Determination of piezoelectric and pyroelectric coefficients and thermal diffusivity of 1-3 PZT/epoxy composites

PZT/epoxy composites with 1-3 connectivity were prepared using the dice-and-fill technique. The samples were poled with an electric field of 10 MV/m for 30 minutes at room temperature. The piezoelectric and pyroelectric coefficients for the composites were measured. From the laser interferometric measurements, it was found that the piezoelectric d/sub 33/ coefficients for the composites were independent of the volume fraction and averaged (190 /spl mnplus/ 10) pm/V, which was about half of the measured value of lead zirconate titanate (PZT) ceramic. Measurements of the pyroelectric coefficient showed that the coefficients increased with the ceramic content and reached values as large as 54 /spl mu/C/m/sup 2/ /spl deg/C. The thermal diffusivity of the composites was also determined using a technique based on the measurement of the phase retardation of a thermal wave passing through the material. The average value for the composites was (2.15/spl mnplus/ 0.05) /spl times/ 10/sup -7/ m/sup 2//s.     

Inorganic ceramic/polymer ferroelectric composite electrets

Ferroelectric composites are now an established alternative to conventional ferroelectric ceramic materials and to the more recently discovered ferroelectric polymers. These materials due to their unique blending of polymetric properties of mechanical flexibility, formability and low cost with high electro-active properties have been been suggested to be a viable alternative both in piezoelectric and pyroelectric transducer applications. This review is devoted to the piezoelectric and pyroelectric properties exhibited by these type of composites with a special reference to those made of ceramic particles embedded in a polymer matrix (i.e. 0-3 connectivity type composite). A review of models predicting the electro-active properties of 0-3 composites is presented together with a proposal for a new mixed connectivity cubes model to be applicable to the case of high ceramic loading and/or when the ceramic grain size incorporated in the polymer matrix is comparable to the thickness of the sample. A review of the experimental results of the piezo- and pyroelectric properties of various ferroelectric composite materials, reported by several workers, is also presented in this paper. Special reference is made to composites made from calcium modified lead titanate and poly(vinyldene fluoride-trifluorethylene) emphasizing their advantages in the poling process which is a critical phase in the process of obtaining successful electro-active 0-3 composite electrets     

A poling study of PZT/P(VDF-TrFE) copolymer 0-3 composites

Abstract

0–3 composites of lead zirconate titanate (PZT) and P(VDF-TrFE) (piezoelectric copolymer of polyvinylidene fluoride and trifluoroethylene) with different volume fraction of piezoelectric ceramic were fabricated. The composites must be polarized by exposure to a high electric field to elicit piezoelectric response. One of the major consideration for poling a composite is the ratio of the resistivities of constituent phases since it governs the effective poling field across each phase. It is observed that the resistivity of the copolymer shows hysteresis upon heating and cooling, and abrupt changes are found at its Curie transition temperature upon heating (Tc↑) and on cooling (Tc↓). Previous reports stated that PZT/copolymer 0–3 composites of 50 volume percent ceramic do not exhibit piezoelectric response because the piezoelectric constants of the two materials are opposite in sign and cancellation occurs. In the present work, different poling conditions are used to pole the two phases oppositely so that the piezoelectric responses of the two phases reinforce each other. Details of poling and the resulting composite properties are reported.     

Influence of Different Substrates on the Detectivity of Pyroelectric Sensors

Nanosized lead titanate doped with calcium and lanthanum (PCLT) powder obtained by the sol-gel method was homogeneously mixed with vinylidene fluoride-trifluoroethylene [P(VDF-TrFE)] to form nanocomposites. Several pyroelectric sensors were prepared on porous silicon dioxide, on poly(ethylene terephthalate) (PET) film and on bulk silicon substrates, respectively. The nanocomposite PCLT/P(VDF-TrFE) sensing film was deposited by spin-coating and Ni-Cr film was deposited as the top electrode and absorption layer. Experimental results showed that the substrate of the pyroelectric sensor could significantly affect the specific detectivity. The porous silicon dioxide and PET plastic film substrates could effectively decrease the thermal conductivity and the thermal fluctuation noise of the pyroelectric element, increase the voltage responsivity and the specific detectivity. The results indicated that the specific detectivity of PCLT/P(VDF-TrFE) pyroelectric sensors based on porous silicon dioxide and PET plastic film substrates reached 4.2E6 and 3.4E7 cmHz 1/2 W m 1 respectively, which is about 1-2 orders of magnitude higher than that of the sensors formed under the same condition on the bulk silicon substrate.     

