A multi-frequency laser ultrasonic holographic system and design method

Abstract

The present application relates to the field of laser ultrasound technology, and specifically discloses a multi-main-frequency laser ultrasound holographic system and a design method. The system includes a laser and a laser beam adjustment module for receiving and adjusting the laser beam, wherein the laser beam adjustment module includes a coaxially arranged beam expander and a collimator, the beam expander is used to adjust the diameter of the laser beam, and the collimator is used to collimate the laser beam so that the beam remains parallel and focused; the frequency-mixing ultrasound holographic lens includes a light focusing layer, an acoustic confinement layer, a light absorption layer, an acoustic matching layer and an acoustic holographic layer stacked in sequence, and the frequency-mixing ultrasound holographic lens is used to receive the laser beam passing through the laser beam adjustment module to generate stable single or multiple focused ultrasound sound fields of multiple different preset frequencies in a time-sharing or simultaneous manner, and the focus position and power are adjustable, and can be used for ultrasound manipulation and driving, ultrasound detection imaging, low-power ultrasound stimulation or power ultrasound treatment, etc.

Description

Technical Field

[0001] This application relates to the field of laser ultrasonic technology. Specifically, it relates to a multi-frequency laser ultrasonic holographic system and a design method. Background Art

[0002] As a new non-destructive testing technology that has emerged in the past decade or so, laser ultrasound has the advantages of high resolution, non-contact, and long detection distance. Acoustic holography technology has become an important part of a wide range of acoustic applications, such as biomedical imaging, medical treatment, and acoustic tweezers. The basis of holography is the spatial storage of the phase and amplitude profiles of the required wavefront, so that when irradiated with a suitable coherent source, the wavefront is interferometrically reconstructed to target the acoustic field.

[0003] Modern computer-generated holograms skip the process of recording holograms from physical scenes and instead calculate the required phase profiles before rendering for reconstruction. In the application of ultrasonic holography technology, traditional phased systems based on array ultrasonic sensors limit the number of channels of the phased system due to the manufacturing difficulty and cost of the system, which restricts the complexity or degrees of freedom that can be obtained in the ultrasonic wavefront. Moreover, the ultrasonic sound fields generated by traditional ultrasonic sensors and focusing acoustic lenses can only have one focused focus, and the position and power of the focused focus are usually fixed and non-adjustable. In practical applications, such as in tumor ablation treatment, a single-frequency single-focus ultrasonic field often has low treatment efficiency. Also, in defect detection, a single-frequency single-focus has low accuracy in evaluating material defects. Therefore, how to generate stable multiple focused ultrasonic sound fields with multiple preset frequencies has become an urgent problem to be solved. Summary of the Invention

[0004] The present invention aims to solve one of the technical problems existing in the related technologies proposed in the background art. Based on this, this application proposes a multi-frequency laser ultrasonic holographic system and a design method.

[0005] In a first aspect, this application provides a multi-frequency laser ultrasonic holographic system, including:

[0006] A laser, electrically connected to a computer and used to emit a laser beam according to the laser parameters set by the computer, where the laser beam includes one of a pulsed laser beam or a continuously modulated laser beam;

[0007] A laser beam adjustment module, used to receive and adjust the laser beam. Among them, the laser beam adjustment module includes a beam expander and a collimator arranged coaxially. The beam expander is used to adjust the diameter of the laser beam, and the collimator is used to collimate the laser beam so that the light beam remains parallel and focused;

[0008] A mixed-frequency ultrasonic holographic lens, which is used to receive the laser beam passing through the laser beam adjustment module to generate multiple focused ultrasonic fields with multiple preset frequencies.

[0009] According to some embodiments of the present application, the mixed-frequency ultrasonic holographic lens includes an optical focusing layer, an acoustic confinement layer, an optical absorption layer, an acoustic matching layer, and an acoustic holographic layer that are sequentially stacked.

[0010] According to some embodiments of the present application, the optical focusing layer is composed of one or more lens arrays. The optical focusing layer is used to focus the laser beam to generate a single or an array of multiple focused spots, and irradiate the focused spots through the acoustic confinement layer to the optical absorption layer.

[0011] According to some embodiments of the present application, the optical absorption layer is used to absorb the light energy of the focused spots to generate a single or an array of multiple ultrasonic spherical waves, and form an amplified laser ultrasonic field based on the reflection and superposition of the acoustic confinement layer.

[0012] According to some embodiments of the present application, the acoustic holographic layer sets multiple regions according to a preset plurality of frequencies. Each region is composed of multiple holographic units, and each region regulates the corresponding ultrasonic frequency.

[0013] According to some embodiments of the present application, the phase and amplitude of the corresponding ultrasonic wave are controlled based on the thickness of each holographic unit.

[0014] According to some embodiments of the present application, the relationship between the thickness of the holographic unit and the phase of the ultrasonic wave satisfies: ,

[0015] In the formula, is the phase value corresponding to the holographic unit , i and j respectively represent the row index and column index of the holographic unit in the two-dimensional plane, is the ultrasonic frequency, and are the sound velocities of the propagation medium and the acoustic holographic layer material respectively.

[0016] According to some embodiments of the present application, the relationship between the thickness of the holographic unit and the amplitude of the ultrasonic wave satisfies: ,

[0017] Where, represents the amplitude of the ultrasonic wave, represents the sound pressure of the ultrasonic spherical wave after acoustic characteristic matching emitted from the acoustic matching layer, represents the thickness of the holographic unit, represents the acoustic impedance of the acoustic matching layer, represents the impedance of the single-frequency acoustic holographic layer, represents the acoustic impedance of the propagation medium, represents the wave number of the single-frequency acoustic holographic layer.

