Large-size air-coupled transducer based on phononic crystal structure

Abstract

The application provides a large-size air coupling transducer based on a phononic crystal structure and belongs to the field of phononic crystals. The large-size air coupling transducer based on the phononic crystal structure comprises a 1-3 type piezoelectric composite material layer, an acoustic impedance gradient matching layer, an upper electrode arranged between the 1-3 type piezoelectric composite material layer and the acoustic impedance gradient matching layer, and a lower electrode arranged at the bottom of the 1-3 type piezoelectric composite material layer; the 1-3 type piezoelectric composite material layer comprises a plurality of piezoelectric material columns and a polymer phase 1; and the acoustic impedance gradient matching layer comprises a plurality of filling cones and a polymer phase 2. The large-size air coupling transducer has the advantages that the transducer is combined with the 1-3 type piezoelectric composite material and the gradient matching layer in the transducer through the phononic crystal structure, the transducer has better suppression on transverse vibration during operation, the vibration in the thickness direction is more pure, and the transducer has better acoustic impedance matching performance with the air medium.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of phononic crystals, and particularly relates to a large-size air-coupled transducer based on a phononic crystal structure. BACKGROUND

[0002] A device that realizes the conversion of electric energy, mechanical energy or acoustic energy from one form of energy to another form of energy is called a transducer, also known as an active sensor. The transducer is the core device of an ultrasonic device, and its characteristic parameters determine the performance of the entire device. The transducer mainly has two types of magnetostrictive and piezoelectric crystal.

[0003] A low-frequency slotted liquid-wall coupled transducer for deep water is disclosed in the published patent application No. CN202010696284.8. This type of transducer belongs to the magnetostrictive type transducer. The invention discloses a low-frequency slotted liquid-wall coupled transducer for deep water, mainly comprising a radiation cover plate, which is located at the upper and lower ends of the transducer. The radiation cover plate is sequentially bonded with the intermediate mass block through the end cap A, piezoelectric ceramic vibrator and end cap B, and the intermediate mass block is fixed by a pre-stressed screw rod. The thin-walled cylindrical sleeve is the transducer shell, which is decoupled connected with the intermediate mass block through the connecting rod and decoupling material, and four hoisting rods are decoupled connected on the outer wall of the thin-walled cylindrical sleeve. The center of the thin-walled cylindrical sleeve is slotted.

[0004] The piezoelectric effect transducer is to convert electrical signals into mechanical vibration to realize energy conversion.

[0005] The air-coupled transducer is mainly used for non-destructive testing with air as the coupling medium. Its advantages mainly have the following two aspects: 1) non-contact detection, suitable for some detection of materials that cannot use liquid coupling agent materials, such as medicines, paper products, porous materials or materials whose performance is easily damaged; 2) because the sound speed in air is low, the wavelength of ultrasonic waves of the same frequency in air is shorter, so theoretically, the air-coupled transducer has higher resolution and accuracy in distance measurement, defect detection and other applications. However, due to the acoustic impedance of traditional piezoelectric material is about 70,000 times that of air, most of the ultrasonic waves emitted by the transducer are reflected on the air interface, and the transmission rate is extremely low. In addition, the vibration mode of the air-coupled transducer with a transverse size greater than 1 / 4 of the longitudinal wave length will exhibit coupling of transverse vibration and longitudinal vibration, not only greatly reducing the longitudinal radiation acoustic power of the transducer, but also causing uneven distribution of longitudinal displacement on the radiation surface due to uneven vibration energy transmission.

[0006] Phononic crystal is a new type of artificial periodic structure, and its most basic feature is the existence of elastic wave band gap. The elastic wave in the band gap frequency range is inhibited when propagating in the phononic crystal, while the elastic wave in other frequency range will propagate almost without loss. This band gap feature can be used to control the propagation of acoustic wave and elastic wave. From the structure, we can combine the phononic crystal theory with the components of air coupled transducer to improve the vibration characteristics, which will greatly promote the performance improvement and application expansion.

[0007] The transverse vibration of the air coupled transducer in the prior art cannot be inhibited when working, which reduces the longitudinal radiation sound power. The uneven vibration energy transmission leads to uneven longitudinal displacement distribution of the radiation surface, and the air medium acoustic impedance matching performance is poor. SUMMARY

[0008] Therefore, the present application provides a large-size air coupled transducer based on phononic crystal structure. Compared with the traditional air coupled transducer, the transverse vibration of the transducer is better inhibited when working by combining the phononic crystal structure with the 1-3 type piezoelectric composite material and the gradient matching layer in the transducer, the thickness direction vibration is more pure, and the air medium has better acoustic impedance matching performance.

