Dispersion relation of piezoelectric periodic structure

The coupled dispersion relation resulting from the interaction of acoustic waves with an infinity long conducting grating deposited along the pure mode axis of a piezoelectric crystal of trigonal class is specified and its implications on different kinds of mode coupling are discussed.     

Propagation of surface acoustic waves in a piezoelectric medium with a periodic groove structure

A system of equations is formulated to describe the propagation of surface acoustic waves in a piezoelectric substrate whose surface has a periodic structure formed by transverse grooves. Dependences of the reflection coefficient and the wave velocity on the geometry of the periodic structure (the width and the depth of the grooves) are obtained in a wide range of variation of these parameters for five different orientations in various piezoelectric crystals (quartz, lithium niobate, lithium tantalate, and langasite).     

Interfacial effects for shear waves in one dimensional periodic piezoelectric structure

Within the full system of Maxwell's equations this paper investigates the effects of three kinds of transmission conditions at the interfaces between the laminae of a periodic piezoelectric structure on band gaps of Bloch-Floquet waves propagating oblique to the interfaces. The results that are obtained show that under both electrically shorted and magnetically closed transmission conditions Bloch-Floquet waves exist only at acoustic frequencies. The effects of piezoelectricity on Bloch-Floquet wave band structures are studied at such frequencies. It is shown that for periodic crystal structures with laminae made of identical materials the propagation of Bloch-Floquet waves can occur under electrically shorted interface conditions but not under magnetically closed interface conditions.For electrically open interfaces with mechanically smooth contacts the dynamic setting of the problem provides solutions only for photonic crystals. In this case the piezoelectricity has no effect on band gaps.     

Electromechanical properties and defect chemistry of high-temperature piezoelectric materials

Langasite and gallium phosphate are shown to exhibit piezoelectrically stimulated bulk acoustic waves up to at least 1,400 and 900 °C, respectively. Most critical issues are stoichiometry changes due to, e.g. low oxygen partial pressures, and high losses. Therefore, the paper discusses the atomistic transport and defect chemistry of those crystals and correlates them with the electromechanical properties. First, the defect chemistry of langasite is investigated. As long as the atmosphere is nearly hydrogen-free, the transport of charge carriers is governed by oxygen movement. A dominant role of hydrogen is observed in hydrogenous atmospheres. Based on the developed defect model, donors are expected to suppress the oxygen vacancy concentration and, thereby, the loss in langasite. The prediction is proven by niobium doping and found to be valid. A one-dimensional physical model of thickness shear mode resonators is summarized. The analysis of the resonance spectra showed that the loss of the resonators can be described satisfactorily by mechanical and electrical contributions expressed as effective viscosity and bulk conductivity, respectively. The mechanical loss in langasite is significantly impacted by the electrical conductivity due to the piezoelectric coupling. The effect of the piezoelectric coupling on the loss is negligible for gallium phosphate since it shows an extremely low electrical conductivity.     

Electromechanical properties of 2-2 cement based piezoelectric composite

A 2-2 type cement based piezoelectric composites were fabricated by dice-and-fill technique. The influences of lead magnesium niobate-lead zirconate-lead titanate (PMN) ceramic volume fraction on the electromechanical properties of the composite were investigated. The results indicate that the planar electromechanical coupling factor K_p of the composite is hardly influenced by the PMN volume fraction, which fluctuates between 35% and 37%, while both the thickness electromechanical coupling factor K_t and the mechanical quality factor Q_m exhibit the trend of increase. When PMN volume fraction is 69.2%, K_t could reach to 49.8%, which is larger than that of the PMN ceramic (K_t = 46%).When PMN volume fraction is 41.7%, Q_m is 4.5, which is also much less than that of the PMN ceramic (Q_m = 70). This means that the composite has wider frequency band and higher sensitivity to be used as transducers. With the increase of PMN volume fraction, the acoustic impedance of the composite also exhibits the trend of increase.     

Acoustic microwave generation in a periodic piezoelectric medium with drifting charges

A novel technique of generation of acoustic microwave is analyzed. The basic principle is similar to the distributed feedback concept used in lasers, where the oscillation feedback is provided by a periodic structure throughout the amplifying medium. A simplified model is analyzed in detail, and a number of configurations for oscillator device development are discussed.     

