Double-layer PVDF transducer and V(z) measurement system for measuring leaky Lamb waves in a piezoelectric plate

This paper presents a new experimental measurement method for leaky Lamb waves propagating in a piezoelectric plate immersed in a conductive fluid. The measurement system is a low-frequency version of lens-less acoustic microscopy which has been developed based on a line-focus double-layer PVDF transducer. The transducer and its defocusing measurement system can perform V(z) measurements on a sample plate immersed in a fluid, and therefore can obtain the leaky Lamb wave velocities with high accuracy. An X-cut LiNbO₃ plate is investigated with this experimental measurement system to find out its fluid-loading effects, especially the conductive loading effects by water of various conductivities. Angular dependence of this conductive loading effect along different propagating directions on the X-cut LiNbO₃ plate is measured. It is found out the conductive loading effects are strongly dependent on the piezoelectric coupling factor. Theoretical calculations based on partial wave theory have also been carried out and compared with experimental data. Good agreements have been observed.     

Interaction of light with acoustic waves excited by an inphase multielement transducer in the 1.0–2.5 GHz range

Interaction between a weakly divergent optical beam and an acoustic wave generated in the range 1.0–2.5 GHz by an inphase multielement electroacoustic piezoelectric transducer is analyzed. A piezoelectric (Y + 36°)-cut LiNbO₃ plate is fixed on the surface of an X-cut LiNbO₃ acoustic duct with the help of metallic sublayers (Cr, Cu, In, Cu, or Cr). The inphase structure of the transducer is formed by the upper electrodes inter-connected by short conductors. The signal is applied through a coaxial Chebyshev transformer. The efficiencies of electroacoustic conversion and acoustooptic interaction are calculated as functions of frequency. The experimental setup, method, and results are described.     

High-frequency PIN–PMN–PT single crystal ultrasonic transducer for imaging applications

A high-frequency (～60 MHz) ultrasonic transducer with a [001]-oriented 0.27Pb(In_1/2Nb_1/2)O₃–0.45Pb(Mg_1/3Nb_2/3)O₃–0.28PbTiO₃ (PIN–PMN–PT) piezoelectric single crystal as an active element has been fabricated and characterized. The poled PIN–PMN–PT single crystal has thickness mode electromechanical coefficient k _t of 0.56 and piezoelectric constant d ₃₃ of 1550 pC/N. The ?6 dB bandwidth of the transducer is 73 % and the insertion loss at its centre frequency is ?20 dB. With the study as a function of temperature, the PIN–PMN–PT transducer shows better thermal stability than the binary single crystal transducer. Furthermore, the transducer was evaluated using a 30-μm aluminum wire phantom image, in which the ?6 dB axial and lateral resolutions are found to be 26 μm and 127 μm, respectively. Ultrasonic images of fish eyes were obtained with the 60-MHz transducer. It is shown that the high-sensitivity transducer can produce the images with high signal-to-noise ratio and good contrast.     

Lead-free KNLNT piezoelectric ceramics for high-frequency ultrasonic transducer application

This paper presents the latest development of a lead-free piezoelectric ceramic and its application to transducers suitable for high-frequency ultrasonic imaging. A lead-free piezoelectric ceramic with formula of (K_0.5Na_0.5)_0.97Li_0.03(Nb_0.9 Ta_0.1)O₃ (abbreviated as KNLNT-0.03/0.10) was fabricated and characterized. The material was found to have a clamped dielectric constant ε₃₃^S/ε₀ = 890, piezoelectric coefficient d₃₃ = 245 pC/N, electromechanical coupling factor k_t = 0.42 and Curie temperature T_c > 300 °C. High-frequency (40 MHz) ultrasound transducers were successfully fabricated with the lead-free material. A representative lead-free transducer had a bandwidth of 45%, two-way insertion loss of -18 dB. This performance is comparable to reported performances of popular lead-based transducers. The comparison results suggest that the lead-free piezoelectric material may serve as an alternative to lead-based piezoelectric materials for high-frequency ultrasonic transducer applications.     

