CN112774961A - Acoustic pressure output amplitude adjustable and controllable photoacoustic transducer and preparation method thereof - Google Patents
Acoustic pressure output amplitude adjustable and controllable photoacoustic transducer and preparation method thereof Download PDFInfo
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Abstract
The invention belongs to the technical field of ultrasonic transducers and discloses an acoustic pressure output amplitude adjustable and controllable photoacoustic transducer and a preparation method thereof, wherein the acoustic pressure transducer comprises a hard substrate (1), a structured base (2) and a flexible composite photoacoustic conversion layer (3), the structured base is of a hollow structure, and the flexible composite photoacoustic conversion layer can deform under the action of external force and correspondingly change the shape and the structure of an air cavity; when the flexible composite photoacoustic conversion layer is deformed to be in direct contact with the hard substrate, sound pressure output with increased sound pressure amplitude can be realized; when the flexible composite photoacoustic conversion layer is not in direct contact with the hard substrate, the sound pressure output with reduced sound pressure amplitude can be realized, and thus the regulation and control on the sound pressure output amplitude can be realized by utilizing the deformation of the flexible composite photoacoustic conversion layer. The invention can realize the regulation and control of the output sound pressure amplitude by improving each detail structure in the device and the matching action relationship of the detail structures, and has simple process and strong feasibility.
Description
Technical Field
The invention belongs to the technical field of ultrasonic transducers, and particularly relates to an optical-acoustic transducer with adjustable sound pressure output amplitude and a preparation method thereof, wherein the device can realize the regulation and control of sound pressure output amplitude ' 0 ' and ' 1 ' (0 ' represents low ultrasonic amplitude, and ' 1 ' represents high ultrasonic amplitude, and the two are relative concepts).
Background
Ultrasonic transducers are widely applied to nondestructive testing and medical diagnosis and treatment, and along with the development of laser technology, the photoacoustic transducer based on the photoacoustic effect has the advantages of wide frequency band and high frequency (ultrasonic energy generated by the photoacoustic transducers has the characteristics of high intensity, high frequency and wide frequency band, and meanwhile, the device can resist electromagnetic interference when being applied, which is not possessed by an electroacoustic transducer). Wherein, for the array type optical-acoustic transducer, the ultrasonic field with larger amplitude and certain spatial amplitude distribution can be realized. The realization of the regulation and control of the ultrasonic amplitude values of 0 and 1 of one ultrasonic transducer unit also means that the units can be combined into an array, and the ultrasonic amplitude value output of different units in the array is regulated and controlled, so that the random dynamically adjustable ultrasonic wavefront output is realized. The method has wide application requirements and wide application prospects in the fields of biomedical imaging, industrial sensing, particle regulation and the like. At present, no relevant report of ultrasonic amplitude '0' and '1' regulation and control technology exists in the field of the photoacoustic transducer for a while.
Disclosure of Invention
Aiming at the defects or improvement requirements of the prior art, the invention aims to provide the photoacoustic transducer with the adjustable sound pressure output amplitude and the preparation method thereof, and the acoustic transducer can realize the adjustment and control of '0' and '1' of the output sound pressure amplitude by improving various detailed structures in a device and the matching action relationship of the detailed structures, and has simple process and strong feasibility. According to the invention, by constructing the flexible composite photoacoustic conversion layer, the flexible composite photoacoustic conversion layer is deformed by means of external force by utilizing the characteristic that the flexible composite photoacoustic conversion layer is easy to deform, so that the back lining of the flexible composite photoacoustic conversion layer is switched between air and a hard substrate, the reflection interface of pulse ultrasound transmitted in the back direction is changed, and due to different acoustic impedances of different interfaces, the ultrasound transmitted in the back direction is reflected by the air back lining to obtain equal-amplitude reverse-phase ultrasound output and is superposed with the ultrasound transmitted in the initial forward direction, so that the final output sound pressure amplitude is close to 0; the ultrasonic transmitted in the back direction is reflected by the hard substrate to obtain ultrasonic output with equal amplitude and same phase, and the ultrasonic output is superposed with the ultrasonic transmitted in the initial forward direction, so that the final output sound pressure is 2 times of the initial amplitude. Therefore, under the condition that the photoacoustic transducer absorbs the same laser energy, the output sound pressure amplitudes of the flexible composite photoacoustic conversion layers with two different backings are greatly different, so that the regulation and control of the output sound pressure amplitudes of the photoacoustic transducer unit are realized by '0' and '1'. In addition, the corresponding preparation method has simple process and strong process feasibility. Based on the invention, the array structure is designed subsequently, and the control on the distribution of the output sound field can be realized under the condition of sharing the same excitation light source.
In order to achieve the above object, according to one aspect of the present invention, there is provided an electroacoustic transducer with adjustable and controllable sound pressure output amplitude, which is characterized by comprising, from bottom to top, a hard substrate (1), a structured base (2), and a flexible composite photoacoustic conversion layer (3); wherein the structured base (2) is provided with a hollow structure, the upper end face of the hollow structure is positioned at the contact surface of the structured base (2) and the flexible composite photoacoustic conversion layer (3), and the lower end face of the hollow structure is positioned at the contact surface of the base and the hard substrate (1); the hard substrate (1), the structured base (2) and the flexible composite photoacoustic conversion layer (3) are connected, so that an air cavity correspondingly formed by the hollow structure can be kept sealed except at a reserved air channel position; the air pressure in the air cavity can be adjusted through the air channel;
the hard substrate (1) is used as an incident end of laser, and the laser is incident to the flexible composite photoacoustic conversion layer (3) through the hard substrate (1); the flexible composite photoacoustic conversion layer (3) is used for absorbing laser beam energy and converting the laser beam energy into acoustic energy to generate initial ultrasonic pulse signals transmitted along the forward direction and transmitted back to the back; taking the contact surface of the structured base (2) and the flexible composite photoacoustic conversion layer (3) as a reference, and taking the normal direction of the contact surface of the structured base (2) pointing to the flexible composite photoacoustic conversion layer (3) as a forward direction and the normal direction of the contact surface of the flexible composite photoacoustic conversion layer (3) pointing to the structured base (2) as a backward direction;
the flexible composite photoacoustic conversion layer (3) can deform under the action of external force, and the shape and the structure of the air cavity are correspondingly changed, wherein:
when the flexible composite photoacoustic conversion layer (3) is deformed to be in direct contact with the hard substrate (1), because the acoustic impedance of the hard substrate (1) is greater than that of the flexible composite photoacoustic conversion layer (3), a signal transmitted along the back direction in a generated initial ultrasonic pulse signal is converted into a first ultrasonic pulse reflection signal which has the same amplitude and phase and is transmitted along the forward direction after being reflected by the surface of the hard substrate (1), and the first ultrasonic pulse reflection signal and another part of the initial ultrasonic pulse signal transmitted along the forward direction are superposed to obtain sound pressure output which is transmitted along the forward direction and has increased sound pressure amplitude;
when the flexible composite photoacoustic conversion layer (3) is not in direct contact with the hard substrate (1), because the acoustic impedance of the flexible composite photoacoustic conversion layer (3) is greater than that of air, a signal transmitted in a reverse direction in the generated initial ultrasonic pulse signal is converted into a second ultrasonic pulse reflection signal which has the same amplitude and is inverted in phase and is transmitted in a forward direction after being reflected by the air cavity, and the second ultrasonic pulse reflection signal is superposed with the initial ultrasonic pulse signal transmitted in the forward direction by the other part in the initial ultrasonic pulse signal to obtain sound pressure output which is transmitted in the forward direction and has reduced sound pressure amplitude;
therefore, the sound pressure output amplitude can be regulated and controlled by utilizing the deformation of the flexible composite photoacoustic conversion layer (3).
As a further preferable aspect of the present invention, the external force includes an electromagnetic action, a piezoelectric action, or an air pressure action.
