems in the medical field all over the world, the arterial pressure oscillogram of a human body is an important clinical index aiming at the cardiovascular and cerebrovascular diseases, and doctors can predict the health condition of the human body through relevant parameters and indexes of the blood pressure of the human body.

For the acquisition of the arterial pressure of a human body, there are two main means nowadays, namely a non-invasive arterial pressure detection method and an invasive arterial pressure detection method.

The non-invasive arterial pressure detection method mainly comprises an auscultation method and an oscillography method. The auscultatory method is also called Korotkoff sound method, and the cuff type mercury sphygmomanometer utilizes the principle, and is widely used in medical institutions all over the world for over one hundred years due to the clinical reliability of the method. However, the auscultatory method requires a high level of expertise for the operator, and cannot monitor the blood pressure of the human body in real time, and medical institutions in many countries of the europe and the america have made the prohibition on the use of mercury sphygmomanometers due to the toxicity of mercury. The oscillography is the detection principle of most of the electronic blood pressure meters on the market today. The oscillography is mainly problematic in that the detection result is based on the existing clinical samples, and the result obtained by the oscillography is often large in error due to the large individual difference of users. And the two methods cannot continuously detect the blood pressure waveform of the human body in real time.

Invasive arterial pressure measurement is performed through an operation, a catheter is inserted into an ascending aorta from a radial artery or a femoral artery along an arterial blood vessel, and blood pressure is directly measured through a pressure sensor, so that a continuous, accurate and stable arterial pressure waveform can be measured, and the standard is the gold standard for measuring the arterial pressure waveform. However, it is very traumatic, expensive, difficult to operate, has sequelae risk and is suitable for some people, such as: patients with vascular diseases and blood coagulation disorders cannot use the blood coagulation system. Therefore, invasive measurement methods are of low use.

With the continuous improvement of the material living standard of people in China, people pay more and more attention to the personal health condition, and the blood pressure detecting instrument cannot meet the increasing medical requirements of people. The invention provides an ultrasonic sensor with a flexible structure, realizes the miniaturization of an ultrasonic sensor probe, has good skin application property and extensibility, is expected to be widely applied in the field of wearable electronics of human bodies, and provides a principle and a method for detecting arterial blood pressure, so that the accurate, quick and real-time detection of the blood pressure of the human body can be realized.

Disclosure of Invention

The invention provides a flexible ultrasonic sensor and an arterial blood pressure detection method thereof for realizing accurate, rapid and real-time detection of human blood pressure, and provides the following technical scheme:

a flexible ultrasonic sensor comprises a flexible packaging layer, an upper conductive bonding layer, a lower conductive bonding layer, an upper electrode, a lower electrode, an acoustic matching layer and a plurality of piezoelectric layers;

the upper electrode, the lower electrode, the upper conductive bonding layer, the lower conductive bonding layer, the piezoelectric layer and the acoustic matching layer are packaged through the flexible packaging layer; the upper electrode and the lower electrode are arranged in parallel, a plurality of piezoelectric layers are arranged in parallel gaps between the upper electrode and the lower electrode, the piezoelectric layers are connected with one sides of the upper electrode and the lower electrode through an upper conductive bonding layer and a lower conductive bonding layer, and the other side of the lower electrode is connected with an acoustic matching layer;

the upper electrode and the lower electrode respectively comprise a first square part, a second rectangular part and a third rectangular part, one end of the first square part of the upper electrode and one end of the first rectangular part of the lower electrode pass through one end of the second rectangular part, the other end of the second rectangular part is connected with one end of the third rectangular part, the width of the first square part is larger than that of the third rectangular part, and the width of the third rectangular part is larger than that of the second rectangular part;

the first square parts of the upper electrode and the lower electrode are arranged outside the flexible packaging layer, the third rectangular part is arranged inside the flexible packaging layer, and the other end of the second rectangular part is packaged in the flexible packaging layer.

Preferably, four side-by-side piezoelectric layers are arranged in the parallel gap of the upper electrode and the lower electrode, and the four side-by-side piezoelectric layers are filled by the flexible packaging layer.

Preferably, the piezoelectric layer is a rectangular piezoelectric ceramic plate arranged in an array.

