Reconfigurable acoustical holography modulation method and device based on crystalline polymer

Abstract

The invention discloses a reconfigurable acoustical holography modulation method and device based on a crystalline polymer. The programmable acoustical holography device is composed of a single-layer photoresponse crystalline polymerization flat plate, is switched between two phases when the temperature irradiated by laser changes, has a crystalline state and a non-crystalline state, and reversibly changes along with the temperature. Space sound field modulation can be realized by spatially arranging the coding units, the crystalline polymer flat plate subjected to laser patterning phase change is recovered to the previous crystalline state after being cooled, the patterned coding acoustical holography disappears, and new phase acoustical holography is written in, so that a new sound field modulation function is realized. According to the programmable phase acoustical holography device based on the crystalline polymer, the incident plane wave of the probe can be modulated into any three-dimensional complex sound field, and the programmable phase acoustical holography device is of a complete plane type, is matched with underwater acoustic impedance, and is high in acoustic energy coupling efficiency, compact in structure, easy to prepare and low in price.

Description

Technical Field

[0001] The invention relates to the technical field of acoustic holography, and in particular to a reconfigurable programmable acoustic holography modulation method and device based on crystalline polymer materials for realizing high-resolution dynamic modulation of an acoustic field. Background Art

[0002] Biomedical ultrasound is one of the important new disciplines that uses ultrasound as a carrier, relies on signal processing technology, electronic science and other engineering technology means, and uses the biological effects of ultrasound to achieve disease diagnosis and treatment. At the same time, ultrasound itself carries huge energy. Medical studies have shown that the low-dose thermal effect produced by ultrasound can promote the metabolism of human functions, promote blood circulation, and accelerate wound healing. At present, the incidence of tumors at home and abroad is increasing year by year. For the treatment of tumors, in addition to traditional surgery, new diagnosis and treatment technologies are emerging in an endless stream. In addition to laparoscopic surgery, minimally invasive treatment has also achieved very good results in clinical application. However, minimally invasive treatment based on radio frequency, microwave or freezing technology is still an invasive method, which may cause bleeding or metastasis of punctured tumors. Therefore, in the past 20 years, invasive high-intensity focused ultrasound (HIFU) ablation treatment has received more and more attention. With the increase of ultrasound excitation power, the high-precision sound beam will propagate in human tissues and focus on the target area. The huge energy carried will cause rapid heating of the local area. The high-temperature thermal effect produced can cause the tissue to heat up rapidly and then cause irreversible coagulative necrosis. Since Lynn proposed the idea of ​​non-invasive surgery from in vitro to in vivo in 1942 and conducted damage experiments on animal brain cells with significant results, medical treatment based on HIFU ultrasound has gradually developed. However, most of the existing ultrasound medical diagnosis and treatment technologies use curved multi-element probes to achieve acoustic energy focusing in the target area, which is difficult to fit perfectly when in contact with the human epidermis, resulting in insufficient acoustic energy coupling and reduced acoustic energy utilization. At the same time, simple single-point focusing can no longer meet the increasingly advanced biomedical applications, especially for multi-target neural stimulation, tissue ablation, medical imaging technology and fixed-point drug delivery technology.

[0003] In addition, the sound field has a mechanical effect. The spatially distributed sound field will scatter on the surface of the particles, and the scattered sound field will further generate acoustic radiation stress along the gradient direction, thereby pushing the particles in the background medium to move toward the direction of the maximum / minimum of the acoustic energy and achieve the final arrangement. As an extension of optical tweezers technology in the field of acoustics, acoustic tweezers have unique advantages in capturing, moving and arranging particles. Based on its deeper penetration ability, better biocompatibility and wavelength that is more compatible with cells, acoustic-based particle manipulation technology has been widely used in the fields of chemistry, biology and medicine, and has gradually developed technologies such as acoustic microfluidics, acoustic cell symbiotic culture technology and drug delivery. To achieve many of the above applications, it is necessary to modulate the sound field in space to the target situation.

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

[0005] Therefore, how to replace the passive phase modulation unit with an active modulation unit while retaining the high information density carried by the phase hologram so that it has both high-resolution sound field and re-modulation capability is of extremely important scientific value. Summary of the invention

[0006] In order to overcome the shortcomings of existing sound field modulation technology, the present invention provides a reconfigurable programmable acoustic holographic modulation preparation method and device based on crystalline polymer materials for realizing high-resolution dynamic modulation of the sound field, in view of the fact that most existing acoustic holography technologies are static single structures, and dynamic acoustic holography technologies are difficult to achieve high resolution and high compactness at the same time.

[0007] In order to realize a codable phase acoustic holographic device based on a crystalline polymer, the technical solution adopted by the present invention is: 1. A reconfigurable acoustic holographic device based on crystalline polymer: It includes a programmable acoustic holographic plate, which is divided into several microstructure areas arranged in a tight array. The microstructure areas have two states, crystalline and non-crystalline, and the two states can change reversibly with temperature; the programmable acoustic holographic plate covers the ultrasonic transducer probe.

[0008] It also includes a reflector, which is arranged on the upper side of the programmable acoustic hologram and at a distance from the programmable acoustic hologram. The ultrasonic wave emitted by the ultrasonic transducer passes through the programmable acoustic hologram and is then reflected by the reflector to irradiate the object to be measured.

[0009] The programmable acoustic holographic plate is made of crystalline polymer material, specifically polycaprolactone material.

[0010] The non-crystalline microstructure region is formed by melting the originally crystalline microstructure region under the irradiation of a laser beam emitted by a laser, and the microstructure region has different material properties and acoustic properties in the crystalline state and the molten state.

