Showing papers on "Piezoelectric sensor published in 2000"

Fundamental Understanding of Piezoelectric Strain Sensors

Abstract: This paper investigates the behavior of piezoelectric elements as strain sensors. Strain is measured in terms of the charge generated by the element as a result of the direct piezoelectric ef- fect. Strain measurements from piezoceramic (PZT) and piezofilm (PVDF) sensors are compared with strains from a conventional foil strain gage and the advantages of each type of sensor are dis- cussed, along with their limitations. The sensors are surface bonded to a beam and are calibrated over a frequency range of 5-500 Hz. Correction factors to account for transverse strain and shear lag ef- fects due to the bond layer are analytically derived and experimentally validated. The effect of tem- perature on the output of PZT strain sensors is investigated. Additionally, design of signal condition- ing electronics to collect the signals from the piezoelectric sensors is addressed. The superior performance of piezoelectric sensors compared to conventional strain gages in terms of sensitivity and signal to noise ratio is demonstrated.

Impedance-based health monitoring of civil structural components

Abstract: This paper presents experimental evidence on the use of the impedance-based health-monitoring technique on components typical of civil structures. The basic principle behind this technique is to utilize high-frequency structural excitations (typically >30 kHz) through a surface-bonded piezoelectric sensor/actuator to detect changes in structural point impedance due to the presence of damage. Real-time damage detection on composite-reinforced concrete walls was investigated and the capability of this technique to detect imminent damage, well in advance of actual failure, was confirmed. Concepts that directly applied to this technique itself, such as effects of boundary condition changes and the effects of temperature changes, were also investigated. Experimental investigations were carried out on a 1/4-scale bridge element and a pipe joint commonly found in civil structures, to verify robustness of the technique to changes in environmental conditions. Data collected from the tests demonstrate the capabilit...

Vibration control with state-switched piezoelectric materials

Abstract: In this paper, a semi-active control law is used to switch the electrical shunt circuit of a piezoelectric actuator for energy dissipation in a simple mechanical system. Switching is carried out between open-circuit (high stiffness) and short- or resistive-circuit (low stiffness) states. The actuator is held in its high stiffness state when the system is moving such that energy can be stored in the actuator. When the system’s motion would cause it to receive energy back from the actuator, the actuator is switched to a low stiffness state, dissipating the energy. In this paper, the concept is developed starting with the governing piezoelectric equations. Numerical simulation results are presented which show that the technique provides energy dissipation that is comparable to other piezoelectric shunt mechanisms, using optimal shunt resistance in each case. Finally, a brief analysis is presented in which the piezoelectric element is used in a flexible beam element to illustrate the effects of a parallel str...

An Integrated Health Monitoring Technique Using Structural Impedance Sensors

Abstract: This paper presents an integrated methodology to detect and locate structural damage. Two different damage detection schemes are combined in this methodology, which involves utilizing the electromechanical coupling property of piezoelectric materials and tracking the changes in the frequency response function data, respectively. Physical changes in the structure cause changes in mechanical impedance. Due to the electromechanical coupling in piezoelectric materials, this change in structural mechanical impedance causes a change in the electrical impedance of the piezoelectric sensor. Hence, by monitoring the electrical impedance one can qualitatively determine when structural damage has occurred or is imminent. Based on the fact that damage produces local dynamic changes, this technique utilizes a high frequency structural excitation (typically greater than 30 kHz) through the surface-bonded piezoelectric sensor/actuators. As a second step, a newly developed model-based technique, using a wave propagation ...

Three-Dimensional Analytical Solution for Hybrid Multilayered Piezoelectric Plates

Abstract: Analytical solutions for the static three-dimensional deformations of multilayered piezoelectric rectangular plates are obtained by using the Eshelby-Stroh formalism. The laminated plate consists of homogeneous elastic or piezoelectric laminae of arbitrary thicknesses. The equations of static, linear, piezoelectricity are exactly satisfied at every point in the body. The analytical solution is in terms of an infinite series; the continuity conditions at the interfaces and boundary conditions at the edges are used to determine the coefficients. The formulation admits different boundary conditions at the edges and is applicable to thick and thin laminated plates. Results are presented for thick piezoelectric plates with two opposite edges simply supported and the other two subjected to various boundary conditions. @S0021-8936~00!01803-1#