Phonon-polariton and band structure of electro-magneto-acoustic SH wave propagation oblique to the periodic layered piezoelectric structures

Electro-magneto-acoustic SH waves propagating oblique to the periodic layered piezoelectric structures are studied under the coupling of the acoustic wave and the electromagnetic wave. Band structures of the so-called piezoelectric superlattice and phononic/photonic crystal are given both at acoustic frequencies and at optical frequencies. For the periodic layered piezoelectric structures, phonon-polaritons (the coupling modes of the phonons and photons) are found not only happening near the center of the Brillouin zone (in the long-wavelength limit) at acoustic frequencies, but also being able to appear in the whole Brillouin zone at optical frequencies. Appearing of these phonon-polaritons may provide a way to design a new type of acousto-optic devices.     

Actuation of a discontinuous structure with piezoelectric actuators

An alternate approach to exciting a one-dimensional structure with discontinuities using a piezoelectric actuator is presented and examined. Instead of being bonded to the uniform side of a beam, the piezoelectric actuator is attached such that it spans two adjacent rib discontinuities. In this configuration, the actuator generates an eccentric actuation force on the structure and induces both axial and transverse motions. The goal of this work is to first model the axial and transverse response caused by the piezoelectric actuator. Then, the change in that response is examined for the case where an external disturbance force is present. The system is modeled by coupling the piezoelectric strain and structural dynamic response. The characteristics of the voltage-generated piezoelectric forces are discussed through numerical examples. The structural response found using the dynamic force–voltage model for the actuator is then compared to the response when the actuator model is approximated by its static or zero-frequency value. Furthermore, the ability of the actuator to potentially provide better control authority by using this alternate configuration is examined. The numerical study shows that when the actuator spans two discontinuities, there is potential for greater control authority than when that same actuator is placed on the uniform side of the structure.     

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.     

Electromechanical impedance measurement from large structures using a dual piezoelectric transducer

This study develops a new electromechanical (EM) impedance measurement technique specifically for continuous monitoring of large structures. Conventionally, a single surface-mounted lead zirconate titanate (PZT) transducer is often used to measure the EM impedance of a coupled PZT-structure system for damage diagnosis. However, when the target structure is massive, the impedance measurement becomes challenging. In this study, a dual piezoelectric transducer, composed of two separate but concentric PZT segments, is used for effective measurement of the EM impedance from large-scale structures. The impedance measurement using the dual PZT is theoretically formulated and numerically verified. Then, a series of experiments are carried out on a laboratory-size specimen and full-scale bridge and building structures. The experimental results reveal that the proposed technique successfully measures the EM impedance signals from massive structures with a high signal-to-noise ratio (SNR) and good repeatability even when the conventional techniques fail to do so. At the same time, the proposed technique allows low-cost and fast measurement of impedance signals.     

Love wave propagation in piezoelectric layered structure with dissipation

We investigate analytically the effect of the viscous dissipation of piezoelectric material on the dispersive and attenuated characteristics of Love wave propagation in a layered structure, which involves a thin piezoelectric layer bonded perfectly to an unbounded elastic substrate. The effects of the viscous coefficient on the phase velocity of Love waves and attenuation are presented and discussed in detail. The analytical method and the results can be useful for the design of the resonators and sensors.     

A periodic surface structure with extreme acoustic properties

Several variational problems of sound absorption and scattering are solved using an impedance-based approach. Analytical expressions are derived for the surface impedances of the best absorber and a perfectly transparent body. A discrete surface structure (coating) is proposed for implementing their acoustic properties. Results of computer simulation are presented.     

Electromechanical properties of lanthanum-doped lead hafnate titanate thin films for integrated piezoelectric MEMS applications

This paper focuses on the deposition and electromechanical characterization of lanthanum-doped lead hafnate titanate (PLHT) thin films as key material in piezoelectric microelectromechanical systems (pMEMS). PLHT (x/30/70) and PLHT(x/45/55) films with a thickness between 150 nm and 250 nm were deposited by chemical solution deposition (CSD). Thereby x varies between 0 and 10% La content. The electrical characterization shows that undoped (x=0) PLHT exhibit ferroelectric behavior similar to PZT of the same composition. La doping results in reduced ferroelectric properties and also affects the electromechanical properties. Measurements using a double beam laser interferometer yield a piezoelectric coefficient d ₃₃ of 60 pm/V, which stays constant with an increasing electric field. This leads to a linear displacement compared to undoped PLHT or conventional PZT films used for MEMS applications.     