[0011] The microstructure region in the crystalline state is called a crystalline region, and the microstructure region in the non-crystalline state is called a molten region.

[0012] The preparation process of the reconfigurable acoustic holographic device includes a crystalline polymer material plate and an infrared laser.

[0013] 2. An acoustic holographic phase modulation method for a reconfigurable acoustic holographic device: The method is to use a laser to emit a laser pulse beam to scan and locally irradiate different areas on the surface of a crystalline polymer material, so that areas with different acoustic properties are formed on the crystalline polymer material, and a patterned molten area is written in the original crystalline area to form an acoustic holographic phase distribution, thereby turning it into a phase acoustic holographic device.

[0014] The crystalline polymer material is originally in a crystalline state. The microstructure region on the crystalline polymer material is irradiated and heated, and the irradiated and heated microstructure region melts and becomes a non-crystalline state (molten state) to form a molten state region, and the microstructure region not irradiated and heated does not change to form a crystalline state region, so that the crystalline polymer material has two states of crystalline and non-crystalline states; The crystalline polymer material has different material properties and acoustic properties in the crystalline state and the amorphous state, which are mainly manifested in Young's modulus and sound velocity. Specifically, the Young's modulus and sound velocity in the amorphous state are both lower than those in the crystalline state.

[0015] Different microstructure regions are scanned and irradiated by a laser pulse beam, so that the microstructure regions in two states on the crystalline polymer material form a patterned arrangement as the acoustic holographic phase distribution of the phase acoustic holographic device.

[0016] Each pulse corresponds to irradiating a microstructure area, and different pulses correspond to different microstructure areas. The longer the laser pulse irradiation time and the higher the energy, the higher the temperature of the crystalline polymer in the corresponding area; and by controlling the duration and energy of the pulse irradiating the microstructure area, the temperature of the microstructure area after irradiation is controlled to stay within 10% above the melting temperature.

[0017] By setting the thickness of the crystalline polymer material, the thickness and frequency are controlled to match, thereby making the transmission phase delay of the crystalline polymer material equal to π.

[0018] The thickness of the crystalline polymer material is set as follows: 1) First, pulsed ultrasound was used to measure the sound velocity of the crystalline polymer material in the crystalline and amorphous states under water immersion conditions, which were v a and v c ; 2) The speed of sound v a and v c Substitute the following simultaneous formulas to obtain the thickness h of the crystalline polymer 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 in: φ represents the phase difference between the crystalline region and the molten region, arg() represents phase extraction, P a represents the acoustic pressure in the molten region, P c represents the sound pressure in the crystalline region, e represents a natural constant, ^ represents a power, k a and kc are the wave numbers of the molten region and the crystalline region, v a and v c are the sound velocities of crystalline polymer materials in crystalline and non-crystalline states, f is the operating frequency, ^ represents the power, and i represents an imaginary number.

[0019] When the overall thickness of the crystalline polymer material is the same, the spatial arrangement of the molten state region and the crystalline state region 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 by scanning localized irradiation is completed, the material in the molten state region scanned by the laser undergoes recrystallization under natural cooling at room temperature, thereby recovering to the original crystalline state, and then being used for the next acoustic holographic phase modulation.

[0020] 3. An ultrasonic processing method for a phase acoustic holographic device made by an acoustic holographic phase modulation method: When 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 an ultrasonic working process; during the ultrasonic working process, a laser pulse beam is emitted by a laser in real time to scan and locally irradiate the crystalline polymer material, so that the crystalline polymer material becomes a phase acoustic holographic device, and a different laser pulse beam is emitted by the laser in real time to scan and locally irradiate the crystalline polymer material, so as to adjust the acoustic holographic phase distribution on the phase acoustic holographic device.

[0021] The present invention requires that the programmable acoustic hologram plate and the object to be measured be spaced apart, and the programmable acoustic hologram plate cannot directly contact the object to be measured, so that the outer laser beam can irradiate the surface of the programmable acoustic hologram plate to perform melting treatment.

[0022] The present invention can generally be used in scenarios such as underwater detection and particle capture.

[0023] Each microstructure area will melt due to the heat when irradiated by the laser beam, and then become amorphous. If the laser beam is removed at this time, the microstructure area 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, the present invention requires that the programmable acoustic holographic plate and the object to be measured be separated, and the external laser beam can continuously scan and irradiate the microstructure area on the programmable acoustic holographic plate, thereby maintaining the reconfigurable acoustic holographic phase distribution, and the reconfigurable acoustic holographic phase distribution can be adjusted and modulated.

[0024] It is known that crystalline polymer materials have two reversible states: crystalline and non-crystalline, and the materials have huge differences in acoustic properties in these two states. The present invention uses a laser to scan and write a high-resolution patterned melting area on a crystalline polymer flat plate, thereby performing spatial acoustic phase encoding on the polymer flat plate. The phase-encoded crystalline polymer flat plate can be used as an acoustic holographic modulation device to realize sound field modulation in three-dimensional space. During use, after one side surface of the crystalline polymer, both of which have flat upper and lower surfaces, is coupled with the surface of a conventional ultrasonic transducer, the mechanical vibration excited by the ultrasonic transducer can be coupled to the crystalline polymer flat plate structure, and plane phase modulation can be performed. Subsequently, the target sound field can be reconstructed by coupling the lower surface of the programmable holographic plate to the transmission background environment; after the sound field modulation is completed, the crystalline polymer with reversible material properties will realize the recrystallization of the melting area by natural cooling, and the encoded acoustic phase information will be erased to re-perform phase acoustic holographic encoding. Therefore, through the above-mentioned programmable acoustic holography device, the plane wave excited by the conventional piezoelectric probe can be simply and conveniently modulated into a target complex sound field in a semi-infinite space to achieve particle capture and acoustic energy guidance, which has the potential for biomedical applications such as medical targeted drug delivery, nerve stimulation, and tissue regeneration.