As a further preferred embodiment of the present invention, the photoacoustic transducer with adjustable sound pressure output amplitude is connected to an air pressure regulating pump (4), and the air pressure regulating pump (4) can regulate the air pressure in the air cavity through the air channel, so as to deform the flexible composite photoacoustic conversion layer (3).
As a further preferable mode of the invention, the structured base (2) has a hollow structure which is a cylindrical hollow structure, and the material adopted by the structured base (2) is metal, plastic, organic glass or polymer; preferably, the structured base (2) is made of Polydimethylsiloxane (PDMS) which is obtained by curing a PDMS prepolymer.
As a further preferable mode of the present invention, the flexible composite photoacoustic conversion layer (3) includes an acoustic matching layer (31) and a photoacoustic conversion composite film (32) from the top down, wherein,
the acoustic matching layer (31) is made of a material which meets the requirement that the acoustic resistance of the material is matched with the acoustic resistance of the target working environment of the photoacoustic transducer;
the photoacoustic conversion composite film (32) is a composite material film consisting of a light absorption micro-nano structure material and a flexible polymer, wherein the light absorption micro-nano structure material is a carbon-based micro-nano structure material or a metal-based micro-nano structure material; the carbon-based micro-nano structure material is preferably selected from candle ash particles (CSNPs), carbon nanotubes, carbon black particles, graphene, carbon fibers or disulfide; the metal-based micro-nano structure material is preferably selected from metal nanoparticles, metal nano films or metal nano arrays.
As a further preferred embodiment of the present invention, Polydimethylsiloxane (PDMS) is used as the acoustic matching layer (31).
As a further preferable aspect of the present invention, the photoacoustic conversion composite film (32) is a composite film composed of candle ash particles (CSNPs) and Polydimethylsiloxane (PDMS).
As a further optimization of the invention, the material adopted by the hard substrate (1) is plastic, piezoelectric ceramic, organic glass or polymer.
According to another aspect of the present invention, there is provided a method for manufacturing the above-mentioned photoacoustic transducer with adjustable sound pressure output amplitude, comprising the steps of:
s10, preparing a structured base; the structural base is made of PDMS material and comprises an upper end face and a lower end face; the structural base is provided with a hollow structure, and an air channel is reserved on the structural base; preferably, the depth dimension of the hollow structure is no more than one quarter of the transverse dimension of the hollow structure;
s20, bonding or gluing one end face of the structured base prepared in the step S10 and a hard substrate;
s30, preparing the flexible composite photoacoustic conversion layer, which specifically comprises the following substeps:
s301, coating a layer of PDMS prepolymer on a substrate to obtain the substrate coated with the PDMS prepolymer; preferably, the thickness of the PDMS prepolymer is 10-50 μm;
s302, inverting the substrate coated with the PDMS prepolymer above candle flame, and performing evaporation on CSNPs (candle ash particles) to obtain a mixed layer of the CSNPs and the PDMS;
s303, curing to obtain a flexible composite photoacoustic conversion layer connected with the substrate;
s40, bonding or gluing the flexible composite photoacoustic conversion layer obtained in the step S30 and the other end face of the structured base processed in the step S20;
and S50, peeling the substrate connected with the flexible composite photoacoustic conversion layer to obtain the photoacoustic transducer with adjustable sound pressure output amplitude.
As a further preferred aspect of the present invention, the step S10 includes the following sub-steps:
s101, preparing a mold of the structured base according to the preset size of the hollow structure and the position of the reserved air channel;
s102, mixing the PDMS precursor and a curing agent, standing and removing bubbles to obtain a liquid PDMS prepolymer;
s103, pouring the liquid PDMS prepolymer obtained in the step S102 into the mold obtained in the step S101 for curing; preferably, the curing temperature is 65-85 ℃, and the curing time is 1-3 hours;
and S104, demolding to prepare the structured base.
Through the technical scheme, compared with the prior art, the photoacoustic transducer with the adjustable sound pressure output amplitude is obtained through the cooperation of the hard substrate, the structured base and the flexible composite photoacoustic conversion layer in the photoacoustic transducer device, wherein in the photoacoustic transducer with the adjustable sound pressure output amplitude, the flexible composite photoacoustic conversion layer is used for absorbing laser energy and generating ultrasonic pulses of positive and negative sound pressure through a photoacoustic effect, and the ultrasonic pulses are transmitted along the forward direction and the reverse direction; when no external force acts, the backing of the flexible composite photoacoustic conversion layer is air, and since the acoustic impedance of the flexible composite photoacoustic conversion layer is larger than that of air, an ultrasonic pulse signal transmitted in the back direction is converted into an ultrasonic pulse with equal amplitude and reversed phase after being reflected by an air cavity and is transmitted in the forward direction. The time delay existing between the ultrasonic pulse with the reversed phase obtained after reflection and the ultrasonic pulse transmitted in the initial forward direction is very small, so that the ultrasonic pulse with the reversed phase and the ultrasonic pulse transmitted in the initial forward direction are superposed and can be mutually counteracted, and the obtained sound pressure output is close to 0, namely corresponding to 0 of the sound pressure output amplitude. When external force acts, for example, the flexible composite photoacoustic conversion layer deforms to be in contact with the hard substrate, and at the moment, because the acoustic impedance of the hard substrate is greater than that of the flexible composite photoacoustic conversion layer, ultrasonic pulses transmitted along the back direction are reflected by the surface of the hard substrate, converted into ultrasonic pulse signals with equal amplitude and same phase, and transmitted along the forward direction. The time delay existing between the constant-amplitude in-phase ultrasonic pulse obtained after reflection and the ultrasonic pulse transmitted in the initial forward direction is very small, so that the constant-amplitude in-phase ultrasonic pulse and the ultrasonic pulse transmitted in the initial forward direction are overlapped, the sound pressure amplitude is changed to be 2 times of the original sound pressure amplitude, and the output of the corresponding sound pressure amplitude is 1.
Taking an external force action as an air pressure action as an example, the hard substrate, the structured base and the flexible composite photoacoustic conversion layer are matched to form an air cavity structure, the transverse size of the air cavity is equal to that of the deformable flexible composite photoacoustic conversion layer, and the flexible composite photoacoustic conversion layer is deformed by controlling the pressure in the structure cavity, so that the backing of the flexible composite photoacoustic conversion layer can be switched between the air and the hard substrate. That is to say, in the photoacoustic transducer of the present invention, since the flexible composite photoacoustic conversion layer can deform under the action of external force, so that the backing of the flexible composite photoacoustic conversion layer is switched between air and the hard substrate, further, since the acoustic impedance matching conditions of the flexible composite photoacoustic conversion layer at different backings are different, when the backing of the flexible composite photoacoustic conversion layer is air, the ultrasonic pulse transmitted in the back direction is changed into the ultrasonic pulse with the same amplitude and the opposite phase after being reflected at the interface, and is transmitted along the forward direction and is superposed with the initial forward ultrasonic pulse, and the final ultrasonic output amplitude is almost 0, that is, the positive sound pressure output is "0"; when the backing of the flexible composite photoacoustic conversion layer is a hard substrate, ultrasonic pulses transmitted in the back direction are reflected by an interface and then changed into ultrasonic pulses with equal amplitude and same phase, the ultrasonic pulses are transmitted along the forward direction and are superposed with the ultrasonic pulses transmitted in the initial forward direction, the final ultrasonic output amplitude is about 2 times of the initial forward pulse amplitude, and namely, the positive sound pressure output is 1.
And the time delay between the forward transmission photoacoustic signal and the backward transmission reflected photoacoustic signal can be made as small as possible by adjusting the thickness of the flexible photoacoustic conversion layer, so that the larger the sound pressure output amplitude difference in the states of "0" and "1". The thickness of the invention is preferably controlled to be 10-50 μm, which can not only avoid that the heat energy generated by the laser can not be diffused into the surrounding medium when the thickness is too thin, but also avoid that the ultrasonic energy is attenuated by too thick.