Preferably, the upper electrode and the lower electrode adopt an island-bridge type snake-shaped interconnection structure, and the upper electrode and the lower electrode are provided with island elements with the number equal to that of the rectangular piezoelectric ceramic pieces arranged in an array manner.

Preferably, the upper conductive bonding layer and the lower conductive bonding layer are made of epoxy resin conductive adhesive or low-temperature tin solder, and the upper conductive bonding layer and the lower conductive bonding layer are printed on the surface of the piezoelectric layer by using a laser-perforated steel mesh.

Preferably, the flexible packaging layer is prepared from polydimethylsiloxane and a curing agent in a ratio of 10:1, the polydimethylsiloxane and the curing agent are uniformly stirred and then vacuumized for 30min by using a vacuum drier to discharge air bubbles in the solution, and the flexible packaging layer is placed in an oven at 60 ℃ for heating and curing for 12h when in use.

An arterial blood pressure detection method comprises the following steps:

step 1: attaching a flexible ultrasonic sensor to the surface of the skin of a human body, wherein the flexible ultrasonic sensor generates high-frequency ultrasonic waves under the excitation action, the high-frequency ultrasonic waves are transmitted in the human body, and echo signals in the human body are received through the flexible ultrasonic sensor;

step 2: determining the sound pressure reflectivity of the ultrasonic wave at the interface between the blood vessel and the blood at different moments according to the acoustic impedance of the wall of the blood vessel of the human body and the acoustic impedance of the blood of the human body;

and step 3: acquiring echo signals in a human body, wherein the echo signals in the human body comprise echo signals of a front wall and a rear wall of a blood vessel, determining a time-varying image of the depths of a front wall boundary and a rear wall boundary of the artery blood vessel according to the echo signals in the human body, and performing difference processing on the time-varying image of the depths of the front wall boundary and the rear wall boundary of the artery blood vessel of the human body to obtain a time-varying image of the section diameter of the blood vessel of the human body;

and 4, step 4: and determining the relationship between the arterial blood pressure of the human body and the diameter of the cross section of the blood vessel to obtain a human arterial pressure waveform diagram.

Preferably, the step 2 specifically comprises:

step 2.1: determining the acoustic impedance of the optimal matching layer of the human tissue according to the acoustic impedance of the wall of the human blood and the acoustic impedance of the human blood, and expressing the acoustic impedance z of the optimal matching layer of the human tissue by the following formula_Matching：

Wherein z is₁Acoustic impedance of the wall of a human blood vessel, z₂The acoustic impedance of human blood;

step 2.2: determining the sound pressure reflectivity of the ultrasonic wave at the interface between the blood vessel and the blood at different moments, and expressing the sound pressure reflectivity by the following formula:

wherein, R is the sound pressure reflectivity of the ultrasonic wave at the interface between the blood vessel and the blood at different moments.

Preferably, the step 3 specifically comprises:

step 3.1: acquiring echo signals in a human body, wherein the echo signals in the human body comprise echo signals of the front wall and the rear wall of a blood vessel, the ultrasonic signals can generate echo signals when reaching the front wall of the blood vessel, and at the time t, the flexible ultrasonic sensor receives the ultrasonic echo signals and outputs pulse electric signals of the echo signals;

step 3.2: determining a time-varying image of the depth of the boundary of the anterior wall of the artery blood vessel and the boundary of the posterior wall of the artery blood vessel according to the echo signals in the human body; determining the distances from the front wall of the blood vessel to the skin surface layer at different moments according to the propagation average speed of the ultrasonic waves in the human body, and expressing the distances by the following formula:

wherein, X_iThe distance of the anterior wall of the blood vessel from the surface layer of the skin at different moments, t_iFor the moment when the flexible ultrasonic sensor receives the echo signal, T_iC is the average sound velocity of the ultrasonic wave propagating in the human tissue at the moment when the flexible ultrasonic wave sensor transmits the ultrasonic wave, and c is 1540 m/s;

step 3.3: and 3.2, analyzing and calculating each group of ultrasonic emission signals and ultrasonic echo signals to obtain the distance between the front wall and the back wall of the blood vessel in a plurality of cardiac cycles and the skin surface layer, and drawing depth images of the front wall and the back wall of the blood vessel in the tissues in the plurality of cardiac cycles.