[0025] The crystalline polymer used in the present invention is doped with a photothermal conversion medium, which refers to Sudan black material, and the total doping mass content is 1.5%. After doping, under the action of infrared laser, the laser action area will undergo a local melting phase transition due to heat absorption, and then change from a crystalline state to a molten state. It should be noted that the material temperature must exceed its melting temperature T m Only when the material in the non-laser action area has a slight temperature rise due to thermal diffusion, the crystalline state will remain unchanged because its temperature does not exceed the melting temperature. At the same time, since the melting temperature of crystalline polymers is usually 10~20℃ higher than the crystallization temperature, considering the cooling rate of the material, the material will be able to maintain the molten state for a period of time during the working process, that is, there is a low sound velocity platform period.

[0026] Considering the penetration depth of light waves, the present invention uses an infrared laser focused beam as a phase encoding writing source. The specific process is: first, the phase distribution calculated based on the target modulated sound field is encoded and drawn as a trajectory file, then the above 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 the local melting of the crystalline polymer material to form a target phase-encoded holographic plate.

[0027] In summary, the working process of the programmable phase holographic device can be divided into the following three processes: (1) Phase information coding writing: First, use a high-power laser to control the laser beam to scan and move along the crystalline polymer material according to the movement trajectory file output by the computer, and locally melt the crystalline polymer in the form of pixels. After the laser scanning is completed, the laser writing of the corresponding phase coding information is completed.

[0028] (2) Phase information maintenance: After the coding information is written, it is considered that the molten area in the crystalline material will recrystallize at room temperature, which leads to the limited reconstruction time of the current holographic sound field. Therefore, after the phase holographic information coding is written, it is necessary to use the laser beam to continue scanning along the original track to maintain local melting. At the same time, considering that repeated laser scanning will accumulate heat in the molten area, the resulting lateral heat diffusion will cause distortion of the phase-coded holographic pattern and ultimately deteriorate the reconstruction of the holographic sound field. Therefore, when maintaining the phase-coded pattern, a low-power laser is used to perform spatial scanning along the track.

[0029] (3) Phase information erasure: After the target acoustic field is reconstructed, the laser is directly turned off. The localized melting phase change region on the crystalline polymer slab will recrystallize at room temperature and restore the initial crystalline state. After a period of time, the crystalline polymer slab can be used to write a new phase encoding distribution for new acoustic field modulation.

[0030] The programmable acoustic holographic device of the present invention is composed of only a single layer of light-responsive crystalline polymer flat plate, and the crystalline polymer will switch between two phases when the temperature changes. When the ambient temperature is lower than its crystallization temperature, the material exhibits a crystalline state, with high modulus material properties and high sound velocity acoustic properties, and when the ambient temperature is higher than its melting temperature, the material exhibits a molten state, with low modulus material properties and low sound velocity acoustic properties. In theory, spatial sound field modulation can be achieved by spatially arranging the above encoding units.

[0031] Therefore, by doping the crystalline polymer material with a photothermal conversion agent, a laser can be used to perform local melt encoding on the crystalline polymer, so that the crystalline and molten polymer units with a sound velocity difference are arranged on the polymer plane, and the wavefront phase modulation of the three-dimensional transmitted sound wave is realized as a phase-coded acoustic holographic device. In addition, the crystalline polymer material has a reversible phase transition characteristic. The crystalline polymer flat plate with laser patterned phase change will restore the previous crystalline state after cooling for a period of time, and its patterned coded acoustic holography disappears, and a new phase acoustic holography can be further written to realize a new sound field modulation function.

[0032] The planar multi-focus acoustic lens device provided by the present invention has the following beneficial effects: (1) The present invention directly replaces the base plate of the phase holographic plate prepared by conventional 3D printing with smart materials, and endows the traditional acoustic holographic device with flexible programmability through the crystalline polymer with reversible material properties, promoting the acoustic holographic device from static to dynamic, and improving the practical application potential of dynamic acoustic holographic devices. During use, specific acoustic field information can be directly written into a single crystalline polymer code. After the modulation is completed, the previous acoustic information can be erased and new acoustic field information can be written.

[0033] (2) The planar programmable acoustic holographic device used in the present invention has a compact structure, strong operability and high reliability. At the same time, the spatial modulation resolution is high. The spatial resolution of the acoustic holographic information written based on the focused laser beam scanning encoding is as high as 80µm, which is much larger than the current dynamic acoustic holographic system. In addition, the crystalline polymer material used in the programmable acoustic holographic device has good sound transmission performance, which can greatly improve the transmittance and conversion rate of the sound field.

[0034] Therefore, the programmable phase acoustic holographic device based on crystalline polymer proposed in the present invention can modulate the plane wave incident by the probe into a three-dimensional arbitrary complex acoustic field, which is used to realize particle capture, target manipulator and acoustic communication in free space field, etc. Moreover, the programmable acoustic holographic device of the present invention is completely planar, relatively matched with the water acoustic impedance, has high acoustic energy coupling efficiency, compact structure, simple preparation and low price. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 This is a schematic diagram of a reconfigurable acoustic holographic device based on programmable crystalline materials; Figure 2 These are the transmission phase diagrams of crystalline materials of different thicknesses in the crystalline and molten states, where the operating frequency is kept fixed at 2.2 MHz.

