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In spite of the significance from both scientific and technological viewpoints, systematical studies on the dielectric spectra of (K,Na)NbO 3 -based lead-free ceramics particularly in the poled state had been scarcely performed so far. In this study, the compositional series of (1- x)(K 0.48 Na 0.52)(Nb 0.96 Sb 0.04)O 3 − x (Bi 0.50 Na 0.50)ZrO 3 ceramics were chosen representatively to shed more light on the characters of dielectric properties. All the ceramics in the unpoled state show dielectric spectra of large dispersion with the relaxational characteristic frequency higher than the measured upper limit of 60 MHz at room temperature. Additional resonance peaks due to the electromechanical coupling of piezoelectric effect appear and are accompanied by a large step-like reduction of dielectric permittivity ε′ in the dielectric spectra after poling. An abnormal phenomenon that poling induces the increase of low-frequency ε′ occurs in those ceramics with x ≥ 0.04 at room temperature, and is confirmed to associate closely with the orthorhombic-tetragonal and rhombohedral-orthorhombic polymorphic phase transitions. Further study of domain structure indicates that the origin of this abnormal phenomenon should be ascribed to the enhancement of domain-wall mobility because of the large reduction of domain-wall density due to the poling. [ABSTRACT FROM AUTHOR]

The (K,Na)NbO 3 -based ceramics are a very promising type of lead-free piezoelectric materials. In spite of the scientific and technological importance, systematical investigations on the dielectric spectra had been rarely performed so far. This paper reports our study results obtained in the (K 0.50 Na 0.50) 1- x Li x NbO 3 ceramics with either x = 0.03 or x = 0.065 (denoted as KNLN-030 and KNLN-065 ceramics, respectively) in the unpoled state and the poled state, respectively. Before poling, the KNLN-030 ceramic shows a dielectric spectrum of strong frequency dependence with a broad peak of dielectric loss around 1 MHz, while the KNLN-065 one has a dielectric spectrum of weak frequency dependence below 60 MHz at room temperature. After poling, piezoelectric resonance peaks appear and are accompanied by a large step-like reduction of dielectric permittivity ε′ in the dielectric spectra of both two ceramics. More interestingly, the KNLN-065 ceramic exhibits an abnormal phenomenon that there is a marked increases in low-frequency ε′ upon poling, whereas the KNLN-030 one shows normally a large decrease of low-frequency ε′. Further, the KNLN-065 ceramic displays the larger low-frequency ε′ in the poled state than in the unpoled state over a considerably wide temperature range. By contrast, such abnormal phenomenon is recognized only in a limited region above the orthorhombic-tetragonal phase transition in the KNLN-030 ceramic. The analysis of domain structure suggests that the observed abnormal dielectric phenomenon possibly arises from the enhancement of domain-wall mobility. [ABSTRACT FROM AUTHOR]

The experimental results of a study of the equivalent temperature of quartz crystals in the presence of a controlled linear gradient of the thermodynamic temperature are presented. Under conditions of non-uniform heating, the equivalent temperature of crystals was determined by measuring the frequencies of the eigenmodes of acoustic resonances on the basis of the preliminary calibration of the resonance frequencies under uniform heating. It is shown that the equivalent temperature determined in this way characterizes the average thermodynamic temperature of the crystal. Non-uniform heating of a crystal, including the use of laser radiation, was simulated. [ABSTRACT FROM AUTHOR]

An experimental study of the microstructural features and complex electromechanical parameters of lead-free ferroelectric ceramics based on solid solutions of the sodium-lithium niobate system was carried out. The phase distribution, as well as grain and domain structure were studied by piezoresponse force microscopy and scanning electron microscopy. A complete set of complex elastic, dielectric, and piezoelectric parameters of lead-free ferroelectric ceramics Na0.87Li0.13Sr0.01Nb0.99O3 + 1 at.% SiO2 was measured and analyzed using the Piezoelectric Resonance Analysis Program automatic iterative method. The frequency dependences of complex electromechanical parameters of the samples were measured in the frequency range up to 90 MHz. [ABSTRACT FROM AUTHOR]

