PZT/环氧树脂1-3-2型压电复合材料的制备及性能

采用压电陶瓷基板与1-3型压电复合材料串联连接,沿表面两相互垂直的方向切割PZT陶瓷,在切槽间浇注环氧树脂,制备出新型的1-3-2型压电复合材料.实验测试了材料的压电和介电性能,结果表明其d33常数达到400 pC/N,振动位移113.5pm,声速3500m/s,声阻抗17.6Mraly,厚度机电耦合系数0.62,带宽3.6kHz,相对介电常数817,介质损耗0.02.     

25 MHz ultrasonic transducers with lead- free piezoceramic, 1-3 PZT fiber-epoxy composite, and PVDF polymer active elements

This paper presents the fabrication and characterization of single-element ultrasonic transducers whose active elements are made of lead-free piezoceramic, 1-3 PZT/polymer composite and PVDF film. The lead free piezoelectric KNNLT- LS(K_0.44Na_0.52Li_0.04)(Nb_0.84Ta_0.10S_0.06b)O₃ powders and ceramics were prepared under controlled humidity and oxygen flow rate during sintering. Due to its moderate longitudinal piezoelectric charge coefficient (175 pC/N) and k_t of 0.50, the KNN-LT-LS composition may be a good candidate for highfrequency transducer applications. PZT fibers with 25 μm diameter formed by the viscose suspension spinning process were incorporated into epoxy to fabricate 1-3 composites with the averaged k_t = 0.64 and d₃₃ = 400 pC/N. Using KNN-LS-LT ceramic, 1-3 PZT fiber composite, and PVDF film, 3 different unfocused single element transducers with center frequencies of 25 MHz were fabricated. The acoustic characterization of the transducers demonstrated that wideband and low insertion loss could be obtained employing KNN-LS-LT ceramic. The ?6 dB bandwidth and insertion loss were 70% and ?21 dB, respectively. In comparison, the insertion loss of the ceramic transducer was much smaller than those made with 1-3 composite and PVDF film. This was attributed to closer electrical impedance match to 50 Ω and higher thickness coupling coefficient of the ceramic transducer.     

Modeling 1-3 composite piezoelectrics: thickness-mode oscillations

A simple physical model of 1-3 composite piezoelectrics is advanced for the material properties that are relevant to thickness-mode oscillations. This model is valid when the lateral spatial scale of the composite is sufficiently fine that the composite can be treated as an effective homogeneous medium. Expressions for the composite's material parameters in terms of the volume fraction of piezoelectric ceramic and the properties of the constituent piezoelectric ceramic and passive polymer are derived. A number of examples illustrate the implications of using piezocomposites in medical ultrasonic imaging transducers. While most material properties of the composite roughly interpolate between their values for pure polymer and pure ceramic, the composite's thickness-mode electromechanical coupling can exceed that of the component ceramic. This enhanced electromechanical coupling stems from partially freeing the lateral clamping of the ceramic in the composite structure. Their higher coupling and lower acoustic impedance recommend composites for medical ultrasonic imaging transducers. The model also reveals that the composite's material properties cannot be optimized simultaneously; tradeoffs must be made. Of most significance is the tradeoff between the desired lower acoustic impedance and the undesired smaller electromechanical coupling that occurs as the volume fraction of piezoceramic is reduced.     

Characteristics of relaxor-based piezoelectric single crystals forultrasonic transducers