Preferably, the step 4 specifically includes:

determining the relation between the human blood pressure value and the cross-sectional area of the human blood vessel at any moment according to the intrinsic functional relation between the diameter of the human blood vessel and the blood pressure of the human body, and expressing the relation between the human arterial blood pressure value and the cross-sectional area of the human blood vessel at any moment by the following formula:

wherein p (t) is the arterial blood pressure value of the human body at any time, p₁Is diastolic blood pressure, A₁The cross-sectional area of the vessel corresponding to the diastolic pressure, A₂Is the cross-sectional area of the heart during systole, p₂The systolic pressure is the systolic pressure, and d is the diameter of a human blood vessel;

and outputting a human arterial pressure oscillogram according to the relation between the human arterial blood pressure value and the cross-sectional area of the human blood vessel at any moment.

The invention has the following beneficial effects:

the invention realizes the miniaturization of the ultrasonic sensor probe, has good skin application property and extensibility, and is expected to be widely applied in the field of wearable electronics of human bodies.

Compared with the traditional B-ultrasonic, the ultrasonic sensor has the advantages that the probe of the ultrasonic sensor is miniaturized, the ultrasonic sensor has good skin application property and extensibility, the sensor can realize good impedance matching without using a coupling agent to achieve better ultrasonic transmission efficiency, the good skin application property of a human body can be realized, the artifact phenomenon caused by instability of a rigid ultrasonic probe when the rigid ultrasonic probe is held by a hand can be avoided, and the accuracy of blood pressure detection is improved. The invention is a non-invasive detection method, has low cost and small wound, can realize the real-time measurement of the blood pressure of a patient in a motion state or a static state, and has great benefits for the prevention and treatment of cardiovascular and cerebrovascular diseases of healthy people and sick people.

Drawings

FIG. 1 is a block diagram of a flexible ultrasonic sensor;

FIG. 2 is a schematic diagram of the implementation of blood pressure detection;

FIG. 3 is a schematic diagram of an ultrasound sensor detecting anterior wall depth at different times during vasodilation;

FIG. 4 is a graph of the depth of the anterior wall of a blood vessel as a function of time;

FIG. 5 is a graph of the depth of the posterior wall of a blood vessel as a function of time;

FIG. 6 is a graph of the change in diameter of a human blood vessel over time;

fig. 7 is a schematic diagram of the detection principle of the pulse echo method.

Detailed Description

The present invention will be described in detail with reference to specific examples.

The first embodiment is as follows:

according to fig. 1, the present invention provides a flexible ultrasonic sensor, which includes a flexible package layer, an upper conductive adhesive layer, a lower conductive adhesive layer, an upper electrode, a lower electrode, an acoustic matching layer, and a plurality of piezoelectric layers;

the upper electrode, the lower electrode, the upper conductive bonding layer, the lower conductive bonding layer, the piezoelectric layer and the acoustic matching layer are packaged through the flexible packaging layer; the upper electrode and the lower electrode are arranged in parallel, a plurality of piezoelectric layers are arranged in parallel gaps between the upper electrode and the lower electrode, the piezoelectric layers are connected with one sides of the upper electrode and the lower electrode through an upper conductive bonding layer and a lower conductive bonding layer, and the other side of the lower electrode is connected with an acoustic matching layer;

the upper electrode and the lower electrode respectively comprise a first square part, a second rectangular part and a third rectangular part, one end of the first square part of the upper electrode and one end of the first rectangular part of the lower electrode pass through one end of the second rectangular part, the other end of the second rectangular part is connected with one end of the third rectangular part, the width of the first square part is larger than that of the third rectangular part, and the width of the third rectangular part is larger than that of the second rectangular part;

the first square parts of the upper electrode and the lower electrode are arranged outside the flexible packaging layer, the third rectangular part is arranged inside the flexible packaging layer, and the other end of the second rectangular part is packaged in the flexible packaging layer.