A hybrid stress ANS solid-shell element and its generalization for smart structure modelling. Part II?smart structure modelling

Abstract: In Part I of the paper, a hybrid-stress-assumed natural strain eight-node solid-shell element immune to shear, membrane, trapezoidal, thickness and dilatational lockings has been developed. Moreover, the element computational cost is reduced by enforcing admissible sparsity in the flexibility matrix. In this part of the paper, the solid-shell element is generalized to a piezoelectric solid-shell element. Using the two solid-shell elements, smart structures with segmented piezoelectric sensors and actuators can be conveniently modelled. A number of problems are studied and comparisons with other ad hoc element models for smart structure modelling are presented. Copyright © 2000 John Wiley & Sons, Ltd.

Method and apparatus for monitoring respiration using signals from a piezoelectric sensor mounted on a substrate

Abstract: A method and apparatus for monitoring and/or quantitatively measuring a patient's respiration using a flexible piezoelectric film sensor The apparatus includes a piezoelectric film which converts acoustical waves generated by the patient's respiration into electrical signals The piezoelectric film sensor can be used to monitor the respiration of a patient by correlating the sound generated in the patient's airway with respiratory activity Further, the data generated by the sensor may be further analyzed by a patient monitor to diagnose respiratory conditions

Ultrasonic density sensor for liquids

Abstract: This paper presents an ultrasonic density sensor for liquids that unifies high accuracy with high durability and is suitable for on-line measurements in a wide range of tube diameters. The sensor consists of a transducer with a piezoceramic disk mounted between two reference rods of quartz glass. Additionally, a second transducer is used as a sound receiver. The density is obtained from the reflection coefficient of ultrasound at the interface between the quartz glass rod and the liquid and the transit time of sound between this interface and the second transducer. Parameters, such as high long-term stability and accuracy of /spl plusmn/0.1% of full scale, were obtained by an internal acoustic reference measurement. The reference signal is generated using the sound radiated from the rear side of the piezoceramic disk. Design aspects such as sensor materials and signal-to-noise ratio are discussed, and experimental results are given in this paper. Applications of the sensor include concentration measurement, and ultrasonic mass flow measurement.

Piezoelectric induced bending and twisting of laminated composite shallow shells

Abstract: The piezoelectric induced bending and twisting deformation of laminated shallow shells has been presented in this report. A simple and efficient method has been developed for the static analysis of shallow shells under mechanical, thermal, and piezoelectric fields. The governing equations are based on the linear theory of piezoelectricity and the classical thin shallow shell assumptions. Approximate solutions have been obtained using the conventional Ritz analysis for different boundary conditions. Comparisons of degenerate cases with published analytical and experimental results show good agreement. Several cases have been reported here, investigating the effects of material stiffness coupling, shell shallowness, and actuator geometric parameters on the bending and twisting deformation of piezoelectric laminated structures. It is shown that the desired shape could be better controlled by a proper selection of the lay-up configuration and geometric characteristics of the structure such as the thickness, size, and location of the piezoelectric actuators.

Cylindrical Bending of Laminated Plates with Distributed and Segmented Piezoelectric Actuators/Sensors

Abstract: The generalized plane quasistatic deformations of linear piezoelectric laminated plates are analyzed by the Eshelby‐Stroh formalism. The laminate consists of homogeneous elastic or piezoelectric laminae of arbitrary thickness and width. The three-dimensional differential equations of equilibrium for a piezoelectric body are exactly satiseed at every point in the body. The analytical solution is in terms of an ine nite series; the continuity conditions at the interfaces between adjoining laminae and boundary conditions at the edges are satise ed in the sense of Fourier series. The formulation admits different boundary conditions at the edges and is applicable to thick and thin laminated plates. Results are presented for laminated elastic plates with a distributed piezoelectric actuator on the upper surface and a sensor on the lower surface and subjected to different sets of boundary conditions at the edges. Results are also provided for a piezoelectric bimorph and an elastic plate with segmented piezoelectric actuators bonded to its upper and lower surfaces.

