Reconfigurable acoustic holographic modulation method and device based on crystalline polymer

Abstract

A reconfigurable acoustic holographic modulation method and device based on a crystalline polymer. The reconfigurable acoustic holographic device comprises a programmable acoustic holographic plate (3) and a reflective plate, wherein the programmable acoustic holographic plate (3) is a flat plate made of a crystalline polymer material. The programmable acoustic holographic device is formed by a single-layer photoresponsive crystalline polymer flat plate, and switches between two phases when the temperature thereof changes upon laser irradiation, so as to have two states, i.e., a crystalline state and an amorphous state, reversibly changing with the temperature. The programmable acoustic holographic device directly uses the state switching of a substrate material itself as coding units of a spatial phase. Spatial acoustic field modulation can be realized by spatially arranging the coding units. A crystalline polymer flat plate which has undergone laser-patterned phase transition recovers a previous crystalline state after cooling, and a patterned coded acoustic hologram disappears and a new phase acoustic hologram is written, thereby realizing a new acoustic field modulation function. The programmable acoustic holographic device based on a crystalline polymer can modulate a planar incident wave from a probe into an arbitrary complex three-dimensional acoustic field, which is completely planar and relatively matches the underwater acoustic impedance. The acoustic energy coupling efficiency is high, the structure is compact, the preparation is simple, and the price is low.

Description

A reconfigurable acoustic holographic modulation method and device based on crystalline polymers Technical Field

[0001] This invention relates to the field of acoustic holography, specifically to a reconfigurable programmable acoustic holographic modulation method and device based on crystalline polymer materials for achieving high-resolution dynamic modulation of sound fields. Background Technology

[0002] Biomedical ultrasound is an important emerging discipline that uses ultrasound as a medium and relies on signal processing technology, electronic science, and other engineering techniques to utilize the biological effects of ultrasound for disease diagnosis and treatment. Ultrasound itself carries enormous energy, and medical research has shown that the low-dose thermal effects of ultrasound can promote human metabolism, blood circulation, and accelerate wound healing. Currently, the incidence of cancer is increasing year by year both domestically and internationally. In addition to traditional surgery, new diagnostic and treatment technologies for cancer are constantly emerging. Besides laparoscopic surgery, minimally invasive treatments have also achieved very good results in clinical application. However, minimally invasive treatments based on radiofrequency, microwave, or cryotherapy are still invasive methods and may lead to bleeding or metastasis of the tumor during puncture. Therefore, in the past 20 years, invasive high-intensity focused ultrasound (HIFU) ablation therapy has received increasing attention. With the increase of ultrasound excitation power, the high-precision sound beam propagates in human tissue and, after focusing in the target area, the enormous energy it carries causes rapid heating of the local area. The resulting high-temperature thermal effect can cause the tissue to heat up rapidly, leading to irreversible coagulative necrosis. Since Lynn proposed the idea of ​​performing non-invasive surgery from outside the body in 1942 and achieved significant results in animal brain cell damage experiments, HIFU-based medical treatments have gradually developed. However, most existing ultrasound medical diagnostic and treatment technologies achieve acoustic energy focusing in the target area through curved multi-element probes, which are difficult to perfectly fit when in contact with the human epidermis, leading to insufficient acoustic energy coupling and reduced acoustic energy utilization. At the same time, simple single-point focusing is no longer sufficient to meet the increasingly advanced biomedical applications, especially for multi-target neural stimulation, tissue ablation, medical imaging techniques, and targeted drug delivery techniques.

[0003] Furthermore, sound fields possess mechanical effects. Spatially distributed sound fields will scatter on the particle surface, and the scattered sound field will further generate acoustic radiation stress along the gradient direction, thereby driving particles in the background medium to move towards the direction of acoustic energy maxima / minimum, ultimately achieving their arrangement. Acoustic tweezers, as an extension of optical tweezers technology into the acoustic field, have unique advantages in particle capture, movement, and arrangement. Based on their deep penetration capability, good biocompatibility, and wavelength matching with cells, acoustic particle manipulation technology has been widely applied in the chemical, biological, and medical fields, and has gradually developed into technologies such as acoustic microfluidics, acoustic cell co-culture technology, and targeted drug delivery technology. To achieve these applications, it is necessary to modulate the sound field in space to the target condition.

[0004] Acoustic holography is an extension and development of computational holography in the field of acoustics. It records the phase or amplitude information of a target holographic sound field onto the positions of acoustic holographic pixel units arranged in two-dimensional space through computation, and reconstructs the target sound field under specific incident conditions. Currently, researchers have used 3D printing technology to fabricate polymer metasurfaces with varying thicknesses, called acoustic holographic phase plates, enabling free control and reconstruction of arbitrarily complex sound fields. However, due to their specific acoustic response characteristics, 3D-printed acoustic holographic phase plates can only realize a single holographic sound field.

[0005] Therefore, how to replace the passive phase modulation unit with an active modulation unit while preserving the high information density of the phase hologram, so that it can simultaneously possess a high-resolution sound field and the ability to be remodulated, is of great scientific value. Summary of the Invention

[0006] To overcome the shortcomings of existing sound field modulation techniques, and considering that most existing sound holography techniques are static and have a single structure, while dynamic sound holography techniques are difficult to achieve both high resolution and high compactness, this invention provides a reconfigurable programmable sound holographic modulation fabrication method and device based on crystalline polymer materials for achieving high-resolution dynamic modulation of sound fields.

[0007] To realize a coded phase acoustic holographic device based on crystalline polymers, the technical solution adopted in this invention is as follows:

[0008] I. A reconfigurable acoustic holographic device based on crystalline polymers:

[0009] The device includes a programmable acoustic hologram, which is divided into several microstructure regions arranged in a close array. The microstructure regions have two states: crystalline and amorphous, and the two states change reversibly with temperature. The programmable acoustic hologram covers the ultrasonic transducer probe.

[0010] It also includes a reflector plate, which is arranged on the upper side of the programmable acoustic hologram plate and at a distance from the programmable acoustic hologram plate. The ultrasonic waves emitted by the ultrasonic transducer pass through the programmable acoustic hologram plate and are then reflected by the reflector plate before illuminating the object under test.