The non-contact excitation of multiple piezoelectric components (PZT) through bidirectional electric field transmission system has been explored. In the proposed technique, two parallel plate capacitor-like structures have been designed with a pair of ground copper electrodes along with a live copper electrode, and two PZT plates are equidistantly placed in between each live and ground electrode. Experimentally, it has been observed that piezoelectric plates are wirelessly energised as a result of both electric and piezoelectric resonances. Maximum vibrational displacement can be obtained over the piezoelectric plates at a point, when the operating frequency of the E-field generator matches with the frequency of the mechanical resonance of the PZT plate. The maximum output power ( P out) across the non-contact stimulated piezoelectric plates principally depends on resonance, resistive load, vibration mode, driving frequency, position of PZT component etc. The output power obtained across the excited piezoelectric device by bidirectional non-contact energy transfer has been appreciably higher than that of the single PZT component excited by simple parallel-plate capacitor structure. The maximum output power of 0.271 mW and 0.298 mW are acquired across piezoelectric plates at a resonance frequency of 924 kHz and 350 Ω optimal loads with 50 V input, when the live and ground electrodes are separated by 4 mm. By enacting the proposed wireless excitation technique, multiple piezoelectric devices can be energised together. [ABSTRACT FROM AUTHOR]

A novel method for temperature measurement of active fibers under conditions of lasing and radiation amplification is introduced. This method allows determination of the longitudinal temperature distribution of active fibers at different optical pump powers. A piezoelectric resonator made of the quartz crystal in the form of a hollow cylinder is used as a temperature sensor. Investigated segment of the active fiber is put thorough the hole of the resonator. Heating temperature of the resonator is determined by measuring a frequency shift of the piezoelectric resonance, which is preliminary calibrated under uniform heating conditions. In order to evaluate the heating temperature of the investigated fiber segment, the last one was substituted with a copper wire coated with polymer. A copper wire was heated by transmitting an electric current and its temperature was determined by measuring the resistance change. Numerical simulations revealed that the heating temperatures of the active and copper fibers differ by less than 9% at 11 W/m thermal load level. Heat transfer coefficient was evaluated using cooling kinetics and stationary state temperature of the "copper" fiber. Heating temperature of the active fiber of the ytterbium fiber laser was measured at different pump levels (up to 150W). [ABSTRACT FROM AUTHOR]

The temperature stability of electromechanical characteristics of Y + 42° cut LiTaO crystals has been studied using dielectric spectroscopy and static and dynamic piezoelectric effect measurements. It has been shown that, during thermal cycling, the piezoelectric properties of crystalline LiTaO samples exhibit a thermal hysteresis and that the thermal history of samples influences their resonance and antiresonance frequencies. [ABSTRACT FROM AUTHOR]

A CaTiO3-doped (K,Na)NbO3 (KNN-CT) film is a lead-free piezoelectric film that is expected to substitute Pb(Zr,Ti)O3 (PZT) film in piezoelectric micro electro mechanical systems (MEMS). However, the full set of the material constants (elastic constants, piezoelectric constants and dielectric constants) of the KNN-CT film have not been reported yet. In this study, all the material constants of a sputter-deposited blanket KNN-CT film were investigated by the resonance responses of MEMS-based piezoelectric resonators and the phase velocities of leaky Lamb waves on a self-suspended membrane. The phase velocities measured by a line-focus-beam ultrasonic material characterization (LFB-UMC) system at different frequencies were fitted with theoretical ones, which were calculated from the material constants, including fitting parameters. A genetic algorithm was used to find the best-fitting parameters. All the material constants were then calculated. Although some problems arising from the film quality and the nature of deliquescence are observed, all the material constants were obtained exhibiting accuracy within 16 m/s in the phase velocity of leaky Lamb wave.

Within the framework of the modified proton model with taking into account the interaction with the shear strain ε6, a dynamic dielectric response of ND4D2PO4 type antiferroelectrics is considered. Dynamics of the piezoelectric strain is taken into account. Experimentally observed phenomena of crystal clamping by high frequency electric field, piezoelectric resonance and microwave dispersion are described. Ultrasound velocity and attenuation are calculated. Character of behaviour of attenuation in the paraelectric phase and the existence of a cut-off frequency in the frequency dependence of attenuation are predicted. At the proper choice of the parameters, a good quantitative description of experimental data for longitudinal static dielectric, piezoelectric and elastic characteristics and sound velocity for ND4D2PO4 and NH4H2PO4 is obtained in the paraelectric phase.

