Depth dynamic focusing acoustic lens device and method based on cascade acoustical holography

Abstract

The invention discloses a depth dynamic focusing acoustic lens device and method based on cascade acoustical holography. Comprising a dynamic focusing acoustic lens cascading structure which is arranged in a liquid filling cavity and is mainly formed by cascading two acoustic holographic phase plates in the axial direction, one acoustic holographic phase plate is kept fixed, the other acoustic holographic phase plate moves freely, and dynamic movement of a focus in the depth direction is achieved through axial movement and circumferential rotation; each phase holographic plate is composed of a plurality of microstructure units with different thicknesses in a close array mode, the two sides of each phase holographic plate are concave-convex and flat, and the concave-convex planes face the interior of the cavity. According to the invention, dynamic sound energy focusing can be simply and conveniently realized at a plurality of positions, so that detection and imaging of a detected object on different planes are realized, and the detection efficiency is greatly improved; when in use, the structure can be directly and tightly attached to the surface of a conventional ultrasonic transducer and the surface of a measured component, and scanning and medical treatment of different plane targets can be achieved through simple movement and rotation between holographic plate components in the structure.

Description

Technical Field

[0001] The present invention relates to an ultrasonic acoustic lens technology, and in particular to a deep dynamic focusing acoustic lens device and method based on cascade acoustic holography. Background Art

[0002] Biomedical ultrasound is one of the important new disciplines that uses ultrasound as a carrier, relies on signal processing technology, electronic science and other engineering technology means, and uses the biological effects of ultrasound to achieve disease diagnosis and treatment. Based on the ultrasonic wave dynamic effect, medical ultrasound imaging-diagnosis technologies such as B-ultrasound, ultrasound guidance, and ultrasound angiography have been developed. The acoustic parameters such as acoustic impedance and acoustic attenuation of biological tissues can be characterized by using medical ultrasound probes based on the pulse-echo method. Compared with industrial non-destructive testing, the complexity of biological tissues makes their echo signals carry richer information. For example, based on the elastic coefficient extracted from the echo signal, the detection of parts such as the prostate and breast can be achieved; based on the harmonic components, the nonlinear characteristics of tissue biology can be obtained, and the pathological diagnosis of endocardial and liver cirrhosis lesions can be achieved. At present, the application of medical ultrasound equipment has also received more and more attention. The characteristics of ultrasound detection such as non-invasive, real-time, repeatable, and widely applicable objects make it an indispensable means of preoperative and intraoperative clinical testing, and thus become one of the five major technologies of medical imaging examination.

[0003] At the same time, ultrasound itself carries huge energy. Medical studies have shown that the low-dose thermal effect produced by ultrasound can promote the metabolism of human body functions, promote blood circulation, and accelerate wound healing. At present, the incidence of tumors at home and abroad is increasing year by year. For the treatment of tumors, in addition to traditional surgery, new diagnosis and treatment technologies are emerging in an endless stream. In addition to laparoscopic surgery, minimally invasive treatment has also achieved very good results in clinical application, but minimally invasive treatment based on radio frequency, microwave or freezing technology is still an invasive method, which may cause bleeding or metastasis of punctured tumors. Therefore, in the past 20 years, invasive high-intensity focused ultrasound (HIFU) ablation treatment has received more and more attention. With the increase of ultrasound excitation power, the high-precision sound beam will propagate in human tissues and focus on the target area. The huge energy carried will cause the local area to heat up rapidly. The high-temperature thermal effect can cause the tissue to heat up rapidly and then cause irreversible coagulative necrosis. Since Lynn proposed the idea of ​​non-invasive surgery from in vitro to in vivo in 1942 and conducted damage experiments on animal brain cells and achieved significant results, medical treatment based on HIFU ultrasound has gradually developed. However, most of the existing ultrasonic medical diagnosis and treatment technologies use curved multi-element probes to achieve acoustic energy focusing in the target area, which is difficult to fit perfectly when in contact with the human epidermis, resulting in insufficient acoustic energy coupling and reduced acoustic energy utilization. At the same time, the focus of most existing medical focusing probes is fixed. Although it is possible to scan the same plane horizontally through a planar moving transducer, it is difficult to achieve acoustic energy focusing in multiple planes based on a single focusing transducer. In addition, the characteristics of multiple array elements and curved surfaces have led to the high price and long preparation period of existing ultrasonic medical probes.

[0004] Acoustic holography is an extension and development of computational holography in the field of acoustics. It records the phase or amplitude information of the target holographic sound field in the position of the acoustic holographic pixel unit arranged in two-dimensional space through calculation, and reconstructs the target sound field under specific incident conditions. At present, researchers have used 3D printing technology to process and prepare polymer metasurfaces with varying thickness, called acoustic holographic phase plates, to freely control and reconstruct arbitrarily complex sound fields. However, due to its specific acoustic response characteristics, the 3D-printed acoustic holographic phase plate can only achieve a single holographic sound field.

[0005] Therefore, the prior art lacks a holographic phase plate and device method with a simple and compact structure and high resolution. Summary of the invention

[0006] In order to overcome the shortcomings of the above-mentioned prior art, the present invention provides a deep dynamic focusing acoustic lens device and method based on cascade acoustic holography, targeting the shortcomings of the existing focusing acoustic lens, such as complex structure, large thickness and only one scanning plane, and taking into account the problem that the existing acoustic holographic phase plate can only achieve a single target sound field.

[0007] The depth-adjustable dynamic focusing achieved by the present invention can not only greatly improve the reconstruction freedom of the acoustic holographic phase plate, but also effectively improve the target scanning imaging efficiency in practical applications to achieve multi-plane tomography, or realize medical diagnosis and treatment applications at different depths.

[0008] The device of the present invention can realize a focused acoustic field that changes dynamically along the depth in the measured component when it perfectly fits with the conventional transducer and the measured component. When in use, the two side surfaces of the dynamic focusing acoustic lens device can directly fit with the conventional ultrasonic transducer and the surface of the measured component, and the multi-plane scanning imaging of the target can be achieved through the assembled ultrasonic transducer-planar multi-focus acoustic lens device without water immersion, greatly improving the resolution and efficiency of target imaging.

[0009] The technical solution adopted by the present invention is: 1. A deep dynamic focusing holographic lens device based on cascaded acoustic holographic lenses: An ultrasonic transducer is included for emitting ultrasonic waves; It includes a dynamic focusing acoustic lens cascade structure with two acoustic holographic phase plates with varying relative positions, arranged in front of the probe of the ultrasonic transducer, and used for performing deep dynamic focusing adjustment on the ultrasonic waves emitted by the ultrasonic transducer, and then focusing on the object to be measured; It includes a connecting piece for optically coaxially connecting an ultrasonic transducer and a dynamic focusing acoustic lens cascade structure.

[0010] The object to be tested can generally be mechanical structure defect detection and human tissue imaging.

[0011] The ultrasonic transducer is a conventional ultrasonic transducer.

[0012] The connecting piece adopts a double-opening flange structure, and coaxial through openings are provided at both ends of the double-opening flange structure, and both openings at the two ends are threaded openings.

[0013] The dynamic focusing acoustic lens cascade structure comprises two acoustic holographic phase plates with phase surfaces whose relative distance varies, and a liquid for sound transmission is arranged between the acoustic holographic phase plates; The dynamic focusing acoustic lens cascade structure specifically includes a first acoustic holographic phase plate, a liquid-filled cavity, a second acoustic holographic phase plate and a sealed bottom plate. The first acoustic holographic phase plate is fixedly installed at one end of the liquid-filled cavity, and the sealed bottom plate is fixedly installed at the other end of the liquid-filled cavity. The second acoustic holographic phase plate is movably installed in the other end of the liquid-filled cavity close to the sealed bottom plate. The second acoustic holographic phase plate can move axially or rotate around the center relative to the first acoustic holographic phase plate, and the liquid-filled cavity between the first acoustic holographic phase plate and the sealed bottom plate is filled with the liquid.

[0014] The second acoustic holographic phase plate is connected via an axial movable guide rail, a circumferential movable guide rail structure and the inner wall of the liquid-filled cavity; the axial movable guide rail and the circumferential movable guide rail both include a gear, a motor and a rack, the rack is fixedly mounted on the inner wall surface of the liquid-filled cavity, the motor is fixedly mounted on the second acoustic holographic phase plate, the output shaft of the motor is coaxially connected to the gear, and the gear and the rack are meshed.

[0015] Specifically, the axially movable guide rail includes an axial gear, a motor and a linear axial rack. The axial rack is fixedly mounted on the inner wall surface of the liquid-filled cavity and arranged along the axial direction. The motor is fixedly mounted on the back of the second acoustic holographic phase plate. The output shaft of the motor is coaxially connected to the axial gear, and the axial gear and the axial rack are meshed.

[0016] The circumferential moving guide rail includes a circumferential gear, a motor and an annular circumferential rack. The annular circumferential rack is fixedly mounted on the inner wall surface of the liquid-filled cavity and arranged along the circumferential direction. The motor is fixedly mounted on the back of the second acoustic holographic phase plate. The output shaft of the motor is coaxially connected to the circumferential gear, and the circumferential gear is meshed with the circumferential rack.

[0017] A pair of axial moving guide rails and circumferential guide rails are processed on the inner side wall of the liquid filling cavity, and the second acoustic holographic phase plate is directly fixed on the above-mentioned axial moving guide rails and circumferential guide rails as a movable structure in the cascade holographic system. The other side of the liquid filling cavity is encapsulated by a polymer flat plate, and finally deionized water can be injected into the liquid filling cavity structure as a liquid background medium.

[0018] The thickness of the package plate at the bottom of the liquid-filled cavity is h d and side wall thickness h m Evenly distributed, and in order to reduce the attenuation and reflection of the incident sound waves from the liquid cavity structure, while maintaining the rigidity, h d The thinner the better.

[0019] In order to facilitate assembly and subsequent rotation of the second acoustic holographic phase plate, the first acoustic holographic phase plate, the second acoustic holographic phase plate and the liquid-filled cavity are all cylindrical structures. The liquid-filled cavity is axisymmetric, while the first acoustic holographic phase plate and the second acoustic holographic phase plate used to form the cascaded acoustic holographic system are also non-axisymmetric as a whole.

