Showing papers on "Piezoelectric sensor published in 1993"

Finite Element Modeling of Piezoelectric Sensors and Actuators

Abstract: A finite element formulation for vibration control of a laminated plate with piezoelectric sensors/actuators is presented. Classical laminate theory with the induced strain actuation and Hamilton's principle are used to formulate the equations of motion. The total charge developed on the sensor layer is calculated from the direct piezoelectric equation. The equations of motion and the total charge are discretized with four-node, 12-degreeof-freedom quadrilateral plate bending elements with one electrical degree of freedom. The piezoelectric sensor is distributed, but is also integrated since the output voltage is dependent on the integrated strain rates over the sensor area. Also, the piezoelectric actuator induces the control moments at the ends of the actuator. Therefore, the number, size, and locations of the sensors/actuators are very important in the control system design. By selective assembling of the element matrices for each electrode, responses with various sensor/actuator geometries can be investigated. The static responses of a piezoelectric bimorph beam are calculated. For a laminated plate under the negative velocity feedback control, the direct time responses are calculated by the Newmark-/? method, and the damped frequencies and modal damping ratios are derived by modal state space analysis.

Active Vibration Control of Laminated Composite Plates Using Piezoelectric Devices: A Finite Element Approach

Abstract: A finite element formulation is presented for modeling the behavior of laminated composites with integrated piezoelectric sensors and actuators. This model is valid for both con tinuous and segmented piezoelectric elements that can be either surface bonded or embedded in the laminated plate. The present model takes into account the mass and the stiffness of the piezoelectric patches. The formulation is based on the first-order shear deformation theory, which is applicable for both thin and moderately thick plates. An additional feature of the present model is that it does not introduce the voltage as an additional degree of freedom. The charge/current generated by the sensor and the response of the plate to an actuator voltage can be computed independently. These features are then coupled with a constant-gain negative-velocity/positive-position feedback control algorithm to actively control the transient response of the plate in a closed loop. Numerical results are presented which indicate the increase in...

Dynamic tactile sensing: perception of fine surface features with stress rate sensing

Abstract: Dynamic tactile sensing, which is defined as sensing during motion for perception of high spatial and temporal frequencies, is presented. Applications include sensing fine surface features and textures and monitoring contact conditions for dextrous manipulation. One type of dynamic tactile sensor, the stress rate sensor, is described in detail. It uses piezoelectric polymer transducers to measure the changes in stress induced in the sensor's rubber skin as it traverses small surface features and textures. The signals are interpreted with the aid of a solid mechanics model of the contact interaction and a linear deconvolution filter. Experimental verification of the sensor's performance, including the detection of surface features only 6.5 mu m high, are presented. >

Exact Solutions for Static Analysis of Intelligent Structures

Abstract: Exact solutions for static analysis of simply supported rectangular plate-type intelligent structures are presented. The intelligent structure proposed here is composed of a laminated substrate of graphite/epox y composite coupled with distributed sensor and actuator layers of a biaxially polarized piezoelectric polymer, polyvinylidene fluoride (PVDF). The study aims at investigating the capability of the actuator and sensor layers to cause and sense the deformations, respectively, of the substrate of the intelligent structure. The results show that the effectiveness of the piezoelectric actuator layer to cause induced strain actuation in the structure significantly increases with the decrease in the length to thickness ratio of the substrate.

Development of a force sensor for atomic force microscopy using piezoelectric thin films

Abstract: A piezoelectric force sensor has been developed to overcome the complexity of the force detector of the conventional non contact atomic force microscope (AFM). The sensor consists of a cantilever with a piezoelectric thin film deposited on one side. The layer is formed on a thermal SiO2 microbeam and is then encapsulated by a thin passivation film. The piezoelectric film is c-axis oriented ZnO deposited by RF magnetron sputtering, or lead-zirconate-titanate (PZT) prepared by the sol-gel method. The cantilever is excited near its first natural resonance and forces are monitored by detecting the change in the admittance of the layer induced by the piezoelectric effect. The gradient of the force between the tip of the vibrating cantilever and the sample when in close proximity modifies the vibration amplitude, hence inducing a change in the admittance of the layer. A typical sensor with a length of 200 mu m and a width of 50 mu m had a calculated spring constant of 8.7 N m-1 and a first resonance frequency of 72.5 kHz. We have measured a sensor signal as a function of the tip-sample spacing and verified the feasibility of the sensor for a non contact AFM.