A bidirectional energy transfer method is proposed and investigated for wireless excitation of piezoelectric devices. In the proposed bidirectional system, two receiving coils are deployed on both sides of a transmitting coil so as to capture the generated magnetic fields based on magnetic resonance coupling. The piezoelectric devices connected across each receiving coils get energized wirelessly because of the mechanism of electromagnetic resonance as well as piezoelectric resonance. It is found that the power across driven piezoelectric devices arrive at maximum for operating resonant frequency. The optimum power received by piezoelectric devices wirelessly through the bidirectional energy transfer system is significantly higher than that of the single-sided receiver system. By implementing the proposed bidirectional energy transfer method, two piezoelectric devices can be energized simultaneously instead of a single piezoelectric device through the usual single-side receiver system without affecting the maximum power transfer efficiency. Copyright © 2015 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

• Avian hair cells solve the RC time constant problem by decreasing the membrane resistance. • Mammalian outer hair cells solve the RC time constant problem by decreasing the membrane capacitance. • The membrane capacitance can be nullified by piezoelectric resonance. Avian hair cells depend on electrical resonance for frequency selectivity. The upper bound of the frequency range is limited by the RC time constant of hair cells because the sharpness of tuning requires that the resonance frequency must be lower than the RC roll-off frequency. In contrast, tuned mechanical vibration of the inner ear is the basis of frequency selectivity of the mammalian ear. This mechanical vibration is supported by outer hair cells (OHC) with their electromotility (or piezoelectricity), which is driven by the receptor potential. Thus, it is also subjected to the RC time constant problem. Association of OHCs with a system with mechanical resonance leads to piezoelectric resonance. This resonance can nullify the membrane capacitance and solves the RC time constant problem for OHCs. Therefore, avian and mammalian ears solve the same problem in the opposite way. This article is part of the Special Issue Outer hair cell Edited by Joseph Santos-Sacchi and Kumar Navaratnam. [ABSTRACT FROM AUTHOR]

Abstract: In this paper, we present the development of a voluntary muscle contraction sensing system that provides motion information of body for computing human body forces for physical human–robot interactions (pHRI). A resonance-based active-muscle stiffness sensor (aMSS) using piezoelectric probes was built and tested to measure stiffness changes in muscles. The sensor is evaluated by comparing the results with those of a force sensor and surface electromyography in terms of accuracy and by assessing the response time test under isometric conditions. Experimental results pertaining to flexor carpi radialis (FCR) contractions are presented to show the feasibility and performance levels of the developed sensing system when sensing muscle contractions. Two notable advantages over sEMG-based sensing are that the proposed sensing method is far less sensitive to skin contact conditions and that it can measure muscle contractions through one''s clothes. Being capable of body force estimations noninvasively, the proposed sensing method is attractive in the field of exoskeleton robots or human-augmentation systems. [Copyright &y& Elsevier]

Abstract: The principal refractive indices of L-lysine monohydrochloride dihydrate (L-LMHCl) single crystal for different wavelengths were measured by minimum deviation method at room temperature. The experimental values of refractive indices fit well with the theoretical Cauchy''s equations. The birefringence and the crossing angle between the optical axes were calculated. The parameters of Sellmeier''s single term dispersion equation were determined by least square method. A simple interferometric technique was used to observe the interference patterns along the optic plane and to qualitatively analyze the optical homogeneity of the grown crystal. The nonlinear refractive index (n 2) and nonlinear absorption coefficient (β) were also determined using Z-scan technique. The piezoelectric resonance in dielectric dispersions was observed at room temperature. [Copyright &y& Elsevier]