Specifically, the present invention can achieve the following advantageous effects:
(1) the invention provides a photoacoustic transducer device with sound pressure output amplitude of 0 and 1 regulated, which structurally comprises a hard substrate, a structured base and a flexible composite photoacoustic conversion layer and can be matched with an air pressure regulating pump for use. The flexible composite photoacoustic conversion layer deforms under the action of external force, so that the backing of the flexible composite photoacoustic conversion layer is switched between air and a hard substrate, the acoustic impedance matching conditions of the flexible composite photoacoustic conversion layer at the interface are different when the backing is different, the ultrasonic output amplitude is 0 or 1, and compared with the traditional ultrasonic device, the ultrasonic device can only change the output sound pressure amplitude by adjusting the laser energy absorbed by the photoacoustic transducer.
(2) The invention provides the photoacoustic transducer device with the sound pressure output amplitude of 0 and 1 regulated and controlled, and the back lining of the flexible composite photoacoustic conversion layer can be changed conveniently by regulating the air pressure.
(3) According to the invention, the selection of the hard substrate, the preparation of the structured base and the flexible composite photoacoustic conversion layer are carried out, then the materials are assembled through gluing and condensation bonding processes to form the photoacoustic transducer device with the structural cavity with the corresponding size, and the arrangement of the pressure adjusting pipeline is matched to obtain the photoacoustic transducer device with the adjustable sound field amplitude of 0 and 1.
(4) The preparation method provided by the invention can prepare the acoustic field amplitude values of 0 and 1 adjustable optical-acoustic transducers with different sizes.
(5) The photoacoustic transducer devices with the sound field amplitude values of 0 and 1 can be combined into an array to form an array type photoacoustic transducer, and the output sound field with any spatial distribution can be obtained by regulating the sound field amplitude values of all components in the array.
Drawings
Fig. 1 is a schematic diagram of an output amplitude control device of an electroacoustic transducer according to embodiment 1 of the present invention.
Fig. 2 is a schematic diagram of an output amplitude regulation operation principle of the optical-acoustic transducer according to embodiment 1 of the present invention, in which (a) in fig. 2 corresponds to a case of low ultrasound amplitude output (i.e., sound pressure output amplitude "0"), and (b) in fig. 2 corresponds to a case of high ultrasound amplitude output (i.e., sound pressure output amplitude "1").
Fig. 3 is a schematic view of a manufacturing process of the output amplitude control device of the photoacoustic transducer in embodiment 1 of the present invention.
Fig. 4 is a comparison graph of the test results of different back-illuminated photoacoustic transducers outputting photoacoustic signals provided in example 1 of the present invention.
Fig. 5 is a schematic diagram of an electroacoustic transducer for adjusting and controlling sound pressure output amplitudes "0" and "1" in embodiment 2 of the present invention.
Fig. 6 is a schematic diagram of an operation principle of regulating an output amplitude of an optical-acoustic transducer according to embodiment 2 of the present invention, in which (a) in fig. 6 corresponds to a case of low ultrasonic amplitude output (i.e., sound pressure output amplitude "0"), and (b) in fig. 6 corresponds to a case of high ultrasonic amplitude output (i.e., sound pressure output amplitude "1")
Fig. 7 is a schematic view of a manufacturing process of the output amplitude control device of the photoacoustic transducer in embodiment 2 of the present invention.
Fig. 8 is a schematic diagram of an electroacoustic transducer for adjusting and controlling sound pressure output amplitudes "0" and "1" in embodiment 3 of the present invention.
Fig. 9 is a schematic diagram of an output amplitude regulation operation principle of an optical-acoustic transducer according to embodiment 3 of the present invention, in which (a) in fig. 9 corresponds to a case of low ultrasound amplitude output (i.e., sound pressure output amplitude "0"), and (b) in fig. 9 corresponds to a case of high ultrasound amplitude output (i.e., sound pressure output amplitude "1")
Fig. 10 is a schematic view of a manufacturing process of an output amplitude control device of an electroacoustic transducer in embodiment 3 of the present invention.
The meaning of each reference numeral in fig. 1, 5, 8 is as follows: the device comprises a rigid substrate 1, a structured base 2, a flexible composite photoacoustic conversion layer 3, an acoustic matching layer 31, a photoacoustic conversion composite film 32, an air pressure regulating pump 4, a glass substrate 5, an air pressure regulating cavity 6, an annular magnet 7, an electromagnet 8, a ventilation catheter 9 and a piezoelectric sheet 10.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is described in further detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention. In addition, the technical features involved in the embodiments of the present invention described below may be combined with each other as long as they do not conflict with each other.
Generally speaking, the sound pressure output amplitude value '0' and '1' regulating device comprises a hard substrate, a structured base and a flexible composite photoacoustic conversion layer, and can be matched with an air pressure regulating pump for use; specifically, the structured base is provided with a hole, one surface of the hole is positioned on the contact surface of the structured base and the flexible composite photoacoustic conversion layer, the other surface of the hole is positioned on the contact surface of the base and the hard substrate, the structured base and the flexible composite photoacoustic conversion layer form an air cavity. The flexible composite photoacoustic conversion layer deforms under the action of external force, so that the backing of the flexible composite photoacoustic conversion layer is switched between air and a hard substrate, and due to the fact that acoustic impedance matching conditions of the flexible composite photoacoustic conversion layer are different when the backing of the flexible composite photoacoustic conversion layer is air, ultrasonic pulses transmitted in a back direction are converted into ultrasonic pulses with equal amplitude and opposite phase after being reflected on an interface, the ultrasonic pulses are transmitted along a forward direction and are superposed with initial forward ultrasonic pulses, and the final ultrasonic output amplitude is almost 0; when the backing of the flexible composite photoacoustic conversion layer is a hard substrate, ultrasonic pulses transmitted in the back direction are reflected by the interface and then changed into ultrasonic pulses with the same amplitude and phase, the ultrasonic pulses are transmitted along the forward direction and are superposed with the ultrasonic pulses transmitted in the initial forward direction, and the final ultrasonic output amplitude is about 2 times of the amplitude of the initial forward direction pulses. Therefore, the regulation and control of the low amplitude (also marked as '0') and the high amplitude (also marked as '1') of the output sound field amplitude are realized.
The hard substrate is used as a backing having a high acoustic impedance to increase the amplitude of output sound pressure, and also as a substrate of the structured base and an incident end of laser light. The flexible composite photoacoustic conversion layer is of a two-layer structure, namely an acoustic matching layer, a composite material film consisting of a light absorption micro-nano material and a polymer. The light absorption micro-nano structure material in the flexible composite photoacoustic conversion layer can be selected from metal nanoparticles, metal nano films, metal nano arrays, carbon black particles, carbon nanotubes, carbon fibers, disulfides (such as tungsten disulfide and molybdenum disulfide) or graphene oxide, and the flexible polymer has elasticity and ductility, and has a large thermal expansion coefficient and good tensile property.
The external force effect that makes flexible compound optoacoustic conversion layer take place deformation can be for the optional mode, makes this conversion layer take place deformation for example under the electromagnetic action, perhaps adds piezoelectric material on this conversion layer, makes this conversion layer take place deformation under the piezoelectric action, for example, one of them realization, flexible compound optoacoustic conversion layer cooperation structured base forms a structure chamber, the horizontal size in structure chamber with the horizontal size of the flexible compound optoacoustic conversion layer that can take place deformation equals, controls through the pressure size of control structure intracavity flexible compound optoacoustic conversion layer's deformation size. The structure cavity is a closed cavity, the deformable flexible composite photoacoustic conversion layer is one surface of the cavity, and the deformation size of the flexible composite photoacoustic conversion layer is controlled by adjusting the pressure in the structure cavity through connecting an air pressure adjusting device outside the structured base, communicating with the structure cavity. The structural cavity is communicated with a conduit of an air pressure adjusting instrument, and other parts are well sealed, and an air pressure adjusting device such as an air pressure adjusting pump and the like (namely, the air pressure adjusting device can be communicated with the structural cavity through an air pressure adjusting channel, the air channel is used as the air pressure adjusting channel, and the air pressure in the air cavity can be adjusted through the air pressure adjusting pump). The size of the structural cavity (i.e. hollow structure) of the structured base can be designed in advance, especially the depth size, which determines the difficulty of switching the flexible composite photoacoustic conversion layer backing between air and the hard substrate. Preferably, the depth of the structural cavity is less than one fourth of the lateral dimension of the structural cavity (taking the structural cavity as a cylinder, and the diameter of the cylinder is d, the height h of the structural cavity is less than d/4), so that the flexible composite photoacoustic conversion layer can be easily attached to the hard substrate when deformed, and the backing of the flexible composite photoacoustic conversion layer can be more conveniently switched between air and the hard substrate.
