Characterization of piezoceramics

A 3-D approach to piezoelectric material characterization, based on the assumption that the coordinate axes are pure mode propagation directions, is described. In this case the general equations simplify and an analytical solution can be achieved. For two geometrical shapes (rectangular and cylindrical), stress and strain tensor components and the electrical impedance of the sample are obtained. These 3-D equations show that the wave velocities and permittivity are intrinsic parameters of the medium and do not depend on either the sample geometry or the mode that is considered. This was not true for the 1-D models where the wave velocities and permittivity are different for each of the modes or geometries.     

Built-in getter-ion pumps

It is shown that theory of the Penning discharge essentially involves taking into account the collective interaction of the electrons in the near-anode region. Following investigations of the Penning discharge in a strong magnetic field (density up to 12 kOe) empirical formulae are proposed for calculating the pumping speed and the minimum operating pressures of getter-ion pumps. Methods of calculation for built-in getter-ion pump parameters and design peculiarities are considered.     

Preparation of hard lead-zirconate-titanate-based piezoceramics

Fluorinated lead zirconate titanate piezoceramics are prepared using mechanical activation of the starting mixture and synthesized ceramic powder in a vibratory mill, and their physical properties are studied. The introduction of fluorine (1–5 mol %) into the starting mixture enhances the dielectric rigidity of the material. The addition of 0.1–0.3 mol % F in combination with 0.3–3 mol % Fe makes it possible to produce hard piezoceramics capable of operating in electric fields of up to 3 kV/cm. The ceramics have a tetragonally distorted perovskite structure and consist of grains 1–2 m in size. X-ray microanalysis of specimens prepared by polishing and etching reveals significant compositional inhomogeneities.Translated from Neorganicheskie Materialy, Vol. 40, No. 12, 2004, pp. 1526–1529.Original Russian Text Copyright © 2004 by Klimov, Selikova, Dorofeeva, Bronnikov.     

Invariants of electromechanical coupling coefficients in piezoceramics

The relationships between coefficients of electromechanical coupling (CEMC) of various types of piezoceramic resonator (PR) vibrations are considered. Being constant for a given piezoceramic state, the range of variation of piezoceramics dielectric permittivity from a mechanically "free" condition at relatively low frequencies up to an "overall clamped" condition at high frequencies is determined by a consecutive "clamping", caused by a complex of CEMCs of various particular vibrational modes peculiar to the resonator. As the difference between "free" and "overall clamped" permittivities is always determined by the maximal piezomaterial /spl kappa//sub i3/ coupling coefficient, the difference does not depend on the path that was gone through the low-high frequency range, which includes all the vibrational modes possible for a particular PR. The influence of the piezoelectric and elastic anisotropy of lead-zirconate-titanate (PZT) piezoceramic materials on relative CEMC variations was experimentally investigated.     

Built-in self-test for phase-locked loops

An effective built-in self-test (BIST) structure of a phase-locked loop (PLL) in digital applications is presented in this paper. The proposed BIST structure can identify possible faults in any block such as the phase detector, charge pump, loop filter, voltage-controlled oscillator and divide-by-N of the PLL. The key advantage of this approach is that it uses all existing blocks in PLL for measuring and testing, reducing the chip area overhead. Restated, the proposed approach does not alter any existing analog circuits. Rather, the proposed approach only adds some small circuits to the PLL and requires a slight modification of the digital part. The final test outputs are digital values which can increase the reliability of the proposed BIST structure. Physical chip design and fault simulation results indicate the characteristics of the proposed BIST structure, namely, high fault coverage (97.2%) and low area overhead (2.78%).     