A float-encoded genetic algorithm technique for integrated optimization of piezoelectric actuator and sensor placement and feedback gains

Abstract: This paper presents a novel float-encoded genetic algorithm and applies it to the optimal control of flexible smart structures bonded with piezoelectric actuators and sensors. A performance function is initially developed, based on the maximization of dissipation energy due to a control action. Then, according to this characteristic, a float-encoded genetic algorithm is presented which is capable of solving this optimization problem reliably and efficiently. The optimization algorithm that is developed for the control of flexible systems allows an integrated determination of actuator and sensor locations and feedback gains. The paper demonstrates the suitability of the proposed technique through its application to three standard benchmark test functions and a collocated cantilever beam.

Class D amplifier for a power piezoelectric load

Abstract: We present a high efficiency inverter (>90%) that can drive an acoustic cavitation reactor with a 2 kW power between 10 and 100 kHz. This reactor is composed of numerous piezoelectric transducers and is particularly used to accelerate various industrial chemical reactions and destroy a variety of organic contaminants in water. The class-D amplifier or inverter is composed of power MOSFETs, type IRFP460, in a full bridge configuration driven by IR2110 circuits in bootstrap mode. The specific nature of the problem comes from the fact that, at frequencies slightly different from a resonant frequency frn, the load is mostly capacitive. The insertion of an appropriate low-pass filter in front of the load allowed an efficient solution to the problem due to the load being capacitive for harmonics. The realized system can provide nearly 2 kW to this type of piezoelectric load, with an efficiency of more than 95%.

Dynamic Responses of Smart Composites Using a Coupled Thermo-Piezoelectric -Mechanical Model

Abstract: A completely coupled thermo-piezcelectricmechanical theory is developed to model the dynamic response of composite plates with surface bonded piezoelectric actuators. A higher order laminate theory is used to describe the displacement fields of both composite laminate and piezoelectric actuator layers to accurately model the transverse shear deformation which is significant in moderately thick constructions. A higher order temperature field is used to accurately describe the temperature distribution through the thickness of composite plates subjected to a surface heat flux. A finite element model is developed to implement the theory. The results obtained using this model are correlated with those using an uncoupled model. Numerical analysis reveals that the thermo-piezoelectricmechanical coupling has a significant effect on the dynamic response of composite plates. It also affects the control authority of piezoclectric actuators.

Optimal placement and size of piezoelectric patches on beams from the controllability perspective

Abstract: This paper is concerned with the optimal design of a collocated pair of piezoelectric patch actuators that are surface bonded onto beams. The design involves selecting the optimal locations and sizes (or lengths) of the piezoelectric actuators based on a controllability perspective. The objective function is referred to as the controllability index, which is the singular value of a control matrix. The index measures the input energy required to achieve a desired structural control by the piezoelectric actuators. The controllability index is dependent on the placement and size of the piezoelectric patches, and thus by maximizing the index the designer can obtain the optimal design of the piezoelectric actuator. As illustrations, various beam examples with a pair of piezoelectric patch actuators are solved and the optimal design characteristics of the actuators are examined.

New shunting parameter tuning method for piezoelectric damping based on measured electrical impedance

Abstract: A new tuning method for passive piezoelectric damping which is based on the electrical impedance model and maximum dissipated energy is proposed and its validity is investigated. In contrast to the conventional tuning method associated with a mechanical vibration absorber, the proposed method uses the electrical impedance model of which the coefficients of the model are found from the measured impedance data. In the tuning process, the optimal shunt parameters are found for maximizing the dissipated energy at the shunt circuit. A mechanical vibration absorber example proves that the result of the proposed method shows a good agreement with that of the conventional tuning method. Examples of piezoelectric cantilever beams and plates are considered to demonstrate the validity of the proposed method in realistic piezoelectric structures. Since this method is based on measured electrical impedance data, it can be easily applied to arbitrary shapes as well as sizes of piezoelectric structures. Also, the proposed method is applicable for multiple-mode piezoelectric damping with one piezoelectric device. Some remarks concerning realistic implementations are addressed.