[0020] The lower surface of the dynamic focusing acoustic lens device is directly bonded to the surface of the component to be measured using a coupling agent, and the assembled transducer-focusing acoustic lens device is moved along the surface of the component to achieve imaging detection of the object to be measured.

[0021] The diameter of the second acoustic holographic phase plate D 2 smaller than the inner diameter of the liquid-filled cavity D 0 , and it is connected and moved with the axial and circumferential slide rails inside the liquid-filled cavity along four angles in the circumferential direction, realizing a mobile cascade system under different intervals and a rotating cascade system under different relative rotation angles.

[0022] The mobile cascade system: the position of the first acoustic holographic phase plate remains fixed, while the second acoustic holographic phase plate moves along the axial moving guide rail, and the control system controls the second acoustic holographic phase plate to move a specific distance along the axial direction and then remain fixed, thereby realizing a specific focused sound field on different target planes of the object under test.

[0023] The rotating cascade system: the position of the first acoustic holographic phase plate remains fixed, while the second acoustic holographic phase plate is fixed on a specific axial plane and rotates along a circumferential moving guide rail on the plane. The second acoustic holographic phase plate is controlled by a control system to rotate circumferentially for a specific distance and then remain fixed, thereby realizing a specific focused sound field on different target planes of the object under test.

[0024] The first acoustic holographic phase plate and the second acoustic holographic phase plate are both polymer flat plate structures with a flat surface on one side and an uneven surface on the other side having a phase distribution. The first acoustic holographic phase plate and the second acoustic holographic phase plate are arranged at intervals along the optical axis, and their respective uneven surfaces are arranged opposite to each other and their respective flat surfaces are arranged outward.

[0025] The uneven surfaces of the first acoustic holographic phase plate and the second acoustic holographic phase plate are partially uneven, or entirely uneven; the partially uneven areas are square or circular.

[0026] The first acoustic holographic phase plate and the second acoustic holographic phase plate are made of a high molecular polymer material with an acoustic attenuation coefficient less than 10%. The high molecular polymer material can usually be a photosensitive resin material, and cannot be rubber, glass, etc.

[0027] The sealing bottom plate and the side wall of the liquid-filled cavity are made of the same polymer material as the acoustic holographic phase plate.

[0028] The optimized phase distribution on the uneven surface of the first and second acoustic holographic phase plates is obtained by adopting the improved multi-layer iterative angular spectrum method design setting of the present invention, and the improved iterative design of optimizing the phase distribution on the plane of the first and second acoustic holographic phase plates achieves further innovation; the thickness of the uneven surface of the first and second acoustic holographic phase plates is further set according to the optimized phase distribution on the uneven surface.

[0029] The multi-layer iterative angular spectrum method designed in the present invention is divided into two parts according to the left and right sides of the second acoustic holographic phase plate plane, and the side of the acoustic holographic metasurface close to the ultrasonic probe is called the incident side, and the side close to the target plane is called the transmission side. The calculation process includes forward and reverse sound field propagation models, and the phase distribution of the first acoustic holographic phase plate and the second acoustic holographic phase plate can be calculated simultaneously by comparing and optimizing with the target plane sound field.

[0030] The phase distribution of the uneven surface of the first acoustic holographic phase plate and the second acoustic holographic phase plate is obtained by multi-layer iterative angular spectrum method processing in the following process; First, before the iterative optimization begins, the phase distributions on the uneven surfaces of the first acoustic holographic phase plate and the second acoustic holographic phase plate are used as the first phase distribution f 1 ’ and the second phase distribution f 2 ’ , randomly set the first phase distribution f 1 ’ and the second phase distribution f 2 ’ For any value, the forward propagation process and reverse optimization process are processed according to the following alternating iterations: 1) Forward propagation process: First, according to the first phase distribution f 1 ’ , get the plane where the first acoustic holographic phase plate is located z =0 Sound field on the transmission side P 0 ( x , y , z =0): P 0 (x , y , z =0)= e ^(j f 1 ’ ) Among them, e represents a natural constant, j represents an imaginary number, x , y , z They represent the three-dimensional coordinates of specific locations, and ^ represents the power; Next, the forward angular spectrum method is used to calculate the ultrasonic wave from the plane where the first acoustic holographic phase plate is located. z =0The transmission side propagates along the positive direction of the z axis to the plane where the second acoustic holographic phase plate is located z = l i ’ The sound field on the incident side is P i ’ ( x , y , z = l i ’ ), and then calculate the plane where the second acoustic holographic phase plate is located z = l i ’ Sound field distribution on the incident side P i ’ ( x , y , z = l i ’ ) through the second phase distribution f 2 ’ The sound field distribution on the transmission side after the second acoustic holographic phase plate is: P i ’’ ( x , y , z = l i ’ )= P i ’ ( x , y , z = l i ’ )* e ^(j f 2 ’ ) The forward angular spectrum method is also used to calculate the acoustic field distribution on the transmission side of the second acoustic holographic phase plate. P i ’’ ( x , y , z = l i ’ ) forward propagates to the target plane z = l i The sound field distribution is P i ’’’ ( x,y , z = l i ); Then, according to the target plane obtained by forward propagation z = l i Sound field distribution P i ’’’ ( x,y , z = l i ) Optimize the target plane as follows z = l i Sound field distribution on Q i ’’’ ( x,y , z = l i ): According to the sound field distribution P i ’’’ ( x,y , z = l i ) to find its phase part: f i = angle ( P i ’’’ ( x,y , z = l i ) ),in angle () represents the phase extraction function, and then the sound field distribution P i’’’ ( x,y , z = l i ) is replaced by the preset target amplitude distribution A i , thus obtaining the forward propagation of this round on the target plane z = l i Optimized sound field distribution Q i ’’’ ( x,y , z = l i ), Q i ’’’ ( x,y , z = l i )= A i *e^(j f i ); 2) Reverse optimization process: First, for the target plane z = l i Optimized sound field distribution Q i ’’’ ( x,y , z = l i ), the reverse angular spectrum method is used to calculate the reverse propagation to the plane where the second acoustic holographic phase plate is located. z = l i ’ The sound field distribution on the transmission side is Q i ’’ ( x , y , z = l i ’ ); Then, according to the plane of the second acoustic holographic phase plate obtained in this round of forward propagation z = l i ’ Sound field distribution on the incident side P i ’ ( x , y ,z = l i ’ ) and the plane where the second acoustic holographic phase plate is located in the reverse propagation process z = l i ’ Sound field distribution on the transmission side Q i ’’ ( x , y , z = l i ’ ), the optimized second phase distribution is obtained by the following process f 2: f 2= angle (∑( Q i ’’ ( x , y , z = l i ’ )*conj( P i ’ ( x , y , z = l i ’ )))) in, conj () represents the conjugate function, angle () represents the phase extraction function; ∑() is the summation function; through this operation, all the situations corresponding to the target sound fields can be integrated into the same second acoustic holographic phase plate.

[0031] At this time, the plane where the second acoustic holographic phase plate is located z = l i ’ Sound field distribution on the transmission side Q i ’’ ( x , y , z = l i ’ ) The second phase distribution is optimized through reverse transmission. f 2, the second acoustic holographic phase plate, and the sound field distribution on the incident side of the second acoustic holographic phase plate Q i’ ( x , y , z = l i ’ )for: Q i ’ ( x , y , z = l i ’ )= Q i ’’ ( x , y , z = l i ’ )*conj( jf 2) Next, the inverse angular spectrum method is used to calculate the plane where the second acoustic holographic phase plate is located. z = l i ’ Sound field distribution on the incident side Q i ’ ( x , y , z = l i ’ ) propagates backward to the first acoustic holographic phase plate plane z =0 Sound field distribution on the transmission side Q i ( x,y , z =0); Finally, from the plane where the first sound holographic phase plate is located z =0 Sound field distribution on the transmission side Q i ( x,y , z =0) to extract and optimize the first phase distribution: f 1= angle (∑ Q i ( x,y , z =0)) 4) The optimized first phase distribution obtained in step 1) f 1 and optimize the second phase distribution f2 Return to step 1) and substitute as the first phase distribution f 2 ’ and the second phase distribution f 2 ’ , and repeat the above steps 1)~3) multiple times to finally obtain the optimized first phase distribution f 1 and optimize the second phase distribution f 2 as the phase distribution on the first acoustic holographic phase plate and the second acoustic holographic phase plate.

[0032] The uneven surfaces in the first acoustic holographic phase plate and the second acoustic holographic phase plate are composed of a plurality of closely arrayed microstructure units, each of which has a constant width and a constant thickness at each location of the microstructure unit, but has different thicknesses; The thickness of the uneven microstructure units on the first acoustic holographic phase plate and the second acoustic holographic phase plate is obtained by the following process according to the optimized phase distribution of the first and second acoustic holographic phase plates: The optimized phase distribution of the first and second acoustic holographic phase plates is equally spaced w Extract the phase value to obtain the corresponding m The phase of the microstructure thickness unit f m , w Represents the periodic interval of the microstructure unit, and then the thickness of each microstructure unit is calculated according to the following formula h um : h um =( f-k w H) / ( k u -k w ) in, k u and k w are the wave numbers of the acoustic holographic phase plate materials of the first and second acoustic holographic phase plates and the liquid inside the liquid-filled cavity, respectively, H A preset fixed distance between the transmission plane and the incident plane. f Represents the phase of the microstructure thickness unit.

[0033] In the present invention, the first acoustic holographic phase plate and the second acoustic holographic phase plate are both configured as a polymer structure of microstructure unit arrays with different thicknesses, and the thickness of each microstructure unit is h m The working frequency of the planar multi-focus acoustic lensf During the design, the thickness dimensions of the thickness microstructure units on the planes of the first acoustic holographic phase plate and the second acoustic holographic phase plate are obtained by multi-layer iterative angular spectrum method. h mi , the width dimension of the thickness microstructure unit is maintained during the design process w constant.