Properties of non-stoichiometric 0.935(K0.5+xNa0.5+x)NbO3-0.065LiSbO3 lead-free piezoelectric ceramics

0.935(K_0.5+xNa_0.5+x)NbO₃-0.065LiSbO₃ lead-free piezoelectric ceramics were prepared by normal sintering, and their piezoelectric and dielectric properties were investigated by varying the compensating amount x of alkaline elements (Na and K) addition. It was found that the crystal structure changed from tetragonal to orthorhombic with increasing x from −0.010 to 0.010. An MPB was tailored by optimizing the alkaline elements contents. Enhanced electrical and electromechanical responses of d₃₃=253 pC/N, k_p=0.47, k_t=0.45 and tanδ=0.027 were obtained in the ceramics with x=0.005. These excellent piezoelectric and electromechanical properties indicate that this system may be an attractive lead-free material for a wide range of electro-mechanical transducer applications.     

Transfer constant of a multilayer acoustic transducer at the direct and inverse transformation

The algorithms for calculating the direct and inverse transfer constants of an acoustic transducer with an arbitrary number of intermediate layers between the piezoelectric layer, the acoustic duct, and the rear acoustic load are described. The results of a numerical analysis are presented and discussed. As an illustration, a 100-MHz transducer formed by a (Y+36°)-cut LiNbO₃ plate fixed on a fused-quartz acoustic duct with the help of five metal layers is considered. The other side of the plate carries two metal layers and a rear load. The phase-frequency characteristics and the transformation loss as a function of frequency are analyzed for the cases of direct and inverse transformation under the assumption that the signal is supplied and retrieved by a two-wire line.     

High-frequency ultrasonic transducer based on lead-free BSZT piezoceramics

This paper describes the fabrication and evaluation of a high-frequency (40 MHz) transducer based on lead-free piezoceramics for ultrasonic imaging. The transducer with an aperture size of 0.9 mm has been fabricated using barium strontium zirconate titanate ((Ba_0.95Sr_0.05)(Zr_0.05Ti_0.95)O₃, abbreviated as BSZT) ceramics. The lead-free BSZT has a piezoelectric d₃₃ coefficient of 300 pC/N and an electromechanical coupling factor k_t of 0.45. High-frequency ultrasound transducers were fabricated and a bandwidth of 76.4% has been achieved with an insertion loss of −26 dB. Applications in high resolution biological and medical imaging could be possible with this lead-free material.     

基于飞秒光频梳的压电陶瓷闭环位移控制系统

利用飞秒光频梳、外腔可调谐半导体激光器和法布里-珀罗干涉仪建立了一套压电陶瓷亚纳米级闭环位移控制系统. 将可调谐半导体激光器锁定至光频梳, 通过精确调谐光频梳的重复频率, 实现了半导体激光器在其工作频率范围内的精密调谐. 利用Pound-Drever-Hall锁定技术将带有压电陶瓷的法布里-珀罗腔锁定至半导体激光器, 进而通过频率发生系统控制压电陶瓷产生亚纳米级分辨率的位移. 实验研究发现锁定至光频梳后可调谐半导体激光器1 s的Allan标准偏差为1.68×10^-12, 将其在30.9496 GHz范围内进行连续闭环调谐, 可获得压电陶瓷的位移行程约为4.8 μm; 以3.75 Hz的步长扫描光频梳的重复频率, 实现了压电陶瓷的450 pm闭环位移分辨率并测定了压电陶瓷的磁滞特性曲线. 该系统不存在非线性测量误差, 且激光频率及压电陶瓷位移均溯源至铷钟频率源. 关键词： 光频梳 压电陶瓷 法布里-珀罗腔 可调谐半导体激光器     

Acousto-optic light deflection in an Al2O3 optical waveguide structure

The total deflection of an optical guided wave by a surface acoustic wave (SAW) in a silicon-based SiO₂/AL₂O₃/SiO₂ optical waveguide structure is reported. The SAW is generated by an interdigital transducer with piezoelectric ZnO deposited on top of the optical waveguide structure.     