For ultrasonic transducers, piezoelectric ceramics offer a range of dielectric constants (K~1000-5000), large piezoelectric coefficients (d_ij~200-700 pC/N), and high electromechanical coupling (k _t≃50%, k₃₃≃75%). For several decades, the material of choice has been polycrystalline ceramics based on the solid solution Pb(Zr_1-xB_2x)O₃ (PZT), compositionally engineered near the morphotropic phase boundary (MPB). The search for alternative MPB systems has led researchers to revisit relaxor-based materials with the general formula, Pb(B₁,B₂)O₃ (B₁:Zn²⁺ , Mg²⁺, Sc³⁺, Ni²⁺..., B₂ :Nb⁵⁺ Ta⁵⁺...). There are some claims of superior dielectric and piezoelectric performance compared to that of PZT materials. However, when the properties are examined relative to transition temperature (T₃), these differences are not significant. In the single crystal form, however, Relaxor-PT materials, represented by Pb(Zn_1/3Nb_2/3)O₃-PbTiO ₃ (PZN-PT), Pb(Mg_1/3Nb_2/3)O₃-PbTiO₃ (PMN-PT) have been found to exhibit longitudinal coupling coefficients (k₃₃)>90%, thickness coupling (k_t)>83%, dielectric constants ranging from 1000 to 5000 with low dielectric loss <1%, and exceptional piezoelectric coefficients d₃₃>2000 pC/N, the later promising for high energy density actuators. For single crystal piezoelectrics to become the next generation material of ultrasonic transducers, further investigation in crystal growth, device fabrication and testing are required     

Fabrication and properties of piezoelectric composites designed for process monitoring of cement hydration reaction

A series of receiving type piezoelectric composites were designed and fabricated by cutting and filling technique. The piezoelectric composites were also optimized from such aspects as matrix phase, functional phase and composite connectivity. The researches show that these piezoelectric composites have larger piezoelectric voltage factor, thickness electromechanical coupling coefficient and lower acoustic impedance than the pure piezoelectric ceramic. The early cement hydration reaction process monitoring result indicates that the ultrasonic wave receiving ability of the piezoelectric composite is obviously better than that of the pure piezoelectric ceramic. Therefore, these kinds of piezoelectric composites have potential application prospect in cement hydration reaction process monitoring.     

Novel integrated impedance matching layer

High performance clinical and industrial ultrasonic transducers require an impedance matching layer with controlled acoustic properties for efficient coupling of acoustic energy between the piezoelectric layer and the propagating medium. The principles of operation, design requirements and performance of a novel integrated impedance matching layer are discussed here. This integrated impedance matching layer is a composite of inert lead zirconate titanate (PZT) ceramic and conformal polymer filler material     

Optimized Stoneley wave device by proper choice of glass overcoat

The characteristics of a Stoneley wave propagated along an interface between a piezoelectric material and an isotropic material were investigated both theoretically and experimentally. First, the condition for the existence of Stoneley waves was shown for various piezoelectric materials. A rule of thumb for selecting the combination of the two materials was obtained. Then, LiTaO₃ was selected as the piezoelectric material and SiO₂ was selected the isotropic material. After the calculation of the Stoneley wave characteristics, actual devices were fabricated and measured. The experimental results were found to be in good agreement with the theory; zero slope temperature and high electromechanical coupling coefficient ( K²=1.5%) were obtained for Stoneley wave propagation between SiO₂/X-148° LiTaO₃. As a result, future surface-acoustic-wave (SAW) devices can be made without any package     

软模板法制备高频超声换能器用1-3复合压电材料

医用高频超声成像技术广泛应用于皮肤、眼睛及血管壁等人体组织的精细结构成像。1-3复合压电材料因具有较高的机电耦合系数而成为高频超声换能器的核心材料。传统的机械切割-填充、等离子蚀刻等1-3复合材料制备方法成本高、效率低, 难以实现工业化制备。本研究提出一种新的基于软模板的高频复合材料制备方法, 在获得高机电耦合系数的同时, 实现高性能1-3复合压电材料的低成本制备。研究采用微米孔径的软模板实现PZT粉的浆料填充, 通过热压烧结获得均匀竖立的PZT陶瓷微柱阵列, 进而制备出PZT/环氧1-3复合材料。对复合材料进行系统的机电性能测试, 并利用不同方法对复合材料的微结构及其均匀性进行表征。结果表明, 软模板法可使压电微柱具有完整的相结构和较高的成分均匀性, 能够实现较高的胚体压缩率, 提高陶瓷微柱的致密度, 同时形成了微柱阵列且微柱直径可控制在70 μm。软模板法有利于在提高复合材料超声频率(30~50 MHz)的同时获得64%的高机电耦合系数, 为医用高频超声成像以及超声生物显微镜等应用提供了一种高效的1-3复合压电材料工业化制备方法。     