DEPP functionally graded piezoceramics via micro-fabrication by co-extrusion

This paper introduces the Dual Electro/Piezo Property (DEPP) gradient technique via Micro-Fabrication through Co-eXtrusion (MFCX) which pairs a high displacement lead zirconate titanate (PZT) piezoceramic with a high permittivity barium titanate (BT) dielectric. By grading with this material combination spatially across an actuator, the electric field is concentrated in the more active region for improved efficiency, higher displacements, and complex motions. To aid in synthesis and analysis of any gradient profile, compositional maps are provided for key material properties (density, stiffness, permittivity, and piezoelectric coefficients). The DEPP technique was validated, independent of the MFCX process, by powder pressing a conventional bimodal gradient beam which demonstrated through experiments high displacement capabilities at lower driving potentials than comparable functionally graded piezoceramic actuators. For more complex gradients, the MFCX process was adapted to the DEPP gradient technique and illustrated by the fabrication of a linearly graded prototype whose monolithic nature and gradual material variation significantly reduces internal stresses, improves reliability, and extends service lifetime.     

Boundary element method for electroelastic interaction in piezoceramics

A boundary element formulation and its numerical realization for the analysis of electroelastic interaction in piezoelectric materials are presented and corroborated numerically. Based on the linear theory of piezoelasticity, the boundary integral equation is developed employing the mechanical displacement and the electric potential as the primary variables. A two-dimensional fundamental solution for transversely isotopic piezoelectric materials is obtained in closed form and numerically implemented using the spline boundary element method. As a numerical example, stress analysis is performed for an infinite piezoceramic medium (PZT-4) containing a cylindrical defect under several mechanical and electric loading conditions. Numerical results are shown to be in good agreement with an available solution.     

A thermodynamically and microscopically motivated constitutive model for piezoceramics

Following the approach in [Smart. Mater. Struct. 9 (1999) 441], a constitutive model based on microscopically motivated internal variables is formulated for piezoceramics under multiaxial electromechanical loadings. The internal variables describe domain switching and reorientation in the material.     

Selectively designed Fe doping of lead-free BaTiO3 piezoceramics

Journal of Materials Science: Materials in Electronics - Fe doping has been investigated to determine the effect of defects on the piezoelectric properties of BaTiO3 ceramics. Fe doping can produce...     

Built-in self-test structure for mixed-mode circuits

A built-in self-test (BIST) structure is presented which provides controllability and observability to analog circuits under test with significantly reduced hardware overhead compared to previously reported methods. The test structure is equally applicable to digital circuits, and lends itself to automated insertion into circuits under test     

Study on pore-forming agents in processing of porous piezoceramics

Porous piezoceramics have wide performance advantages over monolithic ceramic and polymer piezoelectric materials in underwater sensing and actuation applications. This paper describes the effect of various pore-forming agents during burnt plastic spheres (BURPS) processing of porous ceramics. Three kinds of polymeric materials were used as pore forming agents for BURPS processing of porous piezoceramics. Properties such as the piezoelectric charge coefficient, hydrostatic charge coefficient and hydrostatic voltage coefficient were studied. The effect of various pore forming agents on porous piezoceramics was also investigated. The microstructures of the porous piezoceramics were also recorded to study the effect of pore-forming agents on microstructure and properties.     

Shell theory for vibrations of piezoceramics under a bias

A consistent derivation of the shell theory in invariant form for the dynamic fields superimposed on a static bias of piezoceramics is discussed. The fundamental equations of piezoelectric media under a static bias are expressed by the Euler-Lagrange equations of a unified variational principle. The variational principle is deduced from the principle of virtual work by augmenting it through Friedrich's transformation. A set of two-dimensional (2-D), approximate equations of thin elastic piezoceramics is systematically derived by means of the variational principle together with a linear representation of field variables in the thickness coordinate. The 2-D electroelastic equations accounting for the influence of mechanical biasing stress accommodate all the types of incremental motions of a polarized ceramic shell coated with very thin electrodes. Emphasis is placed on the special motions, geometry, and material of the piezoceramic shell. The uniqueness of the solutions to the linearized electroelastic equations of the piezoceramic shell is established by the sufficient boundary and initial conditions.     