Acousto-optic deflector based on a paratellurite crystal using broadband acoustic adhesive contact

A broadband acoustic matching of a piezoelectric transducer made of a lithium niobate crystal with an acousto-optic TeO₂ crystal has been studied. The transducer is acoustically attached to the crystal by the method of adhesive contact. The experimental method of creating a piezoelectric transducer with an acoustic matching layer from a tin film is developed. The conditions of the optimal technological regime when applying the matching layer are determined. The results of the research are used in creating a broadband high-performance deflector with a central ultrasound frequency of 37 MHz, with the frequency band scanning more than 30 MHz, and a diffraction efficiency of about 90% at a wavelength of 1.06 μm.     

Preparation and application of the 3C–SiC substrate to piezoelectric micro cantilever transducers

This study examines the fabrication process and mechanical properties of piezoelectric films with the substrate, which is made from silicon carbide. After depositing the PZT thick film on silicon carbide substrate and silicon substrate respectively, it was shown that silicon carbide substrate formed a stable interface with PZT thick film up to 950?°C, compared with silicon substrate. In addition, the dielectric constant of the PZT thick film sintered at 950?°C on a silicon carbide substrate was 843, and this value was about over 25 % improved value compared with that on a silicon substrate. A thick film piezoelectric micro transducer of a micro cantilever type was fabricated by using a multifunctional 3C–SiC substrate. The fabricated micro cantilever was a micro cantilever with multiple thin films on either silicon or silicon carbide substrate. The piezoelectric thick-film micro cantilever that was fabricated by using a SiC substrate showed excellent mechanical and thermal properties. The piezoelectric micro cantilever on the SiC substrate shows an excellent sensitivity towards the change of mass compared with the piezoelectric micro cantilever on the Si substrate.     

0.90(Bi1/2Na1/2)TiO3–0.05(Bi1/2K1/2)TiO3– 0.05BaTiO3 transducer for ultrasonic wirebonding applications

Lead-free piezoelectric ceramic 0.90(Bi_1/2Na_1/2)TiO₃–0.05(Bi_1/2K_1/2)TiO₃–0.05BaTiO₃ (BNKBT-5) rings (OD=12.7 mm, ID=5.1 mm and 2.3-mm thick) were fabricated and characterized. Four ceramic rings were used as the driving element in an ultrasonic wirebonding transducer and the performance of the transducer was characterized. The lead-free transducer was found to have comparable voltage rise and fall times as a lead-based PZT transducer and has a relatively large vibration amplitude, thus showing that BNKBT-5 has the potential to be used in fabricating lead-free ultrasonic wirebonding transducers. PACS 77.22.Ej; 77.84.-s; 85.50.-n     

Promoting inertial cavitation by nonlinear frequency mixing in a bifrequency focused ultrasound beam

Enhancing cavitation activity with minimal acoustic intensities could be interesting in a variety of therapeutic applications where mechanical effects of cavitation are needed with minimal heating of surrounding tissues. The present work focuses on the relative efficiency of a signal combining two neighbouring frequencies and a one-frequency signal for initiating ultrasound inertial cavitation. Experiments were carried out in a water tank, using a 550 kHz piezoelectric composite spherical transducer focused on targets with 46 μm roughness. The acoustic signal scattered, either by the target or by the cavitation bubbles, is filtered using a spectral and cepstral-like method to obtain an inertial cavitation activity measurement. The ultrasound excitations consist of 1.8 ms single bursts of single frequency f₀ = 550 kHz excitation, in the monofrequency case, and of dual frequency f₁ = 535 kHz and f₂ = 565 kHz excitation, in the bifrequency case. It is shown that depending on the value of the monofrequency cavitation threshold intensity the bifrequency excitation can increase or reduce the cavitation threshold. The analysis of the thresholds indicates that the mechanisms involved are nonlinear. The progress of the cavitation activity beyond the cavitation threshold is also studied. The slope of the cavitation activity considered as a function of the acoustic intensity is always steeper in the case of the bifrequency excitation. This means that the delimitation of the region where cavitation occurs should be cleaner than with a classical monofrequency excitation.     

