Piezoelectric composite material

Abstract

The invention discloses a piezoelectric composite material, and belongs to the technical field of functional materials. The piezoelectric composite material is composed of a piezoelectric phase material of a lead-free piezoelectric crystal based on (1-x) Na0. 5Bi0. 5TiO3-xBaTiO3 and a non-piezoelectric phase material based on epoxy resin, the NBBT single crystal is a quadrangular prism which is uniformly cut into latticed crystal columns, and the epoxy resin is filled in cutting grooves of lattices of the NBBT single crystal; the height of the piezoelectric composite material is 85-95 [mu] m, the side length of each crystal column is 45-55 [mu] m, the width of the cutting groove is 18-22 [mu] m, and the working frequency of the cutting groove is 10-20 MHz. The piezoelectric composite material has the electromechanical coupling coefficient higher than 80%, reaches the performance level of a piezoelectric composite material based on lead-containing piezoelectric crystals such as PMN-PT and the like, can replace the currently used lead-containing piezoelectric composite material to be widely used, and is safe and environmentally friendly.

Description

Technical Field

[0001] The invention belongs to the technical field of functional materials, and in particular relates to a piezoelectric composite material. Background Art

[0002] Ultrasound diagnosis has the advantages of safety, wide adaptability, intuitiveness, repeatability, strong soft tissue identification, portability, flexibility and low price. It has become an important part of modern medical imaging diagnosis and is widely used in cardiology, obstetrics and gynecology, abdominal scanning, brain midline detection, intracranial blood flow detection, eye scanning, etc. The global market for medical ultrasound equipment exceeds 10 billion US dollars. my country also attaches great importance to the development of medical devices, and the ultrasound medical equipment market has gained unprecedented development opportunities. High-frequency medical ultrasound with higher resolution is a new generation of medical ultrasound technology. High-frequency ultrasound technologies such as intravascular ultrasound, ophthalmic ultrasound, and small animal imaging have developed into high-frequency medical ultrasound technologies with great medical application value. For example, intravascular ultrasound imaging technology plays an important role in the diagnosis and treatment of peripheral vascular disease and coronary heart disease.

[0003] Ultrasonic transducers are the core components of ultrasonic diagnosis and treatment systems, and mainly use piezoelectric materials as functional elements. High-frequency ultrasonic imaging such as intravascular and ophthalmology mostly uses 10-80MHz high-frequency ultrasonic transducers in order to obtain a resolution of less than 100 microns. Medical ultrasonic transducers that require higher operating frequencies, large bandwidth, and high sensitivity are also required. The core and difficulty of the technology lies in the preparation of piezoelectric materials with high electromechanical coupling coefficients (which determine the bandwidth and resolution of ultrasonic transducers) and high operating frequencies with a thickness of micrometers (usually between 30 and 100 microns). At present, what has attracted the attention of academic and industrial fields is type 1-3 piezoelectric composite materials, because the lower acoustic impedance of type 1-3 composite piezoelectric materials of piezoelectric ceramics or single crystals and polymers such as epoxy resins is easy to match with human tissues. At the same time, high-frequency ultrasonic transducers can increase the resonance and anti-resonance frequencies by reducing the thickness of the components. Thinner piezoelectric composite materials can still have high electromechanical coupling coefficients and achieve large bandwidth of ultrasonic transducers, which is of great significance for improving the axial resolution of ultrasonic transducers and the resolution of ultrasonic imaging.

[0004] Based on lead magnesium niobate titanate Pb(Mg 1 / 3 Nb 2 / 3 )O3-PbTiO3 (PMN-PT or PMNT) as the representative of lead-containing relaxor ferroelectric single crystal piezoelectric composite materials, such as PMNT single crystal / epoxy resin 1-3 type piezoelectric composite materials, the coupling coefficient k tHigher than 71%, even reaching 80%. Compared with the high-frequency ultrasonic transducer made of lead zirconate titanate Pb(ZrTi)O3(PZT) piezoelectric ceramics, the high-frequency ultrasonic transducer made of it has a 30% higher sensitivity and a 100% higher bandwidth, which can greatly improve the image resolution of intravascular ultrasonic imaging. It has become a frontier hotspot and key technology of international medical ultrasonic transducers. Medical ultrasonic equipment companies at home and abroad are all developing related composite materials and transducers, and the technical competition is fierce.