Accordingly, the method for manufacturing the acoustic transducer device for adjusting the sound pressure output amplitude "0" or "1" may be as follows. The preparation method connects the hard substrate and the structured base together through a gluing or bonding process, and integrates the structured base and the composite photoacoustic conversion layer together through a condensation bonding process, and specifically comprises the following steps:
s10, preparing a structured base; the structural base comprises an upper end face and a lower end face, and the end faces are made of PDMS materials; the structured base further comprises an air pressure regulating channel:
s101, designing a mold of the structured base according to the size of the required structural cavity and the position of an air pressure adjusting channel of the structural cavity;
in particular, the main function of the structured base in the present invention is to fix and support the flexible composite photoacoustic conversion layer, and also to define the size of the deformable flexible composite photoacoustic conversion layer. On the premise of considering the whole size of the device, the size of the structural cavity can be designed in advance, and the die can be processed according to the design. Similar to conventional requirements, the bottom surface of the machined mold is sufficiently smooth so that the open cavity surface of the demolded structured base can meet bonding requirements.
S102, mixing the PDMS precursor and a curing agent, standing and removing bubbles to obtain a liquid PDMS prepolymer;
specifically, the PDMS precursor and the curing agent are uniformly mixed according to a certain proportion to obtain a liquid PDMS prepolymer, and then the liquid PDMS prepolymer is kept stand to remove bubbles. Preferably, the pre-matrix and the curing agent are fully mixed according to the volume ratio of 10:1, and then the mixture is placed into a vacuum air extractor to be kept still for removing bubbles. The Young modulus of the prepared flexible composite photoacoustic conversion layer depends on the ratio of the front matrix to the curing agent, and the larger the ratio is, the smaller the Young modulus is, and the softer the composite photoacoustic conversion layer is at the moment. The hardness of the flexible composite photoacoustic conversion layer determines its mechanical properties, and accordingly the softer the conversion layer, the smaller the gas pressure value required to deform it to conform to the surface of the hard substrate.
S103, pouring the liquid PDMS prepolymer obtained in the step S102 into the mould obtained in the step S101 for curing;
specifically, the liquid PDMS prepolymer after standing is poured into the mold for curing treatment. Preferably, the curing process temperature is 65-85 ℃ and the curing time is 1-3 hours.
And S104, demolding to obtain the structured base.
Specifically, the fully cured structured base is removed from the mold. Similar to conventional requirements, the cleanliness of the open cavity surface (i.e., end surface; when bonding treatment is used, the open cavity surface is also the bonding surface) of the structured base needs to be maintained during demolding, otherwise the bonding process may fail; the susceptor may be inverted in a hermetically sealed device case after demolding for the purpose of preventing rubbing or damage to the open cavity surfaces.
S20, bonding or gluing the structured base and the hard substrate;
in particular, an open cavity surface of the structured base can be fixed on the hard substrate by bonding or gluing, and the air tightness of the connecting surface is also ensured.
S30, preparing a flexible composite photoacoustic conversion layer:
s301, coating a first layer of PDMS prepolymer on a substrate to obtain the substrate coated with the first layer of PDMS prepolymer;
specifically, the substrate needs to be placed in a vacuum environment for surface silanization treatment before the PDMS is coated in a spinning mode, so that the subsequent stripping process becomes easy; preferably, the thickness of the PDMS that is spin-coated is 10-50 μm to avoid that too thin will not allow the thermal energy generated by the laser to diffuse into the surrounding medium and too thick will have a negative attenuation effect on the ultrasonic energy.
S302, inverting the substrate coated with the first layer of PDMS prepolymer above candle flame, and performing CSNPs evaporation to obtain a CSNPs layer;
specifically, the substrate coated with PDMS is directly inverted above candle flame without curing treatment, and CSNPs evaporation is carried out; preferably, the evaporation process needs to control the substrate to be kept horizontal, and the evaporation time of each evaporation area of the substrate is uniformly controlled, so that the CSNPs layer is uniformly distributed. In the evaporation process of the candle ash particles CSNPs, the CSNPs enter the PDMS layer to form a mixed layer of the CSNPs and the PDMS; the thickness of the CSNPs layer can be controlled by the total evaporation time (of course, the CSNPs cannot be fused in PDMS due to too long evaporation time, and the adhesion force is weak), and the actually required evaporation time can be flexibly adjusted by an operator according to specific conditions.
S303, curing to obtain a flexible composite photoacoustic conversion layer;
specifically, the substrate on which the step S302 is completed is subjected to a curing process. Preferably, the curing process parameters are consistent with those in step S103; preferably, the temperature of the curing process is 65-85 ℃, the curing time is 1-3 hours, and the cured substrate is arranged in the closed device box.
And S40, bonding the structured base and the flexible composite photoacoustic conversion layer.
Specifically, the open cavity surface (i.e. the end surface; when bonding treatment is adopted, the open cavity surface is also the bonding surface) of the structured base and the PDMS surface of the flexible composite photoacoustic conversion layer are respectively treated by a plasma machine, the open cavity surface (i.e. the bonding surface) of the structured base is made of PDMS material, the surface of the composite photoacoustic conversion layer is also made of PDMS material, and the two materials form irreversible tight bonding when being naturally attached after being subjected to plasma surface treatment; and (3) processing the PDMS surface to be bonded in an oxygen plasma machine for not less than 1min, and then naturally aligning and bonding. Preferably, the PDMS surface to be bonded can be cleaned with ethanol, dried with nitrogen and then treated in a plasma machine.
And S50, stripping the flexible composite photoacoustic conversion layer from the substrate, and further communicating the air pressure regulating pump conduit with the structural cavity.
Example 1
Fig. 1 shows a schematic diagram of an opto-acoustic transducer device for adjusting and controlling sound pressure output amplitudes "0" and "1" according to an embodiment of the present invention.
As shown in fig. 1, the photoacoustic transducer apparatus for adjusting and controlling sound pressure output amplitudes "0" and "1" according to this embodiment includes: the device comprises a hard substrate 1, a structured base 2, a flexible composite photoacoustic conversion layer 3 and a pressure regulating pump 4; the hard substrate 1 is used as a structural base 2 and as an incident end of laser; the structured base 2 is used for fixing and supporting the flexible composite photoacoustic conversion layer 3 and defining the size of the deformable flexible composite photoacoustic conversion layer; the hard substrate 1, the structured base 2 and the flexible composite photoacoustic conversion layer 3 are matched to form a structural cavity, and the air pressure value in the cavity is controlled by the air pressure adjusting pump 4 through the guide pipe 41; the flexible composite photoacoustic conversion layer 3 is used to absorb laser energy and generate ultrasonic pulses through the photoacoustic effect.