[0018] Among the above technical solutions provided by this application, compared with the prior art, it at least includes the following beneficial effects or advantages:

[0019] In the multi-frequency laser ultrasonic holographic system of this application, through the setting of the mixed-frequency ultrasonic holographic lens, the mixed-frequency ultrasonic holographic lens includes an optical focusing layer, an acoustic confinement layer, an optical absorption layer, an acoustic matching layer, and an acoustic holographic layer that are stacked in sequence. Among them, multiple regions are set on the acoustic holographic layer according to a plurality of preset frequencies, and each region regulates the corresponding ultrasonic frequency. Each region is composed of multiple holographic units. By controlling the thickness of the holographic units, the phase and amplitude of the corresponding ultrasonic waves are controlled. After the ultrasonic frequencies regulated by the acoustic holographic layer are set, continuous modulation laser beams with corresponding frequencies are respectively irradiated on the left and right regions of the optical focusing layer, or broadband pulsed laser beams are irradiated on the left and right regions of the optical focusing layer simultaneously or at different times, so as to achieve the generation of single or multiple focused ultrasonic sound fields with stable and multiple different preset frequencies at different times or simultaneously, and the positions and powers of the focused focal points are usually adjustable. In practical applications, multiple focused ultrasonic sound fields can be used to improve the efficiency of ultrasonic manipulation and driving; the low-frequency ultrasonic waves in multiple focused ultrasonic sound fields can be used for ultrasonic emission of deep defects, while the high-frequency ultrasonic waves can be used for ultrasonic emission of more refined surface defects, thereby improving the accuracy of material evaluation; and in ablation therapy, high-frequency ultrasound is used for tumor imaging to detect tumors; at the same time, low-frequency ultrasound is used for tumor ablation to improve the treatment efficiency.

[0020] In the second aspect, this application provides a design method for the multi-frequency laser ultrasonic holographic system described in the first aspect above. The method includes:

[0021] Use transparent nylon for 3D printing to design the optical focusing layer, the acoustic confinement layer, and the acoustic matching layer;

[0022] Use mixed carbon nanoparticles or black metal films to design the optical absorption layer;

[0023] According to the preset frequencies and focal point parameter information corresponding to the holographic system, determine the different ultrasonic frequency values and distribution regions corresponding to the acoustic holographic layer of the mixed-frequency ultrasonic holographic lens;

[0024] According to the different ultrasonic frequency values and the distribution regions, calculate the phase values corresponding to the working frequencies of each holographic unit in the mixed-frequency ultrasonic holographic lens based on the virtual source time reversal method;

[0025] According to the phase values, determine the thickness values of each holographic unit, and design the corresponding acoustic holographic layer based on the thickness;

[0026] Stack and bond the optical focusing layer, the acoustic confinement layer, the optical absorption layer, the acoustic matching layer, and the acoustic holographic layer in sequence to obtain the mixed-frequency ultrasonic holographic lens;

[0027] Arrange the laser, the laser beam adjustment module, and the frequency-mixing ultrasonic holographic lens such that the laser emits a laser beam that passes through the laser beam adjustment module and enters from the side of the frequency-mixing ultrasonic holographic lens close to the light focusing layer, so as to generate a corresponding multi-focus focused ultrasonic field with multiple working frequencies.

[0028] In a third aspect, the present application further provides an ultrasonic device, which includes a multi-main-frequency laser ultrasonic holographic system as described in the first aspect above. The ultrasonic device is used for ultrasonic manipulation and driving, ultrasonic detection and imaging, low-power ultrasonic stimulation, or power ultrasonic treatment.

[0029] It can be understood that for the beneficial effects of the technical solutions provided in the above second aspect, third aspect, and fourth aspect, reference can be made to the relevant descriptions in the first aspect above, and details will not be elaborated here.

[0030] Additional aspects and advantages of the present invention will be given in part in the following description, become apparent in part from the following description, or be understood through the practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] To more clearly illustrate the technical solutions of the embodiments of the present invention, the following will briefly introduce the drawings required for use in the embodiments. Obviously, the drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0032] Figure 1 is a schematic diagram of a multi-main-frequency laser ultrasonic holographic system shown according to an embodiment of the present application;

[0033] Figure 2 is a schematic diagram of the structure of a frequency-mixing ultrasonic holographic lens shown according to an embodiment of the present application;

[0034] Figure 3 is based on Figure 2 of the frequency-mixing ultrasonic holographic lens to generate a schematic diagram of a corresponding multi-focus focused ultrasonic field;

[0035] Figure 4 is another schematic diagram of the structure of a frequency-mixing ultrasonic holographic lens shown according to an embodiment of the present application;

[0036] Figure 5 is based on Figure 4 of the frequency-mixing ultrasonic holographic lens to generate a schematic diagram of a corresponding multi-focus focused ultrasonic field;

[0037] Figure 6 is another schematic diagram of the structure of a frequency-mixing ultrasonic holographic lens shown according to an embodiment of the present application;

[0038] Figure 7 is based on Figure 6 the schematic diagram of the multi - focal focused ultrasound field generated by the heterodyne ultrasonic holographic lens.

[0039] Reference numerals

[0040] 100, computer;

[0041] 200, laser;

[0042] 300, laser beam adjustment module; 310, beam expander; 320, collimator;

[0043] 400, heterodyne ultrasonic holographic lens; 410, optical focusing layer; 420, acoustic confinement layer; 430, optical absorption layer; 440, acoustic matching layer; 450, acoustic holographic layer; 451, holographic unit. Detailed implementation manners

[0044] The embodiments of the present invention will be described in detail below. The embodiments described with reference to the accompanying drawings are exemplary. It should be understood that the specific embodiments described herein are only used to explain the present application and are not used to limit the present application.

[0045] It should be noted that unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the technical field to which the present invention belongs. The terms used in the description of the present invention in this specification are only for the purpose of describing specific implementation manners and are not intended to limit the present invention. The term "and / or" used herein includes any and all combinations of one or more of the related listed items.