[0036] Figure 3 3D and 2D schematic diagrams of holographic acoustic field modulation based on crystalline polymers according to embodiments 1 and 2 of the present invention, wherein (a) represents the acoustic field reconstruction effect after being modulated by the holographic plate in 3D, and (b) represents the acoustic field reconstruction effect after being modulated by the holographic plate in 2D; Figure 4 The programmable acoustic holographic device based on crystalline polymer according to embodiments 1 and 2 of the present invention is a reconfigurable schematic diagram; Figure 5 The synthesis process of the crystalline polymers of Examples 1 and 2 of the present invention and their microscopic changes with temperature, wherein (a) represents the synthesis process of the crystalline polymer material, and (b) represents the situation in which the molecular chains of the crystalline polymer gradually become looser under temperature stimulation; Figure 6It is the laser scanning trajectory control method based on target acoustic holography of embodiments 1 and 2 of the present invention; Figure 7 1 is a diagram of the holographic acoustic field reconstruction result of Example 1 of the present invention, wherein (a) represents a target acoustic field distribution diagram, (b) represents a phase encoding distribution diagram designed based on the target acoustic field, (c) represents an acoustic holographic plate diagram made on a crystalline polymer plate, and (d) represents a water surface ripple diagram realized on a target plane through an acoustic radiation force effect; Figure 8 1 is a diagram of the holographic acoustic field reconstruction result of Example 2 of the present invention, wherein (a) represents a target acoustic field distribution diagram, (b) represents a phase encoding distribution diagram designed based on the target acoustic field, (c) represents an acoustic holographic plate diagram made on a crystalline polymer plate, and (d) represents a water surface ripple diagram realized on a target plane through an acoustic radiation force effect; Explanation of the reference numerals: ultrasonic transducer 1 , laser pulse beam 2 , programmable acoustic holographic plate based on crystalline polymer 3 , crystalline region 31 , molten region 32 . DETAILED DESCRIPTION

[0037] In order to enable those skilled in the art to better understand the technical solution of the present invention and implement it, the present invention will be described in detail below in conjunction with the accompanying drawings and specific embodiments. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in the field without creative work are within the scope of protection of the present invention.

[0038] In the description of the present invention, it should be understood that the terms "middle", "upper", "lower", "left", "right", "lateral", "longitudinal", "horizontal", "vertical", "axial", "mirror", "length", "width", "thickness" and the like indicate positions or positional relationships based on the positions or positional relationships shown in the accompanying drawings, which are only for the convenience of describing the technical solution of the present invention and simplifying the description, rather than indicating or implying that the device or equipment referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the present invention. In addition, the terms "including" and "having" and any variations thereof are intended to cover non-exclusive inclusions. In the description of the present invention, unless otherwise specified, the meaning of "plurality" is two or more, which will not be described in detail herein.

[0039] The present invention can realize high-resolution regional melting phase change of materials through laser scanning, and work together with the crystallized region to realize phase encoding modulation of the transmitted sound field. The laser-assisted crystalline polymer is used as a programmable phase acoustic holographic device. When in use, after matching one side surface with a conventional transducer, the incident plane wave can be modulated into a target complex sound field along two-dimensional space, and can ultimately be used for particle manipulation or neural stimulation. After use, the crystalline polymer with reversible properties will return to its crystalline state at room temperature, erase the laser-written programmable phase holographic information, and perform laser writing of a new target phase hologram. The programmable acoustic holographic device directly uses the state switching of the substrate material itself as a spatial phase encoding unit. It has a compact structure, high resolution, and flat surfaces on both sides. It can be directly bonded to the surface of a conventional ultrasonic transducer and an object of action, thereby realizing free modulation of the three-dimensional spatial sound field in the background domain.

[0040] In a programmable acoustic holographic device based on a crystalline polymer of 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 of the material, the crystalline polymer is in a crystalline state and a molten state. T m Or below the crystallization temperature of the material T c There is a dynamic switch between the two phases, with the crystalline state having a high Young's modulus and sound velocity, and the molten state having a low Young's modulus and sound velocity. When the two phases are transformed, the thickness of the material is hardly encoded, only the sound velocity changes. The two-dimensional spatial arrangement of microstructure areas with the same thickness and different sound velocities can achieve phase modulation of the transmitted / reflected sound field.

[0041] like Figure 1 As shown, it includes a programmable acoustic holographic plate 3, which is a flat plate of crystalline polymer material. It is a programmable acoustic holographic plate based on crystalline polymer. The programmable acoustic holographic plate 3 is divided into several microstructure areas arranged in a tight array. The microstructure areas have two states, crystalline state and molten state. Each microstructure area has only one state, and the two states can change reversibly with temperature; the programmable acoustic holographic plate 3 covers the ultrasonic transducer 1 probe.

[0042] Figure 1 In the figure, black represents amorphous state and gray represents crystalline state. The programmable acoustic holographic device 3 is a crystalline polymer flat plate, and there are spatially distributed patterned molten state regions 32 on the surface of the flat plate. There is a certain sound velocity difference between the molten state region 32 and the crystalline state region 31, thereby realizing phase distribution on the spatial plane.

[0043] In a specific implementation, the programmable acoustic holographic plate 3 is made of a crystalline polymer material, and specifically, usually a polycaprolactone material.

[0044] The crystalline microstructure area is naturally formed at room temperature and is solid.

[0045] The non-crystalline microstructure region is formed by melting the originally crystalline microstructure region under the irradiation of the infrared laser beam emitted by the infrared laser, and is in a molten state.

[0046] The microstructured region has different material properties and acoustic properties in the crystalline and molten states, which are mainly manifested in the differences in Young's modulus and sound velocity.