1-3型水泥基压电复合材料的制备及性能

采用切割-浇注法, 以硫铝酸盐水泥为基体, 制备了1-3型水泥基压电复合材料。详细阐述了1-3型水泥基压电复合材料的制备过程; 研究了0.375Pb(Mg_1/3Nb_2/3)O₃-0.375PbTiO₃-0.25PbZrO₃压电陶瓷柱的宽厚比w/t对1-3型水泥基压电复合材料的压电性能、 介电性能和声阻抗的影响。结果表明: 压电陶瓷柱的宽厚比w/t对1-3型水泥基压电复合材料性能有很大影响, 随着w/t的增加, 其压电应变常数d₃₃、 机电耦合系数K_p与K_t、 机械品质因数Q_m、 介电常数ε_r和介电损耗tanδ均随着w/t的增加而减小, 而压电电压常数g₃₃值几乎不受w/t的影响。在压电陶瓷体积分数仅为22.72%的条件下, 调节压电陶瓷柱的宽厚比w/t至0.130, 可使复合材料的声阻抗与混凝土的声阻抗十分接近, 从而有效地解决了智能材料在土木工程中的声阻抗相容性问题。      

PVDF/PZNZT压电复合材料的结构与性能

为了扩展压电复合材料的应用领域,首先,通过固相合成法制备了0-3型聚偏氟乙烯(PVDF)/Pb(Zn_1/3Nb_2/3)_0.05Zr_0.47Ti_0.48O₃ (PZNZT)压电复合材料;然后,研究了PVDF含量对PVDF/PZNZT复合材料物相、显微结构及性能的影响。结果表明:PZNZT陶瓷粉料与PVDF粉料混合后,其平均粒度接近于纯PVDF粉料的。于220℃下烧结后, PVDF/PZNZT复合材料在XRD谱图中主要显现出PZNZT钙钛矿结构的衍射峰。当PVDF含量较低时, PZNZT陶瓷晶粒间的结合较松散;随着PVDF含量的增加,陶瓷晶粒几乎都被PVDF相包围。因显微结构不同,不同PVDF含量的PVDF/PZNZT复合材料在极化电场中呈现出不同的串、并联电路。极化后, 5wt% PVDF/PZNZT复合材料的电性能最佳,其介电常数为116、介电损耗tan δ为0.04、压电常数为48 pC/N且机电耦合系数为0.28。随PVDF含量的增加, PVDF/PZNZT复合材料的居里温度降低,维氏硬度有所增加,但仍小于纯PZNZT压电陶瓷的硬度。所得结论显示PVDF/PZNZT压电复合材料的性能可以满足水声、电声及超声换能器等的要求。      

Fabrication and modeling of high-frequency PZT composite thick film membrane resonators

High-frequency, thickness mode resonators were fabricated using a 7 microm piezoelectric transducer (PZT) thick film that was produced using a modified composite ceramic sol-gel process. Initial studies dealt with the integration of the PZT thick film onto the substrate. Zirconium oxide (ZrO2) was selected as a diffusion barrier layer and gave good results when used in conjunction with silicon oxide (SiO2) as an etch stop layer. Using these conditions, devices were produced and the acoustic properties measured and modeled. The resonators showed a resonant frequency of about 200 MHz, an effective electromechanical coupling coefficient of 0.34, and a Q factor of 22. Modeling was based on a Mason-type model that gave good agreement between the experimental data and the simulations. The latter showed, for the PZT thick film, an electromechanical coupling coefficient of 0.35, a stiffness of 8.65 x 10(10) N x m(-2) and an e33,f piezoelectric coefficient of 9 C x m(-2).     