[0046] Terms such as "first", "second", "third", etc. are only used for distinguishing descriptions and cannot be understood as indicating or implying relative importance or implicitly specifying the quantity of the indicated technical features. For example, the first end plate and the second end plate are only for distinguishing different end plates and do not limit their sequence. The first end plate can also be named the second end plate, and the second end plate can also be named the first end plate without departing from the scope of the described embodiments. And terms such as "first", "second", "third", etc. do not necessarily limit the indicated features to be different.

[0047] In the description of the embodiments of the present application, unless otherwise clearly specified or limited, terms such as "connected" and "coupled" shall be understood in a broad sense. For example, it may be a fixed connection, a detachable connection, or integrated; it may be a mechanical connection or an electrical connection; it may be directly connected or indirectly connected through an intermediate medium, and it may be the internal connection or the interaction relationship between two components. For those of ordinary skill in the art, the specific meanings of the above terms in the present application can be understood according to specific circumstances. The meaning of "plural" is at least two, that is, two or more.

[0048] It should be noted that in the present application, words such as "in one embodiment", "exemplarily", and "for example" are used to represent examples, illustrations, or explanations. Any embodiment or design described as "in one embodiment", "exemplarily", or "for example" in the present application should not be construed as more preferred or more advantageous than other embodiments or designs. Specifically, the use of words such as "in one embodiment", "exemplarily", and "for example" aims to present relevant concepts in a specific manner, meaning that the specific features, structures, or characteristics described in combination with the embodiment may be included in at least one embodiment of the present application. The appearance of the above words at various positions in the specification does not necessarily refer to the same embodiment, nor are they independent or alternative embodiments mutually exclusive with other embodiments. Those skilled in the art explicitly and implicitly understand that the embodiments described herein can be combined with other embodiments.

[0049] Please refer to Figure 1 , Figure 1 which shows a schematic diagram of the multi-frequency laser ultrasonic holographic system of this embodiment. The multi-frequency laser ultrasonic holographic system includes a laser 200, a laser beam adjustment module 300, and a mixed-frequency ultrasonic holographic lens 400. The laser 200 is electrically connected to the computer 100 and is used to emit a laser beam according to the laser parameters set by the computer 100. The laser beam may include one of a pulsed laser beam or a continuously modulated laser beam; that is, the laser 200 may be a broadband pulsed laser or a continuously modulated laser.

[0050] It should be noted that for the parameter setting of the laser 200, it can be directly set in the laser 200, or after presetting the parameters through the computer 100, they are sent to the laser 200 for parameter control setting. When the laser 200 is a pulsed laser, it may be a Nd:YAG laser, and when the laser 200 is a continuously modulated laser, it may be a single longitudinal mode continuous laser.

[0051] It should also be noted that when the laser 200 is a continuous modulation laser, its modulation frequency is the same as that of the heterodyne ultrasonic holographic lens 400, and the frequency of the adjustable focusing ultrasonic field generated on the backlight side of the heterodyne ultrasonic holographic lens 400 is the same as that of the heterodyne ultrasonic holographic lens 400; however, since the ultrasonic field generated by the laser beam emitted by the pulsed laser has an infinite bandwidth, when the laser 200 is a pulsed laser, the center frequency of the adjustable focusing ultrasonic field generated on the backlight side of the heterodyne ultrasonic holographic lens 400 is the same as that of the heterodyne ultrasonic holographic lens 400.

[0052] In some embodiments, the laser beam adjustment module 300 is configured to receive and adjust the laser beam. The laser beam adjustment module includes a beam expander 310 and a collimator 320 arranged coaxially. The beam expander 310 is configured to adjust the diameter of the laser beam, and the collimator 320 is configured to collimate the laser beam to keep the beam parallel and focused. A pulsed laser beam is generated by the pulsed laser 200, passes through the beam expander 310 and the collimator 320, and then passes through the heterodyne ultrasonic holographic lens 400 to generate single or multiple focused ultrasonic sound fields with multiple preset frequencies in a time-sharing or simultaneous manner in a propagation medium such as gas, liquid or solid.

[0053] Optionally, the beam expander 310 is configured to adjust the size of the pulsed laser beam or the continuously modulated laser beam. The beam expander 310 can be a 2x - 10x adjustable beam expander, and the collimator 320 can be a reflective collimator or a transmissive collimator, such as a collimator with the model number GLA12 - 010 - 015; the collimator 320 can keep the pulsed laser beam or the continuously modulated laser beam parallel and precisely focused on the heterodyne ultrasonic holographic lens 400.

[0054] In some embodiments, the laser beam enters the heterodyne ultrasonic holographic lens 400; the heterodyne ultrasonic holographic lens 400 includes an optical focusing layer 410, an acoustic confinement layer 420, an optical absorption layer 430, an acoustic matching layer 440 and a heterodyne acoustic holographic layer 450 which are sequentially stacked and adhesively arranged; wherein, the optical focusing layer 410 is arranged at the laser output end of the collimator 320 and is configured to perform light condensation on the laser beam after passing through the collimator 320; the acoustic confinement layer 420 is arranged on the backlight side of the optical focusing layer 410; the optical absorption layer 430 is arranged on the backlight side of the acoustic confinement layer 420 and is configured to absorb the laser beam and jointly convert the laser beam into a laser ultrasonic field through the acoustic confinement layer 420; the acoustic matching layer 440 is arranged on the backlight side of the optical absorption layer 430 and is configured to perform characteristic matching on the laser ultrasonic field; the acoustic holographic layer 450 includes a plurality of holographic units 451 with different thicknesses, and the acoustic holographic layer 450 is arranged on the backlight side of the acoustic matching layer 440 and is configured to perform holographic processing on the laser ultrasonic field. [[ID=,11]]

[0055] Optionally, the light focusing layer 410 consists of one or more lens arrays. The light focusing layer is used to focus the laser beam to generate a single or an array of multiple focused spots, and irradiate the focused spots through the acoustic confinement layer onto the light absorption layer 430. The light absorption layer 430 is used to absorb the light energy of the focused spots to generate a single or an array of multiple ultrasonic spherical waves, and form an amplified laser ultrasonic field based on the reflection and superposition of the acoustic confinement layer 420. The acoustic holographic layer 450 sets multiple regions according to a preset multiple frequencies. Each region consists of multiple holographic units 451, and each region regulates the corresponding ultrasonic frequency.