The piezoelectric layer adopts rectangular piezoelectric ceramic plates (round and other regular polygons are optional) which are arranged in an array mode, and the number n and the pitch p of the piezoelectric ceramic plate arrays can be changed correspondingly according to the attributes of targets to be detected. The dimensions of the individual piezoceramic wafers may also vary, for example their thickness d and side length l. The piezoelectric material can be selected from lead zirconate titanate (PZT-5, PZT-4 series, etc.), lead titanate (PT), piezoelectric composite material (1-3composite), etc., and a grinding wheel dicing saw is used for cutting the sheet-shaped piezoelectric ceramics into rectangular piezoelectric ceramic sheets with required size.

The upper/lower electrode layers adopt island-bridge type snake-shaped interconnection structures, island elements with the number equal to that of the piezoelectric ceramic arrays are arranged on the island-bridge type snake-shaped interconnection structures and used for bonding each piezoelectric ceramic piece, and the snake-shaped structures in the middle can be bent and stretched to provide flexibility and extensibility for the whole device. The electrode layer is composed of two layers, i.e., a polyimide film (PI) and a metal layer. The polyimide film is a polymer with excellent comprehensive performance, has high tensile strength and good light transmission, and can enable the electrode to have good flexibility by using the PI film as a substrate. The desired island bridge pattern can be machined on a full sheet of Polyimide (PI) film using femtosecond laser machining. The metal layer may be deposited using magnetron sputtering, electron beam evaporation, or resistive thermal evaporation to deposit the conductive metal onto the substrate surface.

The conductive adhesive layer can be made of materials with both adhesive and conductive functions, such as epoxy resin conductive adhesive, low-temperature soldering agent and the like, and plays a role in conducting, adhering and fixing between the upper electrode and the conductive layer and between the lower electrode and the conductive layer. The conductive adhesive layer is made of epoxy resin conductive silver adhesive or tin soldering agent, has certain fluidity, can be printed on the surface of each piece of piezoelectric ceramic by using a steel mesh with holes opened by laser, plays a role in adhering the electrode layer and the piezoelectric ceramic, has good conductivity after being cured, and plays a role in conducting the upper electrode and the lower electrode with the piezoelectric ceramic.

The acoustic matching layer is tightly bonded with the outer side of the lower electrode through epoxy resin glue, the acoustic matching layer plays a role in impedance matching of piezoelectric ceramics and human tissues, the reflectivity of an interface where ultrasonic waves are transmitted to a device and the human tissues is reduced, the ultrasonic wave transmittance of the sensor is enhanced, and the transmission efficiency of the ultrasonic waves is improved. The acoustic matching layer acts as an acoustic impedance match between the piezoelectric layer and the skin tissue. The aluminum oxide powder is used as the filler, the epoxy resin and the amine curing agent are used as the matrix for preparation, and the proportion of the filler and the matrix is adjusted, so that the preparation of the impedance layer in the range of 3-15Mrayl can be realized, and the optimal impedance matching requirement required by the sensor in use is met.

The Polydimethylsiloxane (PDMS) is used as the flexible packaging layer of the whole sensor, so that the flexibility of the whole sensor is guaranteed, external water vapor and air can be blocked, and the internal aging failure of a device is prevented.

The packaging layer is made of Polydimethylsiloxane (PDMS), the PDMS monomer and the curing agent are mixed according to the proportion of 10:1, a vacuum drier is used for vacuumizing for 30min after uniform stirring, air bubbles in the solution are discharged, and the packaging layer is placed in an oven (60 ℃) and heated for 12h for curing when in use.

Specific example 2:

as shown in fig. 7, the present invention provides an arterial blood pressure detecting method based on a flexible ultrasonic sensor, comprising the following steps:

step 1: attaching a flexible ultrasonic sensor to the surface of the skin of a human body, wherein the flexible ultrasonic sensor generates high-frequency ultrasonic waves under the excitation action, the high-frequency ultrasonic waves are transmitted in the human body, and echo signals in the human body are received through the flexible ultrasonic sensor;

step 2: determining the sound pressure reflectivity of the ultrasonic wave at the interface between the blood vessel and the blood at different moments according to the acoustic impedance of the human skin tissue and the acoustic impedance of the piezoelectric ceramic sheet;

the step 2 specifically comprises the following steps:

step 2.1: according to acoustic impedance of human vessel wallAnd the acoustic impedance of human blood, determining the acoustic impedance of the optimal matching layer of human tissue, and expressing the acoustic impedance z of the optimal matching layer of human tissue by the following formula_Matching：