[0005] However, both the widely used lead zirconate titanate (PZT) piezoelectric ceramics and the new high-performance lead magnesium niobate titanate (PMNT) relaxor ferroelectric single crystals are piezoelectric materials with a lead oxide content of more than 60wt%. Lead-containing materials will cause lead pollution to humans and the ecological environment during preparation, use, recycling and disposal. With the continuous strengthening of global requirements for improving the ecological environment and stricter control measures on lead pollution, lead-containing piezoelectric materials, devices and electronic devices may gradually be restricted in production and use worldwide. Due to direct use on the human body, such as intravascular ultrasound, which places tiny high-frequency ultrasonic transducers into blood vessels, the urgency of the lead-free requirements of piezoelectric materials for medical ultrasonic transducers is undoubtedly greater than other applications such as the industrial field. Therefore, the use of environmentally friendly lead-free piezoelectric materials instead of lead-containing piezoelectric materials has become a common focus of academic and industrial circles in the field of medical ultrasound.

[0006] At the same time, the preparation of type 1-3 piezoelectric composites is a relatively complicated process. A major difficulty lies in the structural design of high-frequency piezoelectric composites. Due to the crosstalk between interference modes such as lateral vibration modes and thickness / longitudinal length stretching vibration modes, the structural design of the composite material is crucial. Otherwise, the vibration mode of the composite material is impure, which will greatly affect the performance of the ultrasonic transducer and its use effect.

[0007] Patent CN202111461560 provides a lead-free piezoelectric composite material based on sodium bismuth titanate-barium titanate piezoelectric crystals, whose electromechanical coupling coefficient reaches 70%, but there is still a large gap compared with the high electromechanical coupling coefficient (reaching 80%) based on lead-containing piezoelectric composite materials such as PMN-PT.

[0008] So far, the art has not yet developed a piezoelectric composite material and its ultrasonic transducer that can avoid and overcome the pollution disadvantages of lead-containing materials and at the same time have the same superior performance as lead-containing single crystal piezoelectric composite materials with high operating frequency and high electromechanical coupling coefficient. Summary of the invention

[0009] In view of the defects of the prior art, the present invention proposes a novel high-frequency, high-performance, lead-free piezoelectric single crystal composite material and its composite structure, thereby solving the problems existing in the prior art.

[0010] In order to achieve the above object, the present invention provides a piezoelectric composite material, comprising a piezoelectric phase material and a non-piezoelectric phase material, wherein the piezoelectric phase material is based on (1-x)Na 0.5 Bi 0.5 The NBBT single crystal of the lead-free piezoelectric crystal of TiO3-xBaTiO3; the non-piezoelectric phase material is epoxy resin; the NBBT single crystal of the lead-free piezoelectric crystal is a quadrangular prism evenly cut into grid-like crystal columns, and the epoxy resin is filled in the cutting grooves of its grid; the height of the piezoelectric composite material is 85 to 95 μm, the side length of each crystal column is 45 to 55 μm, and the width of the cutting groove is 18 to 22 μm; its operating frequency is 10 to 20 MHz.

[0011] Furthermore, in the composition of the NBBT crystal, x is a molar fraction with a value range of 0.04≤x≤0.06; and its crystallographic direction is

[001] .

[0012] Beneficial effects of the present invention:

[0013] (1) The NBBT piezoelectric crystal of the present invention is a lead-free piezoelectric material and is friendly to the human body and the environment.

[0014] (2) The NBBT / epoxy 1-3 piezoelectric composite material of the present invention has an electromechanical coupling coefficient higher than 80% at an operating frequency of 10 to 20 MHz, which exceeds the lead-free piezoelectric crystal composite material previously applied for in a patent (an electromechanical coupling coefficient of up to 70%) and reaches the performance level of piezoelectric composite materials based on lead-containing piezoelectric crystals such as PMN-PT (an electromechanical coupling coefficient of about 80%). It can replace the currently used lead-containing piezoelectric composite materials and be widely used.

[0015] (3) The composite structure of the present invention ensures that the NBBT / epoxy 1-3 type piezoelectric composite material has a relatively pure thickness expansion mode at an operating frequency higher than 10 to 20 MHz without interference from mixed modes.

[0016] (4) The piezoelectric composite material of the present invention can be prepared by a conventional cutting-filling method, which is easy to prepare and has low cost.

[0017] (5) The piezoelectric composite material of the present invention has important application value in the field of high-frequency medical ultrasound, and also has broad application value in other high-frequency ultrasound fields such as semiconductor high-frequency ultrasound nondestructive testing. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 The figure is a schematic diagram of the structure and dimensions of the NBBT / epoxy 1-3 piezoelectric composite material according to an embodiment of the present invention.