[0056] In one example, the phase and amplitude of the corresponding ultrasonic wave are controlled based on the thickness of each holographic unit 451. Among them, the relationship formula between the thickness of the holographic unit 451 and the phase of the ultrasonic wave satisfies:

[0057] ,

[0058] In the formula, is the phase value corresponding to the holographic unit , i and j respectively represent the row index and column index of the holographic unit in the two-dimensional plane, is the ultrasonic frequency, and are the sound velocities of the propagation medium and the acoustic holographic layer material respectively.

[0059] The relationship formula between the thickness of the holographic unit and the amplitude of the ultrasonic wave satisfies:

[0060] ,

[0061] Among them, represents the amplitude of the ultrasonic wave, represents the sound pressure of the ultrasonic spherical wave after acoustic characteristic matching emitted from the acoustic matching layer, represents the thickness of the holographic unit, represents the acoustic impedance of the acoustic matching layer 440, represents the impedance of the single-frequency acoustic holographic layer, represents the acoustic impedance of the propagation medium, represents the wave number of the single-frequency acoustic holographic layer.

[0062] It should be noted that in the acoustic holographic layer 450, by adjusting the thickness of the holographic unit 451, the phase delay generated by the sound wave when passing through different holographic units 451 can be changed; this difference in phase delay enables the sound wave to form a specific phase distribution during propagation, thereby achieving a focusing effect; the amplitude of the sound wave refers to the vibration amplitude of the sound wave at a certain point in space; although the thickness of the holographic unit 451 mainly affects the phase of the sound wave, it also affects the amplitude of the sound wave to a certain extent; when the sound wave passes through holographic units of different thicknesses, part of the sound wave energy may be absorbed, refracted or reflected, resulting in a change in the amplitude of the sound wave; however, in the design of the acoustic holographic layer 450, more attention is paid to achieving the focusing effect through phase control, and the change in amplitude is considered as a secondary factor; therefore, the thickness of each holographic unit 451 in the acoustic holographic layer 450 can be accurately designed and adjusted according to the required focal length to achieve precise control of the sound wave propagation path and phase difference; when the laser ultrasonic field passes through the acoustic holographic layer 450, the sound wave will be focused and converted into an adjustable focused ultrasonic field with the required number of foci, sound pressure and focal length, thereby achieving the adjustability of the focused ultrasonic field.

[0063] Optionally, the number of foci of the acoustic holographic layer 450 is one or more, and the number of foci of the adjustable focused ultrasonic field generated on the backlight side of the acoustic holographic layer 450 corresponds to one or more. Specifically, by adjusting the parameters and structure of the acoustic holographic layer 450, the mixed-frequency ultrasonic holographic lens 400 can generate multiple clear foci on the backlight side.

[0064] It should be noted that the focus is the point where the mixed-frequency ultrasonic holographic lens 400 converges the ultrasonic energy and is the core part of the adjustable focused ultrasonic field; at the focus, the energy density of the ultrasonic wave is the highest, so it has the strongest effect; the adjustable focused ultrasonic field is formed by the outward expansion of the ultrasonic energy at the focus; in the ultrasonic field, except at the focus, the energy density of the ultrasonic wave gradually decreases in other regions, but still has a certain effect; since the focus is the core part of the ultrasonic field generated by the mixed-frequency ultrasonic holographic lens 400, the number of foci directly determines the number of adjustable focused ultrasonic fields; therefore, when the mixed-frequency ultrasonic holographic lens 400 has multiple foci, the backlight side will generate an adjustable focused ultrasonic field with multiple foci.

[0065] In the above-mentioned embodiment, the multi-frequency laser ultrasonic holographic system is provided with a frequency-mixing ultrasonic holographic lens. The frequency-mixing ultrasonic holographic lens 400 includes a light focusing layer 410, an acoustic confinement layer 420, a light absorption layer 430, an acoustic matching layer 440, and an acoustic holographic layer 450, which are stacked in sequence. In the acoustic holographic layer 450, multiple regions are provided according to multiple preset frequencies (the regional distribution can be arbitrarily set). Each region regulates the corresponding ultrasonic frequency. Each region is composed of multiple holographic units. The phase and amplitude of the corresponding ultrasonic wave are controlled by controlling the thickness of the holographic unit. After the ultrasonic frequency regulated by the acoustic holographic layer 450 is set, the corresponding continuous modulation of the same frequency is used. A laser beam is controlled to irradiate the left and right areas of the light focusing layer, or a wide-band pulsed laser beam is used to irradiate the left and right areas of the light focusing layer simultaneously or time-sharingly, so as to realize the time-sharing or simultaneous generation of single or multiple focused ultrasound fields with stable multiple preset frequencies, and the focus position and power are usually adjustable. In actual application, low-frequency ultrasound waves in multiple focused ultrasound fields can be used for ultrasound emission of deep defects, while high-frequency ultrasound waves can be used for ultrasound emission of finer surface defects, thereby improving the accuracy of material evaluation. In addition, in ablation therapy, high-frequency ultrasound is used to image and detect tumors, while low-frequency ultrasound is used to ablate tumors to improve treatment efficiency.