Active buckling control of smart composite plates-finite-element analysis

Abstract: A finite-element model is developed for the active buckling control of laminated composite plates using piezoelectric materials. The finite-element model is based on the first-order shear deformation plate theory in conjunction with linear piezoelectric theory. The piezoelectric sensors and actuators can be surface bonded or embedded and can be either continuous or segmented. The dynamic buckling behavior of the laminated plate subjected to a linearly increasing uniaxial compressive load is investigated. The sensor output is used to determine the input to the actuator using a proportional control algorithm. The forces induced by the piezoelectric actuators under the applied voltage fields enhance the critical buckling load. Finite-element solutions are presented for composite plates with clamped and simply supported boundary conditions and the effectiveness of piezoelectric materials in enhancing the buckling loads is demonstrated.

Finite element modeling of active periodic structures: Application to 1–3 piezocompositesa)

Abstract: The finite‐element approach has been previously used, with the help of the ATILA code, to model the scattering of acoustic waves by single periodic passive structures, such as compliant tube gratings [A.‐C. Hennion et al., J. Acoust. Soc. Am. 87, 1861–1870 (1990)], or by doubly periodic passive structures, such as Alberich anechoic coatings [A.‐C. Hladky‐Hennion et al., J. Acoust. Soc. Am. 90, 3356–3367 (1991)]. This paper presents an extension of this technique to active periodic structures, and describes with particular emphasis its application to the modeling of 1–3 piezocomposites made of parallel piezoelectric connecting strips in a passive matrix. The method can also be applied to many other piezocomposites or to large high‐frequency arrays. In the proposed approach, only the unit cell of the active structure and a small part of the surrounding fluid domain have to be meshed, while the acoustic field on both sides of this mesh is described by a plane‐wave expansion including progressive and evanescent contributions. Internal losses and anisotropy of the materials as well as normal or oblique incidence of the impinging wave, if this wave exists, can be taken into account in the model. In this paper, the general method is first described, and particularly the aspects related to the piezoelectric elements. Then, one test example is given, for which analytical results exist. This example is followed by a detailed presentation of finite‐element results, which are compared with the corresponding measurements (free‐field voltage sensitivity or transmitting voltage response), in the case of a given 1–3 composite. The accuracy of the whole approach is thus clearly demonstrated. Finally, the influence of the geometric parameters of a 1–3 composite is studied, while at the same time the limitations of previously published simple analytical models are discussed.

Integrated tip strain sensor for use in combination with a single axis atomic force microscope

Abstract: An integrated tip strain sensor is combination with a single axis atomic force microscope (AFM) for determining the profile of a surface in three dimensions. A cantilever beam carries an integrated tip stem on which is deposited a piezoelectric film strain sensor. A high-resolution direct electron beam (e-beam) deposition process is used to grow a sharp tip onto the silicon (Si) cantilever structure. The direct e-beam deposition process permits the controllable fabrication of high-aspect ratio, nanometer-scale tip structures. A piezoelectric jacket with four superimposed elements is deposited on the tip stem. The piezoelectric sensors function in a plane perpendicular to that of a probe in the AFM; that is, any tip contact with the linewidth surface will cause tip deflection with a corresponding proportional electrical signal output. This tip strain sensor, coupled to a standard single axis AFM tip, allows for three-dimensional metrology with a much simpler approach while avoiding catastrophic tip "crashes". Two-dimensional edge detection of the sidewalls is used to calculate the absolute value or the linewidth of overlay, independent of the AFM principle. The technique works on any linewidth surface material, whether conductive, non-conductive or semiconductive.