[0047] The microstructure region in the crystalline state is referred to as a crystalline region 31 , and the microstructure region in the non-crystalline state is referred to as a molten region 32 .

[0048] In a specific implementation, the method is to use a laser to emit a laser pulse beam 2 to scan and locally irradiate different areas on the surface of a crystalline polymer material, so that areas with different material properties and acoustic properties are formed on the crystalline polymer material, and a patterned molten area is written in the original crystalline area to form an acoustic holographic phase distribution, which becomes a phase acoustic holographic device and constitutes a programmable acoustic holographic plate 3.

[0049] In a specific implementation, an infrared / ultraviolet laser may be used to emit an infrared / ultraviolet laser pulse beam, and the crystalline polymer material may be melted by receiving which beam depending on the characteristics of the crystalline polymer material.

[0050] The crystalline polymer material is 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 to form molten regions 32, while the microstructure regions not irradiated and heated do not change to form crystalline regions 31, so that the crystalline polymer material has two states: crystalline and amorphous. The laser pulse beam 2 is used to scan and irradiate different microstructure regions, so that the microstructure regions in the crystalline state and the molten state on the crystalline polymer material form a patterned arrangement as the acoustic holographic phase distribution of the phase acoustic holographic device.

[0051] Each pulse corresponds to irradiating a microstructure area, and different pulses correspond to different microstructure areas, that is, the irradiation area corresponding to the pulse is the microstructure area, and the pulse duration is the irradiation duration of the microstructure area; By controlling the duration and energy of pulse irradiation on the microstructure area, the temperature of the microstructure area after irradiation is controlled to stay within 10% above the melting temperature. In this way, the melting temperature will not be too high and the microstructure area will not be heated too high, thereby affecting the surrounding microstructure areas.

[0052] The sound velocity of crystalline polymer materials does not change much with the operating frequency. For different operating frequencies, the thickness of the material needs to be reselected. The transmitted sound field of materials with the same thickness but different sound velocities has different phase delays. Therefore, when the material thickness and frequency are matched, the transmission phase delay can be controlled to be equal to π.

[0053] By setting the thickness of the crystalline polymer material and controlling the thickness of the material and the frequency of the material, the transmission phase delay of the crystalline polymer material is exactly equal to π. In this way, when the plane sound wave excited by the ultrasonic transducer is vertically incident on the crystalline polymer flat plate with patterned melting, the transmission phase of the molten state and the crystalline state area differs by π, realizing the spatial phase modulation of the sound field, and the modulated sound field propagates forward to achieve the reconstruction of the target sound field. It should be noted that the impedance of the crystalline polymer material is almost completely matched with water, so its transmittance is always higher than 85%, and the energy utilization rate is high.

[0054] like Figure 2 As shown in the figure, in order to ensure that the delayed phase effect of the laser-acting melting area and the non-acting crystalline area on the incident acoustic field is exactly π, the thickness of the acoustic field of the crystalline polymer material needs to be reasonably set. h , the specific process is as follows: The thickness of the crystalline polymer material is set as follows: 1) First, pulsed ultrasound was used to measure the sound velocity of the crystalline polymer material in the crystalline and amorphous states under water immersion conditions, which were v a and v c ; 2) Next, design the thickness of the crystalline polymer material h , specifically the speed of sound v a and v c Substitute the following simultaneous formulas to obtain the thickness h of the crystalline polymer material: φ =arg( P c - P a ) = π P a =e^( ik a h ), P c =e^( ik c h ) ka =2πf / v a , k c =2πf / v c in: φ Represents the phase difference between the crystalline region and the molten region, arg() represents the extracted phase value, P a represents the transmitted acoustic field of the molten material, P c represents the transmitted sound field of crystalline materials, e represents the natural constant, ^ represents the power, k a and k c are the wave numbers of the molten region and the crystalline region, v a and v c are the sound velocities of crystalline polymer materials in the crystalline state and the non-crystalline state (i.e., molten state), f is the operating frequency.

[0055] In a specific implementation, according to the thickness of the crystalline polymer material determined above, h The synthetic preparation is carried out, and finally a programmable acoustic holographic phase plate which can be used for complex sound field modulation is obtained.

[0056] like Figure 3 As shown, 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 arrangement of the molten region 32 and the crystalline region 31 with the same thickness is designed and regulated to achieve spatial encoding of the phase distribution. The sound field reconstruction effects after being modulated by the holographic plate in the three-dimensional case and the two-dimensional case are shown as follows: Figure 3 as shown in (a) and (b).

[0057] The crystalline polymer material is doped with a photothermal conversion medium. Therefore, when the laser beam is focused on a local area, the crystalline polymer material absorbs the energy of the laser and converts it into heat, causing the local crystalline area where the laser is applied to undergo a melting phase change while keeping the thickness almost unchanged.

[0058] The phase distribution designed based on the target holographic acoustic field 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.

[0059] Since the crystallization temperature of crystalline polymer materials is generally about 20°C lower than the melting temperature, the molten region 32 can be well maintained during the process of the laser beam scanning the crystalline material in a pattern, and will not affect the material of the surrounding crystalline region 31. Subsequently, the laser beam is used to repeatedly scan along the target track, which can achieve long-term maintenance of the molten pattern with good stability.

[0060] Since the acoustic holographic pattern is prepared by a spatially scanned laser beam, the structural resolution of the programmable acoustic holography is completely 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.

[0061] After the acoustic holographic phase modulation of the crystalline polymer material is completed by scanning localized irradiation, the material in the molten area 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.