Specifically, in combination with the schematic diagram of the working principle shown in fig. 2, the photoacoustic transducer device for regulating and controlling the sound pressure output amplitude of 0 and 1 is based on the characteristic that the flexible composite photoacoustic conversion layer is easy to deform. The air pressure value in the air cavity is changed, so that the flexible composite photoacoustic conversion layer is deformed to be attached to the hard substrate, the backing of the flexible composite photoacoustic conversion layer is switched between air and the hard substrate, and due to the fact that acoustic impedance matching conditions of different backing are different, when the backing of the flexible composite photoacoustic conversion layer is an air backing, ultrasonic pulses transmitted in a back direction are changed into ultrasonic pulses with equal amplitude and opposite phase after being reflected on an interface, the ultrasonic pulses are transmitted in a forward direction and are overlapped with the initial forward ultrasonic pulses, and the final ultrasonic output amplitude is almost 0; when the backing of the flexible composite photoacoustic conversion layer is a hard substrate, ultrasonic pulses transmitted in the back direction are reflected by the interface and then changed into ultrasonic pulses with the same amplitude and phase, the ultrasonic pulses are transmitted along the forward direction and are superposed with the ultrasonic pulses transmitted in the initial forward direction, and the final ultrasonic output amplitude is about 2 times of the amplitude of the initial forward direction pulses. Thereby realizing the regulation and control of '0' and '1' of the amplitude of the output sound field.
The hard substrate 1 is a glass sheet, and the structured base 2 is obtained by curing a Polydimethylsiloxane (PDMS) prepolymer; the composite photoacoustic conversion layer 3 can be a two-layer structure (i.e., a two-layer structure composed of pure PDMS, candle ash particles and a PDMS mixed layer) composed of PDMS-PDMS/CSNPs, and at this time, the CSNPs permeate into the PDMS for a distance in the evaporation process.
It should be noted that, in the actual use process, the working medium environment of the photoacoustic transducer is generally water, PDMS or a medium with similar acoustic impedance, and the air cavity may be slightly deformed due to the pressure of the medium. In principle, the influence on the performance of the device is negligible, and even if the deformation amount is large for a special working environment, the working performance of the device can be recovered by injecting air from the outside.
Fig. 3 shows a schematic flow chart of a manufacturing process of an acoustic transducer device with sound pressure output amplitude "0" and "1" regulated, and as shown in fig. 3, the manufacturing method includes the following steps:
s10, preparing a structured base; the structural base comprises a bonding surface, and the bonding surface is made of PDMS materials; the structured base further comprises an air pressure regulating channel:
s101, designing a mold of the structured base according to the size of the required structural cavity and the position of an air pressure adjusting channel of the structural cavity;
in particular, the structured base of the present invention serves primarily to hold and support the flexible composite photoacoustic conversion layer, and also to define the dimensions of the deformable flexible composite photoacoustic conversion layer. On the premise of considering the whole size of the device, the size of the structural cavity can be designed in advance, and the die can be processed according to the design. Similar to conventional bonding process requirements, the bottom surface of the machined mold is sufficiently smooth so that the open cavity surface of the demolded structured base can meet bonding requirements.
It should be noted that the structural cavities, except for the communication with the conduit 41, are well sealed everywhere, which is achieved by the irreversible bonding process between PDMS.
S102, mixing the PDMS precursor and a curing agent, standing and removing bubbles to obtain a liquid PDMS prepolymer;
specifically, the PDMS precursor and the curing agent are uniformly mixed according to the volume ratio of 10:1 to obtain a liquid PDMS prepolymer, and then the liquid PDMS prepolymer is placed into a vacuum air extractor to be kept still for removing bubbles.
S103, pouring the liquid PDMS prepolymer obtained in the step S102 into the mould obtained in the step S101 for curing;
specifically, the liquid PDMS prepolymer after standing is poured into the mold for curing treatment. Preferably, the curing process temperature is 65 ℃ and the curing time is 2 hours.
And S104, demolding to obtain the structured base.
Specifically, the fully cured structured base is removed from the mold. Similar to conventional requirements, the cleanliness of the open cavity surface, i.e., the bonding surface, of the structured base needs to be maintained in the demolding process, otherwise the bonding process may fail; the susceptor may be inverted in a hermetically sealed device case after demolding for the purpose of preventing rubbing or damage to the open cavity surfaces.
S20, bonding the structured base and the hard substrate;
in particular, an open cavity surface of the structured base can be fixed on the hard substrate in a bonding mode, and the air tightness of the connecting surface is also ensured.
S30, preparing a flexible composite photoacoustic conversion layer:
s301, coating a first layer of PDMS prepolymer on a substrate to obtain the substrate coated with the first layer of PDMS prepolymer;
specifically, the substrate needs to be placed in a vacuum environment for surface silanization treatment before the PDMS is coated in a spinning mode, so that the subsequent stripping process becomes easy; the thickness of the first PDMS prepolymer is 20 μm.
S302, inverting the substrate coated with the first layer of PDMS prepolymer above candle flame, and performing CSNPs evaporation to obtain a CSNPs layer;
specifically, the substrate coated with the first layer of PDMS is directly inverted at a position 2.5cm above candle flame without curing treatment, and CSNPs are evaporated for 5 s; preferably, the evaporation process needs to control the substrate to be kept horizontal, and the evaporation time of each evaporation area of the substrate is uniformly controlled, so that the CSNPs layer is uniformly distributed. It should be noted that the thickness of the CSNPs layer can be controlled by the total time of evaporation, and different CSNPs layer thicknesses determine different laser absorption intensities.
S303, curing to obtain a flexible composite photoacoustic conversion layer;
specifically, the substrate on which the step S303 is completed is subjected to curing treatment. Preferably, the curing process parameters are consistent with those in step S103; preferably, the curing process temperature is 65 ℃ and the curing time is 2 hours, and the cured substrate is placed in a closed device box.
And S40, bonding the structured base and the flexible composite photoacoustic conversion layer.
Specifically, a plasma machine is adopted to respectively process the open cavity surface, namely the bonding surface, of the structured base and the PDMS surface of the flexible composite photoacoustic conversion layer, the open cavity surface, namely the bonding surface, of the structured base is made of PDMS material, the surface of the composite photoacoustic conversion layer is also made of PDMS material, and after the two are subjected to plasma surface treatment, irreversible tight bonding can be formed when the two are naturally attached; and (3) processing the PDMS surface to be bonded in an oxygen plasma machine for not less than 1min, and then naturally aligning and bonding. Preferably, the PDMS surface to be bonded can be cleaned with ethanol, dried with nitrogen and then treated in a plasma machine.
And S50, stripping the flexible composite photoacoustic conversion layer and the substrate, and communicating the air pressure regulating pump conduit and the structural cavity.
Performing process preparation according to the preparation parameters in the embodiment, and performing photoacoustic signal characterization on the photoacoustic transducer when the excitation laser parameters are 532nm in wavelength, 10ns in pulse width and 5mJ in pulse energy; as can be seen from fig. 4, when the laser energy is kept unchanged, the amplitude of the output positive sound pressure of the flexible composite photoacoustic conversion layer under two different backing conditions is greatly different. The result shows that the sound pressure output amplitude of the photoacoustic transducer provided by the invention is regulated and controlled by '0' and '1'.
Example 2
Fig. 5 shows a schematic diagram of an electroacoustic transducer with sound pressure output amplitude "0" and "1" regulated according to an embodiment of the present invention.
As shown in fig. 5, the photoacoustic transducer apparatus for adjusting and controlling the sound pressure output amplitudes "0" and "1" of this embodiment includes: the device comprises a hard substrate 1, a structured base 2, a flexible composite photoacoustic conversion layer 3, a glass substrate 5, an air pressure adjusting cavity 6, an annular magnet 7, an electromagnet 8 and an air duct 9; the hard substrate 1 is used as an incident end of laser; the structured base 2 is used for fixing and supporting the flexible composite photoacoustic conversion layer 3 and defining the size of the deformable flexible composite photoacoustic conversion layer; the hard substrate 1, the structured base 2 and the flexible composite photoacoustic conversion layer 3 are matched to form a structural cavity, and the flexible composite photoacoustic conversion layer 3 is used for absorbing laser energy and generating ultrasonic pulses through a photoacoustic effect; the glass substrate 5 and the air pressure adjusting cavity 6 are matched to form a right side closed cavity structure. The upper end face of the air pressure adjusting cavity 6 is thin and easy to deform, the annular magnet 7 is arranged, the electromagnet 8 is arranged right above the annular magnet, the air pressure adjusting structure cavity is communicated with the left side structure cavity through the ventilating duct 9, on-off of current in the electromagnet 8 is controlled, the volume of the right side cavity can be changed, accordingly, pressure intensity in the left side cavity is changed, the composite photoacoustic conversion layer 3 is driven to deform, and the back lining of the composite photoacoustic conversion layer is switched between air and the hard substrate 1.