[0066] In some embodiments, a design method for a multi-frequency laser ultrasonic holographic system is provided, the method comprising:

[0067] Step S1, using transparent nylon for 3D printing to design a light focusing layer, an acoustic confinement layer, and an acoustic matching layer 440;

[0068] Step S2, designing a light absorption layer using mixed carbon nanoparticles or a black metal film;

[0069] Step S3, determining different ultrasonic frequency values and distribution areas corresponding to the acoustic holographic layer 450 of the frequency-mixing ultrasonic holographic lens according to the preset frequency and focus parameter information corresponding to the holographic system;

[0070] Step S4, calculating the phase value corresponding to the operating frequency of each holographic unit in the frequency-mixing ultrasonic holographic lens based on the virtual source time reversal method according to different ultrasonic frequency values and distribution areas;

[0071] In one example, a phase-only acoustic holographic layer can be designed by using a virtual source time reversal method, as follows:

[0072] (1) Establish an ultrasonic simulation model and set virtual sound sources in the simulation model according to the distribution of the target reconstructed sound field;

[0073] (2) Simulate the process of ultrasound propagating from the virtual sound source to the acoustic holographic surface, and reverse the ultrasonic time domain signal received by each pixel of the acoustic holographic layer on the time axis;

[0074] (3) Perform a Fourier transform on the time-reversed signal, extract the phase value corresponding to the preset frequency, and the pixel can be obtained The corresponding phase value ;

[0075] (4) Calculate the thickness of each pixel according to the following formula :

[0076] , where is the phase value corresponding to the pixel , is the ultrasonic frequency, and are the sound velocities of the propagation medium and the acoustic matching layer respectively.

[0077] The optical absorption layer and the acoustic matching layer can be preliminarily fabricated according to the relevant dimensional parameters of the ultrasonic holographic lens, and the actual output sound pressure distribution of the acoustic matching layer can be obtained through acoustic field testing and numerical inversion .

[0078] Establish a three-dimensional model of the lens according to the dimensional parameters of the ultrasonic holographic lens, and manufacture the ultrasonic holographic lens by 3D printing technology or other processing methods.

[0079] Step S5, determine the thickness value of each holographic unit according to the phase value, and design the corresponding acoustic holographic layer 450 based on the thickness;

[0080] Step S6, stack and bond the optical focusing layer, the acoustic confinement layer, the optical absorption layer, the acoustic matching layer, and the acoustic holographic layer in sequence to obtain a mixed-frequency ultrasonic holographic lens;

[0081] Optionally, transparent nylon can be used for 3D printing to generate 90×90 hemispherical lenses with a diameter of 0.1 mm. The hemispherical lens array is arranged to obtain the optical focusing layer. Transparent nylon can be used for 3D printing to generate an acoustic confinement layer with a thickness of 1 mm and an acoustic matching layer 440 with a thickness of 0.5 mm. A black metal film with a thickness of 0.2 mm is used as the optical absorption layer. The acoustic confinement layer and the acoustic matching layer 440 are respectively pasted on both sides of the optical absorption layer, and the optical focusing layer is pasted on the side of the acoustic confinement layer away from the optical absorption layer. Through the 3D printing process, polymers with acoustic impedance matching the acoustic propagation medium are made into multiple holographic units with different thicknesses. The mixed-frequency acoustic holographic layer 450 is formed by closely connecting the holographic units, and the acoustic holographic layer 450 is pasted on the side of the acoustic matching layer 440 away from the optical absorption layer to obtain a mixed-frequency ultrasonic holographic lens;

[0082] In step S7, a laser, a laser beam adjustment module, and a frequency-mixing ultrasonic holographic lens are arranged so that the laser beam emitted by the laser passes through the laser beam adjustment module and enters the frequency-mixing ultrasonic holographic lens from a side close to the light focusing layer 410 to generate multiple focal-focused ultrasonic fields of corresponding multiple working frequencies.

[0083] It can be understood that the above-mentioned multi-main frequency laser ultrasonic holographic system only needs to control the excitation pulse laser, and can generate multiple focused ultrasonic sound fields of multiple preset frequencies in time-sharing or simultaneously through the mixing ultrasonic holographic lens, while traditional ultrasonic sensors and focused acoustic lenses can only have one center frequency, and the focus is usually fixed and cannot be adjusted. At the same time, long-distance non-contact pulse laser driving can be achieved without the need for high-voltage excitation and wired connection of cables. Compared with traditional ultrasonic sensors, the durability, safety, convenience and applicability of use are greatly improved. In addition, the mixing ultrasonic holographic lens is easy to miniaturize, micro-miniaturize and array, and can realize a large array of multiple preset frequency focused sound fields. It is easy to use automated processes such as 3D printing and semiconductor etching to achieve large-scale, low-cost industrial production, which is impossible for traditional ultrasonic sensors with large size and complex structure.

[0084] It should be explained that in the multi-main-frequency laser ultrasonic holographic system designed by the above method, the laser enters from the light incident side of the light focusing layer 410; the laser passes through a hemispherical lens or a plurality of hemispherical lenses arranged in an array in the light focusing layer 410; the hemispherical lenses can be quickly designed by 3D printing, and the design of these hemispherical lenses enables the laser beam to be focused, thereby forming a focused light spot or a plurality of focused light spots in an array on the backlight side of the light focusing layer 410; the number and position of the focused light spots depend on the number, shape and arrangement of the hemispherical lenses in the light focusing layer 410; the focused light spots enter from the light incident side of the acoustic constraint layer 420, and the acoustic constraint layer 420 is the first transparent nylon layer, so that the focused light spots generated by the light focusing layer 410 can pass through the first transparent nylon layer to reach the light absorption layer 430, and the first transparent nylon layer The nylon layer can constrain and guide the ultrasonic spherical waves generated by the light absorbing layer 430; the nylon material has good light transmittance and certain acoustic properties, so that the acoustic constrained layer 420 can not only allow the focused light spot to pass through, but also constrain and reflect the ultrasonic waves generated by the light absorbing layer 430; the acoustic constrained layer 420 limits the propagation range of the ultrasonic waves within the layer through its material properties and structural design, preventing it from diffusing to the surroundings, thereby maintaining the focused state of the ultrasonic spherical waves; the focused light spot passing through the acoustic constrained layer 420 enters from the light incident side of the light absorbing layer 430, and the light absorbing layer 430 is a black metal film, which can convert the energy of the focused light spot into mechanical energy; in the black metal film, the focused light spot is absorbed and converted into ultrasonic spherical waves; these ultrasonic spherical waves are emitted simultaneously from the light incident side and the backlight side of the black metal film.