Wherein z is₁Acoustic impedance of the wall of a human blood vessel, z₂The acoustic impedance of human blood;

step 2.2: determining the sound pressure reflectivity of the ultrasonic wave at the interface between the blood vessel and the blood at different moments, and expressing the sound pressure reflectivity by the following formula:

wherein, R is the sound pressure reflectivity of the ultrasonic wave at the interface between the blood vessel and the blood at different moments.

And step 3: acquiring echo signals in a human body, wherein the echo signals in the human body comprise echo signals of a front wall and a rear wall of a blood vessel, and determining a depth-time change image of an artery blood vessel front wall boundary and an artery blood vessel rear wall boundary according to the echo signals in the human body; approximating the cross section shape of the human body blood vessel to a perfect circle, and carrying out difference processing on the obtained depth-time change images of the front wall boundary and the rear wall boundary of the human body artery blood vessel to obtain a time-time change image of the section diameter of the human body artery blood vessel;

the step 3 specifically comprises the following steps:

step 3.1: acquiring echo signals in a human body, wherein the echo signals in the human body comprise echo signals of the front wall and the rear wall of a blood vessel, the ultrasonic signals can generate echo signals when reaching the front wall of the blood vessel, and at the time t, the flexible ultrasonic sensor receives the ultrasonic echo signals and outputs pulse electric signals of the echo signals;

step 3.2: determining a time-varying image of the depth of the boundary of the anterior wall of the artery blood vessel and the boundary of the posterior wall of the artery blood vessel according to the echo signals in the human body; determining the distances from the front wall of the blood vessel to the skin surface layer at different moments according to the propagation average speed of the ultrasonic waves in the human body, and expressing the distances by the following formula:

wherein, X_iThe distance of the anterior wall of the blood vessel from the surface layer of the skin at different moments, t_iFor the moment when the flexible ultrasonic sensor receives the echo signal, T_iC is the average sound velocity of the ultrasonic wave propagating in the human tissue at the moment when the flexible ultrasonic wave sensor transmits the ultrasonic wave, and c is 1540 m/s;

step 3.3: and 3.2, analyzing and calculating each group of ultrasonic emission signals and ultrasonic echo signals to obtain the distance between the front wall and the back wall of the blood vessel in a plurality of cardiac cycles and the skin surface layer, and drawing depth images of the front wall and the back wall of the blood vessel in the tissues in the plurality of cardiac cycles.

And 4, step 4: and determining the relationship between the arterial blood pressure of the human body and the diameter of the cross section of the blood vessel to obtain a human arterial pressure waveform diagram.

The step 4 specifically comprises the following steps:

determining the relation between the human blood pressure value and the cross-sectional area of the human blood vessel at any moment according to the intrinsic functional relation between the diameter of the human blood vessel and the blood pressure of the human body, and expressing the relation between the human arterial blood pressure value and the cross-sectional area of the human blood vessel at any moment by the following formula:

wherein p (t) is the arterial blood pressure value of the human body at any time, p₁Is diastolic blood pressure, A₁The cross-sectional area of the vessel corresponding to the diastolic pressure, A₂Is the cross-sectional area of the heart during systole, p₂The systolic pressure is the systolic pressure, and d is the diameter of a human blood vessel;

the sensor attached to the surface of the skin of a human body can generate high-frequency ultrasonic signals under the excitation action of the ultrasonic signal generator, the propagation process of the signals in human tissue is shown in figure 2, the ultrasonic signals penetrate through the human tissue to reach the interface between the wall of the blood vessel of the human body and the blood of the human body, and due to the fact that the acoustic impedances of two propagation media are different, the ultrasonic signals can respectively generate ultrasonic echo signals on the front wall and the rear wall of the blood vessel.