[0062] The specific process of the ultrasonic processing method using the phase acoustic holographic device of the present invention is as follows: The 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, the laser pulse beam 2 is emitted in real time by the laser to scan and locally irradiate the crystalline polymer material, so that the crystalline polymer material becomes a phase acoustic holographic device; and a different laser pulse beam 2 is emitted in real time by the laser to scan and locally irradiate the crystalline polymer material, so as to adjust the acoustic holographic phase distribution on the phase acoustic holographic device.

[0063] In order to realize the same-side incidence of laser and ultrasound, so as to realize functions such as particle capture and biomedical excitation in the free space above, the working principle of the online dynamic acoustic holographic device based on crystalline polymer provided by the present invention is that the acoustic wave incidence adopts the reflection type: the conventional ultrasonic transducer 1 and the programmable acoustic holographic device 3 are arranged vertically, so that the incident acoustic field of the conventional ultrasonic transducer 1 is vertically incident from the side to the reflector and then vertically incident from the bottom to the programmable acoustic holographic device. At the same time, the laser beam is incident from the top and scans and melts along the space of the programmable acoustic holographic device 3, thereby performing patterned phase encoding.

[0064] like Figure 4 As shown, the laser beam scanning process can encode the phase information of the acoustic holography into the programmable acoustic holography device 3, and modulate the incident plane acoustic wave to achieve target sound field reconstruction.

[0065] Sound pressure amplitude distribution for the target planeA ( x,y , z = l ),in l is the focal plane corresponding to the target sound field. Next, based on the above sound field distribution, the trajectory of the laser beam scanning is designed and encoded. The design process is as follows: The target surface z = l Sound field distribution and holographic surface z =0 acoustic field distribution is brought into the iterative angular spectrum method. First, before the iterative optimization begins, the phase distribution of the holographic surface is φ 0 is set to any value. The entire iterative process can be divided into forward propagation and reverse optimization process: The forward propagation process is as follows: For the transmitted sound field from the holographic surface p 0 ( x , y , z =0)= e ^(i φ 0), first calculate the frequency spectrum distribution of the plane through Fourier transform: P 0( k x , k y , z =0)=∫∫ p 0 ( x , y , z =0)d x d y , and then, as it propagates in the positive direction along the z-axis, its spectrum is multiplied by the phase factor H ( k x , k y , z = l )=e^( ik z l ) then the target image plane can be obtained z = l Spectrum distribution on P ’ ( k x , k y , z = l )= P 0( k x , k y , z=0)* H ( k x , k y , z = l ),in, k z = ( k 0 2 - k x 2 - k y 2 ) 1 / 2 After inverse Fourier transform, the sound field distribution of the plane is obtained p ’ ( x , y , z = l )=∫∫ P ’ ( k x , k y , z = l )d k x d k y .

[0066] After the forward propagation is completed, the target image plane z = l Phase on φ ’ ( x,y , z = l )= arg ( p ’ ( x,y , z = l )) is retained and its amplitude is replaced by the target focus amplitude distribution A ( x,y , z = l );get z = l Sound field on the surface q ’ ( x,y , z = l )= A ( x,y , z = l )*e^(i φ ’ ( x,y , z = l )).

[0067] The reverse optimization process is as follows: z = l Back propagation to z =0 sound field q ’ ( x,y , z = l ), and first calculate the frequency spectrum distribution of the plane through Fourier transform: Q ’ ( k x , k y , z = l )=∫∫ q ’ ( x,y , z = l )d x d y , and then, as it propagates in the negative direction along the z-axis, its spectrum is multiplied by the phase factor H ( k x , k y , z =(- l ))=e^( ik z (- l )) After that, we can get the plane z = 0 spectrum distribution Q 0( k x , k y , z = 0 )= Q ’ ( k x , k y , z = l )* H ( k x , k y , z =(- l )) and obtained the holographic plane z =0 sound field distributionq 0 ( x , y , z =0)=∫∫ Q 0 ( k x , k y , z = 0 )d k x d k y And the updated binary phase distribution is φ =0 or π, when q 0 >0, φ=0; when q 0 When <=0, φ=π.

[0068] After approximately 60 forward and backward propagation iterations, the binary coded phase distribution on the phase hologram can be finally obtained.

[0069] Based on the binary coded phase distribution obtained by the above iterative optimization, the above two-dimensional coded phase distribution is drawn in the two-dimensional drawing software, saved as a file readable and writable by the infrared laser engraving machine (such as a .dxf format file), input into the infrared laser engraving machine and control the scanning path of the infrared laser beam. Under the action of laser scanning, the phase φ The area where 0=π is locally heated by the laser into a molten state. After the scanning is completed, a pattern corresponding to the phase acoustic hologram will be encoded and written on the crystalline polymer plate.

[0070] When the programmable phase acoustic holographic device is 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. Therefore, the preparation accuracy can reach 100um, which greatly improves the resolution of the sound field modulation.

[0071] Considering the size and processing accuracy of the metasurface, the operating frequency of the flat multi-focus acoustic lens can be selected from 100 to 3000 kHz. When the operating frequency changes, the thickness of the programmable acoustic holographic phase plate needs to be redesigned based on the three-medium theory. h , simple and efficient design.

[0072] In addition, the material of the programmable acoustic holographic phase plate is a crystalline polymer, and its acoustic impedance is relatively matched with the impedance of the matching layer of the piezoelectric transducer and the background water medium, so the acoustic energy transmittance is high, which greatly improves the acoustic energy utilization rate.