[0085] It can be understood that due to the structural design of the black metal film, it allows part of the laser energy to be emitted from the backlight side of the black metal film in the form of ultrasonic spherical waves, and at the same time, part of the ultrasonic spherical waves are emitted from the light incident side of the black metal film. The ultrasonic spherical waves emitted from the light incident side of the black metal film are superimposed on the ultrasonic spherical waves emitted from the backlight side of the black metal film under the constrained reflection of the first transparent nylon layer to form a laser ultrasonic field; the laser ultrasonic field enters from the light incident side of the acoustic matching layer 440, and the acoustic matching layer 440 is the second transparent nylon layer; the main function of the second transparent nylon layer is to adjust the acoustic characteristics of the laser ultrasonic field to match the subsequent acoustic holographic layer 450; this includes adjusting the propagation speed and impedance of the laser ultrasonic field to reduce reflection and scattering; after being processed by the acoustic matching layer 440, the laser ultrasonic field is emitted from the backlight side of the acoustic matching layer 440. out, at this time its acoustic characteristics have matched the acoustic holographic layer 450; the laser ultrasonic field after the acoustic characteristics matching enters from the light incident side of the acoustic holographic layer 450; the acoustic holographic layer 450 is composed of a plurality of holographic units of different thicknesses, and these holographic units are all made of polymers whose acoustic impedance matches the sound propagation medium. These holographic units can generate specific ultrasonic fields according to the propagation path and phase difference of the sound waves; in the acoustic holographic layer 450, the laser ultrasonic field is holographically processed, focused and converted into an adjustable focused ultrasonic field; the thickness of the holographic unit can be designed according to the required number of focal points, sound pressure and focal length of the adjustable focused ultrasonic field to obtain an adjustable focused ultrasonic field that meets the design requirements, thereby realizing the adjustability of the adjustable focused ultrasonic field; finally, the adjustable focused ultrasonic field is emitted from the backlight side of the acoustic holographic layer 450, ready for subsequent applications or detection tasks.

[0086] See also Figures 2 to 3 This embodiment improves a design method based on the above embodiment and designs a multi-main-frequency dual-focus laser ultrasound holographic system for liver tumor ablation treatment. The system can generate dual-focus ultrasound fields of two working frequencies in a time-sharing or simultaneous manner. High-frequency ultrasound is used for imaging and detecting tumors, and low-frequency ultrasound is used for ablation of tumors. It is assumed that the tumor is an ellipsoid with a long-axis diameter of 12 mm and a short-axis diameter of 4 mm, located 50 mm below the abdomen.

[0087] Specifically, the laser used is a single longitudinal mode continuous laser, the beam expander is a 2x-10x adjustable beam expander, and the collimator model is COL-OF-S-UV, such as Figure 2As shown, the focal lengths of the two foci of the sound holographic lens sound field used are 40 mm and 60 mm respectively, the projection distance interval is 50 mm, the pixel size is set to 0.1×0.1 μm, the overall size of the ultrasonic holographic lens is given as 20×40 mm, and the optical focusing elements used in the optical focusing layer 410 are a hemispherical lens array of 200×400 with a diameter of 0.1 mm; the material used for the sound constraint layer 420 is a vitreous rigid material; the material used for the light absorption layer 430 is a 0.3 mm black metal film; the material used for the sound matching layer 440 is epoxy resin-aluminum oxide; the sound holographic layer 450 is composed of polygonal holographic units 451 with different thicknesses. Each holographic unit 451 controls the phase and amplitude of ultrasonic waves through its thickness. The sound holographic layer 450 is evenly divided into two regions, each region has a size of 20×20 mm. The ultrasonic frequency controlled by the pixels in the left region is 1 MHz, and the ultrasonic frequency controlled by the pixels in the right region is 2 MHz.

[0088] According to the size of the holographic lens, the sizes of the beam expander and collimator lenses are both set to 20×20 mm. By using continuous laser beams with different modulation frequencies of 1 MHz and 2 MHz with relatively high energy at different times to irradiate the black metal film light absorption layer 430, a high-power focused ultrasonic field can be generated in the tumor area through the laser ablation effect, as Figure 3 shown, and finally the purpose of ablating the tumor is achieved.

[0089] In an example, the virtual source time reversal method is used to calculate the acoustic holographic surface. First, a sound field simulation model is established through the k-wave toolbox of MATLAB. A 20×40 square millimeter acoustic holographic surface is set to receive ultrasonic waves propagated outward from the virtual sound source, and virtual sound sources are set at 40 mm and 60 mm away from the acoustic holographic surface respectively. The process of ultrasonic waves propagating from the virtual sound source to the ultrasonic holographic lens is simulated at the two virtual sound sources respectively, and the time-domain signals of the ultrasonic waves received by each pixel of the ultrasonic holographic lens are flipped on the time axis; then the Fourier transform is performed on the time-flipped signals, and the phase values corresponding to the working frequencies of the corresponding pixels are extracted. The thickness of each pixel is calculated according to the following preferred formula:

[0090]

[0091] where is the phase value corresponding to the pixel , is the ultrasonic frequency, and are the sound velocities of air and the material of the sound holographic layer respectively.

[0092] Please refer to Figures 4 to 5, this implementation improves a design method based on the above embodiments to design a multi-frequency dual-focus laser ultrasonic holographic system for defect detection, which can generate a dual-focus ultrasonic field with two working frequencies in the air in a time-sharing manner. The low-frequency ultrasonic waves can be used for ultrasonic emission of deep defects, while the high-frequency ultrasonic waves can be used for ultrasonic emission of finer surface defects, thereby improving the accuracy of material evaluation.