压电参数d33特性测试装置设计

纵向压电应变常数d33是表征压电陶瓷材料机电转换性能的重要参数之一.有别于常规的静态、动静态检测方式,设计了一种基于扫频方法的新型d33参数测试装置.通过检测不同频率信号激励时线路的电流变化,实现压电陶瓷d33参数的检测计算.该装置具有性能参数检测操作方便、检测过程效率高等特点.     

Poly(vinylidene fluoride-trifluoroethylene) based high performance electroactive polymers

Making use of defects modification to P(VDF-TrFE) via either high energy electron irradiation treatment or copolymerizing VDF-TrFE with a small amount of chlorinated monomer to form a random terpolymer, we demonstrate that high electromechanical responses can be realized in P(VDF-TrFE) based polymers. It will be shown that in the stretched and irradiated 68/32 mol% copolymer, a transverse strain of 4.5% and a transverse electromechanical coupling factor k/sub 31/ of 0.65 can be induced under a field of 85 MV/m. In addition, the irradiated copolymer also exhibits a high elastic energy density, /spl sim/ 1 J/cm/sup 3/. For PVDF based terpolymers such as P(VDF-TrFE-CFE) terpolymer (CFE: chlorofluoroethylene), an electrostrictive strain of more than 7% can be obtained. To elucidate the microstructure changes due to the defects modification in P(VDF-TrFE) based polymers, synchrotron X-ray measurement was carried out on the irradiated copolymers and the results show that, the irradiation converts the polar-phase into a nonpolar phase. In addition, X-ray date show that the polar-phase can be induced, at the expense of the nonpolar phase, by external fields, confirming that the field induced conformation change is responsible for the observed high electromechanical responses. Although the modified PVDF based polymer exhibits the highest room temperature dielectric constant (60 versus below 10), it is still far below those in the inorganic materials. Experimental results show that by using delocalized electrons in conjugated bonds an all-organic composite with a dielectric constant more than 400 can be achieved. As a result, a strain of near 2% with an elastic energy density higher than 0.1 J/cm/sup 3/ can be induced under a low applied field of 13 V//spl mu/m. The strain is proportional to the applied field and the composite has an elastic modulus near 1 GPa.     

Evaluation of PTCa/PEKK composites for acoustic emission detection

The electromechanical properties of calcium modified lead titanate/poly(ether ke-tone ketone) (PTCa/PEKK) composites and their ability after poling to detect acoustic emission (AE) when mounted on carbon fiber reinforced composite (CFRC) panels is reported. They have been characterized by measurements of conductance, G, permittivity, /spl epsi/, pyroelectric, p, and piezoelectric, d/sub 33/, coefficients for different ceramic volume fractions. In addition, the electromechanical coupling coefficient, k/sub t/, the elastic compliance coefficient, s/sub 33/, the acoustic impedance, Z/sub a/, and the quality factor coefficient, Q/sub m/ have been calculated from the measurement of the complex impedance (Z) of the composite samples acting as free resonating transducers. It is demonstrated that in a square array they can be used to locate AE sources with good accuracy and that they will also detect AE caused by the delamination of a CFRC beam.     

Bi0.5(Na0.82-xK0.18Lix)0.5TiO3无铅压电陶瓷的微结构与电性能

采用传统陶瓷制备工艺制备了[Bi0.5(Na0.82-xK0.18Lix)0.5]TiO3(x=0.01~0.07)无铅压电陶瓷.研究了该体系陶瓷的微结构以及应力对平面机电耦合系数kp和压电常数d33的影响.结果表明,[Bi0.5(Na0.82-xK0.18Lix)0.5]TiO3无铅压电陶瓷具有单一钙钛矿结构,Li+有抑制晶粒长大的作用.当x=0.03时,压电陶瓷样品表现出优良的压电性能:压电常数d33和平面机电耦合系数kp分别为154 pC/N和0.296.同时发现,退火可消除内应力,有利于提高d33,但会使kp减小;极化会引起介电常数εr减小,电畴转向过程中产生的应力对d33影响较为明显     

Flashover voltage of alumina ceramic contaminated by metal vapor in vacuum interrupters