Free-space measurement of complex permittivity and complexpermeability of magnetic materials at microwave frequencies

A free-space measurement system operating in the 8.2-40-GHz frequency range is used to measure the reflection and transmission coefficients, S₁₁ and S₂₁, of planar samples. The complex electric permittivity and the magnetic permeability are calculated from the measured values of S₁₁ and S₂₁. The measurement system consists of transmit and receive horn lens antennas, a network analyzer, mode transitions, and a computer. Diffraction effects at the edges of the sample are minimized by using spot-focusing lens antennas. Errors due to multiple reflections between antennas via the surface of the sample are corrected by using a free-space TRL (thru, reflect, line) calibration technique. For thin, flexible samples, the sample had to be sandwiched between two half-wavelength (at mid-band) quartz plates to eliminate sagging. Results are reported in the frequency range of 8.6-13.4 GHz for materials such as Teflon, sodium borosilicate glass, and microwave-absorbing materials     

High-frequency transducers based on integrated piezoelectric thick films for medical imaging

A screen-printed PZT thick film with a final thickness of about 40 microm was deposited on a porous PZT substrate to obtain an integrated structure for ultrasonic transducer applications. This process makes it possible to decrease the number of steps in the fabrication of high-frequency, single-element transducers. The porous PZT substrates allow high acoustic impedance and attenuation to be obtained, satisfying transducer backing requirements for medical imaging. The piezoelectric thick films deliver high electromechanical performance, comparable to that of standard bulk ceramics (thickness coupling factor over 45%). Based on these structures, high-frequency transducers with a center frequency of about 25 MHz were produced and characterized. As a result, good sensitivity and axial resolution were obtained in comparison with similar transducers integrating a lead titanate (PT) disk as active material. The two transducers were integrated into a high-frequency imaging system, and comparative skin images are shown.     

An optical self-calibrating technique for the dynamiccharacterization of PZT's

A system suitable for the measurement of linear sinusoidal vibration amplitudes is described. The signal beam of a Michelson interferometer is focused on the vibrating target while a suitable phase noise is applied to the reference arm of the interferometer. Signal processing is based on the null adjustment of the Bessel coefficients J₁ and J₂ derived from the signal provided by a single photodiode placed in the center fringe of the interference pattern. The system has been shown to be self-calibrating and intrinsically immune to mechanical perturbations induced in the interferometer. The technique proposed has been experimentally demonstrated by measuring the vibration amplitude of a PZT device in the amplitude range from 0.4 to 1.7 μm and in the frequency range from 8 to 22 kHz     

Design, fabrication, and evaluation of high frequency, single-element transducers incorporating different materials

The performance of high frequency, single-element transducers depends greatly on the mechanical and electrical properties of the piezoelectric materials used. This study compares the design and performance of transducers incorporating different materials. The materials investigated include 1-3 lead zirconate titanate (PZT) fiber composite, lead titanate (PbTiO₃) ceramic, poly(vinylidene fluoride) (PVDF) film, and lithium niobate (LiNbO₃) single crystal. All transducers were constructed with a 3-mm aperture size and an f-number between 2 and 3. Backing and matching materials were selected based on design goals and fabrication limitations. A simplified coaxial cable tuning method was employed to match the transducer impedance to 50 Ω for the PZT fiber composite and PbTiO₃ ceramic transducers. Transducers were tested for two-way loss and -6 dB bandwidth using the pulse/echo response from a flat quartz target. Two-way loss varied from 21 to 46 dB, and bandwidths measured were in the range from 47 to 118%. In vitro ultrasonic backscatter microscope (UBM) images of an excised human eye were obtained for each device and used to compare imaging performance. Both press-focusing and application of a lens proved to be useful beam focusing methods for high frequency. Under equal gain schemes, the LiNbO ₃ and PbTiO₃ transducers provided better image contrast than the other materials     

Evaluation of the material parameters of piezoelectric materials byvarious methods

The elastic, dielectric and piezoelectric constants of four piezoelectric materials, including polyvinylidene fluoride, vinylidene fluoride-trifluoroethylene copolymer, PZT/epoxy 1-3 composite, and lead metaniobate ceramic, have been evaluated from the impedance data using five different methods. A method described in ANSI/IEEE Std. 176-1987, though based on formulae derived for loss-less materials, is found to be applicable to materials with moderate loss. However, for high-loss materials such as polyvinylidene fluoride, the electromechanical coupling constant (κ_t) obtained by the method of Std. 176 is substantially higher than the actual value. Calculations based on a piezoelectric resonance analysis program (PRAP) combine the best features of two earlier methods. In addition to the impedance at the parallel resonance frequency, impedances at two other frequencies are required for calculation. The PRAP method gives quite accurate material parameters regardless of the magnitude of the loss, but the parameters (including κ_t) vary by as much as 15% depending on the choice of data. In the nonlinear regression method described in the present work, all the impedance data points around the resonance are least-squares fitted to the theoretical expression for the impedance. Besides the advantage of requiring no arbitrary choice of data, the nonlinear regression method can readily take account of the frequency dependence of the dielectric constant     