[0093] The laser used is a single-longitudinal-mode continuous laser, the beam expander used is a 2x - 10x adjustable beam expander, the collimator model used is COL-OF-S-UV, the focal lengths of the two foci of the acoustic holographic lens sound field are 40 mm and 60 mm respectively, the projection distance interval is 50 mm, and the pixel size is set to 0.1×0.1 μm. The overall size of the ultrasonic holographic lens is given as 30×60 mm, as Figure 4 shown. The optical focusing element used is a 200×400 hemispherical lens array with a diameter of 0.1 mm; the acoustic confinement material used is a vitreous rigid material; the optical absorption material used is 0.3 mm of mixed carbon nanoparticles; the acoustic matching layer material used is epoxy-aluminum oxide; the acoustic holographic layer 450 is composed of polygonal holographic units 451 with different thicknesses. Each holographic unit 451 controls the phase and amplitude of ultrasonic waves through its thickness. The acoustic holographic layer is evenly divided into two regions, each region has a size of 30×30 mm. The ultrasonic frequency controlled by the pixels in the left region is 300 kHz, and the ultrasonic frequency controlled by the pixels in the right region is 500 kHz. According to the size of the holographic lens, the sizes of the beam expander and collimator lenses are both set to 30×30 mm. The laser beam modulated continuously at 300 kHz and 500 kHz is used to irradiate the light absorption layer of the mixed carbon nanoparticles in a time-sharing manner, as Figure 5 shown, and a medium-low power laser ultrasonic field can be generated through the laser thermoelastic effect.

[0094] This embodiment uses the virtual source time reversal method to calculate the acoustic holographic surface. First, a sound field simulation model is established through the k-wave toolbox of MATLAB. A 30×60 square millimeter acoustic holographic surface is set to receive the ultrasonic waves propagated outward from the virtual sound source, and virtual sound sources are set at 40 mm and 60 mm away from the acoustic holographic surface respectively. The process of ultrasonic waves propagating from the virtual sound source to the ultrasonic holographic lens is simulated at the two virtual sound sources respectively, and the time-domain signals of the ultrasonic waves received by each pixel of the acoustic holographic lens are flipped on the time axis; then the Fourier transform is performed on the time-flipped signals, and the phase values corresponding to the working frequencies of the corresponding pixels are extracted. The thickness of each pixel is calculated according to the following formula:

[0095]

[0096] where, is the phase value corresponding to the pixel , is the ultrasonic frequency, and are the sound velocities of the air and the acoustic holographic layer material, respectively.

[0097] Please refer to Figures 6 to 7 , this implementation improves a design method based on the above embodiments, and designs a dual-focus laser ultrasonic holographic system based on pulsed laser multi-main frequencies, which can generate a dual-focus ultrasonic field with two operating frequencies simultaneously or at different times in water.

[0098] The focal lengths of the two foci of the preset sound field are 3 mm and 5 mm respectively, and the projection distance interval is 8 mm; the size of the acoustic holographic layer 450 is 15×15 mm, and the pixel size is 1×1 mm. The holographic unit 451 controls the phase and amplitude of the ultrasonic wave through its thickness. ,

[0099] In the formula, is the phase value corresponding to the holographic unit , is the ultrasonic frequency, and are the sound velocities of the propagation medium and the acoustic holographic layer material, respectively.

[0100] The relationship between the thickness of the holographic unit and the amplitude of the ultrasonic wave satisfies:

[0101] ,

[0102] where represents the amplitude of the ultrasonic wave, represents the sound pressure of the ultrasonic spherical wave that passes through acoustic characteristic matching and is emitted from the acoustic matching layer, represents the thickness of the holographic unit, represents the acoustic impedance of the acoustic matching layer, represents the impedance of the single-frequency acoustic holographic layer, represents the acoustic impedance of the propagation medium, represents the wave number of the single-frequency acoustic holographic layer. The mixed-frequency acoustic holographic layer 450 has two regions, and the size of each region is 15×7.5 mm. The ultrasonic frequency controlled by the pixels in the left region is 2 MHz, and the ultrasonic frequency controlled by the pixels in the right region is 1 MHz.

[0103] The pulsed laser used is a Nd:YAG laser. The beam expander used is a 2x - 10x adjustable beam expander. The collimator used is of the model GLA12 - 010 - 015. The optical focusing layer 410 consists of 150×150 hemispherical lenses with a diameter of 0.1 mm. The overall size is 15×15 mm, and the focal length of the hemispherical lens is 1 mm. First, a photosensitive resin is used by a light - curing 3D printer to print an acoustic confinement layer 420 with a thickness of 1.2 mm and an acoustic matching layer 440 with a thickness of 0.4 mm, and a 0.3 - mm - thick black metal film is bonded between the acoustic confinement layer 420 and the acoustic matching layer 440 with transparent glue as the light - absorbing layer 430. The heterodyne acoustic holographic layer 450 is made of a gas - bubble polymer with an acoustic impedance matching to air through an injection - molding process and is bonded to the other side of the acoustic matching layer 440. The pulsed laser beam is irradiated on the left and right two regions of the optical focusing layer 410 simultaneously or at different times to generate a uniform array of focused beams, and then the focused beams are irradiated on the light - absorbing layer to generate broadband ultrasonic waves, which are reflected and amplified by the acoustic confinement layer, as Figure 7 shown. Finally, a 2 - MHz and 1 - MHz dual - focus ultrasound field is generated by simultaneously or at different times regulating through the heterodyne ultrasonic holographic lens.