A combined experimental and numerical investigation has been conducted to study piezoelectric resonance process in relation to the strain gradient, the local polarization, and the displacement current in a piezoelectric crystal-resonator. Experimental discoveries showed that at certain sub-wavelengths of the fundamental piezoelectric resonant frequencies of a given resonator, electrooptic coefficients and also the optical transmission in an otherwise opaque configuration are greatly enhanced. This paper reports preliminary study by finite element analysis modeling on microwave transmission behavior when the piezoelectric material is modulated by periodic polarization distribution defined by piezoelectric resonance or generated by periodic poling. Transmission parameters are simulated in wide frequency range to characterize wave propagation behavior of the material in various local polarization conditions related to piezoelectric transverse or longitudinal resonance modes. [ABSTRACT FROM AUTHOR]

Changes of piezoelectric and elastic properties of gadolinium calcium oxoborate, GdCa4O(BO3)3 (GdCOB), single crystal caused by γ-irradiation were investigated. The crystal was exposed to γ-radiation of a dose up to 2 MGy. The changes in frequencies of piezoelectric resonances were registered with variation of the dose for two crystal plates: (XY) and (ZX) vibrating in longitudinal modes. The relationship between the radiation dose and the elastic coefficients s11E, s22E as well as the piezoelectric coefficients d31, d12 was found. GdCOB crystal can be recommended for application in high-dose dosimetry. [ABSTRACT FROM AUTHOR]

Within the framework of the modified proton model with taking into account the interaction with the shear strain ϵ6, a dynamic dielectric response of ND4D2PO4 type antiferroelectrics is considered. Dynamics of the piezoelectric strain is taken into account. Experimentally observed phenomena of crystal clamping by high frequency electric field, piezoelectric resonance and microwave dispersion are described. Ultrasound velocity and attenuation are calculated. Character of behaviour of attenuation in the paraelectric phase and the existence of a cut-off frequency in the frequency dependence of attenuation are predicted. At the proper choice of the parameters, a good quantitative description of experimental data for longitudinal static dielectric, piezoelectric and elastic characteristics and sound velocity for ND4D2PO4 and NH4H2PO4 is obtained in the paraelectric phase. [ABSTRACT FROM AUTHOR]

The piezoelectric properties of Pb[(Fe1/3Sb2/3)xTiyZrz]O3 with x + y + z = 1, x = 0.1, y = 0.43-0.48 ceramics have been investigated over a broad temperature range using a resonance technique. The influence of modification of PZT normal ferroelectric synthesized near the morphotropic phase boundary by a relaxor Pb(Fe1/3Sb2/3)O3 compound on its physical properties was studied. The coefficients s11, k31, and d31 were calculated from the parameters characterizing the behavior of damped harmonic oscillator in the vicinity of the piezoelectric resonance. Several anomalies of the piezoelectric coefficients have been found in the temperature range 300-600 K. Two diffuse phase transitions were observed in Pb[(Fe1/3Sb2/3)xTiyZrz]O3. The anomaly near 530 K for y = 0.43 is responsible for the transition from the rhombohedral phase to the tetragonal one. For y > 0.44 this transition is found to be very diffuse and the coexistence of rhombohedral and tetragonal phases occurs. The observation of low piezoelectric activity confirms the existence of polar regions in Pb[(Fe1/3Sb2/3)xTiyZrz]O3 above Tm. [ABSTRACT FROM AUTHOR]

We present parallel-plate (Ba,Sr)TiO 3 and SrTiO 3 thin-film capacitor technology on silicon for RF devices. The in-plane thermal stress that is critical to low expansive Si substrates can be controlled by tuning the sputtering deposition pressure, and a corresponding change in the permittivity due to the electrostrictive effect is observed. The high-frequency dielectric response analysis combined with the equivalent circuit model and electromagnetic simulation enables accurate estimation of the intrinsic dielectric properties, thus demonstrating the linear increase of dielectric loss with frequency. With the bias applied, an electromechanical resonance appears in the GHz band due to piezoelectric effect, which is reproduced using the finite element method. [ABSTRACT FROM AUTHOR]

A dynamic dielectric response of Rochelle salt is considered within a two-sublattice Mitsui model with piezoelectric coupling. Phenomena of crystal clamping, piezoelectric resonance, and microwave dispersion are described. Existence of a cut-off frequency for sound propagation is shown. [ABSTRACT FROM AUTHOR]