On the conductivity of composites with two-dimensional periodic structure

A method is suggested of successive solution of the problem on the conductivity of two-dimensional periodic systems with inclusions of arbitrary shape. The complex potential outside of the inclusions is expressed in terms of the Weierstrass zeta function and its derivatives. The field induced on a separate inclusion is described using the matrix of multipole polarizabilities. The “joining” of potentials is performed at a distance such that R < ρ < a, where R is the characteristic dimension (maximum “radius”) of the inclusion and a is the half-period of the lattice. The approach suggested enables one to find exact virial expansions for the conductivity of other effective characteristics of similar systems as well.     

Elastic guided wave propagation in a periodic array of multi-layered piezoelectric plates with finite cross-sections

In this study, we present a model study of guided wave dispersion and resonance behavior of an array of piezoelectric plates with arbitrary cross-sections. The objective of this work is to analyze the influence of the geometry of an element of a 1D-array ultrasound transducer on generating multi-resonance frequency so as to increase the frequency bandwidth of the transducers. A semi-analytical finite-element (SAFE) method is used to model guided wave propagation in multi-layered 1D-array ultrasound transducers. Each element of the array is composed of LiNbO₃ piezoelectric material with rectangular or subdiced cross-section. Four-node bilinear finite-elements have been used to discretize the cross-section of the transducer. Dispersion curves showing the dependence of phase and group velocities on the frequency, and mode shapes of propagating modes were obtained for different geometry consurations. A parametric analysis was carried out to determine the effect of the aspect ratio, subdicing, inversion layer and matching layers on the vibrational behavior of 1D-array ultrasound transducers. It was found that the geometry with subdiced cross-section causes more vibration modes compared with the rectangular section. Modal analysis showed that the additional modes correspond to lateral modes of the piezoelectric subdiced section. In addition, some modes have strong normal displacements, which may influence the bandwidth and the pressure field in front of the transducer. In addition, the dispersion curves reveal strong coupling between waveguide modes due to the anisotropy of the piezoelectric crystal. The effect of the matching layers was to cluster extensional and flexural modes within a certain frequency range. Finally, inversion layer is found to have a minor effect on the dispersion curves. This analysis may provide a means to analyze and understand the dynamic response of 1D-array ultrasound transducers.     

Giant piezoelectric anisotropy in sodium niobate with a composite-like structure

On the basis of X-ray diffraction and electrophysical data for stoichiometric and nonstoichiometric sodium niobate, it is concluded that a mechanism responsible for the infinite ratio of the electromechanical coupling factors for the thickness and plane modes may be related to the composite-like structure of the material. It is shown that such a structure may result from the presence of ordered extended voids (arising at the joints between perfect structure blocks), which behave as microcracks. Stresses generated at the joints may modify the domain structure and lead to the anisotropic distribution of polarized clusters in the ferroelectric phase. This also may enhance the piezoelectric anisotropy.     

Shear horizontal surface waves on piezoelectric ceramic with layered structure

This paper presents theoretical and experimental results describing the propagation of SH (shear, horizontal) surface waves on a piezoelectric ceramic with a surface layer of different polarization than that in the substrate. An analytical formula for the group velocity of the SH surface waves is developed. The velocity of impulses of the SH surface waves is determined experimentally. Further, the theoretical results are compared to the experimental values.     

弱界面压电覆层复合结构中的声导波

建立压电覆层复合结构中声导波传播模型,结合弱界面“弹簧”模型,推导了压电覆层复合结构存在刚性、滑移联接界面等几种不同界面条件下声导波的广义频散方程,数值计算钛锆酸铅基压电陶瓷覆层复合结构在不同界面条件下声导波的频散曲线,分析了界面特性对导波传播相速度的影响。数值计算和分析表明为了能够有效地评价界面的特性,选择合适的声波模式和声波频率是非常重要的。实验结果验证了界面假设的有效性,为进一步深入研究以多模式声导波参量为基础的压电覆层复合结构界面特性参数反演方法提供了理论基础。     

Electromechanical single electron transistor in strong dissipative structure

In the experiment of electromechanical single electron transistor, two tunneling junctions are not the same completely because of manufacturing processes or quantum effects. We simplify these complexities as an asymmetric-junction device with two unequal initial capacitances. A model system of a single electron transistor with strong dissipation is investigated, where the metal cluster of mechanical motion is coupled to drain and source electrodes. This semiclassical system considers the difference between drain capacitor and source capacitor, simulated by using Monte Carlo methods. The voltage regions are distributed into the efficient-shuttle region and the non-shuttle region by the shuttle mechanism of the island. A symmetric-junction device only works in the efficient-shuttle region. However, both kinds of mechanisms occur in an asymmetric-junction device, where we observe restrained currents and negative differential conductance phenomena.