Piezoelectric element, inkjet recording head, manufacture method thereof

Abstract: PROBLEM TO BE SOLVED: To provide a piezoelectric element wherein piezoelectric constant can be optimized by adjusting the optimum excessive content of lead in accordance with the intensity of an electric field applied to the piezoelectric element. SOLUTION: In the case where a piezoelectric film containing excessive amount of lead more than the amount of lead which is required from stoichiometric ratio is formed, when thickness of the piezoelectric film is t (cm) and an applying voltage is Vh (kV), the excessive ratio of lead contained in the piezoelectric film is adjusted in a range of A(Vh/t)+B by using contants A, B satisfying conditions of -0.005≤A≤-0.0005 and 1.1≤B≤1.6. By adjusting the excessive ratio of lead in the above range, piezoelectric constant d31 can be set to be the maximum value in accordance with the intensity of the electric field applied to the piezoelectric element. COPYRIGHT: (C)2001,JPO

Dynamics of active piezoelectric damping composites

Abstract: A finite element model is developed to investigate the dynamic characteristics of beams treated with discrete patches of Active Piezoelectric Damping Composites (APDC) The APDC patches, under consideration, consist of piezoelectric rods that are obliquely embedded in a viscoelastic matrix to actively control its shear and compression damping characteristics With such active and passive control capabilities, the energy dissipation mechanism of the viscoelastic layer can be enhanced and the dynamic behavior of the system can be improved The effectiveness of the APDC in damping the vibration of beams is compared with the performance of the conventional Passive Constrained Layer Damping (PCLD) The effect of the inclination angle of the piezoelectric rods on the performance of the APDC is presented The results obtained demonstrate that the APDC, with their inherent active and passive capabilities, are an effective means for controlling structural vibrations over a broad frequency band

Improvement in transient piezoelectric responses of NDE transceivers using selective damping and tuning networks

Abstract: NDE ultrasonic applications for quality control purposes, based on piezoelectric devices working as pulsed ultrasonic probes, usually include some tuning circuit either across the pulser output connectors or close to the piezoelectric probe electrodes. Classic criteria to determine tuning parameters in ultrasonic transducers do not perform very well in transient regime under the typical electrical conditions and peculiar output impedances of the required high-voltage pulsers. In most practical situations, the tuning values are manually adjusted in specific circuits for each NDE case, testing each channel of a multiprobe inspection system to find the best sensitivity. In this paper, the positive influences of certain selective damping and tuning networks on the time and frequency behaviors of NDE piezoelectric transceivers are analyzed in detail. Different waveforms and spectra of received ultrasonic signals are comparatively evaluated for different real tuning conditions, after passing through two ultrasonic processes linked in cascade: a transmitter of industrial type and a broad-band ultrasonic receiver. Piezoelectric transducer impedances, transduction transfer functions, and HV output spikes from a piezoelectrically loaded NDE pulser, are computed, to identify separately the influence of each stage. In order to improve amplitude and axial resolution in the received transient responses, relative contributions from emission and reception tuning networks are individually evaluated for a particular NDE two-stage piezoelectric channel. Also shown are the final experimental results relative to the ultrasonic test pulse and detected in a through-transmission NDE configuration, gradually improved by using distinct tuning levels.

Compact piezoelectric stacked actuators for high power applications

Abstract: Small, hollow, multilayer actuators with a diameter of 3 mm were fabricated by the stacking method from piezoelectric hard lead zirconate titanate (PZT) ceramics. Langevin vibrators were also constructed with the hollow multilayer actuators. The performance capabilities of the actuator and Langevin vibrator samples were examined under high-power conditions. The high-power vibration level at a given sinusoidal drive voltage was significantly enhanced by using a multilayer structure under either a nonresonance or resonance condition. A maximum vibration velocity of 0.17 m/sec was obtained for the 9-layer actuator sample under nonresonance conditions. The vibration velocity was further improved with the Langevin vibrator driven at the resonance frequency. The temperature rise due to heat generation under high-power conditions was the immediate limitation on the maximum accessible vibration velocity for the stacked actuators.