We investigated the influence of metal vapor contamination of ceramic surfaces on flashover voltage (FOV) in vacuum. First, disk shape alumina (Al/sub 2/O/sub 3/) ceramics with surface resistivity (/spl rho/) of 10/sup 2/-10/sup 15/ /spl Omega/ were produced using deposition phenomena of metal vapor emitted from CuCr contacts. The impulse FOV for the ceramics decreased, as /spl rho/ reduced; FOV, the conditioning effect on FOV, and the scattering of FOV decreased when /spl rho/ was below 10/sup 12/ /spl Omega/. Therefore, the criterion value /spl rho/, which maintains excellent flashover performances of ceramic surface, is 10/sup 12/ /spl Omega/. Second, experimental vacuum interrupters (VIs) were produced to measure breakdown voltage before and after forty short-circuit current switchings with 20-40 kA/sub rms/ and were disassembled to measure the /spl rho/ of their inner ceramic surface. In a VI, which has inside diameters at both ends of the main shield much larger than the contact diameter, /spl rho/ was reduced to 10/sup 4/ /spl Omega/, further decreasing breakdown voltage between terminals.     

Recent Advances in 1-3 Piezoelectric Polymer Composite Transducer Technology for AUV/UUV Acoustic Imaging Applications

Over the past 5 years, the use of 1-3 piezoelectric polymer composite has been studied under various U.S. Navy-funded transducer research programs. As a transduction material, the 1-3 piezoelectric composite offers many advantages for autonomous undersea vehicles/unmanned undersea vehicle (AUV/UUV) imaging array construction. Broad bandwidth, high transmit/receive response, low cost of fabrication, mechanical ruggedness, and the ability to form conformal shapes make this material both a unique and intriguing medium for the sonar transducer designer. The 1-3 piezocomposite panels are comprised of several piezoceramic rods aligned vertically through the panel's thickness with each rod surrounded with a specific polymer epoxy. Volume fractions of ceramic to polymer can vary up to 50% with panel thickness ranging between fractions of a millimeter (2 to 4 MHz) to 25 millimeters (50 to 70 kHz). This article will elucidate the application of this unique material to a variety of practical transducer designs and describe some of the recent device demonstrations along with measured performance data.     

Ultrasonic transducer based on highly textured PMN-PT piezoelectric ceramic

A successful fabrication process of textured ceramics by homo-template grain growth (HTGG) is described. Two samples fabricated with this technique were characterised. Functional properties obtained are competitive with for example a thickness coupling factor over 50%. Different characteristics were compared with those obtained by a unit cell model previously developed for piezocomposites and extended to the case of two piezoelectric phases. Behaviours of several connectivities (0–3, 3–0 and 3–3) are calculated and results show that the spatial arrangement does not have a great influence on effective parameters. A transducer based on a textured ceramic sample has been fabricated and characterised. The measured performance shows the efficiency of these new piezoelectric materials. Finally, electroacoustic responses of identical single element transducer configurations have been simulated. They show that a sensitivity increase of 3dB can be obtained at equivalent relative bandwidth of 40% with textured ceramic sample in comparison with PMN-PT ceramic used as a matrix in the textured ceramic.     

High performance thin film PZT ultrasonic transducer by CSD for distance measurements in water

Piezoelectric thin film ultrasonic transducers were realised and tested for short range distance measurements. Displacements in air and water as a function of frequency were modelled by Comsol Multiphysics finite element modelling (FEM) and transducer configurations with a two electrode layout were manufactured to enable larger displacements than with the conventional design. The transducer was fabricated on a silicon wafer by chemical solution deposition (CSD) with total PZT (Pb(Zr_0.53Ti_0.47)O₃) thickness of 2 µm. Subsequently, a cavity underneath the PZT was wet etched creating a bending membrane with a total thickness of ??13 µm. The displacements of the transducers as a function of frequency were modelled and measured by fiber-optic laser vibrometer. The effective piezoelectric d₃₃ coefficient of 300 nm/V and 144 nm/V in air and 48 nm/V and 18 nm/V in water was obtained for 260?×?260 µm² and 390?×?390 µm² membranes, respectively. The accuracy of the modelled resonance frequencies both in air and water was relatively good, of ??4-13% and ??5-20%, respectively.     