[0009] The present application is a large-size air coupled transducer based on phononic crystal structure, which comprises a 1-3 type piezoelectric composite material layer based on phononic crystal structure, a sound impedance gradient matching layer based on phononic crystal structure arranged on the 1-3 type piezoelectric composite material layer, an upper electrode arranged between the 1-3 type piezoelectric composite material layer and the sound impedance gradient matching layer, and a lower electrode arranged at the bottom of the 1-3 type piezoelectric composite material layer; the 1-3 type piezoelectric composite material layer comprises a plurality of non-adjacent arranged piezoelectric material columns, a polymer phase 1 filling the gap between the piezoelectric material columns, and the piezoelectric material columns are periodically arranged; the sound impedance gradient matching layer comprises a plurality of filling conical which is fixed with the upper electrode and the bottom is concentric with the piezoelectric material column, and a polymer phase 2 filling between the adjacent filling conical.

[0010] Preferably, the material of the piezoelectric phase material column is PZT-5H, and the polarization direction is along the thickness direction.

[0011] Preferably, the arrangement mode of the piezoelectric material column is hexagonal lattice type.

[0012] Preferably, the materials of the polymer phase 1 and the polymer phase 2 are both epoxy resin.

[0013] Preferably, the polymer phase 1 is connected in three-dimensional direction.

[0014] As preferred, the piezoelectric material column, the number and arrangement of the filling conical are same.

[0015] As preferred, the bottom surface diameter of part of the filling conical is equal to the diameter of the piezoelectric material column.

[0016] As preferred, the bottom surface diameter and height of 7 filling conical located in the center of the acoustic impedance gradient matching layer is 1 / 2 of the rest of the filling conical, the bottom surface diameter of the rest of the filling conical is equal to the diameter of the piezoelectric material column, to form a phononic crystal defect state.

[0017] As preferred, the 1-3 type piezoelectric composite material layer is 3mm, the piezoelectric material column is 40mm in diameter, and the acoustic impedance gradient matching layer is 1.5mm in thickness.

[0018] Compared with the prior art, the present application has the following technical effects:

[0019] 1. The present application combines the phononic crystal structure with each component of the large-size air-coupled transducer, sets the working frequency of the 1-3 type piezoelectric composite material layer and the acoustic impedance gradient matching layer in the band gap of the phononic crystal, better suppresses the transverse vibration, reduces the energy loss caused by the transverse coupling vibration, makes the thickness working mode more pure, has higher vibration efficiency, and has a larger electromechanical coupling coefficient;

[0020] 2. The present application combines the phononic crystal lattice theory, and the arrangement of the piezoelectric material column and the filling conical of the acoustic impedance gradient matching layer is a hexagonal lattice, which not only widens the band gap of the phononic crystal, but also effectively improves the working bandwidth of the large-size air-coupled transducer;

[0021] 3. The present application combines the flexible polymer epoxy resin with the piezoelectric material and the matching layer, which can effectively reduce the acoustic impedance of the large-size air-coupled transducer, and better realize impedance matching with the air medium.

[0022] 4. The present application combines the phononic crystal defect state with the acoustic impedance gradient matching layer, constructs defects in the perfect periodic phononic crystal structure, makes the gradient matching layer located at the working frequency produce Anderson localization at the defect position, further improves the vibration emission efficiency of the large-size transducer, and makes the displacement of the radiation surface more uniform. BRIEF DESCRIPTION OF DRAWINGS

[0023] Figure 1 A perspective structural schematic view of a large-size air-coupled transducer based on a phononic crystal structure is provided in the specific embodiment of the present application.

[0024] Figure 2A front view of a large-size air coupled transducer based on phononic crystal structure and a hexagonal lattice unit cell provided in the specific embodiment of the present application;

[0025] Figure 3 A cross-sectional view of a large-size air coupled transducer based on phononic crystal structure provided in the specific embodiment of the present application;

[0026] Figure 4 A unit cell band diagram of a 1-3 type piezoelectric composite layer of a large-size air coupled transducer based on phononic crystal structure provided in the specific embodiment of the present application;

[0027] Figure 5 A unit cell band diagram of an acoustic impedance gradient matching layer of a large-size air coupled transducer based on phononic crystal structure provided in the specific embodiment of the present application;

[0028] Figure 6 A conductance curve of a large-size air coupled transducer based on phononic crystal structure provided in the specific embodiment of the present application;

[0029] Figure 7 A transmit voltage response level curve of a large-size air coupled transducer based on phononic crystal structure provided in the specific embodiment of the present application;

[0030] Figure 8 A transmit voltage response level curve of a conventional large-size air coupled transducer.