[0011] The programmable acoustic holographic panel is made of crystalline polymer material, specifically polycaprolactone.

[0012] The amorphous microstructure region is formed by melting the originally crystalline microstructure region under the irradiation of a laser beam emitted by a laser. The microstructure region has different material properties and acoustic properties in the crystalline and molten states.

[0013] The microstructure region is called the crystalline region when it is in a crystalline state, and the microstructure region is called the molten region when it is in an amorphous state.

[0014] The fabrication process of reconfigurable acoustic holographic devices includes a crystalline polymer material plate and an infrared laser.

[0015] II. An acoustic holographic phase modulation method for a reconfigurable acoustic holographic device:

[0016] The method involves using a laser to emit a laser pulse beam to scan and locally irradiate different areas on the surface of a crystalline polymer material, thereby creating regions with different acoustic properties on the crystalline polymer material. Patterned molten regions are then written into the original crystalline regions to form an acoustic holographic phase distribution, thus transforming it into a phase acoustic holographic device.

[0017] The crystalline polymer material is originally in a crystalline state. When the microstructure regions on the crystalline polymer material are irradiated and heated, the irradiated and heated microstructure regions melt and become a non-crystalline (molten) state, forming molten regions. The microstructure regions that are not irradiated and heated do not change and form crystalline regions, so that the crystalline polymer material has two states: crystalline and non-crystalline.

[0018] The crystalline polymer material has different material and acoustic properties in its crystalline and amorphous states, mainly manifested in Young's modulus and sound velocity. Specifically, the Young's modulus and sound velocity are both lower in the amorphous state compared to the crystalline state.

[0019] Furthermore, the laser pulse beam scans and irradiates different microstructure regions, causing the two states of microstructure regions on the crystalline polymer material to form a patterned arrangement, which serves as the acoustic holographic phase distribution of the phase acoustic holographic device.

[0020] Each pulse corresponds to irradiating a microstructure region. Different pulses correspond to different microstructure regions. The longer the laser pulse irradiation time and the higher the energy, the higher the temperature of the crystalline polymer in the corresponding region. Furthermore, by controlling the duration and energy of the pulse irradiation of the microstructure region, the temperature of the irradiated microstructure region can be controlled to remain within 10% above the melting temperature.

[0021] By setting the thickness of the crystalline polymer material and controlling the thickness-frequency matching, the transmission phase delay of the crystalline polymer material can be made equal to π.

[0022] The thickness of the crystalline polymer material is set as follows:

[0023] 1) First, using pulsed ultrasound under water immersion conditions, the sound velocity of the crystalline polymer material in both crystalline and amorphous states was measured, and the velocity was v0 respectively. a and v c ;

[0024] 2) The speed of sound v a and v c Substituting the following simultaneous formulas, we can obtain the thickness h of the crystalline polymer material:

[0025] φ=arg(P c -P a )=π

[0026] P a =e^(ik a h), P c =e^(ik c h)

[0027] k a =2πf / v a k c =2πf / v c

[0028] Where: φ represents the phase difference between the crystalline and molten regions, arg() represents phase extraction, and P a P represents the sound pressure in the molten region. c The sound pressure level in the crystalline region is represented by e, the natural constant is represented by ^, and k is represented by k. a and k c The wavenumbers of the molten and crystalline regions are respectively, v a and v c , , respectively, represent the sound velocity of the crystalline polymer material in its crystalline and amorphous states, f is the operating frequency, ^ represents the power, and i represents the imaginary number.

[0029] When the overall thickness of the crystalline polymer material is the same, the spatial arrangement of the molten and crystalline regions with the same thickness is designed and controlled to achieve spatial encoding of the phase distribution. After the acoustic holographic phase modulation of the crystalline polymer material is completed by scanning localized irradiation, the material in the molten region that was scanned by the laser undergoes recrystallization under natural cooling at room temperature, thereby restoring it to the original crystalline state, and then it can be used for the next acoustic holographic phase modulation.

[0030] III. An ultrasonic processing method for a phase acoustic holographic device fabricated using an acoustic holographic phase modulation method:

[0031] A crystalline polymer material is placed on the surface of an ultrasonic transducer probe, with a gap between it and the ultrasonic object. The ultrasonic transducer probe emits ultrasonic waves, which pass through the crystalline polymer material and act on the ultrasonic object, forming the ultrasonic working process. During the ultrasonic working process, a laser pulse beam is emitted in real time to scan and locally irradiate the crystalline polymer material, turning the crystalline polymer material into a phase acoustic holographic device. Furthermore, different laser pulse beams are emitted in real time to scan and locally irradiate the crystalline polymer material, adjusting the acoustic holographic phase distribution on the phase acoustic holographic device.

[0032] This invention requires that the programmable acoustic hologram and the object under test be separated, and the programmable acoustic hologram cannot directly contact the object under test, so that there is a possibility that the outer laser beam can irradiate the surface of the programmable acoustic hologram for melting treatment.

[0033] The present invention can typically be used in scenarios such as underwater detection and particle capture.

[0034] Each microstructure region is heated and melted when irradiated by a laser beam, thus becoming a non-crystalline state. If the laser beam is removed at this time, the microstructure region will gradually return to room temperature and then return to the crystalline state. This process is relatively short and can only last for a few minutes. Therefore, this invention requires that the programmable acoustic hologram and the object under test be separated, and that an external laser beam continuously scans and irradiates the microstructure region on the programmable acoustic hologram to maintain the reconfigurable acoustic holographic phase distribution and to adjust and modulate the reconfigurable acoustic holographic phase distribution.

