Electrical-mechanical Coupling Research Articles

Influence of Stress on the Performance of PZT Thin Films for Microphone Application

ABSTRACTA series of microphone cells based on integrated PZT thin films were fabricated by typical MEMS process. The thickness of back silicon as a load of the vibrating diaphragm was controlled by changing ICP (Inductive Coupling Plasma) etching time and power. Concaved diaphragms with different radius were formed due to the balanced tensile stress among the multi-layer films structure. The remnent and saturated polarization strength of microphone cells decreased with the increased deformation of diaphragm. The phenomenon was explained as the weakening of mechanical-electrical coupling in piezoelectric thin films in stressed state.

Periodic permeable interface cracks in piezoelectric materials

This work revisits the generalized 2D problem of electrically permeable collinear interface cracks in piezoelectric materials with two motivations: one is to present a more explicit approach to the considered problem; the other is to derive some new results for periodical interface crack problem in piezoelectric materials with the use of the new approach. Based on the Stroh formalism, the mechanical–electric coupling boundary equations are decoupled into two equations: the first one is related only to the applied mechanical loads, and the second one only to the applied electric field. According to the traditional method or available results, the solution for the first equation can be given, and then the solution for the second equation can be directly written out by using the results of the first equation. Furthermore, the solutions for infinite number of periodical collinear interface cracks are at the first time presented in closed form. The solutions include the field intensity factors and the electric fields both inside and outside the cracks. It is shown that under the electric loading only, the electric fields are uniform not only in the materials but also inside the cracks, while the stress is zero wherever. However, when the combined mechanical–electric loadings are applied at infinity, the electric fields inside the cracks may be singular and oscillatory, and such is the case for the stresses near the crack tips, but the intensities of all singularities depend on the material properties and the applied mechanical loads, not on the applied electric loads. Finally, a numerical example is given for the case of a single interface crack, and the electric fields inside the crack is shown analytically and graphically.

Dynamic Electrical-Mechanical Energy Coupling in Electrolyte-Mineral Systems

Electrical-mechanical and mechanical-electrical coupling phenomena have been observed in geo-materials. Underlying internal phenomena are not always clear. In this paper, we identify potential microscale processes on the bases of previously published research; fundamental physical principles and analytical models are included. Second, we notice important inconsistencies between theoretically predicted values or high-frequency laboratory data with respect to low-frequency field observations. To explore these differences, we conduct a laboratory experimental study that simulates field conditions, placing emphasis on low frequency coupling, that is, less than 10 kHz. Both, mechanical-electrical and electrical-mechanical effects are observed. Finally, hypotheses are presented in an attempt to explain observed differences.

Transient response of an insulating crack between dissimilar piezoelectric layers under mechanical and electrical impacts

The dynamic response of an interface crack between two dissimilar piezoelectric layers subjected to mechanical and electrical impacts is investigated under the boundary condition of electrical insulation on the crack surface by using the integral transform and the Cauchy singular integral equation methods. The dynamic stress intensity factors, the dynamic electrical displacement intensity factor, and the dynamic energy release rate (DERR) are determined. The numerical calculation of the mode-I plane problem indicates that the DERR is more liable to be the token of the crack growth when an electrical load is applied. The dynamic response shows a significant dependence on the loading mode, the material combination parameters as well as the crack configuration. Under a given loading mode and a specified crack configuration, the DERR of an interface crack between piezoelectric media may be decreased or increased by adjusting the material combination parameters. It is also found that the intrinsic mechanical-electrical coupling plays a more significant role in the dynamic fracture response of in-plane problems than that in anti-plane problems.

2-Aminoethoxydiphenyl borate causes dissociation between membrane electrical and mechanical activity in guinea-pig urinary bladder smooth muscle.