[0031] Wherein; 1-3 type piezoelectric composite layer 1, piezoelectric material column 11, polymer phase 1a, acoustic impedance gradient matching layer 2, filled cone 21, polymer phase 2b, upper electrode 3, lower electrode 4. DETAILED DESCRIPTION

[0032] The present application will be described in detail below with reference to specific embodiments.

[0033] Please refer to Figure 1The application discloses a large-size air coupling transducer based on a phononic crystal structure, which comprises a 1-3 type piezoelectric composite layer 1 based on a phononic crystal structure, a sound impedance gradient matching layer 2 based on a phononic crystal structure arranged on the 1-3 type piezoelectric composite layer 1, an upper electrode 3 arranged between the 1-3 type piezoelectric composite layer 1 and the sound impedance gradient matching layer 2, and a lower electrode 4 arranged at the bottom of the 1-3 type piezoelectric composite layer 1; the 1-3 type piezoelectric composite layer 1 comprises a plurality of piezoelectric material columns 11 arranged in a non-adjacent mode, and a polymer phase 1a filling the gaps between the piezoelectric material columns 11; the piezoelectric material columns 11 are arranged in a periodic mode; the sound impedance gradient matching layer 2 comprises a plurality of filling cones 21 fixed to the upper electrode 3 and concentric with the piezoelectric material columns 11 at the bottom, and a polymer phase 2b filling between the filling cones 21.

[0034] The piezoelectric phase material column is made of PZT-5H and is polarized along the thickness direction. The filling cone 21 is made of inorganic non-metallic material with a density greater than twice that of epoxy resin and a Young's modulus greater than 50 times that of epoxy resin.

[0035] The piezoelectric material column 11 is arranged in a hexagonal lattice mode, that is, six piezoelectric material columns 11 at the corners of a regular hexagon and a piezoelectric material column 11 at the center of the regular hexagon form a hexagonal lattice unit cell, and each hexagonal lattice unit cell is arranged in a periodic mode.

[0036] The polymer phase 1a and the polymer phase 2b are both made of epoxy resin.

[0037] The piezoelectric phase is connected in one-dimensional direction, and the polymer phase 1a is connected in three-dimensional direction.

[0038] The number and arrangement mode of the piezoelectric material column 11 and the filling cone 21 are the same. The bottom surface diameter of part of the filling cone 21 is equal to the diameter of the piezoelectric material column 11, for example, the bottom surface diameter and height of the seven filling cones 21 located at the center of the sound impedance gradient matching layer 2 (it can be understood that the seven filling cones 21 are arranged in a hexagonal mode at the center position, and the total number of the filling cones 21 is seven) are 1 / 2 of those of the remaining filling cones 21, and the bottom surface diameter of the remaining filling cones 21 is equal to the diameter of the piezoelectric material column 11, so as to form a phononic crystal defect state.

[0039] Figure 2 In the embodiment, the structure sizes are as follows: lattice constant a2=2 mm, r2=0.8 mm, the 1-3 type piezoelectric composite layer 1 is 3 mm, the piezoelectric material column 11 is 40 mm in diameter, the sound impedance gradient matching layer 2 is 1.5 mm in thickness, and the piezoelectric material column 11 and the filling cone 21 are arranged in a hexagonal lattice mode.

[0040] Figure 3 As shown, the diameters and heights of the seven filling conical 21 located in the center of the gradient matching layer are 1 / 2 of the rest of the filling conical 21, to form a phononic crystal defect state, which will produce Anderson localization at the defect when the transducer is at the working frequency, so as to localize the energy of the transverse vibration at the defect, further improve the longitudinal emission power of the transducer, and improve the displacement distribution of the radiation surface, so as to make it more uniform.

[0041] Figure 4 The band diagram of the unit cell of the 1-3 type piezoelectric composite layer 1 of the large-size air-coupled transducer based on the phononic crystal structure can be obtained that there is a band gap between 280 kHz and 520 kHz, and the band gap width is 240 kHz.

[0042] Figure 5 The band diagram of the unit cell of the acoustic impedance gradient matching layer 2 of the large-size air-coupled transducer based on the phononic crystal structure can be obtained that there is a band gap between 430 kHz and 600 kHz, and the band gap width is 170 kHz.

[0043] As shown in Figure 6 The maximum value of the conductance map of the air-coupled transducer corresponds to the thickness resonance frequency of the transducer, which is about 490 kHz. It can be found that the resonance frequency of the embodiment is located in the phononic crystal band gap, which means that the transverse coupling vibration produced by the air-coupled transducer working in the thickness mode will be well suppressed due to the band gap characteristics of the phononic crystal, and will not be coupled with the thickness mode to cause the decline of the vibration efficiency.