Built-in self-test design of current-mode algorithmicanalog-to-digital converters

Analog MOS circuits are becoming increasingly sophisticated in terms of checking and correcting themselves. Self-correcting, self-compensating, or self-calibrating techniques has been employed in analog-to-digital (A/D) converters to eliminate errors caused by offset and low frequency noise, and to cancel the error effect. However, the self-compensating/calibration techniques may no longer work properly in the presence of faulty switching elements. This paper presents the fault behaviors and test generation of a current-mode algorithmic A/D converter, where the single stuck-at faults in the switching elements of the converter are assumes. The converter requires only two test currents to achieve a full testability. Due to the simplicity of generating test currents and the expected outputs, a simple built-in self-test (BIST) structure is proposed. Two extra pins for test enable signal and error indicator are needed. Results show that the full self-testability of the BIST structure is achieved with a low pin/hardware overhead, and the use of expensive test equipment is not necessary     

Piezoelectric properties and unipolar fatigue behavior of KNN-based Pb-free piezoceramics

Single-phase perovskite ceramics were synthesized using a Pb-free (K(0.44)Na(0.52)Li(0.04))(Nb(0.86)Ta(0.10)Sb(0.04))O(3) (LF4) piezoelectric material both with and without CuO as a dopant additive. Bipolar hysteresis measurements showed a relatively high remanent polarization (20 μC/cm(2), 16 μC/cm(2)) and maximum polarization (25 μC/cm(2), 21 μC/cm(2)) values were found for undoped LF4 and 0.2 wt% CuO-doped LF4, respectively. Unipolar fatigue behavior for this system was found to decrease strongly with increased applied testing fields and increased test durations. For undoped LF4, the maximum polarization values were stable after 10 cycles after testing for 100,000 cycles duration. For the CuO-doped samples, increasing the testing field to 3E(C) resulted in twice the decrease in P(MAX) (?32%) compared with the 2E(C) tests at 10(6) cycles (-17%). At 2E(C) testing for CuO doping, polarization decreases continually through 10(7) cycles, with the decreases in P(MAX) and d(33) both reaching a maximum (-22% and -30%, respectively) after 10(7) cycles. In the CuO-doped samples, the fatigue is exacerbated because of the influence of space charge on the increased number of defects present.     

Support-Vector-Machine-Based False Alarm Filter of Mechatronic Built-in Test

Diagnosing intermittent fault is an important approach to reduce built-in test（BIT） false alarms. Aiming at solving the shortcoming of the present diagnostic method of intermittent fault, and according to the merit of support vector machines （ SVM） which can be trained with a small-sample, an SVM-based diagnostic model of 3 states that include OK state, intermittent state and faulty state is presented. With the features based on the reflection coefficients of an alarm rate （ AR ） model extracted from small vibration samples, these models are trained to diagnose intermittent faults. The experimental results show that this method can diagnose multiple intermittent faults accurately with small training samples and BIT false alarms are reduced.     

Broadband generation of ultrasonic guided waves using piezoceramics and sub-band decomposition

Classically, damage detection or dispersion curve determination using piezoceramic-generated guided waves has been based on analysis of propagation properties of multiple narrowband excitation signals. However, dispersion and multimodal propagation impair the determination of propagation properties. More recently, it has been proposed to consider broadband excitations for both damage imaging and group velocity estimation. Among existing transducer technologies, although laser excitation is prone to practical limitations in terms of dimensions and generated amplitudes, it allows generation of noncontact, point-like broadband displacement. Thus, broadband generation of guided waves using piezoceramics can be envisioned. However, direct impulse response measurements are limited by the generated amplitude, leading to low SNR measurements. For this purpose, chirp excitations have been proposed using variable-frequency bursts, leading to phase and amplitude variations with respect to the frequency, such that this approach is not suitable for precise estimation of time of flight (ToF) or modal amplitude. In this paper, a sub-band decomposition technique that allows high-SNR measurements of impulse response in a given frequency range is proposed. Broadband excitation is decomposed over a given number of frequency sub-bands, generated by a piezoceramic element and measurement is performed using a laser Doppler vibrometer (LDV) or a piezoceramic sensor. Application to experimental estimation of group velocity and damage detection in pitchcatch configuration is proposed. It is shown that the proposed method allows damage estimation without a priori knowledge of the damage size, whereas narrowband techniques can fail at specific wavelengths.