[0019] Figure 2Optical microscope image of the piezoelectric composite material according to the embodiment of the present invention.

[0020] Figure 3 Impedance spectrum and phase diagram of the piezoelectric composite material according to an embodiment of the present invention. DETAILED DESCRIPTION

[0021] The present invention will be further described below in conjunction with the accompanying drawings and specific embodiments. However, it should be understood that these embodiments are only used to illustrate the present invention and do not constitute a limitation of the scope of the present invention. The test methods in the following examples that do not specify specific conditions are usually carried out under conventional conditions or under conditions recommended by the manufacturer.

[0022] The embodiment of the present invention provides a piezoelectric composite material, comprising: (1-x)Na 0.5 Bi 0.5 The NBBT single crystal of the lead-free piezoelectric crystal composed of TiO3-xBaTiO3 is used as the piezoelectric phase material of the composite material, and epoxy resin is used as the non-piezoelectric phase material of the composite material. The NBBT single crystal of the lead-free piezoelectric crystal is a quadrangular prism uniformly cut into a grid-like crystal column, and epoxy resin is filled in the cutting groove of its grid. The height of the piezoelectric composite material is 85 to 95μm, the side length of each crystal column is 45 to 55μm, and the width of the cutting groove is 18 to 22μm; its operating frequency is 10 to 20MHz. The crystallographic direction of the NBBT chip is

[001] , and x in its composition is the molar fraction, and the value range is 0.04≤x≤0.06.

[0023] The 1-3 type single crystal piezoelectric composite material is prepared by a cutting-filling method commonly used in the art.

[0024] The upper and lower electrodes are prepared for the piezoelectric composite material, and the piezoelectric chip is polarized. The impedance spectrum of the composite material is tested by the resonance-antiresonance method. According to the following formula (1), substitute it into formula (1) and calculate the resonance frequency f r , anti-resonance frequency f a The electromechanical coupling coefficient k is calculated t .

[0025]

[0026] The material impedance test involved in the embodiment is to measure the sample capacitance using an Agilent 4294A impedance analyzer (Agilent Technologies, Inc.), which is approximately calculated based on a flat plate capacitor; the electrode is obtained by magnetron sputtering deposition; the single crystal is polarized along the

[001] direction; and the single crystal is cut using a precision dicing machine.

[0027] Example 1

[0028] The 1-3 type lead-free single crystal piezoelectric composite material is prepared by the common cutting-filling method in the art. 0.5 Bi 0.5 The NBBT lead-free piezoelectric crystal composed of TiO3-0.05BaTiO3 has a crystallographic direction of

[001] . It is prepared according to the following structure: the side length of the NBBT crystal quadrangular prism is 50μm, the width of the cutting groove is 20μm, and the height of the composite material is 90μm. The resonance-antiresonance method is used to test the electromechanical coupling performance. The resonant frequency f of the NBBT / epoxy1-3 piezoelectric composite material is r and the anti-resonance frequency f a are 11.6MHz and 18.5MHz respectively. The electromechanical coupling coefficient k is obtained by calculation. t It is 80.8%.

[0029] The typical performance of this material is compared with other existing piezoelectric composite materials as shown in Table 1, where Patent 1 is the composite material given in Patent CN202111461560. It can be seen that the piezoelectric composite material given in the embodiment of the present invention has a higher electromechanical coupling coefficient.

[0030] Table 1

[0031]

[0032]

[0033] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the principles and spirit of the present invention should be included in the protection scope of the present invention.

Claims

1. A piezoelectric composite material, characterized in that: It includes piezoelectric phase material and non-piezoelectric phase material, wherein the piezoelectric phase material is based on (1-x)Na 0.5 Bi 0.5 The lead-free piezoelectric crystal NBBT single crystal of TiO3-xBaTiO3 is a tetrahedral prism uniformly cut into grid-like crystal columns, and the epoxy resin is filled in the cutting grooves of the grid; the height of the piezoelectric composite material is 85 to 95 μm, the side length of each crystal column is 45 to 55 μm, and the width of the cutting groove is 18 to 22 μm; Its operating frequency is 10~20MHz.

2. The piezoelectric composite material according to claim 1, characterized in that: In the composition of the NBBT crystal, x is a molar fraction, and its value range is 0.04≤x≤0.06; and its crystallographic direction is [001].

Images