Specifically, in combination with the schematic diagram of the working principle shown in fig. 6, a photoacoustic transducer device with a sound pressure output amplitude of "0" or "1" is combined with a communicating cavity structure, when the electromagnet is not electrified, the air pressure in the cavity structures at the left side and the right side is kept constant, and the back lining of the composite photoacoustic conversion layer is air; when the electromagnet is electrified, attractive force exists between the annular magnet and the electromagnet, the annular magnet drives the upper end face of the right cavity to generate upward displacement, so that the pressure in the right cavity is increased, gas flows into the right cavity from the left cavity structure, the pressure in the left cavity is reduced, the composite photoacoustic conversion layer on the left cavity is deformed to be partially attached to the hard substrate, and therefore the back lining of the composite photoacoustic conversion layer is switched between air and the hard substrate through the on-off of current in the electromagnet. Due to the fact that acoustic impedance matching conditions are different when backing is different, when the backing of the flexible composite photoacoustic conversion layer is an air backing (an electromagnet is not electrified), ultrasonic pulses transmitted in a back direction are changed into ultrasonic pulses with equal amplitude and opposite phase after being reflected by an interface, the ultrasonic pulses are transmitted along a forward direction and are superposed with the initial forward ultrasonic pulses, and the final ultrasonic output amplitude is almost 0; when the back lining of the flexible composite photoacoustic conversion layer is a hard substrate (the electromagnet is electrified), the ultrasonic pulse transmitted in the back direction is changed into an ultrasonic pulse with the same amplitude and phase after being reflected by the interface, the ultrasonic pulse is transmitted along the positive direction and is superposed with the ultrasonic pulse transmitted in the initial positive direction, and the final ultrasonic output amplitude is about 2 times of the amplitude of the initial positive pulse. Thereby realizing the regulation and control of '0' and '1' of the amplitude of the output sound field.
The hard substrate 1 is a glass sheet, and the structured base 2 is obtained by curing a Polydimethylsiloxane (PDMS) prepolymer; the composite photoacoustic conversion layer 3 can be a two-layer structure (i.e., a two-layer structure composed of pure PDMS, candle ash particles and a PDMS mixed layer) composed of PDMS-PDMS/CSNPs, and at this time, the CSNPs permeate into the PDMS for a distance in the evaporation process.
It should be noted that, in the actual use process, the working medium environment of the photoacoustic transducer is generally water, PDMS or a medium with similar acoustic impedance, and the air cavity may be slightly deformed due to the pressure of the medium. In principle, the influence on the performance of the device is negligible, and even if the deformation amount is large for a special working environment, the working performance of the device can be recovered by injecting air from the outside.
Fig. 7 shows a schematic flow chart of a manufacturing process of an acoustic transducer device with sound pressure output amplitude "0" and "1" adjusted, and as shown in fig. 7, the manufacturing method includes the following steps:
s10, respectively preparing a structured base and an air pressure adjusting cavity structure;
s101, designing molds of a structural base and an air pressure adjusting cavity according to the sizes of the required structural cavity and the air pressure adjusting cavity and the position of an air pressure adjusting channel;
s102, mixing the PDMS precursor and a curing agent, standing and removing bubbles to obtain a liquid PDMS prepolymer;
specifically, the PDMS precursor and the curing agent are uniformly mixed according to the volume ratio of 10:1 to obtain a liquid PDMS prepolymer, and then the liquid PDMS prepolymer is placed into a vacuum air extractor to be kept still for removing bubbles.
S103, pouring the liquid PDMS prepolymer obtained in the step S102 into the two molds obtained in the step S101 for curing;
specifically, the liquid PDMS prepolymer after standing is poured into the mold for curing treatment. Preferably, the curing process temperature is 75 ℃ and the curing time is 3 hours.
And S104, demolding to obtain the structured base and the air pressure adjusting cavity structure.
S20, gluing the structured base and the hard substrate;
specifically, the lower end face of the structured base may be fixed on the hard substrate using an ultraviolet curing adhesive, and the coated portion may be irradiated with an ultraviolet lamp for 30 seconds.
S30, preparing a flexible composite photoacoustic conversion layer:
s301, coating a first layer of PDMS prepolymer on a substrate to obtain the substrate coated with the first layer of PDMS prepolymer;
specifically, the substrate needs to be placed in a vacuum environment for surface silanization treatment before the PDMS is coated in a spinning mode, so that the subsequent stripping process becomes easy; the thickness of PDMS obtained by the first spin coating is 25 μm
S302, inverting the substrate coated with the first layer of PDMS prepolymer above candle flame for evaporation to obtain a CSNPs/PDMS layer;
specifically, the substrate coated with the first layer of PDMS is directly inverted at a position 3cm above candle flame without curing treatment, and CSNPs are evaporated for 6 s; preferably, the evaporation process needs to control the substrate to be kept horizontal, and the evaporation time of each evaporation area of the substrate is uniformly controlled, so that the CSNPs layer is uniformly distributed. It should be noted that the thickness of the CSNPs layer can be controlled by the total time of evaporation, and different CSNPs layer thicknesses determine different laser absorption intensities.
S303, curing to obtain a flexible composite photoacoustic conversion layer;
specifically, the substrate on which the step S303 is completed is subjected to curing treatment. Preferably, the curing process parameters are consistent with those in step S103; preferably, the curing process temperature is 75 ℃ and the curing time is 2.5 hours, and the cured substrate is placed in the closed device box.
And S40, gluing the upper end face of the structured base and the flexible composite photoacoustic conversion layer.
Specifically, the upper end face of the structured base is coated with ultraviolet curing glue, is attached to the flexible composite photoacoustic conversion layer, and is irradiated for 30 seconds by an ultraviolet lamp.
And S50, peeling the flexible composite photoacoustic conversion layer and the substrate.
And S60, gluing the lower end of the communicating cavity and the glass substrate to form a right cavity structure.
Specifically, the lower end of the air pressure adjusting cavity is coated with ultraviolet curing glue, and is attached to the glass substrate, and the glass substrate is irradiated by an ultraviolet lamp for 30 seconds.
And S70, fixing the through ring-shaped magnet at the middle position of the upper end face of the air pressure adjusting cavity by using UV glue.
Performing process preparation according to the preparation parameters in the embodiment, and performing photoacoustic signal characterization on the photoacoustic transducer when the excitation laser parameters are 532nm in wavelength, 10ns in pulse width and 9mJ in pulse energy; when the laser energy is kept unchanged, the amplitude difference of the output positive sound pressure of the flexible composite photoacoustic conversion layer is large under two different backing conditions. Therefore, the light-sound transducer provided by the invention realizes the regulation and control of '0' and '1' of sound pressure output amplitude.
Example 3
Fig. 8 shows a schematic diagram of an electroacoustic transducer with sound pressure output amplitude "0" and "1" regulated according to an embodiment of the present invention.
As shown in fig. 8, the photoacoustic transducer apparatus for adjusting and controlling the sound pressure output amplitudes "0" and "1" of this embodiment includes: the device comprises a hard substrate 1, a structured base 2, a flexible composite photoacoustic conversion layer 3, a glass substrate 5, an air pressure adjusting cavity 6, a piezoelectric sheet 10 and an air duct 9; the hard substrate 1 is used as an incident end of laser; the structured base 2 is used for fixing and supporting the flexible composite photoacoustic conversion layer 3 and defining the size of the deformable flexible composite photoacoustic conversion layer; the hard substrate 1, the structured base 2 and the flexible composite photoacoustic conversion layer 3 are matched to form a left cavity, and the flexible composite photoacoustic conversion layer 3 is used for absorbing laser energy and generating ultrasonic pulses through a photoacoustic effect; the glass substrate 5, the air pressure adjusting cavity 6 and the piezoelectric plate 10 are matched to form a right cavity, and the left cavity is communicated with the right cavity through a ventilation catheter.