Novel piezoelectric transducers for high voltage measurements

Abstract: A prerequisite for safe and stable operation of an electric power system is the accurate and reliable measurement of the system parameters, in particular, current and voltage. Conventionally, this has been achieved on High Voltage (H.V.) systems by expensive, bulky iron-core transformers and also by capacitor transformers. Both of them are increasingly coming under review (chapter 1) in modern power system due to their cost, safety implications for personnel and surrounding plant if failure occurs, installation time and indeed substation land requirements. Research effort into viable alternatives to instrument transformers has been ongoing for many years to reduce the cost and improve the safety and accuracy of this devices. In the last years, this research has accelerated due to the new requirements of the modern metering and protection systems based on electronic and microprocessor devices. This trend in the modern systems has allowed the development of novel transducers where the accuracy, the reliability and the safety has been significantly improved. The main alternative incorporate optic fibre viewed as the most realistic method of providing cheap and safe isolation between the chosen sensor at phase potential and earth. The sensor itself is, in the case of current measurement, based on the Faraday effect while in the case of the voltage measurement is generally a Pockels or Kerr effect device measuring a fraction of the actual phase voltage by employing a capacitive voltage divider. In parallel to the development of the optical alternative other different transducers have been studied based on the properties offer for new materials and technologies developed in the last years. A clear example of new emergent technologies is found in the piezoelectricity (chapter 2). In just over 100 years piezoelectricity has moved from a laboratory curiosity to big business. During this period, several technologies have been developed to utilise the piezoelectric effect. In turn, each of these technologies has become an essential component in many kinds of electronic products. The U.S. piezoelectric industry, good mirror for analyse the international technologic development, has gone through several boom and bust cycles. However, new applications are emerging for piezoelectricity because of the developments in piezoelectric ceramics and polymers. Even though piezoelectric quartz crystal still holds the largest market segment, several new piezoelectric ceramic and piezoelectric polymer materials are being developed that represent good, attractive market segments in terms of growth, competition, and investment. This thesis proposes an alternative for the measurement in High Voltage environments by using the piezoelectric technology. The thesis was initially concentrated in the alternative of the voltage measurement, but the successfully results in this field have open the way to propose alternatives for measuring current. Accordingly, the present thesis develops a novel instrument transformer based on the mechanical forces developed for the piezoelectric materials under the influence of an electric field. The transformer consists of an actuator piezoelectric column and a sensor piezoelectric column. The actuator column is connected to the a.c. High Voltage to be measured. This electrical voltage produces the generation of mechanical forces within the material. The forces can be measured by means of the piezoelectric sensor and convert it back into a low electrical signal which can drive an electronic protection or measuring system. The novel piezoelectric transformer herein treated is of wide application in electrical networks for measuring, providing both advantageous accuracy and large transformation ratio. Furthermore, It is expected to reduce the volume, weight and manufacturing cost of the traditional electromagnetic transformers.

Piezoelectric Shunt Vibration Damping of F-15 Panel under High Acoustic Excitation

Abstract: At last year's SPIE symposium, we reported results of an experiment on structural vibration damping of an F-15 underbelly panel using piezoelectric shunting with five bonded PZT transducers. The panel vibration was induced with an acoustic speaker at an overall sound pressure level (OASPL) of about 90 dB. Amplitude reductions of 13.45 and 10.72 dB were achieved for the first and second modes, respectively, using single- and multiple-mode shunting. It is the purpose of this investigation to extend the passive piezoelectric shunt-damping technique to control structural vibration induced at higher acoustic excitation levels, and to examine the controllability and survivability of the bonded PZT transducers at these high levels. The shunting experiment was performed with the Thermal Acoustic Fatigue Apparatus (TAFA) at the NASA Langley Research Center using the same F-15 underbelly panel. The TAFA is a progressive wave tube facility. The panel was mounted in one wall of the TAFA test section using a specially designed mounting fixture such that the panel was subjected to grazing-incidence acoustic excitation. Five PZT transducers were used with two shunt circuits designed to control the first and second modes of the structure between 200 and 400 Hz. We first determined the values of the shunt inductance and resistance at an OASPL of 130 dB. These values were maintained while we gradually increased the OASPL from 130 to 154 dB in 6-dB steps. During each increment, the frequency response function between accelerometers on the panel and the acoustic excitation measured by microphones, before and after shunting, were recorded. Good response reduction was observed up to the 148dB level. The experiment was stopped at 154 dB due to wire breakage from vibration at a transducer wire joint. The PZT transducers, however, were still bonded well on the panel and survived at this high dB level. We also observed shifting of the frequency peaks toward lower frequency when the OASPL was increased. Detailed experimental results will be presented.