[0034] In a specific implementation, the position and size resolution of each focus in the multi-focus focused sound field realized by the planar multi-focus acoustic lens are designed according to the target plane and the detection accuracy. l i , the focal spot size is s The target sound field, at this time the plane z= l i The amplitude distribution of the focused sound field on is expressed as: A ( x,y , z = l i )=e^-(( x - x 0) 2 +( y - y 0) 2 / s 2 ) in, l i For the focus distance, x 0 and y 0 means the sound energy is focused on the focal plane l i The coordinates on , ^ represents the power.

[0035] For the dynamic focused sound field with changing axial focal length, we have: x 0=0, y 0=0, and the focal length and size resolution of each focus are preset respectively l i and s i , so each focal plane z = l i Each corresponds to a target sound field distribution A i ( x,y , z = l i )=e^-( x 2 + y 2 / s i 2 ).

[0036] Then, according to the target depth focused sound field distribution, the mobile cascade system and the rotating cascade system are designed respectively. In particular, for the mobile cascade system, the preset distances between the second acoustic holographic phase plate and the first acoustic holographic phase plate are z = l i ’ For the rotating cascade system, the distance between the second acoustic holographic phase plate and the first acoustic holographic phase plate is preset to z = l 1 ’ , and the rotation angles of the second acoustic holographic phase plate compared to the first acoustic holographic phase plate are i i ’ .

[0037] During implementation, the above-mentioned preset conditions (the distance between the two holographic plates and the rotation angle) and the target sound field are introduced into the multi-layer iterative angular spectrum method of the present invention for processing.

[0038] The surfaces of the first acoustic holographic phase plate and the second acoustic holographic phase plate prepared are concave-convex on one side and flat on the other side. When in use, the two acoustic holographic phase plates are placed with the concave-convex surfaces facing each other. At this time, there is no need for water immersion. It is only necessary to directly stick the flat surface of the first acoustic holographic phase plate on the surface of the ultrasonic transducer matching layer to achieve modulation of the plane incident wave excited by the ultrasonic transducer and propagate it to the liquid-filled cavity. After being modulated by the second acoustic holographic phase plate, it is coupled to the object to be measured by the flat bottom of the liquid-filled cavity, thereby directly realizing a dynamically changing focused acoustic field distribution in the object to be measured for multi-plane defect detection imaging.

[0039] When the dynamic focusing acoustic lens is used for detecting and imaging the object to be measured, it is assembled with the ultrasonic transducer using a double-head flange structure to form a transducer-acoustic lens device. Then, a layer of ultrasonic coupling agent is applied under the dynamic focusing acoustic lens and then directly pressed against the surface of the component to be measured, so as to generate a focused acoustic field with a depth that dynamically changes in the component to be measured. Then, based on the acoustic reciprocity theorem, the defect echo signal is collected and phase-demodulated, so that enhanced reception of the echo signal can be achieved. Therefore, the dynamic focusing acoustic lens with multiple axial focal points can realize dynamic detection and imaging of defects at different depths, has the application potential of tomographic imaging, and greatly improves the efficiency of ultrasonic detection.

[0040] The device of the present invention can realize dynamic switching between focused sound fields with different focal lengths by designing a cascade focused acoustic hologram composed of the first acoustic holographic phase plate and the second acoustic holographic phase plate, thereby improving the degree of freedom of sound field modulation.

[0041] Considering the size and processing accuracy of the metasurface, the operating frequency of the flat multi-focus acoustic lens can be selected from 100 to 3000 kHz. When the operating frequency changes, the unit thickness of the first acoustic holographic phase plate and the second acoustic holographic phase plate structure needs to be redesigned. h um , simple and efficient design.

[0042] In addition, the first acoustic holographic phase plate, the second acoustic holographic phase plate, the liquid-filled cavity and the bottom plate are all prepared by 3D printing and use the same resin material. The acoustic impedance thereof is relatively matched with the impedance of the matching layer of the piezoelectric transducer and the background water medium, so the acoustic energy transmittance is high, which greatly improves the acoustic energy utilization rate.

[0043] 2. A method for modulating a deep dynamic focusing holographic lens of a deep dynamic focusing holographic lens device: An ultrasonic transducer emits ultrasonic waves which are focused onto a target plane through a dynamic focusing acoustic lens cascade structure. The method can change the focusing sound field distribution of the overall dynamic focusing acoustic lens cascade structure by changing the relative distance and relative rotation angle between the first acoustic holographic phase plate and the second acoustic holographic phase plate, and modulate the focal length of the focused target plane.

[0044] In the present invention, the target plane is the plane where the target sound field is located, that is, the focal plane or the focusing plane.

[0045] In a dynamic focusing acoustic lens device based on cascade acoustic holography of the present invention, it includes a first acoustic holographic phase plate and a second acoustic holographic phase plate prepared by 3D printing technology, which together constitute a moving / rotating cascade acoustic holographic system, and a liquid-filled cavity for fixing the above-mentioned cascade acoustic holographic system, which are finally combined to form a dynamic focusing acoustic lens device.

[0046] Both sides of the dynamic focusing acoustic lens device are flat surfaces. In actual operation, the upper and lower flat surfaces of the dynamic focusing acoustic lens device can be directly attached to the surface of a conventional ultrasonic transducer and the surface of the object to be measured, respectively. After the dynamic focusing acoustic lens device is directly assembled with the conventional ultrasonic transducer using a double-opening flange structure, a focused acoustic field with a specific focal length can be generated in the object to be measured. Then, by changing the distance and rotation angle of the second acoustic holographic phase plate relative to the first acoustic holographic phase plate in the cascade acoustic holography device, the axial focus position can be dynamically changed. By moving the assembled transducer-acoustic lens device along the surface of the object to be measured, scanning imaging on different planes of the object can be achieved, greatly improving the imaging range and degree of freedom.

[0047] The present invention forms a dynamic focusing acoustic lens with flat surfaces on both sides by cascading two acoustic holographic phase plates in an axial direction and encapsulating them in a liquid-filled cavity structure. When in use, the upper and lower surfaces of the dynamic focusing acoustic lens device can be closely fitted with the surface of a conventional ultrasonic transducer and the surface of a component to be measured, respectively. During the process, the mechanical vibration excited by the ultrasonic transducer is first coupled to the dynamic focusing acoustic lens, and after wavefront phase modulation is performed through the cascaded acoustic holographic device, it is radiated to the component to be measured below through the lower surface coupling interface of the dynamic focusing acoustic lens, and finally any target focused acoustic field can be achieved in the component to be measured; then, by changing the spacing and relative rotation angle between the cascaded acoustic holographic devices, acoustic energy focusing at different depths can be achieved. Therefore, through the above-mentioned planar multi-focus acoustic lens device, the inspector can simply and conveniently realize dynamic acoustic energy focusing of the plane wave excited by the conventional piezoelectric probe at multiple positions, thereby realizing detection and imaging on different planes of the object being tested, greatly improving the detection efficiency; when in use, it can be directly and tightly fitted with the conventional ultrasonic transducer and the surface of the component being tested, and the scanning and medical treatment of targets on different planes can be realized by simply moving the holographic plate components within the structure.

[0048] The planar multi-focus acoustic lens device provided by the present invention has the following beneficial effects: (1) The present invention utilizes a cascade acoustic holography system, and by rapidly moving / rotating the second acoustic holographic phase plate, a focused acoustic field with a focus point dynamically moving along the z-axis direction can be realized, thereby realizing multi-plane scanning imaging of the target object in a simple and efficient manner. During use, by assembling the first acoustic holographic phase plate and the second acoustic holographic phase plate in the liquid-filled cavity, a planar focusing acoustic lens with both sides being flat can be prepared. During detection, the flat surfaces on both sides can be directly and perfectly fitted with the conventional ultrasonic transducer and the surface of the component to be tested, thereby realizing in-situ detection of the object to be tested under non-water immersion.

[0049] (2) The planar polymer acoustic lens used in the present invention is easy to process, inexpensive, and can be quickly prepared by 3D printing. At the same time, the preparation material can be selected to match the impedance of the ultrasonic transducer matching layer material, greatly improving the transmittance and conversion rate of the sound field. In addition, by directly replacing the first acoustic holographic phase plate and the second acoustic holographic phase plate, a multi-group focus moving focusing acoustic lens can be realized, which has high operability and reliability.

[0050] The present invention can modulate the plane wave incident by the probe into a focused sound field at different depths and use it to generate a focused sound field that dynamically changes along the depth under the skin of the diagnostic and treatment object, thereby realizing high-resolution tomographic imaging and ablation treatment at different depths. In addition, the acoustic lens device is completely planar, relatively matched with the water acoustic impedance, has high acoustic energy coupling efficiency, simple structure and low price. BRIEF DESCRIPTION OF THE DRAWINGS

[0051] Figure 1 This is a detection principle diagram based on a cascade type dynamic focusing acoustic lens; Figure 2 It is a schematic diagram of a moving and rotating cascade acoustic holographic phase holographic panel device; Figure 3 is a partial cross-sectional view of a dynamic focusing acoustic lens based on cascade acoustic holography according to Example 1 of the present invention; Figure 4 yes Figure 3 AA section view; Figure 5 It is a detailed view of the liquid-filled cavity and the axial and circumferential moving guide rails inside the dynamic focusing acoustic lens 3 based on cascade acoustic holography in Example 1 of the present invention; Figure 6 It is a schematic diagram of a fixed phase holographic plate and a mobile phase holographic plate of a dynamic focusing acoustic lens 3 based on cascade acoustic holography in Example 1 of the present invention; Figure 7 1. The fixed acoustic holographic phase plate and the movable acoustic holographic phase plate and their size diagrams, wherein (a) represents a side view of the first acoustic holographic phase plate, (b) represents a side view of the second acoustic holographic phase plate, (c) represents a cross-sectional view of the first acoustic holographic phase plate, and (d) represents a cross-sectional view of the second acoustic holographic phase plate; Figure 8 1 is a schematic diagram of the design principle of the first and second acoustic holographic phase plates of embodiments 1 and 2 of the present invention, wherein (a) represents the schematic diagram of the design principle of the first and second acoustic holographic phase plates in a mobile cascade system, and (b) represents the schematic diagram of the design principle of the first and second acoustic holographic phase plates in a rotating cascade system; Figure 9 is a flow chart of the phase distribution design of the first acoustic holographic phase plate and the second acoustic holographic phase plate in the moving and rotating cascade system of embodiments 1 and 2 of the present invention; Figure 10 It is a focused sound field distribution diagram of different focal lengths implemented in Example 1 of the present invention. At this time, the second acoustic holographic phase plate moves to different distances corresponding to focused sound fields of different focal lengths, wherein (a) represents the first optimized phase distribution diagram and the second optimized phase distribution diagram, (b) represents the sound field propagation diagram after the incident ultrasound is modulated by the first phase acoustic holographic phase plate, (c) represents the amplitude phase distribution diagram of the transmission side of the second acoustic holographic phase plate when it is located in different planes, (d) represents the sound field propagation diagram propagating from the transmission side of the second acoustic holographic phase plate to the target plane; (e) represents the sound field amplitude distribution diagram on different target planes.