Physiological functions of urinary bladder profoundly reflect smooth muscle mechanical activity. Urinary bladder smooth muscle itself produces myogenic rhythmic contraction, and this spontaneous mechanical event could be the fundamental determinant of urinary bladder functions. The spontaneous contraction of urinary bladder smooth muscle is thought to be triggered primarily by the action potential generated in this smooth muscle cell. Modulators of ion channels contributing to the configuration of action potential also affect urinary bladder smooth muscle mechanical activity as expected exactly from the effects on the electrical event. In the present study, we show that the frequency of action potential recorded in intact strip of guinea-pig urinary bladder smooth muscle is dramatically increased by 2-aminoethoxydiphenyl borate (2-APB; 30 microM) from 0.2 Hz to 1 Hz (approximately 500% increments). In contrast to an increasing effect expected from the membrane electrical alterations, mechanical activity (both contraction amplitude and frequency) of this smooth muscle is unexpectedly reduced by the same concentration of 2-APB to approximately 35% of the control. The present results firstly show an apparent dissociation of electrical-mechanical coupling in urinary bladder smooth muscle. The alteration of membrane electrical activity might not be the exclusive trigger mechanism responsible for the generation of spontaneous rhythmic contraction of this smooth muscle.

Magnetic resonance imaging and ventricle mechanics

Methods for cardiac geometry and motion reconstruction from multi–planar tagged magnetic resonance images (MRI) have been developed and refined over the last decade. This paper firstly provides an overview of a finite–element reconstruction method, including variants for interactive three–dimensional reconstruction. The second part of this paper discusses recent applications of MRI and ventricular modelling in the study of electrical–mechanical coupling.

Transient response of a crack in piezoelectric strip subjected to the mechanical and electrical impacts: mode-I problem

Mode-I transient responses of a piezoelectric ceramic strip containing a center-situated crack under the in-plane mechanical and electrical impacts are investigated based on integral transforms and the singular integral equation techniques. Numerical results reveal the great dependence of crack extension on both the loading combination and the ratio of crack length to strip width. It can be expected that the crack extension may be retarded by adjusting the loading combination parameter for a certain ratio of crack length to strip width. In addition, numerical results also indicate that the intrinsic mechanical–electrical coupling effects play more important roles in the dynamic fracture analysis of the in-plane problem than in the anti-plane case.

Nonlinear piezoelectricity in PZT ceramics for generating ultrasonic phase conjugate waves

We have succeeded in the generation of acoustic phase conjugate waves with nonlinear PZT piezoelectric ceramics and applied them to ultrasonic imaging systems. Our aim is to make a phase conjugator with 100% efficiency. For this purpose, it is important to clarify the mechanism of acoustic phase conjugation through nonlinear piezoelectricity. The process is explained by the parametric interaction via the third-order nonlinear piezoelectricity between the incident acoustic wave at angular frequency ω and the pump electric field at 2 ω. We solved the coupling equations including the third-ordered nonlinear piezoelectricity and theoretically derived the amplitude efficiency of the acoustic phase conjugation. We compared the efficiencies between the theoretical and experimental values for PZT ceramics with eight different compositions. Pb[(Zn 1/3Nb 2/3) 1− X Ti X ]O 3 ( X=0.09, PZNT91/9) piezoelectric single crystals have been investigated for high-performance ultrasonic transducer application, because these have large piezoelectric constants, high electrical–mechanical coupling factors and high dielectric constants. We found that they have third-order nonlinear piezoelectric constants much larger than PZT and are hopeful that the material as a phase conjugator has over 100% efficiency.

Theory of indentation of piezoelectric materials

A general theory is presented for the axisymmetric indentation of piezoelectric solids within the context of fully coupled, transversely isotropic elasticity models. Explicit expressions for P– h curves are derived for spherical, conical as well as cylindrical punch indenter geometries in a manner that can be directly related to the experimental measurements. In addition, results for different electrical boundary conditions that employ conducting or insulating indenters are also presented. The theory reveals that the indentation load vs penetration depth, and the contact area vs penetration depth relations have the same mathematical structure as the classical elastic indentation problem. It is, however, demonstrated that the electric field induced during indentation as a result of the electrical–mechanical coupling can resist or aid in the penetration of the indenter into the piezoelectric material depending on the electrical conductivity of the indenter and the surface boundary conditions of the indented substrate. It is also shown that the piezoelectric material exhibits pile-up or sink-in of material around the indenter as a consequence of electromechanical coupling, despite the absence of any inelastic deformation processes or strain hardening. The theoretical predictions are corroborated with detailed finite-element simulations for different indenter geometries. The theoretical results facilitate the prediction of some transient electrical effects which can be used in conjunction with experiments for the estimation of some of the elastic, dielectric and piezolectric constants during instrumented indentation. Specific examples and details of such applications are addressed in separate papers.