[0104] In the description of the present invention, it should be understood that the orientation or positional relationship indicated by the terms "center", "longitudinal", "transverse", "length", "width", "thickness", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", "clockwise", "counterclockwise", "axial", "radial", "circumferential", etc. is based on the orientation or positional relationship shown in the drawings. It is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and thus should not be construed as a limitation of the invention.

[0105] In the description of this specification, the description referring to terms such as "one embodiment", "some embodiments", "schematic embodiments", "examples", "specific examples", or "some examples", etc. means that the specific features, structures, materials, or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic expressions of the above - mentioned terms do not necessarily refer to the same embodiment or example.

[0106] Obviously, the described embodiments are only a part of the embodiments of this application, rather than all of them. The mention of "embodiment" in this context means that the specific features, structures, or characteristics described in connection with the embodiment may be included in at least one embodiment of this application. The appearance of this phrase at various positions in the specification does not necessarily refer to the same embodiment, nor is it an independent or alternative embodiment that is mutually exclusive with other embodiments. Those skilled in the art can explicitly and implicitly understand that the embodiments described herein can be combined with other embodiments. Based on the embodiments in this application, all other embodiments obtained by those of ordinary skill in the art without creative efforts belong to the scope of protection of this application.

[0107] Although the embodiments of the present invention have been shown and described, those of ordinary skill in the art can understand that various changes, modifications, substitutions, and variations can be made to these embodiments without departing from the principles and spirit of the present invention. The scope of the present invention is defined by the claims and their equivalents.

[0108] Those skilled in the art will readily conceive of other implementations of this application upon considering the specification and the practice of the disclosure herein. This application is intended to cover any variations, uses, or adaptations of this application that follow the general principles of this application and include common general knowledge or conventional technical means in the technical field not disclosed in this application. The specification and the embodiments are only regarded as exemplary, and the true scope and spirit of this application are pointed out by the following claims.

Claims

1. A multi-frequency laser ultrasonic holographic system, characterized in that: include: a laser, electrically connected to the computer and configured to emit a laser beam according to laser parameters set by the computer, wherein the laser beam includes a pulsed laser beam or a continuously modulated laser beam; a laser beam adjustment module, configured to receive and adjust the laser beam, wherein the laser beam adjustment module comprises a coaxially arranged beam expander and a collimator, wherein the beam expander is configured to adjust the diameter of the laser beam, and the collimator is configured to collimate the laser beam so that the beam remains parallel and focused; A frequency-mixing ultrasonic holographic lens is used to receive the laser beam passing through the laser beam adjustment module to generate stable single or multiple focused ultrasonic sound fields of multiple different preset frequencies in a time-sharing or simultaneous manner, and the focus position and power are adjustable; the frequency-mixing ultrasonic holographic lens includes a light focusing layer, an acoustic confinement layer, a light absorption layer, an acoustic matching layer, and an acoustic holographic layer stacked in sequence; the acoustic holographic layer is provided with multiple regions according to multiple preset frequencies, each of the regions is composed of multiple holographic units, and each of the regions regulates the corresponding ultrasonic frequency.

2. The multi-frequency laser ultrasonic holographic system according to claim 1, characterized in that: The light focusing layer is composed of one or more lens arrays, and is used to focus the laser beam to generate a single or arrayed multiple focused light spots, and irradiate the focused light spots to the light absorption layer through the acoustic confinement layer.

3. The multi-frequency laser ultrasonic holographic system according to claim 2, characterized in that: The light absorption layer is used to absorb the light energy of the focused light spot to generate a single or arrayed multiple ultrasonic spherical wave, and to form an amplified laser ultrasonic field based on the reflection and superposition of the acoustic confinement layer.

4. The multi-frequency laser ultrasonic holographic system according to claim 3, characterized in that: The phase and amplitude of the corresponding ultrasonic wave are controlled based on the thickness of each holographic element.

5. The multi-main-frequency laser ultrasonic holographic system according to claim 4, characterized in that: The relationship between the thickness of the holographic unit and the phase of the ultrasonic wave satisfies: , Where, Holographic unit The corresponding phase value, i and j denote the row index and column index of the holographic unit in the two-dimensional plane, is the ultrasonic frequency, and are the sound velocities of the propagation medium and the acoustic holographic layer material, respectively.

6. A design method for a multi-frequency laser ultrasonic holographic system according to any one of claims 1 to 5, characterized in that: The method comprises: 3D printing with transparent nylon to design light focusing layers, acoustic confinement layers, and acoustic matching layers; Designing light-absorbing layers using hybrid carbon nanoparticles or black metal films; Determine different ultrasonic frequency values and distribution areas corresponding to the acoustic holographic layer of the frequency-mixing ultrasonic holographic lens according to the preset frequency and focus parameter information corresponding to the holographic system; According to the different ultrasonic frequency values and the distribution areas, a phase value corresponding to the operating frequency of each holographic unit in the frequency mixing ultrasonic holographic lens is calculated based on a virtual source time reversal method; Determining a thickness value of each holographic unit according to the phase value, and designing a corresponding acoustic holographic layer based on the thickness value; The light focusing layer, the acoustic confinement layer, the light absorbing layer, the acoustic matching layer and the acoustic holographic layer are sequentially stacked and bonded to obtain the frequency mixing ultrasonic holographic lens; The laser, the laser beam adjustment module, and the frequency-mixing ultrasonic holographic lens are arranged so that the laser beam emitted by the laser passes through the laser beam adjustment module and is injected from a side of the frequency-mixing ultrasonic holographic lens close to the light focusing layer, so as to generate stable single or multiple focused ultrasonic sound fields of multiple different preset frequencies in a time-sharing or simultaneous manner, and the focus position and power are adjustable.

7. An ultrasonic device, characterized in that The ultrasound device includes a multi-main-frequency laser ultrasound holographic system as described in any one of claims 1 to 5, and the ultrasound device is used for ultrasound manipulation and driving, ultrasound detection imaging, low-power ultrasound stimulation or power ultrasound treatment.

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