Specifically, in combination with the schematic diagram of the working principle shown in fig. 9, an acoustic-optical transducer device for adjusting and controlling the sound pressure output amplitude "0" and "1" is based on the characteristic that a piezoelectric material deforms under the action of an external electric field. When no voltage is applied to the piezoelectric sheet, the air pressure in the left side cavity and the right side cavity is kept constant, and the back lining of the composite photoacoustic conversion layer is air; when voltage is applied to the piezoelectric sheet, the piezoelectric sheet can generate upward displacement, the pressure intensity in the right cavity is increased, gas flows into the right cavity from the left cavity through the ventilation conduit, the air pressure in the left cavity is reduced, and the composite photoacoustic conversion layer is driven to deform to be attached to the hard substrate; therefore, the back lining of the flexible composite photoacoustic conversion layer is switched between air and a hard substrate, and due to different acoustic impedance matching conditions when different back linings are used, when the back lining of the flexible composite photoacoustic conversion layer is an air back lining (no voltage is applied to a piezoelectric plate), ultrasonic pulses transmitted in a back direction are changed into ultrasonic pulses with equal amplitude and opposite phase after being reflected on an interface, the ultrasonic pulses are transmitted in a forward direction and are superposed with the initial forward ultrasonic pulses, and the final ultrasonic output amplitude is almost 0; when the backing of the flexible composite photoacoustic conversion layer is a hard substrate (voltage is applied to the piezoelectric sheet), ultrasonic pulses transmitted in the back direction are reflected by the interface and then changed into ultrasonic pulses with the same amplitude and phase, the ultrasonic pulses are transmitted along the forward direction and are superposed with the ultrasonic pulses transmitted in the initial forward direction, and the final ultrasonic output amplitude is about 2 times of the amplitude of the initial forward direction pulses. Thereby realizing the regulation and control of '0' and '1' of the amplitude of the output sound field.
The hard substrate 1 is made of glass sheets, and the structured base 2 and the air pressure adjusting cavity 6 are obtained by curing Polydimethylsiloxane (PDMS) prepolymer; the piezoelectric sheet 10 is a PZT piezoelectric material, the composite photoacoustic conversion layer 3 can be a two-layer structure (i.e., a two-layer structure composed of pure PDMS, candle ash particles, and a PDMS mixed layer) composed of PDMS-PDMS/CSNPs, and at this time, the CSNPs penetrate into the PDMS for a distance in the evaporation process.
It should be noted that, in the actual use process, the working medium environment of the photoacoustic transducer is generally water, PDMS or a medium with similar acoustic impedance, and the air cavity may be slightly deformed due to the pressure of the medium. In principle, the influence on the performance of the device is negligible, and even if the deformation amount is large for a special working environment, the working performance of the device can be recovered by injecting air from the outside.
Fig. 10 is a schematic view showing a flow of manufacturing an acoustic transducer device for adjusting and controlling sound pressure output amplitudes "0" and "1", in which the manufacturing method includes the following steps:
s10, respectively preparing a structured base and an air pressure adjusting cavity:
s101, designing a mold of a structural base and an air pressure adjusting cavity according to the size of a required structural cavity and the position of an air pressure adjusting channel of the structural cavity;
s102, mixing the PDMS precursor and a curing agent, standing and removing bubbles to obtain a liquid PDMS prepolymer;
specifically, the PDMS precursor and the curing agent are uniformly mixed according to the volume ratio of 10:1 to obtain a liquid PDMS prepolymer, and then the liquid PDMS prepolymer is placed into a vacuum air extractor to be kept still for removing bubbles.
S103, pouring the liquid PDMS prepolymer obtained in the step S102 into the two molds obtained in the step S101 for curing;
specifically, the liquid PDMS prepolymer after standing is poured into the mold for curing treatment. Preferably, the curing process temperature is 75 ℃ and the curing time is 2 hours.
And S104, demolding to obtain the structured base and the air pressure adjusting cavity.
Specifically, the fully cured structured base and the air pressure regulating cavity are removed from the mold.
S20, gluing the bottom surface of the structured base cavity and the hard substrate;
specifically, an open cavity surface of the structured base can be fixed on the hard substrate by using ultraviolet curing glue, and the glued part is irradiated by an ultraviolet lamp for 30 s.
S30, preparing a flexible composite photoacoustic conversion layer:
s301, coating a first layer of PDMS prepolymer on a substrate to obtain the substrate coated with the first layer of PDMS prepolymer;
specifically, the substrate needs to be placed in a vacuum environment for surface silanization treatment before the PDMS is coated in a spinning mode, so that the subsequent stripping process becomes easy; the thickness of PDMS obtained by the first spin coating is 25 μm
S302, inverting the substrate coated with the first layer of PDMS prepolymer above candle flame for evaporation to obtain a CSNPs/PDMS layer;
specifically, the substrate coated with the first layer of PDMS is directly inverted at a position 3cm above candle flame without curing treatment, and CSNPs are evaporated for 5 s; preferably, the evaporation process needs to control the substrate to be kept horizontal, and the evaporation time of each evaporation area of the substrate is uniformly controlled, so that the CSNPs layer is uniformly distributed. It should be noted that the thickness of the CSNPs layer can be controlled by the total time of evaporation, and different CSNPs layer thicknesses determine different laser absorption intensities.
S303, curing to obtain a flexible composite photoacoustic conversion layer;
specifically, the substrate on which the step S303 is completed is subjected to curing treatment. Preferably, the curing process parameters are consistent with those in step S103; preferably, the curing process temperature is 75 ℃ and the curing time is 2.5 hours, and the cured substrate is placed in the closed device box.
And S40, gluing the structured base and the flexible composite photoacoustic conversion layer.
Specifically, the upper end face of the structured base is coated with ultraviolet curing glue, the ultraviolet curing glue is attached to the flexible composite photoacoustic conversion layer, and the ultraviolet curing glue is irradiated for 30 seconds by an ultraviolet lamp.
And S50, peeling the flexible composite photoacoustic conversion layer and the substrate.
And S60, gluing the air pressure adjusting cavity and the piezoelectric sheet.
Specifically, the upper end face of the air pressure adjusting cavity is coated with ultraviolet curing glue, the ultraviolet curing glue is attached to the piezoelectric sheet, and the piezoelectric sheet is irradiated for 30 seconds by an ultraviolet lamp.
And S70, gluing the air pressure adjusting cavity and the glass substrate.
Specifically, the lower end face of the air pressure adjusting cavity is coated with ultraviolet curing glue, the ultraviolet curing glue is attached to a glass substrate, and an ultraviolet lamp is used for irradiating for 30 seconds.
And S80, communicating the left and right cavities by using the ventilation catheter.
Performing process preparation according to the preparation parameters in the embodiment, and performing photoacoustic signal characterization on the photoacoustic transducer when the excitation laser parameters are 532nm in wavelength, 10ns in pulse width and 5mJ in pulse energy; when the laser energy is kept unchanged, the amplitude difference of the output positive sound pressure of the flexible composite photoacoustic conversion layer is large under two different backing conditions. Therefore, the light-sound transducer provided by the invention realizes the regulation and control of '0' and '1' of sound pressure output amplitude.
In addition to the above embodiments, the rigid substrate may also be made of transparent material with acoustic impedance greater than PDMS, such as organic glass, plastic, or polymer. The above embodiments are all examples of planar hard substrate structures, and in addition to planar, focusing type hard substrate structures (for example, refer to [ 1 ] Li Q, Zhu H, Feng C, et al, simple layer non-reactive substrate structure for a focusing type photo-electric transmitter [ J ]. Optic left 44(6),1300-1303(2019) ]. Li Y, Guo Z, Li G, et al, miniature fiber-optical High-intensity Focused layer using a Lens nanoparticles-polymerizable substrate [ J ]. 26 ], and [ 2018 ] optical fibers-coated substrates [ 17 ] and [ 17 ] D, J.8, J., the key point of the invention for realizing the regulation and control of the sound pressure amplitude is that the substrate of the composite photoacoustic conversion layer is switched by, for example, a pneumatic regulation and control cavity structure, and when the hard substrate is of a focusing type, a larger positive sound pressure output can be generated (of course, the output waveform of the positive sound pressure output is different from that of a plane type hard substrate).