[0052] Figure 11It is a focused sound field distribution diagram of different focal lengths implemented in Example 2 of the present invention. At this time, the second acoustic holographic phase plate rotated to different azimuth angles will correspond to focused sound fields of different focal lengths, wherein (a) represents the first optimized phase distribution diagram and the second optimized phase distribution diagram, (b) represents the sound field propagation diagram after the incident ultrasound is modulated by the first phase acoustic holographic phase plate, (c) represents the amplitude phase distribution diagram of the transmission side of the second acoustic holographic phase plate when it is rotated to different angles, (d) represents the sound field propagation diagram propagated from the transmission side of the second acoustic holographic phase plate to the target plane; (e) represents the sound field amplitude distribution diagram on different target planes.

[0053] Explanation of the accompanying drawings: ultrasonic transducer 1, double-opening flange structure 2, dynamic focusing acoustic lens cascade structure 3, first acoustic holographic phase plate 31, liquid-filled cavity 32, second acoustic holographic phase plate 33, sealing bottom plate 34, axial moving guide rail 35, circumferential moving guide rail 36. DETAILED DESCRIPTION

[0054] In order to enable those skilled in the art to better understand the technical solution of the present invention and implement it, the present invention will be described in detail below in conjunction with the accompanying drawings and specific embodiments. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in the field without creative work are within the scope of protection of the present invention.

[0055] In the description of the present invention, it should be understood that the terms "middle", "upper", "lower", "left", "right", "lateral", "longitudinal", "horizontal", "vertical", "axial", "mirror", "length", "width", "thickness" and the like indicate positions or positional relationships based on the positions or positional relationships shown in the accompanying drawings, which are only for the convenience of describing the technical solution of the present invention and simplifying the description, rather than indicating or implying that the device or equipment referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the present invention. In addition, the terms "including" and "having" and any variations thereof are intended to cover non-exclusive inclusions. In the description of the present invention, unless otherwise specified, the meaning of "plurality" is two or more, which will not be described in detail herein.

[0056] like Figure 1 and Figure 2As shown, the cascaded deep dynamic focusing acoustic lens of the present invention is composed of two phase holographic acoustic lens structures cascaded in the axial direction, wherein one phase holographic acoustic lens remains fixed, while the other phase holographic acoustic lens can move in the axial direction and rotate circumferentially. The two phase holographic acoustic lenses are axially fixed in a liquid cavity, and the relative position is changed by moving the internal guide rail. Both phase holographic plates are polymer structures, and are composed of a plurality of microstructure units in a tight array. The thickness of each microstructure unit is different, forming a structure with a concave convex on one side and a flat one side. At this time, the concave and convex plane of the fixed phase plate is facing the inside of the cavity, so that the upper and lower surfaces of the cascaded acoustic lens structure are both flat. In actual use, the cascaded deep dynamic focusing acoustic lens can be directly connected to a commercial flat probe through a flange connector and then used. At this time, the flat surface of the fixed-phase holographic lens in the cascaded deep dynamic focusing acoustic lens is directly coupled to the ultrasonic transducer matching layer, and the mechanical vibration signal excited by the ultrasonic transducer is coupled to the cascaded dynamic focusing acoustic lens, and phase modulated therein. Then, the other side plane of the cascaded deep dynamic focusing acoustic lens is directly and perfectly fitted with the surface of the object to be measured, and the modulated ultrasonic signal can be coupled to the object to be measured, thereby realizing a dynamically variable focused sound field along the depth direction.

[0057] The specific design of the dynamic focusing acoustic lens device is as follows: Figure 3-Figure 4 shown.

[0058] It includes an ultrasonic transducer 1 for emitting ultrasonic waves; A dynamic focusing acoustic lens cascade structure 3 including two acoustic holographic phase plates with varying relative heights on the surfaces is arranged in front of the probe of the ultrasonic transducer 1 and is used to dynamically adjust the depth of the ultrasonic wave emitted by the ultrasonic transducer 1 and further focus it on the object to be measured; It includes a connector for optically coaxially connecting the ultrasonic transducer 1 and the dynamic focusing acoustic lens cascade structure 3 .

[0059] The connector adopts a double-opening flange structure 2, and coaxial through openings are provided at both ends of the double-opening flange structure 2, and both openings are threaded, so that both openings are connected to the ultrasonic transducer 1 and the dynamic focusing acoustic lens cascade structure 3 through threads, respectively, and then the ultrasonic transducer 1 and the dynamic focusing acoustic lens cascade structure 3 are coaxially connected. The dynamic focusing acoustic lens 3 can be screwed with the through hole below the double-opening flange structure 2 through the side threads, and positioned by a limit platform inside the double-opening flange structure 2.

[0060] The dynamic focusing acoustic lens cascade structure 3 includes two acoustic holographic phase plates whose phase surfaces have a changing relative distance and angle, and a liquid for sound transmission is arranged between the acoustic holographic phase plates, so that the acoustic holographic phase plates are always covered with liquid when the relative distance between the phase surfaces changes. The acoustic holographic phase plate is actually a phase holographic acoustic lens.

[0061] More specifically, the dynamic focusing acoustic lens cascade structure 3 specifically includes a first acoustic holographic phase plate 31, a liquid-filled cavity 32, a second acoustic holographic phase plate 33 and a sealed bottom plate 34. The first acoustic holographic phase plate 31 is fixedly mounted on one end of the liquid-filled cavity 32, the sealed bottom plate 34 is fixedly mounted on the other end of the liquid-filled cavity 32, the second acoustic holographic phase plate 33 is movably mounted in the other end of the liquid-filled cavity 32 close to the sealed bottom plate 34, the second acoustic holographic phase plate 33 can move axially or rotate around the center relative to the fixed first acoustic holographic phase plate 31, and the liquid-filled cavity 32 between the first acoustic holographic phase plate 31 and the sealed bottom plate 34 is filled with liquid. The liquid can be water.

[0062] The first acoustic holographic phase plate 31 is relatively fixed and sealed to one end of the liquid-filled cavity 32 , the sealing bottom plate 34 is relatively fixed and sealed to the other end of the liquid-filled cavity 32 , and the second acoustic holographic phase plate 33 is relatively movable relative to the liquid-filled cavity 32 .

[0063] like Figure 5 As shown, the second acoustic holographic phase plate 33 is connected to the inner wall of the liquid-filled cavity 32 through the axial movable guide rail 35, the circumferential movable guide rail 36 structure, as shown in FIG. Figure 6 As shown, the axial moving guide rail 35 and the circumferential moving guide rail 36 are respectively used for the axial movement or rotation around the center of the second acoustic holographic phase plate 33 relative to the first acoustic holographic phase plate 31; the axial moving guide rail 35 and the circumferential moving guide rail 36 both include gears, motors and racks, the racks are fixedly mounted on the inner wall surface of the liquid-filled cavity 32, the motor is fixedly mounted on the second acoustic holographic phase plate 33, the output shaft of the motor is coaxially connected with the gear, and the gear and the rack are meshed. The operation of the motor drives the gear to rotate, and since the rack is fixed, it drives the motor, the gear and the second acoustic holographic phase plate 33 to move along the rack.

[0064] Specifically, the axially movable guide rail 35 includes an axial gear, a motor and a linear axial rack. The axial rack is fixedly mounted on the inner wall surface of the liquid-filled cavity 32 and arranged along the axial direction. The motor is fixedly mounted on the back side of the second acoustic holographic phase plate 33. The output shaft of the motor is coaxially connected to the axial gear, and the axial gear is meshed with the axial rack.

[0065] The circumferential movable guide rail 36 includes a circumferential gear, a motor and an annular circumferential rack. The annular circumferential rack is fixedly mounted on the inner wall surface of the liquid-filled cavity 32 and arranged along the circumferential direction. The motor is fixedly mounted on the back side of the second acoustic holographic phase plate 33. The output shaft of the motor is coaxially connected to the circumferential gear, and the circumferential gear and the circumferential rack are meshed.

[0066] In a specific implementation, it includes an ultrasonic transducer 1, a double-opening flange structure, a first acoustic holographic phase plate with a fixed structure, a second acoustic holographic phase plate with a movable structure, and a fixed polymer sealing bottom plate 34 arranged in sequence from top to bottom.

[0067] It should be noted that in order to ensure sufficient contact and coupling between the ultrasonic transducer 1 and the dynamic focusing acoustic lens 3, two small holes are processed at the opening above the double-opening flange structure 2, which are used for water inlet and outlet, respectively, so that the interface between the ultrasonic transducer 1 and the dynamic focusing acoustic lens is in a wet state. Among them, the ultrasonic transducer 1, the double-opening flange structure 2, and the dynamic focusing acoustic lens 3 are symmetrical relative to the axis of the ultrasonic transducer 1. The direction perpendicular to the upper and lower surfaces of the dynamic focusing acoustic lens 3 is recorded as the z direction, and the plane parallel to the upper and lower surfaces of the dynamic focusing acoustic lens 3 is recorded as xoy flat.