[0035] It is known that crystalline polymer materials have two reversible states: crystalline and amorphous, and the material exhibits significant differences in acoustic properties between these two states. This invention uses a laser to scan and write high-resolution patterned molten regions onto a crystalline polymer plate, thereby performing spatial acoustic phase encoding on the polymer plate. The phase-encoded crystalline polymer plate can then be used as an acoustic holographic modulation device to achieve three-dimensional sound field modulation. During use, one surface of the crystalline polymer, which has flat upper and lower surfaces, is coupled to the surface of a conventional ultrasonic transducer. This couples the mechanical vibrations excited by the ultrasonic transducer into the crystalline polymer plate structure, performing planar phase modulation. Subsequently, the target sound field can be reconstructed by coupling the lower surface of the programmable holographic plate to a transmission background environment. After sound field modulation, the crystalline polymer, with its reversible material properties, recrystallizes the molten region through natural cooling, erasing the encoded acoustic phase information, and allowing for re-encoding of the phase acoustic holographic information. Therefore, the aforementioned programmable acoustic holographic device can easily and conveniently modulate the plane wave excited by a conventional piezoelectric probe into a complex target sound field in a semi-infinite space to achieve particle capture and acoustic energy guidance, and has potential for biomedical applications such as targeted drug delivery, nerve stimulation, and tissue regeneration.

[0036] The crystalline polymer used in this invention is doped with a photothermal conversion medium, specifically Sudan Black material, with a total dopant content of 1.5%. After doping, under the action of an infrared laser, the laser-affected region will undergo a localized melting phase transition due to heat absorption, thus transforming from a crystalline state to a molten state. It is important to note that the material temperature must exceed its melting temperature T. m Only through this process can the material transition from a crystalline state to a molten state; otherwise, it will remain in a crystalline state. Therefore, even if the material in the non-laser-affected region experiences a slight temperature rise due to thermal diffusion, it will still maintain its crystalline state because its temperature does not exceed the melting temperature. Furthermore, since the melting temperature of crystalline polymers is typically 10-20°C higher than their crystallization temperature, considering the material's cooling rate, the molten state can be maintained for a period of time during operation, i.e., a low-velocity plateau period exists.

[0037] Considering the penetration depth of light waves, this invention uses an infrared laser focused beam as the phase encoding writing source. The specific process is as follows: First, the phase distribution calculated based on the target modulated sound field is encoded and drawn as a trajectory file. Then, the trajectory file is input into the laser system, and the laser beam is controlled to scan along a specific trajectory on the crystalline polymer plane, triggering local melting of the crystalline polymer material to form a target phase-encoded holographic plate.

[0038] In summary, the operation of a programmable phase holographic device can be divided into the following three processes:

[0039] (1) Phase information encoding and writing: First, using a high-power laser, the laser beam is controlled to scan and move along the crystalline polymer material according to the movement trajectory file output by the computer, and the crystalline polymer is locally melted in a pixel-by-pixel manner. After the laser scan is completed, the laser writing of the corresponding phase encoding information is completed.

[0040] (2) Phase Information Maintenance: After the encoded information is written, considering that the molten region in the crystalline material will recrystallize at room temperature, resulting in a limited reconstruction time for the holographic sound field, a laser beam needs to be used to continue scanning along the original trajectory after the phase holographic information is encoded to maintain local melting. At the same time, considering that repeated laser scanning will accumulate heat in the molten region, the resulting lateral thermal diffusion will cause distortion of the phase-encoded holographic pattern and ultimately worsen the reconstruction of the holographic sound field. Therefore, when maintaining the phase-encoded pattern, a low-power laser is used for spatial scanning along the trajectory.

[0041] (3) Phase information erasure: After the target sound field is reconstructed, the laser is turned off directly. The local melting phase transition region on the crystalline polymer plate will recrystallize at room temperature and restore the initial crystalline state. After a period of time, the crystalline polymer plate can be used to write a new phase coding distribution for new sound field modulation.

[0042] The programmable acoustic holographic device of this invention consists of only a single layer of photoresponsive crystalline polymer plate. The crystalline polymer switches between two phases when the temperature changes. When the ambient temperature is below its crystallization temperature, the material exhibits a crystalline state, possessing high modulus and high acoustic velocity properties. Conversely, when the ambient temperature is above its melting temperature, the material exhibits a molten state, possessing low modulus and low acoustic velocity properties. Theoretically, spatial sound field modulation can be achieved by spatially arranging the aforementioned coding units.

[0043] Therefore, by doping photothermal conversion agents into crystalline polymer materials, lasers can be used to perform localized melting encoding on the crystalline polymer, thereby arranging crystalline and molten polymer units with sound velocity differences on the polymer plane. This serves as a phase-encoded acoustic holographic device to achieve wavefront phase modulation of three-dimensional transmitted sound waves. Furthermore, crystalline polymer materials possess reversible phase transition characteristics. A crystalline polymer plate patterned by laser phase transition will revert to its previous crystalline state after cooling for a period of time, causing the patterned encoded acoustic hologram to disappear. Further writing of new phase acoustic holograms can then be performed to achieve new sound field modulation functions.

[0044] The planar multifocal acoustic lens device provided by this invention has the following beneficial effects:

[0045] (1) This invention directly replaces the base plate of the phase holographic plate prepared by conventional 3D printing with a smart material. By using a crystalline polymer with reversible material properties, traditional acoustic holographic devices are endowed with flexible programmability, promoting the transformation of acoustic holographic devices from static to dynamic, and improving the practical application potential of dynamic acoustic holographic devices. During use, specific sound field information can be directly encoded and written into a single crystalline polymer. After modulation, the previous acoustic information can be erased and new sound field information can be written.

[0046] (2) The planar programmable acoustic holographic device used in this invention has a compact structure, strong operability, and high reliability. At the same time, it has high spatial modulation resolution, with the spatial resolution of acoustic holographic information written based on focused laser beam scanning encoding reaching up to 80µm, which is much greater than that of current dynamic acoustic holographic systems. In addition, the crystalline polymer material used in the programmable acoustic holographic device has good sound transmission performance, which can significantly improve the transmittance and conversion rate of the sound field.

[0047] Therefore, the programmable phase acoustic holographic device based on crystalline polymers proposed in this invention can modulate the plane wave incident on the probe into a three-dimensional arbitrarily complex sound field, which can be used to realize particle trapping in free space, target manipulation, and acoustic communication. Furthermore, the programmable acoustic holographic device of this invention is completely planar, which is well matched to underwater acoustic impedance, has high acoustic coupling efficiency, a compact structure, and is simple and inexpensive to fabricate. Attached Figure Description

[0048] Figure 1 is a schematic diagram of a reconfigurable acoustic holographic device based on programmable crystalline materials;

[0049] Figure 2 shows the transmission phase diagrams of crystalline materials of different thicknesses in the crystalline and molten states, with the operating frequency kept constant at 2.2 MHz.