[0044] As shown in Figure 7 It can be obtained from the transmission voltage response level curve (TVR) of the large-size air-coupled transducer based on the phononic crystal structure that the -3dB bandwidth thereof is about 65 kHz.

[0045] As shown in Figure 8 It can be obtained from the transmission voltage response level curve (TVR) of the traditional large-size air-coupled transducer that the -3dB bandwidth thereof is about 32 kHz. Figure 7 Figure 8 It can be found that the -3dB bandwidth of the large-size air-coupled transducer based on the phononic crystal structure is improved by 33 kHz compared with the traditional structure air-coupled transducer.

[0046] ​The working frequency of the 1-3 type piezoelectric composite layer 1 and the acoustic impedance gradient matching layer 2 is arranged in the band gap of the phononic crystal, so that the transverse vibration is better inhibited, the energy loss caused by the transverse coupling vibration is reduced, the thickness working mode is more pure, the vibration efficiency is higher, and the electromechanical coupling coefficient is larger; the arrangement mode of the piezoelectric material column 11 and the filled cone 21 is a hexagonal lattice, which not only widens the band gap of the phononic crystal, but also effectively improves the working bandwidth of the large-size air coupling transducer; the epoxy resin is combined with the piezoelectric material and the matching layer, and can better realize impedance matching with the air medium; by constructing defects in the perfect periodic phononic crystal structure, the displacement of the radiation surface is more uniform.

[0047] The present application makes the working efficiency of the large-size air coupling transducer in the thickness mode higher, widens the bandwidth, improves the acoustic impedance matching performance of the transducer and the air medium, and is expected to be widely applied in the fields of nondestructive testing, medical imaging and the like.

[0048] Those skilled in the art can understand that, unless otherwise defined, all terms (including technical terms and scientific terms) used herein have the same meaning as commonly understood by those skilled in the art to which the present application belongs. It should also be understood that terms such as those defined in a general dictionary should be understood to have meanings consistent with those in the context of the prior art, and should not be interpreted in an idealized or overly formal sense unless otherwise defined.

[0049] The above specific embodiments further illustrate the purposes, technical solutions and beneficial effects of the present application, and it should be understood that the above description is only a specific embodiment of the present application and is not used to limit the present application, and any modification, equivalent replacement, improvement, etc. within the spirit and principles of the present application should be included in the protection scope of the present application.

Claims

1. A large-size air-coupled transducer based on a phononic crystal structure, characterized in that, The device includes a type 1-3 piezoelectric composite material layer based on a phononic crystal structure, an acoustic impedance gradient matching layer based on a phononic crystal structure disposed on the type 1-3 piezoelectric composite material layer, an upper electrode disposed between the type 1-3 piezoelectric composite material layer and the acoustic impedance gradient matching layer, and a lower electrode disposed at the bottom of the type 1-3 piezoelectric composite material layer; the type 1-3 piezoelectric composite material layer includes a plurality of non-adjacent piezoelectric material pillars and a polymer phase 1 filling the gaps between adjacent piezoelectric material pillars, wherein the piezoelectric material pillars are periodically arranged; the acoustic impedance gradient matching layer includes a plurality of filling cones fixed to the upper electrode and whose bottoms are concentric with the piezoelectric material pillars, and a polymer phase 2 filling the gaps between adjacent filling cones; The piezoelectric material pillars are arranged in a hexagonal lattice pattern; The bottom diameter and height of the seven filling cones located at the center of the acoustic impedance gradient matching layer are half that of the remaining filling cones. The bottom diameter of the remaining filling cones is equal to the diameter of the piezoelectric material column, so as to form a phononic crystal defect state.

2. A large-size air-coupled transducer based on a phononic crystal structure according to claim 1, characterized in that, The piezoelectric material pillar is made of PZT-5H and is polarized along the thickness direction.

3. A large-size air-coupled transducer based on a phonon crystal structure according to claim 2, characterized in that, Both polymer phase 1 and polymer phase 2 are made of epoxy resin.

4. A large-size air-coupled transducer based on a phononic crystal structure according to claim 1, characterized in that, The polymer phase 1 is interconnected in three dimensions.

5. A large-size air-coupled transducer based on a phononic crystal structure according to claim 1, characterized in that, The number and arrangement of the piezoelectric material pillars and filling cones are all the same.

6. A large-size air-coupled transducer based on a phononic crystal structure according to claim 1, characterized in that, The piezoelectric composite material layer of type 1-3 is 3mm thick, the diameter of the piezoelectric material column is 40mm, and the thickness of the acoustic impedance gradient matching layer is 1.5mm.

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