Vibration control of a laminated plate with piezoelectric sensor/actuator: finite element formulation and modal analysis

Abstract: The combined effects of passive and active control on the vibration control of a com posite laminated plate with piezoelectric sensors/actuators are investigated. Finite element formula tion and mo...

Piezoelectric tubes and tubular composites for actuator and sensor applications

Abstract: Piezoelectric actuators and sensors made with a tubular structure can provide a great agility of effective response in the radial direction. For a radially poled piezoelectric tube, the effective piezoelectric constant in that direction can be tuned to be positive, zero or negative by varying the ratio of the outer radius (Ro) to the inner radius (ro) of the tube. For a suitable ratio of Ro/ro, this effective constant can also be changed in sign or set to zero by adjusting the d.c. bias field level for tubes made of electrostrictive materials. Therefore, one can make a piezoelectric transducer with all the effective piezoelectric tensile constants having the same sign. End-capped thin-walled tubes also exhibit an exceptionally high hydrostatic response, and the small size of the tubular structure makes it very suitable for integration into a 1–3 composite which possesses low acoustic impedance and high hydrostatic response.

A unified analysis of both active and passive damping for a plate with piezoelectric transducers

Abstract: The complete set of equations for describing the mechanical and electrical behavior of a piezoelectric medium is given. From these equations, the electromechanical equations describing the dynamical behavior of discrete PZTs and their mounting plate are derived. The electromechanical equations are used to explain active damping with the PZTs as actuators and an accelerometer as the sensor. The active damping model is applied to a more realistic case. The transverse displacement and the plate vibration damping are calculated using the electromechanical equations and compared with the experimental results. A comparison of the open loop transverse displacement of the plate as a function of the applied PZT voltage with the corresponding experimental case shows good agreement. The damping of the plate vibration is found to be approximately 20 dB for both the calculation and the corresponding experiment when the plate is driven at the lowest modal plate frequency. A sensor equation describing the output of a PZT used as a sensor is derived with the PZT terminated with an arbitrary impedance. Using the sensor equation, a concise and unified approach is developed for constructing both active and passive damping methods. Two limiting active damping cases (the terminal impedance zero or infinity) and one passive damping case are considered using the sensor equation. A useful design guide for the corresponding active and passive damping methods is determined.

Piezoelectric device and process for production thereof

Abstract: A sheet-form piezoelectric device having improved mechanical strengths as represented by an electrode peel strength while retaining flexibility and piezoelectric performances of a polymer-type piezoelectric device, is obtained by embedding a perforated sheet electrode into at least one surface layer of a polymer piezoelectric film treated with a solvent in advance. The sheet-form piezoelectric device may be wound or curved about a certain central axis to provide a tubular or curved piezoelectric device having wave-transmitting and/or -receiving characteristics suitable for wave-transmitting and/or -receiving devices, such as a hydrophone and microphone.

Method and apparatus for testing a piezoelectric force sensor

Abstract: A test system for a piezoelectric element per se or a piezoelectric element in a physical system, which is subject to forces which deform the piezoelectric element, couples an electrical pulse to the piezoelectric element sufficient to stress the element and induce mechanical ringing upon pulse removal. The ringing electrical signal developed by the piezoelectric element characterizes the functionality of the piezoelectric element. A response circuit which is responsive to the ringing electrical signal provides an electrical signal indicative of the functional condition of the piezoelectric element. The electrical signal is peak detected. The peak detected voltage is compared with a reference voltage to provide an indication of the functionality of the piezoelectric element.

Strain-sensitive elastic scattering from cylinders.