[0050] Figure 3 is a three-dimensional and two-dimensional schematic diagram of holographic sound field modulation based on crystalline polymer in Embodiments 1 and 2 of the present invention, wherein (a) represents the sound field reconstruction effect after modulation by the holographic plate in the three-dimensional case, and (b) represents the sound field reconstruction effect after modulation by the holographic plate in the two-dimensional case.

[0051] Figure 4 is a schematic diagram of the reconfigurable principle of the programmable acoustic holographic device based on crystalline polymer in Embodiments 1 and 2 of the present invention;

[0052] Figure 5 shows the synthesis process of the crystalline polymers in Examples 1 and 2 of the present invention and their microscopic changes with temperature. (a) shows the synthesis process of the crystalline polymer material, and (b) shows the situation where the molecular chains of the crystalline polymer gradually become looser under temperature stimulation.

[0053] Figure 6 illustrates the laser scanning trajectory control methods based on target acoustic holography in Embodiments 1 and 2 of the present invention.

[0054] Figure 7 is a holographic sound field reconstruction result diagram of Embodiment 1 of the present invention, wherein (a) represents the target sound field distribution diagram, (b) represents the phase encoding distribution diagram based on the target sound field design, (c) represents the acoustic holographic plate diagram prepared on the crystalline polymer plate, and (d) represents the water surface ripple diagram realized on the target plane through the acoustic radiation force effect.

[0055] Figure 8 is a holographic sound field reconstruction result diagram of Embodiment 2 of the present invention, wherein (a) represents the target sound field distribution diagram, (b) represents the phase encoding distribution diagram based on the target sound field design, (c) represents the acoustic holographic plate diagram prepared on the crystalline polymer plate, and (d) represents the water surface ripple diagram realized on the target plane through the acoustic radiation force effect.

[0056] Figure labeling: 1. Ultrasonic transducer; 2. Laser pulse beam; 3. Programmable acoustic hologram based on crystalline polymer; 4. Crystalline region; 5. Molten region. Detailed Implementation

[0057] To enable those skilled in the art to better understand and implement the technical solutions of this invention, the invention will be described in detail below with reference to the accompanying drawings and specific embodiments. Obviously, the described embodiments are merely some, not all, of the embodiments of this invention. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0058] In the description of this invention, it should be understood that the terms "middle," "upper," "lower," "left," "right," "lateral," "longitudinal," "horizontal," "vertical," "axial," "mirror image," "length," "width," and "thickness," etc., indicating orientation or positional relationships based on the orientation or positional relationships shown in the accompanying drawings, are only for the convenience of describing the technical solutions of this invention and simplifying the description, and do not indicate or imply that the device or equipment referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of this invention. Furthermore, the terms "comprising" and "having," and any variations thereof, are intended to cover non-exclusive inclusion. In the description of this invention, unless otherwise stated, "a plurality of" means two or more, and will not be elaborated further here.

[0059] This invention utilizes laser scanning to achieve high-resolution, regionalized melting phase transitions in materials, which, in conjunction with crystalline regions, enable phase-encoded modulation of the transmitted sound field. The laser-assisted crystalline polymer, used as a programmable phase-holographic acoustic device, modulates incident plane waves into a complex target sound field across two-dimensional space by matching one side of its surface with a conventional transducer. This modulates the target sound field for particle manipulation or nerve stimulation. After use, the reversible crystalline polymer reverts to its crystalline state at room temperature, erasing the laser-written programmable phase-holographic information and allowing for the laser writing of new target phase holograms. The programmable acoustic holographic device directly utilizes the state switching of the substrate material itself as the encoding unit for the spatial phase. With its compact structure, high resolution, and flat surfaces on both sides, it can be directly bonded to the surfaces of conventional ultrasonic transducers and the target object, thereby achieving free modulation of the three-dimensional spatial sound field in the background domain.

[0060] In a programmable acoustic holographic device based on a crystalline polymer according to the present invention, the crystalline polymer has two reversible states: a crystalline state and a molten state. When the external temperature is higher than the melting temperature T of the material, the crystalline polymer can be used to achieve the desired holographic state. m Or below the material's crystallization temperature T c During this process, a dynamic switching occurs between two phases. The crystalline state exhibits high Young's modulus and sound velocity, while the molten state has low Young's modulus and sound velocity. Furthermore, during the phase transition, the material thickness hardly changes; only the sound velocity changes. The two-dimensional spatial arrangement of microstructural regions with different sound velocities at the same thickness can achieve phase modulation of the transmitted / reflected sound field.

[0061] As shown in Figure 1, the device includes a programmable acoustic holographic plate 3, which is a flat plate made of crystalline polymer material. The programmable acoustic holographic plate 3 is divided into several microstructure regions arranged in a close array. The microstructure regions have two states: crystalline and molten. Each microstructure region has only one state, and the two states change reversibly with temperature. The programmable acoustic holographic plate 3 covers the ultrasonic transducer 1 probe.

[0062] In Figure 1, black represents the amorphous state and gray represents the crystalline state. The programmable acoustic holographic device 3 is a crystalline polymer plate with spatially distributed patterned molten state regions 32 on its surface. There is a certain sound velocity difference between the molten state regions 32 and the crystalline state regions 31, which can achieve phase distribution on a spatial plane.

[0063] In practice, the programmable acoustic holographic board 3 uses crystalline polymer materials, typically polycaprolactone.

[0064] The crystalline microstructure regions are formed naturally at room temperature and are in a solid state.

[0065] The non-crystalline microstructure region is formed by melting the originally crystalline microstructure region under the irradiation of an infrared laser beam emitted by an infrared laser, and is in a molten state.

[0066] Microstructural regions exhibit different material and acoustic properties in the crystalline and molten states, primarily manifested in differences in Young's modulus and sound velocity.

[0067] The microstructure region in the crystalline state is called the crystalline region 31, and the microstructure region in the amorphous state is called the molten region 32.