An optimized strain demodulation method based on dynamic double matched fiber Bragg grating filtering

An optimized strain demodulation method based on dynamic double matched fiber Bragg grating (FBG) filtering driven by a piezoelectric transducer (PZT) is proposed and experimentally demonstrated. Using an optimized triangular waveform to drive PZT, the nonlinear effect is eliminated, and extraction and processing of the peak signals are more convenient. Furthermore, taking advantage of double matched-FBGs and strain amplification structure to demodulate the Bragg wavelength, the wavelength scanning range can be extended to 6.3 nm, so that a large-scale and high-precision strain measurement can be achieved. The experimental results show that in the strain range of 0-3800με, the linearity of the relationship between strain and scanning time-difference is greater than 99.8%, and the stability of repeated measurements is up to 99.5%. This demodulation method can be widely applied in the FBG measurement system.     

Study of field distribution,acoustical efficiency and harmonic generation for pseudo-interdigital surface-wave transducers by a finite-difference method

A pseudo-interdigital Rayleigh-wave transducer consists of an ordinary grating deposited on a quartz crystal surface and a counter electrode separated from the grating by a dielectric layer. The electric potential distribution from this transducer is calculated, in an isotropic approximation, under small piezoelectric coupling conditions, using a numerical relaxation technique (Frankel-Young's Method). Potential maps are given as the thickness e and permittivity ? of the dielectric layer are varied.A figure of merit is defined and its value as a function of e and ? are shown. Express ions for the spatial harmonic content are derived from the superficial potential distribution and compared to the case of interdigital combs (according to H. Engan). Some experiments on both types of transducer are given and the results obtained are consistent with theoretical calculations.     

PMN-PT single crystal thick films on silicon substrate for high-frequency micromachined ultrasonic transducers

In this work, a novel high-frequency ultrasonic transducer structure is realized by using PMNPT-on-silicon technology and silicon micromachining. To prepare the single crystalline PMNPT-on-silicon wafers, a hybrid processing method involving wafer bonding, mechanical lapping and wet chemical thinning is successfully developed. In the transducer structure, the active element is fixed within the stainless steel needle housing. The measured center frequency and −6 dB bandwidth of the transducer are 35 MHz and 34%, respectively. Owing to the superior electromechanical coupling coefficient (k _t ) and high piezoelectric constant (d ₃₃) of PMNPT film, the transducer shows a good energy conversion performance with a very low insertion loss down to 8.3 dB at the center frequency.     

On the tuning of variable piezoelectric transducer circuitry network for structural damage identification

The concept of using piezoelectric transducer circuitry with tunable inductance has been recently proposed to enhance the performance of frequency-shift-based damage identification method. While this approach has shown promising potential, a piezoelectric circuitry tuning methodology that can yield the optimal damage identification performance has not been synthesized. This research aims at advancing the state-of-the-art by exploring the characteristics of inductance tuning such that the enrichment of frequency measurements can be effectively realized to highlight the damage occurrence. Analysis shows that when the inductance is tuned to accomplish eigenvalue curve veering, the change of system eigenvalues induced by structural damage will vary significantly with respect to the change of inductance. Therefore, by tuning the inductance near the curve-veering range, one may obtain a family of frequency response functions that could effectively reflect the damage occurrence. When multiple tunable piezoelectric transducer circuitries are integrated to the mechanical structure, multiple eigenvalue curve veering can be simultaneously accomplished, and a series of inductance tunings can be formed by accomplishing curve veering between different pairs of system eigenvalues. It will then be shown that, to best characterize the damage occurrence, the favorable inductance tuning sequence should be selected as that leads to a “comprehensive” set of eigenvalue curve veering, i.e., all measurable natural frequencies undergo curve veering at least once. An iterative second-order perturbation-based algorithm is used to identify the locations and severities of the structural damages based on the frequency measurements before and after the damage occurrence. Numerical analyses on benchmark beam and plate structures have been carried out to examine the system performance. The effects of measurement noise on the effectiveness of the proposed damage identification method are also evaluated. It is demonstrated that the damage identification results can be significantly improved by using the variable piezoelectric transducer circuitry network with the favorable inductance-tuning scheme proposed in this research.     