[0068] In the present invention, the moving / rotating cascade acoustic holographic system composed of the first acoustic holographic phase plate 31 and the second acoustic holographic phase plate 33 arranged in parallel along the axial direction is the core component of the invention. There is relative movement and rotation between the two. During operation, the first acoustic holographic phase plate 31 is kept fixed on the end face of one side of the liquid-filled cavity 32 and remains unchanged, and the second acoustic holographic phase plate 33 is fixed on the axial moving guide rail 35 and the circumferential moving guide rail 36 of the liquid-filled cavity 32, and can move or rotate along the guide rail. Its movement and rotation are controlled by an external control system.

[0069] The first acoustic holographic phase plate 31 and the second acoustic holographic phase plate 33 are both polymer flat plate structures with a flat surface on one side and an uneven surface on the other side having a phase distribution. The first acoustic holographic phase plate 31 and the second acoustic holographic phase plate 33 are arranged at intervals along the optical axis, and their respective uneven surfaces are arranged opposite to each other, and their respective flat surfaces are arranged outward.

[0070] The uneven surfaces of the first acoustic holographic phase plate 31 and the second acoustic holographic phase plate 33 may be partially uneven or completely uneven; if they are partially uneven, the locally uneven area is square or circular.

[0071] The first acoustic holographic phase plate 31 and the second acoustic holographic phase plate 33 are both provided with local unevenness, and the sizes of the local unevenness of the two are the same.

[0072] The first acoustic holographic phase plate 31 and the second acoustic holographic phase plate 33 are made of a polymer material with an acoustic attenuation coefficient less than 0.2, and the polymer material can generally be a resin used in conventional 3D printing, and cannot be rubber, etc. The body parts of the first acoustic holographic phase plate 31 and the second acoustic holographic phase plate 33 are made of the same material as the uneven surface, and are integrally formed.

[0073] For the sealing base plate 34 a polymer material is used which is consistent with the liquid filled cavity.

[0074] In a specific implementation, the sealing bottom plate 34 can be made of the same material as the first acoustic holographic phase plate 31 and the second acoustic holographic phase plate 33 .

[0075] One end of the liquid-filled cavity 32 in contact with the conventional ultrasonic transducer 1 is sealed by a first acoustic holographic phase plate fixed on the structure, while the other end is sealed by a polymer sealing bottom plate 34, which can be directly contacted and coupled with the target to be measured through a coupling agent.

[0076] The fixed liquid-filled cavity 32 is directly fixed to the conventional ultrasonic transducer 1 through the double-opening flange structure 2, and maintains close contact coupling with the matching layer of the ultrasonic transducer 1, while the movable second acoustic holographic phase plate 33 can move or rotate in the liquid of the liquid-filled cavity 32, and the space vacated after the second acoustic holographic phase plate 33 moves or rotates is occupied by the liquid.

[0077] The second acoustic holographic phase plate 33 realizes axial movement along the cascaded acoustic holographic dynamic focusing lens device or circumferential rotation around the cascaded acoustic holographic dynamic focusing lens device through the axial movement guide 35 and the circumferential movement guide 36 structure on the liquid-filled cavity 32, thereby realizing different focusing sound fields in the measured structure.

[0078] The optimized phase distribution on the uneven surface of the first acoustic holographic phase plate 31 and the second acoustic holographic phase plate 33 is obtained by adopting the improved multi-layer iterative angular spectrum method design setting of the present invention, and the optimized iterative algorithm simultaneously optimizes the design of the phase distribution on the plane of the first acoustic holographic phase plate and the second acoustic holographic phase plate, achieving further innovation; the thickness of the uneven surface of the first acoustic holographic phase plate 31 and the second acoustic holographic phase plate 33 is further set according to the optimized phase distribution on the uneven surface.

[0079] In the present invention, based on the known target focal length, the relative distance or relative rotation angle between the first acoustic holographic phase plate and the second acoustic holographic phase plate, the conventional iterative angular spectrum method is firstly improved to form a multi-layer iterative angular spectrum method, and the phase distribution on the plane of the first acoustic holographic phase plate and the second acoustic holographic phase plate is iteratively designed by the multi-layer iterative angular spectrum method, and then the surface thickness at different pixel positions is designed, and finally the first acoustic holographic phase plate and the second acoustic holographic phase plate can be prepared by additive manufacturing.

[0080] The phase distribution of the uneven surfaces of the first acoustic holographic phase plate 31 and the second acoustic holographic phase plate 33 is obtained by multi-layer iterative angular spectrum method using the following process: z = 0represents the plane where the first acoustic holographic phase plate 31 emits ultrasonic waves, z = l i ’ represents the plane perpendicular to the optical axis at the second acoustic holographic phase plate 33, z = l i Indicates the target plane. The sides of the acoustic holographic phase plate close to and far from the ultrasonic transducer are respectively the incident side and the transmission side.

[0081] First, before the iterative optimization begins, the relative distance between the two acoustic holographic phase plates and the target sound field distribution are known in advance, and the phase distributions on the uneven surfaces of the first acoustic holographic phase plate 31 and the second acoustic holographic phase plate 33 are respectively used as the first phase distribution f 1' and second phase distribution f 2', randomly set the first phase distribution f 1' and second phase distribution f 2' is an arbitrary value. The entire iterative optimization process is divided into a forward propagation process and a reverse optimization process that are continuously alternating and iterative. The forward propagation process and the reverse optimization process that are continuously alternating and iterative are processed as follows: 1) Forward propagation process: First, calculate the sound field distribution of the ultrasonic transducer 1 when the ultrasonic wave propagates in the forward direction through the first acoustic holographic phase plate and on its transmission side. P 0 ( x , y , z =0) is: P 0 ( x , y , z =0)= e ^(j f 1') Among them, e represents a natural constant, j represents an imaginary number, x , y , z They represent the three-dimensional coordinates of specific locations, and ^ represents the power; Then the forward angular spectrum method is used to calculate the sound field on the transmission side of the first acoustic holographic phase plate. P 0 ( x , y , z =0) propagates in the positive direction along the z axis l i ’ Sound field distribution from the incident side of the second acoustic holographic phase plate plane P i’ ( x , y , z = l i ’ ).

[0082] Then, when the incident side sound field P i ’ ( x , y , z = l i ’ ) propagates through the phase distribution: f 2 ’ The sound field distribution on the transmission side of the second acoustic holographic phase plate P i ’’ ( x , y , z = l i ’ ) can be further expressed as: P i ’’ ( x , y , z = l i ’ )= P i ’ ( x , y , z = l i ’ )* e ^(j f 2 ’ ) Then, the conventional forward angular spectrum method is used to calculate the sound field on the transmission side of the second acoustic holographic phase plate. P i ’’ ( x , y , z = l i ’ ) propagates along the z-axis to the target plane z = l i Sound field distribution Pi ’’’ ( x,y , z = l i ); Finally, after the above process is completed, according to the target plane z = l i Sound field distribution P i ’’’ ( x,y , z = l i ) According to the following formula, the target plane is obtained z = l i Sound field distribution on: First, according to the sound field distribution P i ’’’ ( x,y , z = l i ) to obtain its phase distribution: f i = angle ( P i ’’’ ( x,y , z = l i )),in angle () represents the phase function, that is, the phase distribution in the sound field distribution is retained and the target plane is z = l i The amplitude distribution in the sound field on the target is partially replaced by the amplitude distribution in the target sound field. A i , thus obtaining the forward propagation to the target plane z = l i Optimized sound field distribution Q i ’’’ ( x,y , z = l i ): Q i ’’’ ( x,y , z = l i )= A i*e^(j f i ( x,y , z = l i )) in, f i ( x,y , z = l i ) represents the phase distribution after optimization on the target plane.

[0083] 2) Reverse optimization process: For the target plane z = l i Optimized sound field Q i ’’’ ( x,y , z = l i ), using the reverse angular spectrum method from the target plane z = l i Propagate along the negative direction of the optical axis z to the plane of the second acoustic holographic phase plate z = l i ’ The sound field distribution on the transmission side is Q i ’’ ( x , y , z = l i ’ ).

[0084] 3) When the second acoustic holographic phase plate is located on the plane z = l i ’ Sound field distribution in front of the transmission side Q i ’’ ( x , y , z = l i ’ ) is propagated backward to the second acoustic holographic phase plate whose phase distribution is to be optimized, the following formula is used according to the acoustic field distribution on the incident side of the second acoustic holographic phase plate obtained during the forward propagation process of step 1) in this round: P i ’ ( x ,y , z = l i ’ ) and the second acoustic holographic phase plate transmission side sound field distribution obtained in the reverse propagation process of step 2). P i ’ ( x , y , z = l i ’ ), and the optimized second phase distribution is obtained by joint processing f 2: f 2=angle(∑( Q i ’’ ( x , y , z = l i ’ )*conj( P i ’ ( x , y , z = l i ’ )))), Among them, conj() represents the conjugate function, angle() represents the extracted phase function, and ∑() is the summation function.

[0085] Then, based on the optimized phase distribution of the second acoustic holographic phase plate, f 2 Calculate the second acoustic holographic phase plate plane according to the following formula z = l i ’ Sound field distribution on the incident side Q i ’ ( x , y , z = l i ’ )for: Q i ’ ( x , y , z = l i ’ )=Q i ’’ ( x , y , z = l i ’ )*conj(i f 2) Then the inverse angular spectrum method is used to analyze the sound field distribution Q i ’ ( x , y , z = l i ’ ) is calculated to obtain the reverse propagation to the first acoustic holographic phase plate plane z =0 The sound field distribution on the transmission side is: Q i ( x,y , z =0) Finally, according to the sound field distribution Q i ( x,y , z =0) and obtain the optimized first phase distribution according to the following formula: f 1=angle(∑ Q i ( x,y , z =0)) 4) The optimized first phase distribution obtained in step 1) f 1 and optimize the second phase distribution f 2 Return to step 1) and repeat the above steps 1) to 3) for multiple times. The specific implementation can be carried out after about 60 forward and backward propagation iterations, and the optimized first phase distribution obtained in the final step is f 1 and optimize the second phase distribution f 2 as the optimized phase distribution on the first acoustic holographic phase plate and the second acoustic holographic phase plate.