Where acoustic impedance refers to the complex ratio of the acoustic pressure of a medium over an area of the wavefront to the volumetric velocity through that area. It is defined as z ═ ρ c

Where z-the acoustic impedance of a certain medium, ρ is the density, and c is the speed of sound of the sound wave propagating in that medium. Known from the literature, z_{Blood, blood-enriching agent and method for producing the same}＝1.49Mrayl，z_{Vessel wall}＝1.63Mrayl

The calculation can be carried out when the reflectivity of the ultrasonic wave at the interface of the blood vessel tissue and the blood is as follows:

and outputting a human arterial pressure oscillogram according to the relation between the human arterial blood pressure value and the cross-sectional area of the human blood vessel at any moment.

The ultrasonic echo signals can be transmitted to the position of the piezoelectric sensor, the ultrasonic piezoelectric transducer generates mechanical vibration under the action of ultrasonic waves, the ultrasonic transducer can output weak current (voltage) signals under the positive piezoelectric effect at the moment, the echo signals are collected and processed, and then the depth-time change images of the front wall boundary of the artery blood vessel and the back wall boundary of the artery blood vessel can be obtained respectively.

The excitation signal used in ultrasonic medical detection is mostly pulse signal, the commonly used pulse waveform mainly includes single exponential decay pulse, decay oscillation pulse and square wave modulation pulse, and the function expressions are respectively

p＝p_me^-at

p＝p_me^-atsin(ωt)

In the blood pressure detection process, a signal generator of the ultrasonic sensor generates pulse excitation signals at certain time intervals, the pulse duration is short relative to the whole working period time, and in the working mode with extremely low duty ratio, echo signals can be received and processed outside the short working period of the transmitted pulses.

In each cardiac cycle, the heart contracts and expands repeatedly, and accordingly, the diameter of the blood vessel repeats the expansion-diameter increase and expansion-diameter decrease processes. During this process, the ultrasonic signal is generated by excitation at a Pulse Repetition Frequency (PRF), i.e. at T₀、T₁、T₂、T₃、T₄、T₅……T_nGenerating a transmitting ultrasonic signal at a moment, generating an echo signal when the ultrasonic signal reaches the front wall of the blood vessel, and generating a signal at t₀、t₁、t₂、t₃、t₄、t₅At that time, the flexible ultrasonic sensor receives the ultrasonic echo signal and outputs a pulse electric signal of the echo signal.

The average sound velocity c of ultrasonic waves propagating in human tissues is 1450m/s, and the distance of propagation of each ultrasonic wave is 2 times of the detection depth, namely

Wherein, X_iThe distance between the front wall of the blood vessel and the skin surface layer (sensor attaching position) at different moments

As shown in FIG. 3, the depth of the anterior wall in the tissue at different times during the vasodilation process can be obtained by analyzing and calculating each set of the ultrasonic emission signal and the ultrasonic echo signal

X₀＝2c(T₀-t₀)

X₁＝2c(T₁-t₁)

X₂＝2c(T₂-t₂)

X₃＝2c(T₃-t₃)

X₅＝2c(T₄-t₄)

……

X_n＝2c(T_n-t_n)

Similarly, depth images of the anterior wall of the blood vessel in the tissue can be rendered for several cardiac cycles in this way.

And by changing the pulse repetition frequency, namely changing the number of pulses emitted per second when detecting the blood pressure, images of the change of the depth of the vascular wall tissues with time in different degrees of fineness can be obtained, and the obtained front wall depth-time image is shown in fig. 4.

Time-varying images of the distance of the posterior wall of the human blood vessel from the skin surface at different times were obtained using the same method, and the results are shown in FIG. 5

The depth of the anterior wall of the blood vessel is subtracted from the depth of the posterior wall of the blood vessel to obtain a time-dependent curve of the diameter of the blood vessel, as shown in FIG. 6

The above description is only a preferred embodiment of the flexible ultrasonic sensor and the arterial blood pressure detection method thereof, and the protection scope of the flexible ultrasonic sensor and the arterial blood pressure detection method thereof is not limited to the above embodiments, and all technical solutions belonging to the idea belong to the protection scope of the present invention. It should be noted that modifications and variations which do not depart from the gist of the invention will be those skilled in the art to which the invention pertains and which are intended to be within the scope of the invention.