[0068] In specific implementation, the method involves a laser pulse beam 2 emitted by a laser to scan and locally irradiate different areas on the surface of a crystalline polymer material, thereby forming regions with different material and acoustic properties on the crystalline polymer material. Patterned molten regions are then written into the original crystalline regions to form an acoustic holographic phase distribution, transforming it into a phase acoustic holographic device, which constitutes a programmable acoustic holographic plate 3.

[0069] In a specific implementation, an infrared / ultraviolet laser can be used to emit infrared / ultraviolet laser pulse beams, depending on the characteristics of the crystalline polymer material to receive which type of beam for melting.

[0070] Crystalline polymer materials are originally in a crystalline state. When different microstructure regions on the crystalline polymer material are irradiated and heated, the irradiated and heated microstructure regions melt and become amorphous, forming molten regions 32. The microstructure regions that are not irradiated and heated remain unchanged, forming crystalline regions 31. This results in the crystalline polymer material having both crystalline and amorphous states.

[0071] Furthermore, the laser pulse beam 2 scans and irradiates different microstructure regions, causing the microstructure regions in both crystalline and molten states on the crystalline polymer material to form a patterned arrangement, which serves as the acoustic holographic phase distribution of the phase acoustic holographic device.

[0072] Each pulse corresponds to the irradiation of a microstructure region. Different pulses correspond to different microstructure regions. That is, the irradiation region corresponding to the pulse is the microstructure region, and the pulse duration is the irradiation duration of the microstructure region.

[0073] By controlling the duration and energy of pulse irradiation on the microstructure region, the temperature of the irradiated microstructure region can be kept within 10% above the melting temperature. This prevents the melting temperature from becoming too high and the microstructure region from being heated too much, thus avoiding affecting the surrounding microstructure regions.

[0074] The sound velocity of crystalline polymer materials does not change much with the operating frequency. For different operating frequencies, the material thickness needs to be reselected. However, materials with the same thickness but different sound velocities have different phase delays in their transmitted sound fields. Therefore, when the material thickness and frequency are matched, the transmission phase delay can be controlled to be equal to π.

[0075] By adjusting the thickness of the crystalline polymer material and controlling its frequency matching, the transmission phase delay of the crystalline polymer material is made exactly equal to π. When a plane acoustic wave excited by an ultrasonic transducer is incident perpendicularly onto a patterned molten crystalline polymer plate, a π-phase difference occurs in the transmission phase between the molten and crystalline regions, achieving spatial phase modulation of the sound field. The modulated sound field then propagates forward to reconstruct the target sound field. It is important to note that the impedance of the crystalline polymer material is almost perfectly matched to that of water, therefore its transmittance is consistently above 85%, resulting in high energy utilization.

[0076] As shown in Figure 2, to ensure that the delay phase of the incident sound field by the molten region and the non-crystalline region affected by the laser is exactly π, the thickness h of the sound field of the crystalline polymer material needs to be set appropriately. The specific process is as follows:

[0077] The thickness of crystalline polymer materials is set as follows:

[0078] 1) First, using pulsed ultrasound under water immersion conditions, the sound velocity of the crystalline polymer material in both crystalline and amorphous states was measured, and the velocity was v0 respectively. a and v c ;

[0079] 2) Next, design the thickness h of the crystalline polymer material, specifically the sound velocity v a and v c Substituting the following simultaneous formulas, we can obtain the thickness h of the crystalline polymer material:

[0080] φ=arg(P c -P a )=π

[0081] P a =e^(ik a h), P c =e^(ik c h)

[0082] k a =2πf / v a k c =2πf / v c

[0083] Where: φ represents the phase difference between the crystalline and molten regions, arg() represents the extracted phase value, and Pa P represents the transmitted sound field of a molten material. c The transmitted sound field of a crystalline material is represented by e, which represents the natural constant, ^ which represents the power, and k. a and k c The wavenumbers of the molten and crystalline regions are respectively, v a and v c , , respectively, are the sound velocities of the crystalline polymer material in the crystalline state and the amorphous state (i.e., molten state), and f is the operating frequency.

[0084] In specific implementation, the crystalline polymer material is synthesized and prepared according to the thickness h determined above, and finally a programmable acoustic holographic phase plate that can be used for complex acoustic field modulation is obtained.

[0085] As shown in Figure 3, when the overall thickness of the crystalline polymer material is the same, that is, the thickness of each microstructure region is the same, the spatial encoding of the phase distribution is achieved by designing and controlling the spatial arrangement of the molten region 32 and the crystalline region 31 with the same thickness. The sound field reconstruction effects after modulation by the holographic plate in the three-dimensional and two-dimensional cases are shown in Figure 3(a) and (b), respectively.

[0086] The crystalline polymer material is doped with a photothermal conversion medium. Therefore, when a focused laser beam is applied to a local area, the crystalline polymer material absorbs the laser energy and converts it into heat, causing a melting phase transition in the local crystalline region affected by the laser while maintaining almost no change in thickness.

[0087] The phase distribution based on the target holographic acoustic field design will serve as the trajectory of the laser beam scanning along the surface of the crystalline polymer, encoding the acoustic holographic phase information into the crystalline polymer flat plate structure.

[0088] Since the crystallization temperature of crystalline polymer materials is generally about 20°C lower than their melting temperature, the molten region 32 can be well maintained during the laser beam pattern scanning of the crystalline material without affecting the material in the surrounding crystalline region 31. Subsequently, by repeatedly scanning along the target trajectory with the laser beam, the molten pattern can be maintained for a long time, exhibiting good stability.

[0089] Since the acoustic holographic pattern is prepared by a laser beam that scans in space, the structural resolution of the programmable acoustic hologram is entirely determined by the size of the laser pulse beam, which can reach 100µm. That is, the minimum size of the molten region 32 and the crystalline region 31 can be 100µm.

[0090] After the acoustic holographic phase modulation of the crystalline polymer material is completed by scanning localized irradiation, the material in the molten region scanned by the laser undergoes recrystallization under natural cooling at room temperature, thereby restoring the original crystalline state and being used for the next acoustic holographic phase modulation.