[0086] In the case of multiple target sound fields, the sound field distribution Q set when passing through the second acoustic holographic phase plate and the first acoustic holographic phase plate is i ’’ (x,y,z=l i ’ ) and Q iThere are many (x, y, z=0), so the phase distribution of each target sound field on the above two planes is integrated into the final optimized first phase distribution φ1 and second phase distribution φ2 through the summation operation ∑().

[0087] If there are multiple target sound fields, the phase distribution of all i situations is summed by phase summation ∑(), and the phase information corresponding to different target sound fields is integrated into the first and second acoustic holographic phase holographic plates. In the subsequent experimental process, multiple target sound fields can be reconstructed by moving and rotating the second acoustic holographic phase plate.

[0088] The uneven surface in the first acoustic holographic phase plate and the second acoustic holographic phase plate is composed of a plurality of closely arrayed microstructure units, each of which has a constant thickness and different thicknesses, thereby forming an uneven surface structure; in a specific implementation, each microstructure unit is a square, and the side length is the same and preset, that is, the periodic intervals of the microstructure units are w .

[0089] Next, the thickness of the uneven surface on the plane of the first acoustic holographic phase plate and the second acoustic holographic phase plate is designed. The thickness of the uneven surface on the first acoustic holographic phase plate 31 and the second acoustic holographic phase plate 33 is obtained by the following process according to the optimized phase distribution of the uneven surface: The optimized phase distribution of the first acoustic holographic phase plate / the second acoustic holographic phase plate is equally spaced. w Extract the phase value to obtain the corresponding m The phase of the microstructure thickness unit f m , w Represents the periodic interval of the microstructure unit, and then the thickness of each microstructure unit is calculated according to the following formula h um : h um =( f-k w H) / ( k u -k w ) in, k u and k w are the wave numbers of the sound waves of the liquid inside the cavity 32 filled with the acoustic holographic phase plate material liquid of the first and second acoustic holographic phase plates, respectively, f Represents the phase of the microstructure thickness unit. His the measurement plane on the transmission side. Finally, the thickness of each microstructure unit of the first acoustic holographic phase plate and the second acoustic holographic phase plate is obtained. h um ( x , y ).

[0090] In a specific implementation, the ultrasonic transducer 1 emits ultrasonic waves which are focused onto the plane of the target object through the dynamic focusing acoustic lens cascade structure 3. The method changes the relative distance and relative rotation angle between the first acoustic holographic phase plate 31 and the second acoustic holographic phase plate 33, thereby changing the focused acoustic field distribution of the overall dynamic focusing acoustic lens cascade structure 3 based on the cascade acoustic holography, modulating the focal length of the focused target plane, and greatly improving the acoustic field modulation freedom and application potential of the dynamic focusing acoustic lens device.

[0091] like Figure 7 Figures (a) and (b) show side views of the first and second acoustic holographic phase plates provided by the present invention. It can be seen that the first acoustic holographic phase plate 31 and the second acoustic holographic phase plate 33 are both composed of microstructure unit arrays of different thicknesses, and both have a concave-convex surface on one side and a flat surface on the other side. D equal. Figure 7 (c) and (d) are cross-sectional views of the first and second acoustic holographic phase plates, and the width of the microstructure units of both plates is fixed at w It should be noted that the thickness of the first acoustic holographic phase plate 31 and the second acoustic holographic phase plate 33 is h m Based on the incident frequency f When the target sound field distribution is changed, only the thickness of each microstructure unit on the first acoustic holographic phase plate 31 and the second acoustic holographic phase plate 33 needs to be redesigned. h m The target focused sound field can be reproduced.

[0092] Next, the deep dynamic focusing sound field realization of the dynamic focusing acoustic lens 3 in the embodiment of the present invention is described in detail. Assuming that the working frequency is f = 2.5 MHz, the liquid in the liquid filling cavity 32 and the background medium are water (sound velocity c 0 =1500 m / s, wavelength λ=c 0 / f =0.6 mm), and the sound velocity and wave number of the liquid-filled cavity prepared by 3D printing are c u = 2650 m / s and ku =2πf / c w = 5.9×10 3 .

[0093] At this time, the side wall thickness and the end plate thickness of the liquid filling cavity 32 are set to be uniform. h s = 2 mm, with inner and outer diameters of D 1 = 72 mm and D 2 = 76 mm, the diameters of the first acoustic holographic phase plate 31 and the second acoustic holographic phase plate 32 are D= 50 mm. Then, based on the optimized first and second phase distribution f 1' and f 2' Design the thickness of the first acoustic holographic phase plate 31 and the second acoustic holographic phase plate 32 h u .

[0094] Example 1 is as follows: For a dynamic focusing acoustic lens based on a mobile cascade acoustic holography system, the following steps are included: S1: Based on Figure 8 (a), the focal lengths of the three depth focused sound fields are set to be l 1 = 30 mm, l 2 = 40 mm and l 3=50 mm, and the size resolution of the three focal points is σ= 0.8 l Therefore, the sound field amplitudes on the three target planes are: A 10 ( x , y , z=l 1)= A 20 ( x , y , z=l 2)= A 30 ( x , y , z=l 3)=e^-( x 2 + y 2 / s 2 ); at the same time, set the first acoustic holographic phase plate at z= 0 plane, and the second acoustic holographic phase plate can be moved axially toz=l 1 ’ =12 mm, l 2 ’ =14 mm and l 3 ’ =16 mm.

[0095] Then, if Figure 9 As shown, the first acoustic holographic phase plate 31 is designed based on the multi-layer iterative angular spectrum method of the present invention. z= 0 and second sound holographic phase plate 32 plane z=l i ’ Phase distribution on f 1' and f 1': First, calculate the first acoustic holographic phase plate plane z= 0 Transmitted side sound field P 0 ( x , y , z =0)= e ^( if 1 ) propagates along the z-axis to the three target planes. The calculation process is as follows: Calculate the first acoustic holographic phase plate plane z= 0 Spectral distribution on the transmission side P 0 ( k x , k y , z= 0) Forward propagation l 1 ’ , l 2 ’ ,and l 3 ’ Sound field distribution on the incident side of the second acoustic holographic phase plate after the distance P 1 ’ ( x , y , z = l 1 ’ ), P 2 ’ ( x , y , z = l 2 ’ )and P3 ’ ( x , y , z = l 3 ’ ). Next, the sound field distribution of the transmission side sound field transmitted through the second acoustic holographic phase plate 33 is calculated as P i ’’ ( x , y , z = l i ’ )= P i ’ ( x , y , z = l i ’ )* e ^( if 2 ). Based on the forward angular spectrum method, we further obtain P 1 ’’ ( x , y , z = l 1 ’ ), P 2 ’’ ( x , y , z = l 2 ’ )and P 3 ’’ ( x , y , z = l 3 ’ ) propagates forward along the z axis and calculates the target focal plane z = l 1 , l 2 , l 3 Sound field distribution P 1 ’’’ ( x , y ,z = l 1 ), P 2 ’’’ ( x , y , z = l 2 ), P 3 ’’’ ( x , y , z = l 3 ). The phase distribution of the three planes is retained respectively. f 01 = arg ( P 1 ’’’ ( x , y , z = l 1 )), f 02 = arg ( P 2 ’’’ ( x , y , z = l 2 )), f 03 = arg ( P 3 ’’’ ( x , y , z = l 3 )), and replace the sound field amplitude with A 1, A 2, A 3. The sound field distribution of the target plane can be obtained as Q 1 ’’’ ( x , y , z=l 1)= A 1*e^( jf 01 ), Q 2 ’’’ ( x , y , z=l 1)=A 2*e^( jf 02 ), Q 3 ’’’ ( x , y , z=l 1)= A 3*e^( if 03 ).

[0096] Next, the optimized sound field distribution Q i ’’’ ( x , y , z=l i ) propagates backward along the z-axis to the first acoustic holographic phase plane and the second acoustic holographic phase plane. The calculation process is as follows: z = l 1 , l 2 , l 3 Sound field Q 1 ’’’ ( x , y , z=l 1), Q 2 ’’’ ( x , y , z=l 2), Q 3 ’’’ ( x , y , z=l 3) Back propagation ( l i -l i ’ ) to the transmission side of the second acoustic holographic phase plate z = l 1 ’ , l 2 ’ , l 2 ’ , and obtain the sound field distribution Q 1 ’’ ( x , y , z= l 1 ’ ), Q 2 ’’ ( x , y , z = l 2 ’ )and Q 3 ’’ ( x , y , z = l 3 ’ ). Then, based on the acoustic field distribution on the incident and reflected sides of the second acoustic holographic phase plate in forward and reverse propagation, P i ’ ( x , y , z = l i ’ )and Q i ’’ ( k x , k y , z = l i ’ ), update the phase of the second acoustic holographic phase plate to f 2 ’ =angle( P 1 ’ ( x,y , z = l 1 ’ )*conj( Q 1 ’’ ( x,y , z = l 1 ’ ))+ P 2 ’ ( x,y , z = l 2 ’ )*conj(Q 2 ’’ ( x,y , z = l 2 ’ ))+ P 3 ’ ( x,y , z = l 3 ’ )*conj( Q 3 ’’ ( x,y , z = l 3 ’ ))). Then, based on f 2 ’ and three transmission side sound fields Q 1 ’’ ( x,y , z = l 1 ’ ), Q 2 ’’ ( x,y , z = l 2 ’ ), Q 3 ’’ ( x,y , z = l 3 ’ ), and the incident side sound field of the second acoustic holographic phase plate is obtained Q i ’ ( x,y , z = l i ’ )= Q i ’’ ( x,y , z = l i ’ )*conj( e ^( if 2 )),WillQ 1 ’ , Q 2 ’ , Q 3 ’ Continue to separate z = l i ’ Propagate to the transmission side of the first acoustic holographic phase plate z = 0 plane, get the sound field distribution Q 1 ( x , y , z =0), Q 1 ( x , y , z =0) and Q 1 ( x , y , z =0), and then update the phase distribution of the first acoustic holographic phase plate to f 1 ’ =angle( Q 1 ( x , y , z =0)+ Q 2 ( x , y , z =0)+ Q 3 ( x , y , z =0)).