Green functions of piezoelectric material with an elliptic hole or inclusion

In this paper, the Green functions of infinite two-dimensional piezoelectric material containing an elliptic hole or an elliptic piezoelectric inclusion are obtained with the extended Stroh formalism. The results can be used to investigate the mechanical-electric coupling behaviours of infinite piezoelectric material with hole or inclusion acted by a set of generalized concentrated forces, and more importantly as kernels of boundary integral equations in BEM analyses for finite size piezoelectric materials with general forces and boundary conditions.

Effect of different calcium channel blockers on inhibitory junction potentials and slow waves in porcine ileum

The effect of several calcium channel blockers was evaluated: (i) on spontaneous electrical and mechanical activities and (ii) on the response to electrical field stimulation. The study was carried out on whole-thickness preparation of porcine ileum. Glass microelectrodes were used to record membrane potential from smooth muscle cells. Resting membrane potential was -60 +/- 2mV (n = 18) and preparations generated spontaneous slow waves. Electrical field stimulation (EFS) was applied using different parameters. The amplitude and duration of inhibitory junction potentials (IJPs) increased with EFS strength. IJPs were abolished by tetrodotoxin (1 microM). Nifedipine (1 microM) did not modify the amplitude or duration of IJPs. The frequency of slow waves was not modified, however a slight but significant (p < 0.001) reduction in slow wave duration was observed. Mechanical activity was abolished in presence of nifedipine within approximately 6 min. omega-agatoxin IVA (50 nM) or omega-conotoxin MVIIC (100 nM), respectively a P-type and a Q-type calcium channel blockers, did not modify slow wave and IJP characteristics. In contrast, in presence of omega-conotoxin GVIA (100 nM), a N-type calcium channel blocker, or omega-conotoxin MVIIC (1 microM), IJPs were completely abolished. These data suggest that, in porcine ileum, N-type but not P-,Q- or L-type calcium channels are involved in the release of the non-adrenergic non-cholinergic neurotransmitters mediating IJPs. L-type calcium channels underlie electrical mechanical coupling but are not involved in slow wave generation.

A general solution and the application of space axisymmetric problem in piezoelectric material

According to the structure feature of the governing equations of space axisymmetric problem in transversely isotropic piezoelectric material, using the method of introducing potential function one by one, in this paper we obtain the so-called general solution of displacement and electric potential function denoted by unique potential function which satisfies specific partiality equations. As an applying example of the general solution, we solve problem of semi-infinite body made of piezoelectric material, on the surface of the semi-infinite body a concentrative force is applied, and get the analytic formulations of stress and electric displacement components. The general solution provided by this paper can be used as a tool to analyse the mechanical-electrical coupling behavior of piezoelectric material which contains defects such as cavity, inclusion, penny-shape crack, and so on. The result of the solved problem can be used directly to analyse contact problems which take place between two piezoelectric bodies or piezoelectric body and elastic body.

Penny-shaped crack in transversely isotropic piezoelectric materials

Using a method of potential functions introduced successively to integrate the field equations of three-dimensional problems for transversely isotropic piezoelectric materials, we obtain the so-called general solution in which the dis- placement components and electric potential functions are represented by a singular function satisfying some special partial differential equations of 6th order. In order to analyse the mechanical-electric coupling behaviour of penny-shaped crack for above materials, another form of the general solution is obtained under cylindrical coordi- nate system by introducing three quasi-harmonic functions into the general equations obtained above, It is shown that both the two forms of the general solutions are complete. Furthermore, the mechanical-electric coupling behaviour of penny-shaped crack in transversely isotropic piezoelectric media is analysed under axisymmetric tensile loading case, and the crack-tip stress field and electric displacement field are obtained. The results show that the stress and the electric displacement components near the crack tip have (r -1/2) singularity.