[0091] The specific process of the ultrasonic processing method using the phase acoustic holographic device of the present invention is as follows:

[0092] A crystalline polymer material is placed on the surface of the ultrasonic transducer 1 probe, with a gap between it and the ultrasonic object. The ultrasonic transducer 1 probe emits ultrasonic waves, which pass through the crystalline polymer material and act on the ultrasonic object, forming an ultrasonic working process. During the ultrasonic working process, a laser pulse beam 2 is emitted in real time to scan and locally irradiate the crystalline polymer material, making the crystalline polymer material into a phase acoustic holographic device. Furthermore, different laser pulse beams 2 are emitted in real time to scan and locally irradiate the crystalline polymer material, adjusting the acoustic holographic phase distribution on the phase acoustic holographic device.

[0093] To achieve co-lateral incidence of laser and ultrasound, enabling particle trapping and biomedical stimulation in the free space above, this invention provides an online dynamic acoustic holographic device based on crystalline polymers. The acoustic wave incidence employs a reflection method: a conventional ultrasonic transducer 1 and a programmable acoustic holographic device 3 are arranged perpendicularly, allowing the incident sound field from the conventional ultrasonic transducer 1 to be incident perpendicularly from the side to the reflector and then perpendicularly from below to the programmable acoustic holographic device. Simultaneously, a laser beam is incident from above and scans and melts along the space of the programmable acoustic holographic device 3, thereby performing patterned phase encoding.

[0094] As shown in Figure 4, the laser beam scanning process can encode the phase information of the acoustic holography into the programmable acoustic holographic device 3 and modulate the incident plane acoustic wave to achieve target sound field reconstruction.

[0095] For the sound pressure amplitude distribution A(x,y,z=l) of the target plane, where l is the focal plane corresponding to the target sound field, the trajectory of the laser beam scanning is then designed and encoded based on the above sound field distribution. The design process is as follows:

[0096] Substituting the sound field distributions of the target surface z=l and the holographic surface z=0 into the iterative angular spectrum method, firstly, before the iterative optimization begins, the phase distribution φ0 of the holographic surface is set to an arbitrary value. The entire iterative process can be divided into forward propagation and backward optimization processes:

[0097] The forward propagation process is as follows: For the transmitted sound field p0(x,y,z=0)=e^(iφ0) from the holographic surface, first calculate the spectral distribution of the plane using Fourier transform: P0(k x ,ky The expression is: ∫∫p0(x,y,z=0)dxdy. Then, as it propagates along the positive z-axis, its spectrum is multiplied by the phase factor H(k). x ,k y ,z=l)=e^(ik z After l), the spectral distribution P on the target image plane z=l can be obtained. ’ (k x ,k y ,z=l)=P0(k x ,k y ,z=0)*H(k x ,k y ,z=l), where k z =(k0 2 -k x 2 -k y 2 ) 1 / 2 The sound field distribution p of the plane is obtained after the inverse Fourier transform. ’ (x,y,z=l)=∫∫P ’ (k x ,k y ,z=l)dk x dk y .

[0098] After forward propagation is complete, the phase φ on the target image plane z=l is... ’ (x,y,z=l)=arg(p ’ (x,y,z=l) is preserved, and its amplitude is replaced with the target focusing amplitude distribution A(x,y,z=l); the sound field q on the z=l plane is obtained. ’ (x,y,z=l)=A(x,y,z=l)*e^(iφ ’ (x,y,z=l)).

[0099] The reverse optimization process is as follows: For the sound field q propagating backward from the target image plane z=l to z=0... ’ (x,y,z=l), similarly, the spectral distribution of this plane is first calculated using Fourier transform: Q ’ (k x ,k y ,z=l)=∫∫q ’ (x,y,z=l)dxdy, and then, as it propagates along the negative z-axis, its spectrum is multiplied by the phase factor H(k). x ,k y ,z=(-l))=e^(ik z After (-l)), the spectral distribution Q0(k) on the plane z=0 can be obtained. x ,ky ,z=0)=Q ’ (k x ,k y ,z=l)*H(k x ,k y ,z=(-l)). And the sound field distribution on the holographic plane z=0 was obtained as q0(x,y,z=0)=∫∫Q0(k x ,k y ,z=0)dk x dk y The updated binary phase distribution is φ=0 or π, where φ=0 when q0>0 and φ=π when q0<=0.

[0100] After approximately 60 forward and backward propagation iterations, the binary coded phase distribution on the phase hologram can be finally obtained.

[0101] Based on the binary coded phase distribution obtained through the above iterative optimization, the two-dimensional coded phase distribution is plotted in two-dimensional drawing software and saved as a file readable and writable by an infrared laser marking machine (e.g., a .dxf format file). This file is then input into the infrared laser marking machine, controlling the scanning path of the infrared laser beam. Under laser scanning, the region with phase φ0=π will be locally heated to a molten state by the laser. After scanning, a pattern corresponding to the phase acoustic holography will be encoded and written onto the crystalline polymer plate.

[0102] When programmable phase acoustic holographic devices are used for target sound field modulation, the resolution and accuracy of the phase-encoded sound field pattern are completely determined by the spot resolution of the laser beam, thus the fabrication accuracy can reach 100µm, which greatly improves the resolution of sound field modulation.

[0103] Considering the size and processing precision of the metasurface, the operating frequency of the planar multifocal acoustic lens can be selected from 100 to 3000 kHz. When the operating frequency changes, the thickness h of the programmable acoustic holographic phase plate needs to be redesigned based on the three-medium theory, which is simple and efficient.

[0104] In addition, the programmable acoustic holographic phase plate material is a crystalline polymer, and its acoustic impedance is well matched with the impedance of the matching layer of the piezoelectric transducer and the background water medium. Therefore, the acoustic energy transmittance is high, which greatly improves the acoustic energy utilization rate.