Disposable PVDF ultrasonic transducers for nondestructive testingapplications

Disposable ultrasonic contact transducers have been constructed with inexpensive PVDF films for nondestructive testing (NDT) applications. This paper reports the temperature-dependent ultrasonic performance of commercial polyvinylidene fluoride (PVDF) films and PVDF sensors. PVDF film was evaluated for its material properties of interest for ultrasonic transducer performance including the relative dielectric constant ε_r, dielectric loss tangent tan δ_e , electromechanical coupling constant k_t, mechanical quality factor Q_m, and acoustic impedance Z. Disposable PVDF transducers were then coupled to both low and high acoustic impedance test panels and their ultrasonic insertion loss/sensitivity and frequency bandwidth measured as a function of temperature in both the pulse-echo and pitch-catch modes. The results yielded center frequencies in the 3.5-16 MHz range, with -6-dB fractional bandwidths for some of the transducers exceeding 100%. The temperature dependence of the transducers' performance is reported for the -40 to 80°C range and shows an approximate linear decrease in center frequency and increase in fractional bandwidth with increasing temperature. These measured results are compared with predictions from computer simulations based on Mason's model. These tests showed that the same disposable transducers can be used for both ultrasonic and acoustic emission sensing NDT applications. This paper summarizes the quantitative ultrasonic and vibration sensing performance for all of the disposable PVDF film transducers which were tested     

An uncertainty analysis for the measurement of intrinsic propertiesof materials by the combined transmission-reflection method

The uncertainty of measurements of the complex permittivity ϵ_r and permeability μ_r as a function of the normalized sample length l/Λ' due to the measured errors in the scattering coefficients S₁₁ and S ₂₁ is discussed. A simple analysis of ϵ_r and μ_r and some measured data are given, which allows one to determine the extent of l/Λ' and maximum uncertainty of the combined total transmission-reflection method in application to radar absorber measurements     

Characterization of all the elastic,dielectric, and piezoelectric constants of uniaxially oriented poled PVDF films

Polyvinylidene fluoride (PVDF), a piezoelectric material, has many useful applications, for example, as sensors, transducers, and surface acoustic wave (SAW) devices. Models of performance of these devices would be useful engineering tools. However, the benefit of the model is only as accurate as the material properties used in the model. The purpose of this investigation is to measure the elastic, dielectric and piezoelectric properties over a frequency range, including the imaginary part (loss) of these properties. Measurements are difficult because poled material is available as thin films, and not all quantities can be measured in that form. All components of the elastic stiffness, dielectric tensor, and electromechanical coupling tensor are needed in the models. The material studied here is uniaxially oriented poled PVDF that has orthorhombic mm2 symmetry. Presented are the frequency dependence of all nine complex elastic constants, three complex dielectric constants, and five complex piezoelectric constants. The PVDF was produced at Raytheon Research Division, Lexington, MA. Measurements were made on thin films and on stacked, cubical samples. The elastic constants c₄₄^D and c₅₅^D, the dielectric constants e₁₁^T and e₂₂^T , as well as the piezoelectric constants g₁₅ and g₂₄ reported here have not been published before. The values were determined by ultrasonic measurements using an impedance analyzer and a least square data-fitting technique     

Measurement of frequency response functions in noisy environments

The geometric mean is proposed as an alternative averaging technique for frequency response function (FRF) measurements of a linear system. It is shown that it produces almost unbiased measurements even if the input and output measurements are both disturbed with (normal distributed) noise. The properties of the arithmetic and geometric mean of expression are compared to those of the H₁ and H₂ methods. It is shown that if the S/N ratio on the input and the output measurements is higher than 3 dB, then it is possible to generate measurements without systematic errors