[0073] like Figure 5The figure shows the schematic diagram of the preparation of the reconfigurable acoustic holographic device based on programmable polymer and the microscopic performance of the melting process provided by the present invention. The present invention uses a common crystalline polymer material: polycaprolactone (PCL). Figure 5 As shown in (a), it has a large modulus change before and after the crystallization / melting phase transition. Specifically, as the temperature rises, the short-range ordered crystallization intervals on the molecular chain are free to expand, which in turn shows a lower modulus. Based on the relationship between the material modulus and the speed of sound, the material will have different speeds of sound in the crystallized and molten states. The experimental measurements show that they are 1520 and 1880 m / s, respectively. Assuming the operating frequency at this time f =2.2 MHz, the thickness of the crystalline polymer material can be calculated based on the three-medium theory to be h =1.75 mm.

[0074] like Figure 5 (b) shows the preparation flow chart of red light responsive PCL material. In order to realize the patterned phase encoding of laser responsive melting, it is necessary to dope the PCL polymer network with photothermal conversion medium (Sudan Black) during the preparation process to give it a good photothermal effect, so that it absorbs light in a specific band (in the infrared wavelength region) and converts it into thermal energy, thereby realizing the crystallization-melting phase transition under light conditions.

[0075] During the experiment, the illuminated area of ​​the prepared PCL film was heated to T m The material changes from crystalline to amorphous state, and when the infrared light is removed, the temperature of the irradiated area drops to T c Next, the material returns to the crystalline state. Under the action of the focused infrared laser beam scanning, the patterned molten area is encoded and written on the crystalline polymer material as the acoustic holographic spatial phase coding distribution, which is the crystalline polymer material after pattern coding. At this time, the material as a whole is in the alternation of crystalline and molten states.

[0076] It should be noted that the subsequent polymerization can be achieved by regulating the molecular weight of PCL. T m and T c regulation to match the application scenarios of acoustic metamaterials.

[0077] like Figure 6The figure shows the preparation flow chart of the programmable acoustic holographic device provided by the present invention, including the whole process from the target acoustic field to the phase distribution of the holographic plane, and then to the laser beam scanning trajectory. It should be noted that, since the crystalline material will recrystallize after the temperature is reduced, the laser beam needs to repeatedly scan the molten area along the original path at a low power.

[0078] Next, the realization of the dynamic modulation sound field of the programmable acoustic holographic device 3 in the embodiment of the present invention will be described in detail with reference to the accompanying drawings.

[0079] At this time, the thickness of the programmable acoustic holographic device 3 is set to h= 1.7 mm, width D= 50 mm, conventional ultrasonic phased array excitation frequency f = 2.2 MHz. A 1064 nm infrared laser beam was used to scan and phase encode a crystalline polymer slab.

[0080] Embodiment 1: Firstly, the annular sound field is reconstructed based on the programmable acoustic holographic device 3, comprising the following steps: S1: Based on Figure 7 , set the focal plane corresponding to the annular sound field to l =20 mm, and the sound pressure distribution A’ ( x , y , z=l )like Figure 7 As shown in (a).

[0081] Next, the programmable phase acoustic holographic device 3 is designed based on the improved binary iterative angular spectrum method. z= Phase distribution on 0 φ : First, assume that the holographic surface z= Phase distribution on the 0 plane φ is an arbitrary value, and then the sound field is calculated P 0 ( x , y , z =0)= e ^( iφ ) propagates along the z-axis to the target image plane z=l The calculation process is as follows: Based on z = 0 Spectral distribution on the plane P 0 ( k x , k y , z= 0), forward propagation yields z =l Sound field distribution on a plane P ’ ( x , y , z = l ), preserving the phase distribution of the plane φ' ( x,y,z = l )= arg ( P ’ ( x , y , z = l )), and replace its amplitude distribution with A’ ( x , y , z=l ), the sound field distribution on the target plane can be obtained as P ’ ( x , y , z=l )= A’ ( x , y , z=l )*e^( iφ' ( x,y,z = l )).

[0082] Next, the sound field distribution on the target plane P ’ ( x , y , z=l )along z Axis back propagation to the holographic plane z= 0, the calculation process is as follows: Based on z = l Spectrum distribution on a plane Q ’ ( k x , k y , z=l ), back propagation yields z = 0 Spectrum on a plane Q 0 ( k x , k y , z = 0 ) and sound field distribution q 0 ( x ,y , z = 0 ), and update the holographic phase plane z = 0 The binary phase φ =0 or π, when q 0 >0, φ=0; when q 0 <=0, φ=π, and form a new sound field distribution on the plane p 0 ( x , y , z = 0 )= e ^( iφ ).

[0083] According to the above forward and back propagation models z= Phase distribution on the 0 plane φ After repeated optimization iterations, convergence can be achieved after about 60 times, and finally the encoding phase distribution is obtained. φ The sound field distribution on the target image plane is as follows: Figure 7 as shown in (b).

[0084] S2: Next, z= Binary phase distribution on the 0 plane φ The output is a laser scanning trajectory file, which is transmitted to the laser to control the laser beam scanning trajectory. The final programmable phase holographic plate is as follows: Figure 7 As shown in (c), under experimental conditions, the height of the programmable acoustic holographic device at the water surface distance is set to be exactly the focal plane of the target image. l =20 mm. Based on the mechanical effect and water surface tension, the reconstructed sound field will form water ripples of a specific shape on the water surface, such as Figure 7 as shown in (d).

[0085] S3: Then, turn off the infrared laser, and the molten area heated by infrared local heating will gradually cool down. When the temperature of this area drops to the crystallization temperature, T c When the temperature drops below 0.05, the molten area will recrystallize and return to the crystalline state.

[0086] Embodiment 2: Next, a holographic sound field with letter 'Z' distribution is realized based on the programmable acoustic holographic device 3, including the following steps: S1: Based on Figure 8 , set the focal plane corresponding to the letter 'Z' sound field to l =20 mm, and the sound pressure distribution A’ ( x ,y , z=l )like Figure 8 As shown in (a).