[0105] Figure 5 shows a schematic diagram of the fabrication of the reconfigurable acoustic holographic device based on programmable polymer provided by this invention and the microscopic manifestation of the melting process. This invention uses a common crystalline polymer material: polycaprolactone (PCL). As shown in Figure 5(a), it exhibits a significant modulus change before and after the crystallization / melting phase transition. Specifically, with increasing temperature, short-range ordered crystalline regions on the molecular chains freely expand, resulting in a lower modulus. Based on the relationship between material modulus and sound velocity, the material will have different sound velocities in the crystalline and molten states, which, according to experimental measurements, are 1520 and 1880 m / s, respectively. Assuming an operating frequency f = 2.2 MHz, the thickness of the crystalline polymer material at this point can be calculated as h = 1.75 mm based on the three-medium theory.

[0106] Figure 5(b) shows the preparation flow chart of red light responsive PCL material. In order to achieve patterned phase encoding of laser-responsive melting, during the preparation process, a photothermal conversion medium (Sudan Black) needs to be doped into the PCL polymer network to give it a good photothermal effect, so that it absorbs light in a specific wavelength band (in the infrared wavelength region) and converts it into heat energy, thereby realizing the crystallization-melting phase transformation based on light conditions.

[0107] During the experiment, the area of ​​the prepared PCL film exposed to light was heated to T due to the photothermal effect. m Above this, the material transforms from a crystalline state to an amorphous state, and when the infrared light is removed, the temperature of the irradiated area drops to T. c Next, the material is restored to its crystalline state. Under the scanning action of a focused infrared laser beam, patterned molten regions are encoded and written onto the crystalline polymer material as an acoustic holographic spatial phase encoding distribution. This results in a patterned crystalline polymer material, at which point the material as a whole exhibits alternating crystalline and molten phases.

[0108] It should be noted that polymer T can be achieved by subsequently adjusting the molecular weight of PCL. m and T c The regulation is designed to match the application scenarios of acoustic metamaterials.

[0109] Figure 6 shows a flowchart of the fabrication process of the programmable acoustic holographic device provided by this invention, including the entire process from the target acoustic field to the holographic plane phase distribution, and then to the laser beam scanning trajectory. It should be noted that, since crystalline materials will recrystallize after the temperature decreases, the laser beam needs to repeatedly scan the molten region along the original path at low power.

[0110] The dynamic modulation sound field implementation of the programmable acoustic holographic device 3 in the embodiments of the present invention will now be described in detail with reference to the accompanying drawings.

[0111] At this point, the thickness of the programmable acoustic holographic device 3 is set to h = 1.7 mm, the width to D = 50 mm, and the excitation frequency of the conventional ultrasonic phased array is f = 2.2 MHz. An infrared laser beam with a wavelength of 1064 nm is used to scan, melt, and phase-encode the crystalline polymer plate.

[0112] Example 1: First, the ring sound field is reconstructed based on the programmable acoustic holographic device 3, including the following steps:

[0113] S1: Based on Figure 7, the focal plane corresponding to the annular sound field is set to l=20 mm, and the sound pressure distribution A'(x,y,z=l) is shown in Figure 7(a).

[0114] Next, based on the improved binary iterative angular spectrum method, the phase distribution φ on the 3-plane z=0 of the programmable phase acoustic holographic device is designed:

[0115] First, assume the phase distribution φ on the holographic plane z=0 is arbitrary. Then, calculate the sound field distribution P0(x,y,z=0)=e^(iφ) propagating along the positive z-axis to the target image plane z=l. The calculation process is as follows: Based on the spectral distribution P0(k) on the z=0 plane... x ,k y (z=0), forward propagation yields the sound field distribution P on the z=l plane. ’ (x,y,z=l), preserving the phase distribution of this plane φ'(x,y,z=l)=arg(P ’ (x,y,z=l)) and its amplitude distribution is replaced by A'(x,y,z=l), so that the sound field distribution on the target plane is P. ’ (x,y,z=l)=A'(x,y,z=l)*e^(iφ'(x,y,z=l)).

[0116] Next, the sound field distribution P on the target plane is... ’ (x,y,z=l) propagates backward along the z-axis to the holographic plane z=0. The calculation process is as follows: Based on the spectral distribution Q on the z=l plane... ’ (k x ,k y Backpropagation yields the spectrum Q0(k) on the z=0 plane. x ,k y The sound field distribution q0(x,y,z=0) is generated and the binary phase φ=0 or π of the holographic phase plane z=0 is updated. When q0>0, φ=0; when q0<=0, φ=π, and a new sound field distribution p0(x,y,z=0)=e^(iφ) is formed on the plane.

[0117] The phase distribution φ on the z=0 plane is repeatedly optimized and iterated according to the above forward and backward propagation models. After about 60 iterations, convergence can be achieved. Finally, the encoded phase distribution φ and the sound field distribution on the target image plane are shown in Figure 7(b).

[0118] S2: Next, the binary phase distribution φ on the z=0 plane is output as a laser scanning trajectory file and transmitted to the laser to control the laser beam scanning trajectory. The final programmable phase holographic plate is shown in Figure 7(c). Under experimental conditions, the height of the programmable acoustic holographic device with the water surface distance is set to be exactly 20 mm at the focal plane of the target image. Based on mechanical effects and water surface tension, the reconstructed sound field will form water surface ripples of a specific shape on the water surface, as shown in Figure 7(d).

[0119] S3: Next, the infrared laser is turned off, and the molten region heated by the infrared localization will gradually cool down. When the temperature of this region drops to the crystallization temperature T... c When the temperature drops below a certain point, the molten region will recrystallize and return to a crystalline state.

[0120] Example 2: Next, a holographic sound field with the letter 'Z' distribution is realized based on the programmable acoustic holographic device 3, including the following steps:

[0121] S1: Based on Figure 8, the focal plane corresponding to the sound field of the letter 'Z' is set to l=20 mm, and the sound pressure distribution A'(x,y,z=l) is shown in Figure 8(a).

[0122] Similarly, the phase distribution φ on the 3 plane z=0 of the programmable phase acoustic holographic device is designed based on the improved binary iterative angular spectrum method, and the coded phase distribution φ and the sound field distribution on the target image plane are finally obtained as shown in Figure 8(b).