Abstract: Morphology-dependent resonance features are observed in the elastic-scattering spectra of 125-μm-diameter cylinders (optical fibers) as a function of wavelength. The positions of the resonances are strain sensitive and can be tuned in a controlled manner by the application of strain with a piezoelectric transducer. The measured wavelength shifts yield a linear slope of 0.14 nm/mstrain, in good agreement with calculated shifts based on published data for the elastic moduli and the strain-optic coefficients for fused quartz. This demonstrates a new miniature optical strain-sensor technique capable of microstrain sensitivity at a single point.

Aluminum nitride thin film sensor for force, acceleration, and acoustic emission sensing

Abstract: To meet the real‐time process monitoring and control needs in machining automation, aluminum nitride thin film sensors have been implemented on WC–Co cutting inserts by rf sputtering. These piezoelectric sensors detect force, acceleration, and acoustic emission signals. Method of constructing, characterizing and evaluating AlN piezoelectric sensors are presented here. It is shown that c‐axis oriented AlN films can be deposited on WC–Co substrates to sense force, acceleration and acoustic emission signals. As the transducer characteristics vary with rf sputtering conditions, parametric studies have been carried out to determine ‘‘best processing’’ conditions to obtain the needed transducers sensitivities and process reproducibility. Results of these studies are also presented here. It is shown, in addition, that AlN films deposited WC–Co can provide useful signals even though the cutting tool substrate may experience temperature rise during use in metal machining.

Advanced PZT glide head design and implementation for a small slider

Abstract: An enhanced piezoelectric sensor for detecting a predetermined bending mode frequency in the vibrational response of a slider with dimensions smaller than the conventional 100% slider during contact with one or more surface asperities on a recording surface. A method for making the enhanced sensor is also disclosed. The sensor comprises a substantiality rectangular slab of piezoelectric material having a charge response which corresponds to in-plane stress under free boundary conditions. Enhancement is achieved by partitioning an upper conductive layer along the lines of symmetry of the slider's stress distribution, which is related to the piezoelectric material's generated charge. In the preferred embodiment, the conductive layer is partitioned into two electrically isolated regions symmetric about the sensor's lateral axis. The design facilitates the isolation of a high frequency bending component which has been found to be monotonic with increasing surface asperity interference.

Vibration suppression with optimal sensor/actuator location and feedback gain

Abstract: An analytical model is developed for structure vibration suppression with collocated piezoelectric sensor/actuator in optimal placement and optimal feedback gain. Two different control algorithms-active damping control and output feedback control-are applied to obtain the control law, and the optimal set of sensor/actuator location and feedback gain is determined by the modified method of feasible direction. Analytical results show that a collocated piezoelectric actuator/sensor can lead to instability of the closed loop system. In active damping control, the optimal sensor/actuator location is not at the root of a cantilever beam as commonly believed. However, for LQ formulation of output feedback control, the optimal location is at the beam root with the feedback gain determined by the Ricatti equation. The analytical predictions are verified by experiments.

Production method of laminated piezoelectric device and polarization method thereof and vibration wave driven motor

Abstract: In one aspect of the present invention, a large number of thin sheets of piezoelectric ceramic are disposed one on another via electrode films formed on the surfaces of the sheets of piezoelectric ceramic, then electrode films of the piezoelectric elements are connected to each other with electric conductors to form a single piece of laminated piezoelectric device Thus, it becomes possible to perform polarization of the whole of a large number of piezoelectric elements at one time

Method and apparatus for testing fluid pressure in a sealed vessel

Abstract: An apparatus (20) for sensing pressure in a stiff wall sealed vessel (30) comprises a piezoelectric transducer (200) operatively coupled to the vessel (30) for transferring energy to pressurized fluid in the vessel (30). A piezoelectric sensor (202) is operatively coupled to the vessel (30) for providing a received electrical signal having a frequency value indicative of the oscillation frequency of the pressurized fluid. A receiver circuit (224, 226, 228) is operatively connected to the sensor (202) and provides a fluid resonating signal having a frequency indicative of the fluid pressure in the vessel (30). A drive circuit (230) is operatively connected to the receiver circuit (224, 226, 228) and to the piezoelectric transducer (200). The drive circuit (230) initially drives the piezoelectric transducer (206) with noise. Subsequently, the drive circuit (230) drives the piezoelectric transducer (200) with an energy wave having a frequency equal to a frequency value functionally related to the natural frequency of the pressurized fluid in the vessel (30).