[0087] Similarly, the programmable phase acoustic holographic device 3 plane is designed based on the improved binary iterative angular spectrum method z = Phase distribution on 0 φ , and finally get its encoding phase distribution φ The sound field distribution on the target image plane is as follows: Figure 8 as shown in (b).

[0088] S2: Next, z= Binary phase distribution on the 0 plane φ The output is a laser scanning trajectory file, which is transmitted to the laser to control the laser beam scanning trajectory. The final programmable phase holographic plate is as follows: Figure 8 As shown in (c), under experimental conditions, the height of the programmable acoustic holographic device at the water surface distance is set to be exactly the focal plane of the target image. l =20 mm. Based on the mechanical effect and water surface tension, the reconstructed sound field will form water ripples of a specific shape on the water surface, such as Figure 8 as shown in (d).

[0089] S3: Then, turn off the infrared laser, and the molten area heated by infrared local heating will gradually cool down. When the temperature of this area drops to the crystallization temperature, T c When the temperature drops below 0.05, the molten area will recrystallize and return to the crystalline state.

[0090] In the above embodiments, the description of each embodiment has its own emphasis. For parts that are not described in detail in a certain embodiment, reference can be made to the relevant descriptions of other embodiments.

[0091] The embodiments of the present application are introduced in detail above. Specific examples are used in the present invention to illustrate the principles and implementation methods of the present invention. The description of the above embodiments is only used to help understand the method of the present invention and its core idea. At the same time, for general technicians in this field, according to the idea of ​​the present invention, there will be changes in the specific implementation method and application scope.

[0092] In summary, the contents of this specification should not be understood as limiting the present invention.

Claims

1. A reconfigurable acoustic holographic device based on a crystalline polymer, characterized in that: It comprises a programmable acoustic holographic plate (3), wherein the programmable acoustic holographic plate (3) is divided into a plurality of microstructure regions arranged in a close array, the microstructure regions having two states, a crystalline state and a non-crystalline state, and the two states are reversibly changeable with temperature; the programmable acoustic holographic plate (3) covers the probe of the ultrasonic transducer (1).

2. The reconfigurable acoustic holographic device based on crystalline polymer according to claim 1, characterized in that: It also includes a reflector, which is arranged on the upper side of the programmable acoustic hologram (3) and is arranged at a distance from the programmable acoustic hologram (3). The ultrasonic wave emitted by the ultrasonic transducer (1) passes through the programmable acoustic hologram (3) and is then reflected by the reflector to irradiate the object to be measured.

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

4. The acoustic holographic phase modulation method applied to the reconfigurable acoustic holographic device according to any one of claims 1 to 3, characterized in that: The method comprises the following steps: a laser is used to emit a laser pulse beam (2) to scan and locally irradiate different areas on the surface of a crystalline polymer material, so that areas with different acoustic properties are formed on the crystalline polymer material, and a patterned molten area is written in the original crystalline area to form an acoustic holographic phase distribution, thereby converting it 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. The microstructure region on the crystalline polymer material is irradiated and heated, and the irradiated and heated microstructure region melts and becomes a non-crystalline state to form a molten state region (32), while the microstructure region not irradiated and heated does not change to form a crystalline state region (31), so that the crystalline polymer material has two states, crystalline and non-crystalline; Furthermore, a laser pulse beam (2) is used to scan and irradiate different microstructure regions, so that microstructure regions in two states on the crystalline polymer material 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 area, and different pulses correspond to different microstructure areas; and by controlling the duration and energy of the pulse irradiating the microstructure area, the temperature of the microstructure area after irradiation is controlled to stay 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, the thickness and frequency are controlled to match, thereby making the transmission phase delay of the crystalline polymer material 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, pulsed ultrasound was used to measure the sound velocity of the crystalline polymer material in the crystalline and amorphous states under water immersion conditions, which were v a and v c ; 2) The speed of sound v a and v c Substitute the following simultaneous formulas to obtain the thickness h of the crystalline polymer 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 in: φ represents the phase difference between the crystalline region and the molten region, arg() represents phase extraction, P a represents the sound pressure in the molten region, P c represents the sound pressure in the crystalline region, e represents a natural constant, ^ represents a power, k a and k c are the wave numbers of the molten region and the crystalline region, v a and v c are the sound velocities of crystalline polymer materials in crystalline and non-crystalline states, f is the 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, spatial encoding of the phase distribution is achieved by designing and regulating the spatial arrangement of the molten region (32) and the crystalline region (31) having the same thickness; After the acoustic holographic phase modulation of the crystalline polymer material is completed by scanning the localized irradiation, the material in the molten area scanned by the laser undergoes recrystallization under natural cooling at room temperature, thereby recovering to the original crystalline state and being used for the next acoustic holographic phase modulation.

10. An ultrasonic processing method for a phase acoustic holographic device manufactured by the acoustic holographic phase modulation method according to any one of claims 4 to 9, characterized in that: When a crystalline polymer material is placed on the surface of an ultrasonic transducer (1) probe and there is a gap between the material 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, thereby forming an ultrasonic working process; during the ultrasonic working process, a laser pulse beam (2) is emitted in real time by a laser to scan and locally irradiate the crystalline polymer material, so that the crystalline polymer material becomes a phase acoustic holographic device, and a different laser pulse beam (2) is emitted in real time by the laser to scan and locally irradiate the crystalline polymer material, thereby adjusting the acoustic holographic phase distribution on the phase acoustic holographic device.

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