In addition, even if the shape of the air cavity is changed compared with the initial state, as long as the film backing is still air, the output sound pressure amplitude is very small, which is still much smaller than the sound pressure generated when the film is stressed to be tightly adhered to the hard substrate, and the adjustment of 0 and 1 can be realized together with the tight state.
It will be understood by those skilled in the art that the foregoing is only a preferred embodiment of the present invention, and is not intended to limit the invention, and that any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the scope of the present invention.
Claims (10)
1. A photoacoustic transducer with adjustable sound pressure output amplitude is characterized by sequentially comprising a hard substrate (1), a structured base (2) and a flexible composite photoacoustic conversion layer (3) from bottom to top; wherein the structured base (2) is provided with a hollow structure, the upper end face of the hollow structure is positioned at the contact surface of the structured base (2) and the flexible composite photoacoustic conversion layer (3), and the lower end face of the hollow structure is positioned at the contact surface of the base and the hard substrate (1); the hard substrate (1), the structured base (2) and the flexible composite photoacoustic conversion layer (3) are connected, so that an air cavity correspondingly formed by the hollow structure can be kept sealed except at a reserved air channel position; the air pressure in the air cavity can be adjusted through the air channel;
the hard substrate (1) is used as an incident end of laser, and the laser is incident to the flexible composite photoacoustic conversion layer (3) through the hard substrate (1); the flexible composite photoacoustic conversion layer (3) is used for absorbing laser beam energy and converting the laser beam energy into acoustic energy to generate initial ultrasonic pulse signals transmitted along the forward direction and transmitted back to the back; taking the contact surface of the structured base (2) and the flexible composite photoacoustic conversion layer (3) as a reference, and taking the normal direction of the contact surface of the structured base (2) pointing to the flexible composite photoacoustic conversion layer (3) as a forward direction and the normal direction of the contact surface of the flexible composite photoacoustic conversion layer (3) pointing to the structured base (2) as a backward direction;
the flexible composite photoacoustic conversion layer (3) can deform under the action of external force, and the shape and the structure of the air cavity are correspondingly changed, wherein:
when the flexible composite photoacoustic conversion layer (3) is deformed to be in direct contact with the hard substrate (1), because the acoustic impedance of the hard substrate (1) is greater than that of the flexible composite photoacoustic conversion layer (3), a signal transmitted along the back direction in a generated initial ultrasonic pulse signal is converted into a first ultrasonic pulse reflection signal which has the same amplitude and phase and is transmitted along the forward direction after being reflected by the surface of the hard substrate (1), and the first ultrasonic pulse reflection signal and another part of the initial ultrasonic pulse signal transmitted along the forward direction are superposed to obtain sound pressure output which is transmitted along the forward direction and has increased sound pressure amplitude;
when the flexible composite photoacoustic conversion layer (3) is not in direct contact with the hard substrate (1), because the acoustic impedance of the flexible composite photoacoustic conversion layer (3) is greater than that of air, a signal transmitted in a reverse direction in the generated initial ultrasonic pulse signal is converted into a second ultrasonic pulse reflection signal which has the same amplitude and is inverted in phase and is transmitted in a forward direction after being reflected by the air cavity, and the second ultrasonic pulse reflection signal is superposed with the initial ultrasonic pulse signal transmitted in the forward direction by the other part in the initial ultrasonic pulse signal to obtain sound pressure output which is transmitted in the forward direction and has reduced sound pressure amplitude;
therefore, the sound pressure output amplitude can be regulated and controlled by utilizing the deformation of the flexible composite photoacoustic conversion layer (3).
2. The photoacoustic transducer of claim 1 wherein the external force comprises an electromagnetic effect, a piezoelectric effect, or a pneumatic effect.
3. The photoacoustic transducer of claim 1 wherein the photoacoustic transducer with adjustable sound pressure output amplitude is configured to be connected to an air pressure regulating pump (4), and the air pressure regulating pump (4) is configured to regulate the air pressure in the air cavity through the air channel, so as to deform the flexible composite photoacoustic conversion layer (3).
4. The photoacoustic transducer of claim 1 wherein the structured base (2) has a cylindrical hollow structure, and the structured base (2) is made of metal, plastic, plexiglass or polymer; preferably, the structured base (2) is made of Polydimethylsiloxane (PDMS) which is obtained by curing a PDMS prepolymer.
5. The photoacoustic transducer of claim 1 wherein the flexible composite photoacoustic conversion layer (3) comprises, from top to bottom, an acoustic matching layer (31) and a photoacoustic conversion composite film (32), wherein,
the acoustic matching layer (31) is made of a material which meets the requirement that the acoustic resistance of the material is matched with the acoustic resistance of the target working environment of the photoacoustic transducer;
the photoacoustic conversion composite film (32) is a composite material film consisting of a light absorption micro-nano structure material and a flexible polymer, wherein the light absorption micro-nano structure material is a carbon-based micro-nano structure material or a metal-based micro-nano structure material; the carbon-based micro-nano structure material is preferably selected from candle ash particles (CSNPs), carbon nanotubes, carbon black particles, graphene, carbon fibers or disulfide; the metal-based micro-nano structure material is preferably selected from metal nanoparticles, metal nano films or metal nano arrays.
6. The photoacoustic transducer of claim 5 wherein the acoustic matching layer (31) is Polydimethylsiloxane (PDMS).
7. The photoacoustic transducer of claim 5 wherein the photoacoustic conversion composite film (32) is a composite film of candle ash particles (CSNPs) and Polydimethylsiloxane (PDMS).
8. An opto-acoustic transducer according to claim 1, characterized in that the material used for the rigid substrate (1) is plastic, piezoceramic, plexiglass or polymer.
9. A method for manufacturing an acoustic pressure output amplitude controllable photoacoustic transducer according to any one of claims 1-8, comprising the steps of:
s10, preparing a structured base; the structural base is made of PDMS material and comprises an upper end face and a lower end face; the structural base is provided with a hollow structure, and an air channel is reserved on the structural base; preferably, the depth dimension of the hollow structure is no more than one quarter of the transverse dimension of the hollow structure;
s20, bonding or gluing one end face of the structured base prepared in the step S10 and a hard substrate;
s30, preparing the flexible composite photoacoustic conversion layer, which specifically comprises the following substeps:
s301, coating a layer of PDMS prepolymer on a substrate to obtain the substrate coated with the PDMS prepolymer; preferably, the thickness of the PDMS prepolymer is 10-50 μm;
s302, inverting the substrate coated with the PDMS prepolymer above candle flame, and performing evaporation on CSNPs (candle ash particles) to obtain a mixed layer of the CSNPs and the PDMS;
s303, curing to obtain a flexible composite photoacoustic conversion layer connected with the substrate;
s40, bonding or gluing the flexible composite photoacoustic conversion layer obtained in the step S30 and the other end face of the structured base processed in the step S20;
and S50, peeling the substrate connected with the flexible composite photoacoustic conversion layer to obtain the photoacoustic transducer with adjustable sound pressure output amplitude.
10. The method of claim 9, wherein the step S10 includes the following substeps:
s101, preparing a mold of the structured base according to the preset size of the hollow structure and the position of the reserved air channel;
s102, mixing the PDMS precursor and a curing agent, standing and removing bubbles to obtain a liquid PDMS prepolymer;
s103, pouring the liquid PDMS prepolymer obtained in the step S102 into the mold obtained in the step S101 for curing; preferably, the curing temperature is 65-85 ℃, and the curing time is 1-3 hours;
and S104, demolding to prepare the structured base.
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