Piezoelectric composites with a high stability of the piezoelectric modulus under the action of mechanical and temperature fields

New technologies have been proposed for increasing the stability of the piezoelectric modulus d _ij of “polymer-ferroelectric/piezoelectric ceramic” composites under the action of mechanical stresses and temperatures. It has been shown that a decrease in the electronegativity of cations or in the covalency of cation-oxygen bonds of the piezoelectric phase, as well as the cyclic electric and thermal polarization and the crystallization under the action of an electric discharge plasma, leads to an increase in the stability of the piezoelectric modulus of polymer-piezoelectric ceramic composites under the mechanical and temperature actions. A possible mechanism has been proposed underlying the effect of an increase in the stability range of the piezoelectric modulus d _ij due to the crystallization under the action of the electric discharge plasma, the decrease in the covalency of cation-oxygen bonds of the piezoelectric phase, and the cyclic electric and thermal polarization of piezoelectric composites.     

Full piezoelectric tensors of wurtzite and zinc blende ZnO and ZnS by first-principles calculations

The complete piezoelectric tensors of both the wurtzite and zinc blende polymorphs of ZnO and ZnS have been computed by ab initio periodic linear combination of atomic orbitals (LCAO) methods, based mainly on the Hartree-Fock Hamiltonian, with an all-electron Gaussian-type basis set. The computational scheme was based on the Berry phases theory, yielding directly the proper piezoelectric stress coefficients e_ik=(∂P_i/∂ε_k)_E; also the strain coefficients d_ik=(∂ε_k/∂E_i)_τ were obtained, by intermediate calculation of the full elasticity tensors of all four crystals. In particular, the e₁₅ wurtzite shear constants were included for the first time in such calculations. A careful study of the clamped-ion and internal-strain piezoelectric components shows that the latter ones are well simulated by classical point-charge calculations including quantum-mechanical structural relaxation. The much larger piezoelectric response of ZnO with respect to ZnS is explained by analysing signs and ratios of the respective clamped-ion and internal-strain components.     

Static and dynamic characterization of AlN-driven microcantilevers using optical interference microscopy

We have developed an optomechanical methodology, combining interferometric deflection data, the nanoindentation technique and analytical modeling to perform the characterization of piezoelectrically driven microcantilevers operating as MEMS actuators. Here, the association of standard Twyman–Green interferometry (TGI) with time averaged and stroboscopic techniques permits the evaluation of the 3-D out-of-plane deflections of microdevices and provides feedback of measurements that helps us to optimize MEMS structures and improve the reliability and stability of microcantilevers.The goal of the presented study was investigation of high-quality cantilevers composed from silicon beam and a transducer including the aluminum nitride (AlN) layer. It is a material with piezoelectric properties, which can be an alternative for PZT films in micromachining technology. After presenting the fabrication process of the testing devices, the rest of the paper will focus on non-contact measurements of cantilevers deflection by interferometry: static data (e.g., initial shape, deformation, stress) and dynamic parameters of samples (e.g., resonance frequency and amplitude distributions in vibration modes). On the basis of these experimental data, parameters such as piezoelectric coefficient d₃₁ have been calculated taking into account multiple film stacking.