Incidental structural and functional effects of experimental procedures used to study transmitter release mechanisms

The discovery of structural-functional correlations at the cellular level is one of the most fruitful methods in cell physiology and has contributed much to our understanding of the fine mechanisms of secretion of synaptic transmitters and, in particular, to the elucidation of the quantum-vesicular nature of its exocytosis. It will be clear that this situation calls for a particularly careful evaluation of the effect of the experimental procedureg on the results. Detubulation of a muscle, which disturbs electrical-mechanical coupling, facilities intracellular recording of electrical responses to its direct stimulation, and it is therefore widely used to study synaptic processes. The statistical characteristics of transmitter secretion after this procedure remain substantially unchanged, but some anomalies of shape of postsynaptic potentials in neuromuscular junctions of detubulated preparations [4] can be explained by disturbance of their ultrastructure, similar to what is observed with an increase in the osmotic gradient [3]. As regards the use of such a popular fixative as formaldehyde, it is to be expected that if one source of extracellular calcium is blocked by detubulation, its familiar functional effect will also be changed [I].

Electrical-mechanical coupling of dislocations in KCl, NaCl, LiF, and CaF2

By measuring the direct and converse piezoelectric defect together with the mechanical damping and modulus defect of bent ionic single crystals, the electrical charge on the dislocations formed on bending is determined. These properties are measured at room temperature on bent 〈100〉 KCl, NaCl, LiF, and CaF2 single crystals at a frequency of 40 kHz and strain amplitudes of 4.6 × 10−10 to 7.5 × 10−5. The dislocation charge, which is always negative, ranges in magnitude from a low of 5 × 10−13 C/m for CaF2 to a high of 2.4 × 10−11 C/m for KCl. The dependence of the damping on dislocation charge for five 〈100〉 KCl crystals (two from this work, three from previous experiments) is found to be in agreement with the predictions of the charge cloud damping theory of Robinson and Birnbaum. The shape of the force-displacement hysteresis loops in the amplitude dependent region suggests that break away models for amplitude dependence are not applicable. Zur Messung des direkten und inversen piezoelektrischen Defektes sowie der mechanischen Dämpfung und des Moduldefektes wird die in der Nähe von Versetzungen beim Biegen entstehende elektrische Ladung in Ioneneinkristallen bestimmt. Diese Eigenschaften werden an Einkristallen von 〈100〉 KCl, NaCl, LiF und CaF2 bei Raumtemperatur und einer Frequenz von 40 kHz mit einer Dehnungsamplitude zwischen 4,6 × 10−10 und 7,5 × 10−5 gemessen. Die Versetzungsladung, die immer negativ ist, liegt im Bereich 5 × 10−13 C/m an CaF2 (kleinster Wert) bis 2,4 × 10−11 C/m an KCl (höchster Wert). Die Abhängigkeit der Dämpfung und des Moduldefektes an der Versetzungsladung bei fünf 〈100〉 KCl-Einkristallen (zwei aus dieser Forschung, drei aus früheren Experimenten) stimmt mit den Vorhersagen der Dämpfungstheorie der Ladungswolken von Robinson and Birnbaum überein. Die Form der Kraft-Absetzung-Hysteresisschleifen im amplitudenabhängigen Bereich läßt vermuten, daß die „break away”︁-Modelle der Amplitudenabhängigkeit nicht anwendbar sind.

Electrical-mechanical coupling due to charged dislocations

Abstract A theory for the relationship between the mechanical damping, compliance defect, piezoelectric moduli and electric susceptibility due to charged dislocations is discussed. A damping and piezoelectric (direct and converse) experiment on a <100> single crystal of KCl at 40 kHz and strain amplitudes of 1·6 × 10−10 to 1·5 × 10−5 is reported. The method is shown to be suitable for the measurement of a piezoelectric modulus as small as 5 × 10−19 coulomb/newton. The mechanical damping, compliance defect and piezoelectric modulus are found to be strongly amplitude dependent above a strain of 3 × 10−7. From this experiment the charge on the dislocations is calculated to range between 1 and 3% of the maximum allowed on a dislocation. The behaviour of this measured charge with strain amplitude suggests that the damping is due to charged dislocations interacting with their compensating charge clouds. The charge cloud radius of 13 Å calculated from the impurity concentration agrees favourably with the value of 20 Å obtained from the experimental results suggesting that the restrictions on the theory for eV ∞/kT>l are not severe. The electric susceptibility due to charged dislocations is estimated as 10−4.