Monitoring system and method

Abstract: A system including piezoelectric material (24) wherein a force exerted on the piezoelectric material (24) is determined by subjecting (64) the piezoelectric material (24) to an input signal of sweeping frequency and evaluating the response of the piezoelectric material (24) to the applied (64) signal.

Three-dimensional asymptotic analysis of multiple-electroded piezoelectric laminates

Abstract: Theproblemofpiezoelectriclaminateswithspecie edsurfacetractionsandsurfaceandinternalelectricpotentials is studied. By writing the governing equations in the state-space formulation, employing an asymptotic expansion technique, and expressing electric displacement jumps across internal electrodes in terms of basic unknowns, the three-dimensional problem is reduced to a hierarchy of two-dimensional equations with the same homogeneous operators for each order. Different nonhomogeneous terms are only related to the preceding-order solution and can be readily determined by recurrence relations. Moreover, for pure elasticity, the present e eld equations of the leading order represent the classical thin elastic plate model. The proposed formulation is illustrated by considering arectangular piezoelectric plate madeof an orthotropic material, and with its edges simplysupported and grounded. The convergence of the solution is discussed and the repeated averaging technique for partial sums is used to accelerate the convergenceof the series solution. Computed results arefound toagree well with available analytical results, and new results for electromechanically coupled problems are presented.

Topological optimization of mechanical amplifiers for piezoelectric actuators under dynamic motion

Abstract: Topological optimization is used to systematically design mechanical amplifiers that magnify the limited actuation stroke of a piezoelectric actuator. The design problem is posed as a material distribution problem using a variable thickness method. Two design goals are formulated for the design of the mechanical amplifier. They are the maximum dynamic stroke and the maximum dynamic magnification factor. The optimization problems are then solved using a method of moving asymptotes. The design domain is modelled as a plane-stress solid, and is actuated by harmonic excitation without the inclusion of damping. To model the actuator and workpiece, their stiffness is included and idealized as rod elements in the finite-element analysis. To show the capability of the design methodology, an elliptic amplifier and a magnification mechanism, used in a dot-matrix printer head, are reinvented using topological optimization. The dynamic effects on the optimum topology are also studied using different excitation frequencies.

Modal Vibration Control for PVDF Coated Plates

Abstract: Since advanced technical systems, such as aircrafts, space structures and automobiles, have to combine high performance with low weight, passive vibration absorbers reach their limits. This is why ...

Compact and precise positioner based on the Inchworm principle

Abstract: In this paper, we present a piezoelectric linear micropositioner. Its principle and configuration provide an elegant solution to confined positioning problems requiring compact systems. The developed device shows a high accuracy together with large travel ranges, due to a stepwise operation principle. A simple, low-cost realization process combined with an assembly step has been used to implement the device. The positioner operation principle is based on the well known Inchworm principle: the accurate synchronization of piezoelectric actuation and the use of electrostatic forces as clamping systems produces a step-by-step driving of a slider along the direction of the piezotransducer expansion. The applied principle makes possible a flexible and reliable control of the slider positioning speed, either through the `step-by-step' sequence frequency or through the step length. A positioner was designed and realized to demonstrate the device working principle. Bidirectional, millimeter-range slider motion was performed and slider speeds ranging from a few µm s-1 to a few hundreds of µm s-1 were measured. Three hundred nm steps were estimated at 10 V driving voltage. The process used also allows the realization of similar X-Y positioner designs combining several degrees of freedom.

Design of a linear piezomotor with ultra-high stiffness and nanoprecision

Abstract: An ultra-stiff nanoprecision linear piezomotor was recently designed for grinding application. This piezomotor consists of three high-voltage piezoelectric actuators integrated by a monolithic flexure frame. This monolithic frame was designed to have multiple functions such as protecting and pre-loading three piezoelectric actuators and withstanding all the shearing forces during operation. The monolithic frame as a motion mechanism eliminates the backlash problem. The stiffness distributions in certain directions over the frame were designed using the finite-element method.