Processing and Characterization of Micromachined Actuators Based on Proton-Irradiated P(VDF-TrFE) Copolymer

ABSTRACT

Copolymers of vinylidene fluoride and trifluoroethylene (P(VDF-TrFE)) have been used in a variety of devices such as transducers, actuators and sensors because of their good electroactive properties. Our earlier work showed that the electric field-induced strain in P(VDF-TrFE) copolymers can be enhanced significantly after high energy proton irradiation. In this study, micromachined actuators using proton-irradiated P(VDF-TrFE) copolymer as the active element have been fabricated. P(VDF-TrFE) 70/30 mol% copolymer film with a thickness of ～ 3.3 μ m was spin-coated on a silicon (Si) substrate. After etching the Si substrate by bulk micromachining, an actuator in the form of a suspended membrane was obtained. High energy proton irradiation with a dose of 107 Mrad was carried out to modify the properties of the copolymer film. The resonance characteristics of the actuators based on these irradiated copolymer films were studied and the displacement induced in the actuators was measured using a laser vibrometer. These types of polymer-based micromechanical systems have the advantages of being lightweight and have high toughness, thereby reducing the risk of breakage. By applying different d.c. bias voltages, the magnitude of the displacement induced in the actuator can be varied.     

Orthogonal control of femtosecond mode-locked laser having zero carrier-offset frequency with three-axis PZT

The authors demonstrate an optical frequency synthesizer based on a femtosecond (fs) mode-locked Ti:sapphire (Ti:s) laser by simultaneously stabilizing the carrier-offset frequency f/sub ceo/ and repetition rate f/sub rep/, referenced to the Cs atomic frequency standard. By using two wide-band digital phase-detectors they realize a phase-coherent link between f/sub rep/ and f/sub ceo/ with the relation f/sub ceo/=f/sub AOM/-5/6f/sub rep//spl equiv/0, where f/sub AOM/=5/6f/sub rep/ is the phase-locked driving frequency of an acousto-optic modulator in a self-referencing interferometer and f/sub rep/=100 MHz. For the simultaneous control of f/sub rep/ and f/sub ceo/, an orthogonalization scheme using a three-axis piezoelectric transducer is introduced by which the end mirror of fs laser is controlled. As a result, the authors could stabilize all components of the fs laser comb at once with an equal frequency separation f/sub rep/=100 MHz with f/sub ceo/=0. In their optical frequency synthesizer, the frequency of the nth component (f/sub n/) is given exactly by the simple relation f/sub n/=nf/sub rep/, enabling them to use the fs laser comb as a frequency ruler in the optical frequency metrology.     

Piezoelectric Properties of Novel Oriented Ceramic-Polymer Composites with 2-2 and 3-3 Connectivity

The processing of novel 2-2 and 3-3 PZT ceramic-polymer composites with various orientation of the ceramic phase with respect to the poling direction is presented. The volume fraction of the ceramic was chosen to be 30 percent for both types of composites. The orientation angle () of the ceramic phase varied between 0° and 75° for both types of composites with 15° increments. The ceramic structures were fabricated using one of the Solid Freeform Fabrication (SFF) methods, particularly Fused Deposition of Ceramics (FDC). The sintered structures were embedded in hard epoxy and the effect of orientation angle on the electrical properties of the composites was evaluated. By increasing the orientation angle of the ceramic phase, the dielectric constant and the piezoelectric strain coefficient of both types of composites decreased. Although the piezoelectric voltage coefficient of the 2-2 composites showed a minor improvement with increasing at 45°, the g ₃₃ value of the 3-3 composites increased considerably with and reached 80 mV/N at = 45°. Further increase of the orientation angle reduced the g ₃₃ of such composites.     

Design, development, and characteristics of an in-shoe triaxial pressure measurement transducer utilizing a single element of piezoelectric copolymer film

In gait analysis, there is growing awareness of the need to simultaneously measure shear and vertical forces for the diagnosis and treatment assessment of pathological foot disorders. This is especially the case in the measurement of the forces between the plantar surface of the foot and the shoe. Although clinical awareness of the need to simultaneously measure shear and vertical forces under the foot has increased little has been done to provide the technology. This is mainly due to the difficulty in constructing devices capable of carrying out this task in the in-shoe environment. The aim of this paper is to describe the development and characteristics of a miniature triaxial transducer measuring 10 /spl times/ 10 /spl times/ 2.7 mm and a weight of only 2 g. This transducer is capable of simultaneously measuring three orthogonal forces under any location of the plantar surface of the foot utilizing a single element piezoelectric copolymer P(VDF-TrFE). Transducer sensitivity, linearity, hysteresis, crosstalk and temperature dependence is presented. As well as in-shoe force measurement, this triaxial transducer could have other biomedical and general engineering applications, e.g., prosthetic interface forces, handgrip forces, sport, robotics, etc.     