[0097] According to the above forward and back propagation models z= 0 and z = l i ’ Phase distribution on the plane f 1 ’ and f 2 ’ After repeated optimization iterations, convergence can be achieved after about 60 times, and the final phase distribution is f 1 ’ and f2 ’ like Figure 10 As shown in (a).

[0098] S2: The thickness of the array unit of the first acoustic holographic phase plate and the second acoustic holographic phase plate h um It can be calculated by the following formula: h um =( f-k w H) / ( k u -k w ),in, H =3λ.

[0099] At this time, the sound field after the incident ultrasound is modulated by the first acoustic holographic phase plate is as follows Figure 10 As shown in (b), when the first acoustic holographic phase plate 31 is assembled with the conventional ultrasonic transducer, the original plane wave sound field will be modulated by the first acoustic holographic phase plate 31 and display different sound field distributions in the three planes of 10mm, 12mm, and 14mm. The corresponding amplitude and phase distributions are shown as follows: Figure 10 (c) (the left column is the amplitude distribution after modulation, and the right column is the phase distribution after modulation). After further modulation by the second acoustic holographic phase plate 33, the transmitted sound field will be focused at the planes of 30 mm, 40 mm and 50 mm respectively. The sound field propagating from the transmission side of the second acoustic holographic phase plate to the target plane is shown as follows: Figure 10 (d), the sound fields of different target planes are as follows Figure 10 (e).

[0100] Example 2 is as follows: For a dynamic focusing acoustic lens based on a rotating cascade acoustic holography system, the following steps are included: S1: based on Figure 8 (b), first set the focal length of the deep focused sound field to be l 1 = 30 mm, l 2 = 40 mm and l 3=50 mm, and the lateral resolution of the three focal points is σ= 0.8 l Therefore, the sound field amplitudes on the three target planes are: A 10 ( x , y , z=l 1)= A 20 ( x , y , z=l 2)=A 30 ( x , y , z=l 3)= A e^-( x 2 + y 2 / s 2 ),in A =1; at the same time, set the first acoustic holographic phase plate to z= 0 plane, and the second acoustic holographic phase plate is located at z=l 1 ’ = 12 mm plane, but it will be rotated 0°, 90° and 180° around the axis respectively.

[0101] Then, if Figure 9 As shown, the first acoustic holographic phase plate 31 is designed based on the multi-layer iterative angular spectrum method of the present invention. z= 0 and second sound holographic phase plate 33 plane z=l 1 ’ Phase distribution on f 1 ’ and f 2 ’ : First, the sound field is calculated to propagate along the z-axis to the target plane. The calculation process is as follows: Calculate the sound field on the transmission side of the first acoustic holographic phase plate 31 P 0 ( x , y , z =0)=e^-( jf 1 ’ ) propagates in the forward direction l 1 ’ After the distance, the sound field distribution on the incident side of the second acoustic holographic phase plate 33 P 1 ’ ( x , y , z = l 1 ’ ). Then, the acoustic field distribution on the transmission side of the second acoustic holographic phase plate 33 is calculated as follows: P 1 ’’ ( x , y , z = l 1 ’ )= P 1 ’ ( x ,y , z = l 1 ’ ) e ^( jf 2 ’ ), P 2 ’’ ( x , y , z = l 1 ’ )= P 1 ’ ( x , y , z = l 1 ’ ) e ^( j ( f 2 ’ ) T ), P 3 ’’ ( x , y , z = l 1 ’ )= P 1 ’ ( x , y , z = l 1 ’ ) e ^( j ( f 2 ’ ) R ). Wherein, 'T' and 'R' represent the transposition and upside-down flipping of the matrix respectively. Further, the above sound field is propagated forward ( l i - l 1 ’ ) distance to the target focal plane, and obtain the target focal plane z = l 1 , l 2 , l 3 Sound field distribution P 1 ’’’ ( x , y , z = l 1 ),P 2 ’’’ ( x , y , z = l 2 ), P 3 ’’’ ( x , y , z = l 3 ). The phase distribution of the three planes is retained respectively. f 01 = arg ( P 1 ’’’ ( x , y , z = l 1 )), f 02 = arg ( P 2 ’’’ ( x , y , z = l 2 )), f 03 = arg ( P 3 ’’’ ( x , y , z = l 3 )), and replace the sound field amplitude with A 1, A 2, A 3. The target plane sound field distribution can be obtained as Q 1 ’’’ ( x , y , z=l 1)= A 1*e^( jf 01 ), Q 2 ’’’ ( x , y , z=l 1)= A 2*e^( jf 02 ),Q 3 ’’’ ( x , y , z=l 1)= A 3*e^( if 03 ).

[0102] Next, the optimized target plane sound field distribution Q i ’’’ ( x , y , z=l i ) propagates backward along the z axis to the first acoustic holographic phase plate plane. The calculation process is as follows: the target plane sound field Q 1 ’’’ ( x , y , z=l 1), Q 2 ’’’ ( x , y , z=l 2), Q 3 ’’’ ( x , y , z= l 3) Back propagation ( l i -l 1 ’ ) and obtain the second acoustic holographic phase plate plane z = l 1 ’ The sound field distribution on the transmission side is Q 1 ’’ ( x , y , z = l 1 ’ ), Q 2 ’’ ( x , y , z = l 1 ’ ), Q 3 ’’ ( x , y , z = l 1 ’). Then, based on the acoustic field distribution on the incident side of the second acoustic holographic phase plate in forward propagation P 1 ’ ( x , y , z = l 1 ’ ) and the acoustic field distribution on the transmission side in reverse propagation Q i ’’ ( k x , k y , z = l i ’ ), update the second sound holographic phase plate phase to f 2 ’ =angle( P 1 ’’ ( x,y , z = l 1 ’ )*conj( Q 1 ’’ ( x,y , z = l 1 ’ ))+ P 1 ’’ ( x,y , z = l 1 ’ )*conj( Q 2 ’’ ( x,y , z = l 1 ’ ))+ P 1 ’’ ( x,y , z = l 1 ’ )*conj( Q 3 ’’ ( x,y , z = l 1 ’ ))). Then, based on f 2 ’ and the transmitted side sound field Q 1 ’’( x,y , z = l 1 ’ ), Q 2 ’’ ( x,y , z = l 1 ’ ), Q 3 ’’ ( x,y , z = l 1 ’ ), calculate the incident side sound field of the second acoustic holographic phase plate Q 1 ’ ( x,y , z = l 1 ’ )= Q 1 ’’ ( x,y , z = l 1 ’ )*conj( e ^( if 2 ’ )), Q 2 ’ ( x,y , z = l 1 ’ )= Q 2 ’’ ( x,y , z = l 1 ’ )*conj( e ^( i ( f 2 ’ ) T )), Q 3 ’ ( x,y , z = l 1 ’ )= Q 3 ’’ ( x,y , z = l 1 ’)*conj( e ^( i ( f 2 ’ ) R )), and continue to propagate along the negative direction of the z-axis to the transmission side of the first acoustic holographic phase plate z = 0 plane, and obtain its sound field distribution Q 1 ( x , y , z =0), Q 1 ( x , y , z =0) and Q 1 ( x , y , z =0), and update the phase distribution of the first acoustic holographic phase plate to f 1 ’ =angle( Q 1 ( x , y , z =0)+ Q 2 ( x , y , z =0)+ Q 3 ( x , y , z =0)).

[0103] According to the above forward and back propagation models z= 0 and z = l i ’ Phase distribution on the plane f 1 ’ and f 2 ’ After repeated optimization iterations, convergence can be achieved after about 60 times, and the final phase distribution is f 1 ’ and f 2 ’ like Figure 11 As shown in (a).

[0104] S2: Then, based on the above phase distribution, the array unit thickness of the first acoustic holographic phase plate and the second acoustic holographic phase plate is h ui It can be calculated by the following formula: h um =( f-k w H) / ( k u -k w ),in, H =3λ.

[0105] like Figure 11 (a) shows the phase distribution of the first acoustic holographic phase plate 31 and the second acoustic holographic phase plate 33. First, when the first acoustic holographic phase plate 31 is assembled with a conventional ultrasonic transducer, the original plane wave sound field will be modulated by the first acoustic holographic phase plate 31. At this time, the sound field of the incident ultrasound after being modulated by the first acoustic holographic phase plate is as shown in FIG. Figure 11 (b). The modulated sound wave continues to propagate forward, and then after coupling with the second acoustic holographic phase plate 33 rotated by 0°, 90° and 180°, the sound field at z=12mm will be remodulated, and the amplitude and phase distribution are respectively as follows: Figure 11 (c) (the left column is the amplitude distribution after modulation, and the right column is the phase distribution after modulation). The modulated sound wave continues to propagate forward. At this time, the sound field propagating from the transmission side of the second acoustic holographic phase plate to the target plane is as follows: Figure 11 (d), after being modulated by the second acoustic holographic phase plate 33, the acoustic energy is focused at the planes of 30 mm, 40 mm and 50 mm respectively. At this time, the sound fields of different target planes are as follows Figure 11 (e).

[0106] In the above embodiments, the description of each embodiment has its own emphasis. For parts that are not described in detail in a certain embodiment, reference can be made to the relevant descriptions of other embodiments.

[0107] The embodiments of the present application are described in detail above. Specific examples are used herein to illustrate the principles and implementation methods of the present invention. The description of the above embodiments is only used to help understand the method of the present invention and its core idea. At the same time, for those skilled in the art, according to the idea of ​​the present invention, there will be changes in the specific implementation method and application scope. In summary, the content of this specification should not be understood as a limitation of the present invention.

Claims

1. A deep dynamic focusing acoustic lens device based on cascade acoustic holography, characterized in that: It comprises an ultrasonic transducer (1) for emitting ultrasonic waves; It comprises a dynamic focusing acoustic lens cascade structure (3) with two acoustic holographic phase plates with varying relative positions, arranged in front of a probe of an ultrasonic transducer (1) and used for dynamically adjusting the depth of the ultrasonic wave emitted by the ultrasonic transducer (1) so as to focus on the object to be measured; It comprises a connecting piece used for optically coaxially connecting an ultrasonic transducer (1) and a dynamic focusing acoustic lens cascade structure (3).