We discuss here the realization of tactile sensors based on the principle of change in piezoelectric resonance frequency with the applied pressure. An array of electrodes has been adopted on either side of the PZT material to have independent resonators. The common areas sandwiched between the electrodes and excitable at resonance frequency of the PZT material are used to form the sensitive area of the tactile sensor. The electrodes were deposited using sputtering technique. Tactile sensors with 3×3, 7×7, and 15×15 array of electrodes are developed with different electrode dimensions and separation between the electrodes. The tactile sensor has been interfaced to computer for the convenience of automatic scanning and making it more user interactive. The tactile sensors developed with different spatial resolution were tested for different shaped objects placed in contact with the sensor. The 3×3 matrix tactile sensor showed relatively poor spatial resolution, whereas the 15×15- matrix tactile sensor showed improved spatial resolution. The sensor with 7×7 matrix elements was tested for its sensitivity to different extents of applied force/pressure. The output response study carried out on the sensors indicated that these sensors can provide information not only about the extent of force/pressure applied on the object, but also the contour of the object which is in contact with the sensor. [ABSTRACT FROM PUBLISHER]

For materials with piezoelectric activity the application of forced harmonic oscillator model with complex amplitude gives the possibility to determine the complex elastic coefficient s = s - is . Temperature dependence of the complex elastic coefficient s E 11 has been investigated for a Li 2 B 4 O 7 single crystal in the temperature range 20-200 °C. It was shown that the imaginary part s ″ E 11 is more sensitive to abnormal behaviour of physical properties than the real part s ′ E 11 . Distinct maximum of s ″ E 11 was observed at 68°C and 93°C. Between these temperature points the piezoelectric response splits into two resonances. Clear anomalies simultaneously on s ′ E 11 ( T ) and s ″ E 11 ( T ) dependencies accompany a phase transition at 155°C. [ABSTRACT FROM AUTHOR]

Temperature calibrated piezoelectric resonances of internal acoustic vibration modes of a nonlinear-optical crystal during its heating by high-power laser radiation are used for noncontact measurements of both the non-uniform temperature distribution in the crystal volume and in the surrounding air. A novel notion of equivalent temperature of a crystal heated by laser radiation is introduced in laser physics. The true non-uniform crystal thermodynamic temperature at a given laser power is substituted by the measured equivalent crystal temperature, which is constant at that laser power. Using appropriate laser heating model the measured value of the equivalent crystal temperature allows one to calculate the unknown linear and nonlinear optical absorption coefficients as well as the heat transfer coefficient of the crystal with the surrounding air.

Within the framework of proton model with taking into account the piezoelectric interaction with the shear strain ε6, a dynamic dielectric response of KD2PO4 type ferroelectrics is considered. Experimentally observed phenomena of crystal clamping by high frequency electric field, piezoelectric resonance and microwave dispersion are described. Ultrasound velocity and attenuation are calculated, peculiarities of their temperature dependence at the Curie points are described. Existence of a cut-off frequency in the frequency dependence of attenuation is predicted.

We have researched piezoelectric, dielectric properties and ion conductivity in near-stoichiometric LiNbO 3 crystals (NSLN) in order to establish conditions for application of LiNbO 3 based piezoelectric resonators in the high-temperature region (∼300–850 K) which implies high conductivity. NSLN crystals have been grown from a congruent melt (R = Li/Nb ≈ 0.946) with 5.5 wt% K 2 O flux. We have revealed that piezoelectric resonance in NSLN crystals appears in a certain temperature range Δ T and resonance frequencies Δ ω R provided that τ V − 1 ≪ ω R. The temperature range Δ T corresponds to certain values of conductivity (Δ σ) and relaxation time (Δ τ V) range. We have concluded that application of high-temperature piezoelectric resonators based on crystal NSLN is possible at certain kinetic parameters of charge transport in a temperature range Δ T and at piezoelectric resonance frequencies corresponding to the temperature range. • Near-stoichiometric lithium niobate crystals were studied. • Piezo-, dielectric properties and ion conductivity were studied. • The study temperature range is ∼300–850 K. • Criterion of high-temperature application of piezoelectric resonator was determined. • The criterion: τ V − 1 ≪ ω R , τ V − 1 -relaxation time; ω R -resonance frequencies. [ABSTRACT FROM AUTHOR]