Mixed and passive filtering for linear switched systems with average dwell time

In this paper, a new performance index is proposed for switched systems. The new performance index can be viewed as the mixed weighted and passivity performance. This new performance index covers the weighted performance and the passivity performance as special cases. Based on this new performance index, the weighted filtering problem and the passive filtering problem of linear switched systems with unstable subsystems are solved in a unified framework. The states of the filtering error system constructed by the augmentation technique will be divergent when unstable subsystems are activated. To overcome this problem, a set of mode‐dependent filters of a Luenberger‐like observer type is constructed. The multiple Lyapunov function approach and the average dwell‐time technique are employed to solve the mixed filtering problem. New sufficient conditions for the existence of mixed and passive filters are developed, which ensure the filtering error system to be asymptotically stable with a prescribed mixed and passivity performance index. Moreover, the desired mixed and passive filters can be constructed by solving a set of linear matrix inequalities. Finally, numerical examples are given to demonstrate the applicability and advantage of the obtained results.     

Soliton induced supercontinuum generation in photonic crystal fiber

Soliton induced supercontinuum (SC) generation using an index-guiding triangular photonic crystal fiber (PCF) is experimentally studied by pumping with 140-fs pulses at several wavelengths in the positive slope anomalous dispersion region. The focused beam incident upon the PCF core is first confirmed by in situ observation based on the reflection method to make sure accurate input coupling conditions. The influence of pumping wavelength on the spectral profile of SC is examined as a function of input peak power P/sub 0/. Processes initiating SC generation are governed by the fission of higher-order solitons, which lead to the soliton self-frequency shift (SSFS) by intrapulse Raman scattering associated with blue-shifted Cherenkov type phase matched radiation. The fission of higher-order solitons is clearly observed in the input P/sub 0/ dependent spectrum and a plot of the square root of frequency shift versus input P/sub 0/. Further increase of input P/sub 0/ leads to a new SSFS accompanied by an additional blue-shifted peak located at shorter wavelength than that of the previous one. These processes continue to develop successive blue-shifted and SSFS peaks as increasing the input P/sub 0/, which determine the spectral width of SC. Spectral profile of SC is also dominated by these initial and growth processes. SC spectra obtained in the vicinity of zero dispersion wavelength shows smooth but relatively narrow, while SC generation at deep anomalous dispersion site exhibits broad bandwidth at relatively low P/sub 0/. The input P/sub 0/ required for approaching a saturated SC which is almost the same feature within the tuning pump wavelengths is decreased as increasing the degree of anomalous dispersion.     

Five-phase permanent-magnet motor drives

A five-phase brushless permanent-magnet (PM) motor is introduced. The proposed motor has concentrated windings such that the produced back electromotive force is almost trapezoidal. The motor is supplied with the combined sinusoidal plus third harmonic of currents. This motor, while generating the same average torque as an equivalent PM brushless dc motor (BLDC), overcomes its disadvantages. The motor equations are obtained in the d/sub 1/q/sub 1/d/sub 3/q/sub 3/0 rotating reference frame. Therefore, the so-called vector control is easily applicable to this kind of motors and the motor has the same controllability as a PM synchronous motor (PMSM). For presenting the superior performance of the proposed five-phase motor, its three and five-phase PMSM and BLDC counterparts are also analyzed. Finite element method is used for studying the flux density and calculating the developed static torque. Also, the developed torque is obtained using the mathematical model in the d-q reference frame. The average torque and the torque ripple for all cases are calculated and compared. Experimental results are in good agreement with the simulation results.     

Switching of capacitive currents and the correlation of restrike and pre-ignition behavior

The new IEC 62271-100 requires an extensive proof of the capability of capacitive switching for a breaker under test. For vacuum circuit breakers, dielectric properties are mainly determined by the condition and topology of the contact surfaces, which are modified by in-rush currents as well as load-breaking currents and other effects. A synthetic single-phase test device has been erected in order to simulate three-phase network conditions and to collect more data on the statistical properties of the relevant processes. The distribution of pre-ignition field strengths is evaluated for different contact strokes and surface conditions, when discharging a capacitor through the closing interrupter. On the other side, the probability of restrikes for a given switching condition defined by full contact gap d/sub 0/ and peak recovery voltage U/sub re//spl circ/ is measured and compared with the cumulative probability of pre-ignition just at the field strength E=U/sub re//spl circ//d/sub 0/. A correlation between pre-ignition and restrike probabilities suggests a breakdown mechanism being field-emission dominated. In addition a rather strong conditioning effect has been observed at smaller contact gaps smoothening the contact surfaces.