Magnetostrictive linear displacement transmitter having improved piezoelectric sensor

Abstract: An improved magnetostrictive wire based position transducer that has applications in both liquid level measuring systems and in position indicating systems. A cylindrically structured and circularly polarized piezoelectric element directly measures the torsional acoustic waves in the magnetostrictive wire as they are received by the sensor. The cylindrical structure of the sensor eliminates many of the inadvertently detected acoustic and electrical pulses within the wire that are not indicative of the passage of the torsional wave of concern. The present system provides an improved sensor configuration which is selectively sensitive to torsional waves while being insensitive to vibrations in alternate planes. This improved piezoelectric sensor in combination with the electrical configuration allows placement of the magnetostrictive wire apart from the liquid whose level is being measured or from the indicator whose position is of concern. The system provides a means for transmitting the liquid level within a container to a sensor column outside of the container in a manner that improves access, maintenance, calibration, and installation. In the preferred embodiment, each of the above improvements is provided in a system that incorporates an instrumentation loop powered microprocessor based transmitter with low current requirements and increased sensitivity.

Cleaning blade equipped with a vibration sensor

Abstract: A piezoelectric sensor (60) is mounted on the cleaning blade (58) and/or the blade support member (62) of a blade cleaning apparatus contained within a electrostatic copying machine. The piezoelectric sensor generates a waveform (Fig. 2) indicative of the wear characteristics of the cleaning blade and pressure loading of the cleaning blade against the photosensitive surface (4). A detection circuit (70,71,72,74) monitors the waveform generated by the piezoelectric sensor to predict the imminent failure of the cleaning blade due to wear and damage. The detection circuit also monitors the waveform to detect a build up of frictional and adhesional forces between the cleaning blade and the photosensitive surface and adjusts the pressure loading through a feedback loop to extend the usable life-span of the cleaning blade. Thus, unscheduled maintenance due to sudden and unpredictable failure of the cleaning blade can be avoided and the usable life-span of the cleaning blade can be extended.

Thick-film acoustic wave sensor structure

Abstract: The scope for thick-film sensor development has largely been limited by the lack of special-purpose sensing pastes. Using a new piezoelectric thick-film we have developed a novel acoustic wave sensor which allows an expansion of the technology into areas previously overlooked.

Piezoelectric force sensor

Abstract: A piezoelectric force sensor is proposed in which a piezoelectric plate (1) has an electrode (4, 5) on the upper side and lower side, respectively One of the electrodes (4, 5) is connected electrically via a conductive track (20, 21) In the event of a breakage of the piezoelectric plate (1), the conductive track (20, 21) is interrupted and the remaining residual capacitance of the conductive track (20, 21) becomes so small that reliable detection of the breakage is possible (Figure 2)

System and method for load sensing

Abstract: An intelligent load sensing system employs a piezoelectric sensor and digital processor for providing accurate sensing of loads, collisions, and vibrations.

Torsional Actuators Using LiNbO3 Plates with an Inversion Layer

Abstract: By utilization of a ferroelectric inversion layer formed in a LiNbO3 plate by heat treatment at just below the Curie temperature, a piezoelectric torsional actuator consisting of a single-crystal plate with no bonding layer can be obtained. The optimal cut suitable for generating torsional motion efficiently without causing bending motion is theoretically examined. It is experimentally demonstrated that torsional actuators fabricated using 140°-rotated Y-cut LiNbO3 plates with an inversion layer as thick as half the plate thickness exhibit no hysteresis and little creep. When an actuator with dimensions of 16×7.0×0.1 mm3 is used as a light deflector, a light beam deflection angle as large as 2.08° is obtained at an applied voltage of 220 Vp-p.