2. The deep dynamic focusing acoustic lens device based on cascade acoustic holography according to claim 1, characterized in that: The connecting piece adopts a double-opening flange structure (2), and the double-opening flange structure (2) has coaxial through openings at both ends, and both openings at the two ends are threaded openings.

3. The deep dynamic focusing acoustic lens device based on cascade acoustic holography according to claim 1, characterized in that: The dynamic focusing acoustic lens cascade structure (3) comprises two acoustic holographic phase plates with phase surfaces whose relative distance varies, and a liquid for sound transmission is arranged between the acoustic holographic phase plates; the dynamic focusing acoustic lens cascade structure (3) specifically comprises a first acoustic holographic phase plate (31), a liquid-filled cavity (32), a second acoustic holographic phase plate (33) and a sealed bottom plate (34); the first acoustic holographic phase plate (31) is fixedly mounted on one end of the liquid-filled cavity (32); the sealed bottom plate (34) is fixedly mounted on the other end of the liquid-filled cavity (32); the second acoustic holographic phase plate (33) is movably mounted in the other end of the liquid-filled cavity (32) close to the sealed bottom plate (34); the second acoustic holographic phase plate (33) can move axially relative to the first acoustic holographic phase plate (31) or rotate around the center; the liquid-filled cavity (32) between the first acoustic holographic phase plate (31) and the sealed bottom plate (34) is filled with the liquid.

4. The deep dynamic focusing acoustic lens device based on cascade acoustic holography according to claim 3 is characterized in that: The second acoustic holographic phase plate (33) is connected to the inner wall of the liquid-filled cavity (32) via an axial movable guide rail (35), a circumferential movable guide rail (36) structure; the axial movable guide rail (35) and the circumferential movable guide rail (36) both comprise a gear, a motor and a rack; the rack is fixedly mounted on the inner wall surface of the liquid-filled cavity (32); the motor is fixedly mounted on the second acoustic holographic phase plate (33); the output shaft of the motor is coaxially connected to the gear, and the gear and the rack are meshed.

5. The deep dynamic focusing acoustic lens device based on cascade acoustic holography according to claim 3, characterized in that: The first acoustic holographic phase plate (31) and the second acoustic holographic phase plate (33) are both polymer flat plate structures with a flat surface on one side and an uneven surface on the other side having a phase distribution. The first acoustic holographic phase plate (31) and the second acoustic holographic phase plate (33) are arranged at intervals along the optical axis, with their respective uneven surfaces arranged opposite to each other and their respective flat surfaces arranged facing outwards.

6. The deep dynamic focusing acoustic lens device based on cascade acoustic holography according to claim 3, characterized in that: The first acoustic holographic phase plate (31) and the second acoustic holographic phase plate (33) are made of a high molecular polymer material with an acoustic attenuation coefficient of less than 10%, and the sealing bottom plate (34) and the side wall of the liquid-filled cavity are made of the same high molecular material as the acoustic holographic phase plate.

7. The deep dynamic focusing acoustic lens device based on cascade acoustic holography according to claim 3, characterized in that: The optimized phase distribution of the uneven surfaces on the first acoustic holographic phase plate (31) and the second acoustic holographic phase plate (33) is obtained by using a multi-layer iterative angular spectrum method; and the thickness of the uneven surfaces on the first acoustic holographic phase plate (31) and the second acoustic holographic phase plate (33) is set according to the optimized phase distribution of the uneven surfaces.

8. The deep dynamic focusing acoustic lens device based on cascade acoustic holography according to claim 7, characterized in that: The phase distribution of the uneven surfaces on the first acoustic holographic phase plate (31) and the second acoustic holographic phase plate (33) is obtained by multi-layer iterative angular spectrum method processing using the following process; First, before the iterative optimization begins, the phase distributions on the uneven surfaces of the first acoustic holographic phase plate (31) and the second acoustic holographic phase plate (33) are respectively used as the first phase distribution φ 1 ’ and the second phase distribution φ 2 ’ , randomly set the first phase distribution φ 1 ’ and the second phase distribution φ 2 ’ For any value, the forward propagation process and reverse optimization process are processed according to the following alternating iterations: 1) Forward propagation process: First, according to the first phase distribution φ 1 ’ , get the plane where the first acoustic holographic phase plate is located z =0 Sound field on the transmission side P 0 ( x , y , z =0): P 0 ( x , y , z =0)= e ^(j φ 1 ’ ) Among them, e represents a natural constant, j represents an imaginary number, x , y , z Respectively represent the three-dimensional coordinates of specific locations, and ^ represents the power; Next, the forward angular spectrum method is used to calculate the ultrasonic wave from the plane where the first acoustic holographic phase plate is located. z =0The transmission side propagates along the positive direction of the z axis to the plane where the second acoustic holographic phase plate is located z = l i ’ The sound field on the incident side is P i ’ ( x , y , z = l i ’ ), and then calculate the plane where the second acoustic holographic phase plate is located z = l i ’ Sound field distribution on the incident side P i ’ ( x , y , z = l i ’ ) through the second phase distribution φ 2 ’ The sound field distribution on the transmission side after the second acoustic holographic phase plate is: P i ’’ ( x , y , z = l i ’ )= P i ’ ( x , y , z = l i ’ )* e ^(j φ 2 ’ ) The forward angular spectrum method is also used to calculate the acoustic field distribution on the transmission side of the second acoustic holographic phase plate. P i ’’ ( x , y , z = l i ’ ) forward propagates to the target plane z = l i The sound field distribution is P i ’’’ ( x,y , z = l i ); Then, according to the target plane obtained by forward propagation z = l i Sound field distribution P i ’’’ ( x,y , z = l i ) Optimize the target plane as follows z = l i Sound field distribution on Q i ’’’ ( x,y , z = l i ): According to the sound field distribution P i ’’’ ( x,y , z = l i ) to find its phase part: φ i = angle ( P i ’’’ ( x,y , z = l i ) ),in angle () represents the phase extraction function, and then the sound field distribution P i ’’’ ( x,y , z = l i ) is replaced by the preset target amplitude distribution A i , thus obtaining the forward propagation of this round on the target plane z = l i Optimized sound field distribution Q i ’’’ ( x,y , z = l i ); 2) Reverse optimization process: First, for the target plane z = l i Optimized sound field distribution Q i ’’’ ( x,y , z = l i ), and then the reverse angular spectrum method is used to calculate the reverse propagation to the plane where the second acoustic holographic phase plate is located. z = l i ’ The sound field distribution on the transmission side is Q i ’’ ( x , y , z = l i ’ ); Then, according to the plane of the second acoustic holographic phase plate obtained in this round of forward propagation z = l i ’ Sound field distribution on the incident side P i ’ ( x , y , z = l i ’ ) and the plane where the second acoustic holographic phase plate is located in the reverse propagation process z = l i ’ Sound field distribution on the transmission side Q i ’’ ( x , y , z = l i ’ ), the optimized second phase distribution is obtained by the following process φ 2: φ 2= angle (∑( Q i ’’ ( x , y , z = l i ’ )*conj( P i ’ ( x , y , z = l i ’ )))) in, conj () represents the conjugate function, angle () represents the phase extraction function; ∑() is the summation function; At this time, the plane where the second acoustic holographic phase plate is located z = l i ’ Sound field distribution on the transmission side Q i ’’ ( x , y , z = l i ’ ) The second phase distribution is optimized through reverse transmission. φ 2, the second acoustic holographic phase plate, and the sound field distribution on the incident side of the second acoustic holographic phase plate Q i ’ ( x , y , z = l i ’ )for: Q i ’ ( x , y , z = l i ’ )= Q i ’’ ( x , y , z = l i ’ )*conj( jφ 2) Next, the inverse angular spectrum method is used to calculate the plane where the second acoustic holographic phase plate is located. z = l i ’ Sound field distribution on the incident side Q i ’ ( x , y , z = l i ’ ) propagates backward to the first acoustic holographic phase plate plane z =0 Sound field distribution on the transmission side Q i ( x,y , z =0); Finally, from the plane where the first sound holographic phase plate is located z =0 Sound field distribution on the transmission side Q i ( x,y , z =0) to extract and optimize the first phase distribution: φ 1= angle (∑ Q i ( x,y , z =0)) 4) The optimized first phase distribution obtained in step 1) φ 1 and optimize the second phase distribution φ 2 Return to step 1) and repeat steps 1) to 3) multiple times to obtain the optimal first phase distribution. φ 1 and optimize the second phase distribution φ 2 as the phase distribution on the first acoustic holographic phase plate and the second acoustic holographic phase plate.

9. The deep dynamic focusing acoustic lens device based on cascade acoustic holography according to claim 7, characterized in that: The uneven surfaces of the first acoustic holographic phase plate and the second acoustic holographic phase plate are composed of a plurality of closely arrayed microstructure units, each microstructure unit has a constant thickness at various locations, and each microstructure unit has a different thickness; the thickness of the uneven microstructure units on the first acoustic holographic phase plate (31) and the second acoustic holographic phase plate (33) is obtained by the following process based on the optimized phase distribution of the first and second acoustic holographic phase plates: The optimized phase distribution of the first and second acoustic holographic phase plates is equally spaced w Extract the phase value to obtain the corresponding m The phase of the microstructure thickness unit φ m , w Represents the periodic interval of the microstructure unit, and then the thickness of each microstructure unit is calculated according to the following formula h um : h um =( φ-k w H) / ( k u -k w ) in, k u and k w are the wave numbers of the acoustic holographic phase plate material and the liquid inside the liquid-filled cavity (32), respectively, H A preset fixed distance between the transmission plane and the incident plane. φ Represents the phase of the microstructure thickness unit.

10. A deep dynamic focusing holographic lens modulation method applied to the deep dynamic focusing acoustic lens device according to any one of claims 3 to 9, characterized in that: An ultrasonic transducer (1) emits ultrasonic waves which are focused onto a target plane via a dynamic focusing acoustic lens cascade structure (3). The method modulates the focal length of the focused target plane by changing the relative distance and relative rotation angle between the first acoustic holographic phase plate (31) and the second acoustic holographic phase plate (33) to change the focused acoustic field distribution of the entire dynamic focusing acoustic lens cascade structure (3).

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