[0123] S2: Next, the binary phase distribution φ on the z=0 plane is output as a laser scanning trajectory file and transmitted to the laser to control the laser beam scanning trajectory. The final programmable phase holographic plate is shown in Figure 8(c). Under experimental conditions, the height of the programmable acoustic holographic device with the water surface distance is set to be exactly 20 mm at the focal plane of the target image. Based on mechanical effects and water surface tension, the reconstructed sound field will form water surface ripples of a specific shape on the water surface, as shown in Figure 8(d).

[0124] S3: Next, the infrared laser is turned off, and the molten region heated by the infrared localization will gradually cool down. When the temperature of this region drops to the crystallization temperature T... c When the temperature drops below a certain point, the molten region will recrystallize and return to a crystalline state.

[0125] In the above embodiments, the descriptions of each embodiment have different focuses. For parts not described in detail in a certain embodiment, please refer to the relevant descriptions in other embodiments.

[0126] The embodiments of this application have been described in detail above. Specific examples have been used to illustrate the principles and implementation methods of this invention. The description of the above embodiments is only for the purpose of helping to understand the method and core ideas of this invention. At the same time, for those skilled in the art, there will be changes in the specific implementation methods and application scope based on the ideas of this invention.

[0127] In conclusion, the contents of this specification should not be construed as a limitation of the present invention.

Claims

1. A reconfigurable acoustic holographic device based on a crystalline polymer, characterized in that: The system includes a programmable acoustic hologram (3), which is divided into several microstructure regions arranged in a close array. The microstructure regions have two states: crystalline and amorphous, and the two states change reversibly with temperature. The programmable acoustic hologram (3) covers the ultrasonic transducer (1) probe.

2. A reconfigurable acoustic holography device based on crystalline polymer according to claim 1, characterized in that: It also includes a reflector plate, which is arranged on the upper side of the programmable acoustic hologram plate (3) and at a distance from the programmable acoustic hologram plate (3). The ultrasonic waves emitted by the ultrasonic transducer (1) pass through the programmable acoustic hologram plate (3) and are then reflected by the reflector plate before irradiating the object under test.

3. A reconfigurable acoustic holography device based on crystalline polymer according to claim 1, characterized in that: The amorphous microstructure region is formed by melting the originally crystalline microstructure region under the irradiation of a laser beam emitted by a laser. The microstructure region has different material properties and acoustic properties in the crystalline and molten states.

4. The method of acoustic holographic phase modulation for use in the reconfigurable acoustic holographic device according to any of claims 1 to 3, characterized in that: The method involves using a laser pulse beam (2) emitted by a laser to scan and localize different areas on the surface of a crystalline polymer material, thereby forming regions with different acoustic properties on the crystalline polymer material. Patterned molten regions are then written into the original crystalline regions to form an acoustic holographic phase distribution, thus transforming the material into a phase acoustic holographic device.

5. The acoustic holographic phase modulation method according to claim 4, characterized in that: The crystalline polymer material is originally in a crystalline state. When the microstructure regions on the crystalline polymer material are irradiated and heated, the irradiated and heated microstructure regions melt and become a non-crystalline state to form molten regions (32), while the microstructure regions that are not irradiated and heated do not change and form crystalline regions (31), so that the crystalline polymer material has two states: crystalline and non-crystalline. Furthermore, the laser pulse beam (2) scans and irradiates different microstructure regions, causing the two states of microstructure regions on the crystalline polymer material to form a patterned arrangement, which serves as the acoustic holographic phase distribution of the phase acoustic holographic device.

6. The acoustic holographic phase modulation method according to claim 4, characterized in that: Each pulse corresponds to irradiating a microstructure region, and different pulses correspond to different microstructure regions; and by controlling the duration and energy of the pulse irradiation of the microstructure region, the temperature of the microstructure region after irradiation is controlled to remain within 10% above the melting temperature.

7. The acoustic holographic phase modulation method according to claim 4, characterized in that: By setting the thickness of the crystalline polymer material and controlling the thickness-frequency matching, the transmission phase delay of the crystalline polymer material can be made equal to π.

8. The acoustic holographic phase modulation method according to claim 4, characterized in that: The thickness of the crystalline polymer material is set as follows: 1) First, the sound velocity of the crystalline polymer material is measured in the crystalline state and in the amorphous state, respectively, using pulsed ultrasound waves under water immersion conditions, as v a and v c , respectively; 2) the sound velocity v a and v c are substituted into the following system of equations to solve for the thickness h of the crystalline polymeric material: φ = arg(P c - P a ) = π P a = e^(ik a h), P c = e^(ik c h) k a = 2πf / v a , k c = 2πf / v c wherein: φ represents a phase difference between the crystalline region and the molten region, arg() represents a phase extraction, P a represents a sound pressure of the molten region, P c represents a sound pressure of the crystalline region, e represents a natural constant, k a and k c are wave numbers of the molten region and the crystalline region, respectively, v a and v c are sound velocities of the crystalline polymer material in the crystalline state and the non-crystalline state, respectively, f is an operating frequency, and i represents an imaginary number.

9. The acoustic holographic phase modulation method according to claim 4, characterized in that: When the overall thickness of the crystalline polymer material is the same, the spatial encoding of the phase distribution can be achieved by designing and controlling the spatial arrangement of the molten region (32) and the crystalline region (31) with the same thickness; After the acoustic holographic phase modulation of the scanned localized irradiation is completed, the material in the molten region scanned by the laser undergoes recrystallization under natural cooling at room temperature, thereby restoring it to its original crystalline state, and then it can be used for the next acoustic holographic phase modulation.

10. An ultrasonic processing method applied to a phase acoustic holographic device fabricated using any one of the acoustic holographic phase modulation methods described in claims 4-9, characterized in that: A crystalline polymer material is placed on the surface of the ultrasonic transducer (1) probe, and there is a gap between it and the ultrasonic object. The ultrasonic transducer (1) probe emits ultrasonic waves, which are transmitted through the crystalline polymer material and act on the ultrasonic object to form an ultrasonic working process. During the ultrasonic working process, a laser pulse beam (2) is emitted in real time to scan and irradiate the crystalline polymer material, so that the crystalline polymer material becomes a phase acoustic holographic device. Different laser pulse beams (2) are emitted in real time to scan and irradiate the crystalline polymer material, and the acoustic holographic phase distribution on the phase acoustic holographic device is adjusted.

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