Showing papers on "Piezoelectric sensor published in 1994"

Piezothermoelasticity and Precision Control of Piezoelectric Systems: Theory and Finite Element Analysis

Abstract: Piezothermoelastic effects of distributed piezoelectric sensor/actuator and structural systems are studied . Distributed controls (static and dynamic) of pizeoelectric laminates subjected to a steady state temperature field are investigated. Piezothermoelastic constitutive equations are defined, followed by three energy functionals for the displacement, electric, and temperature fields, respectively. A new 3D piezothermoelastic thin hexahedron finite element with three internal degrees of freedom is formulated using a variational formulation which includes thermal, electric, and mechanical energies. A system equetion for the piezoelcectric continuum exposed to combined displacement, electic, and temperature fields is formulated. Thermal influences on the sensing and control of piezoelectric PZT/steel laminates are ivestigated

Tunable acoustic resonator for clinical ultrasonic transducers

Abstract: A tunable ultrasonic probe includes a body of a first piezoelectric material acoustically coupled in series with a body of a second piezoelectric material. The second piezoelectric material has a Curie temperature that is substantially different than that of the first piezoelectric material. Preferably, the first piezoelectric material is a conventional piezoelectric ceramic, such as lead zirconate titanate, while the second piezoelectric material is a relaxor ferroelectric ceramic, such as lead magnesium niobate. At an operating temperature of the probe, the first piezoelectric material has a fixed polarization. In contrast, the second piezoelectric material has a polarization that is variable relative to the fixed polarization of the first piezoelectric material. A preferred novel arrangement of electrodes electrically couples the bodies in parallel with one another. An oscillating voltage for exciting the acoustic signals in the probe is coupled with the electrodes. The polarization of the second piezoelectric material is variably controlled by a bias voltage coupled with the electrodes. In a preferred embodiment, the bias voltage has a reversible electrical polarity for selecting one resonant frequency from a plurality of resonant frequencies of the probe. In another preferred embodiment, the bias voltage source has a variable voltage level for selecting at least one of a plurality of resonant frequencies of the probe.

Piezoresistive input device

Abstract: An input device for computers or electronic games using piezoelectric elements. Four piezoelectric devices are mounted on a base in positions ninety degrees apart. A user actuation element, such as a directional control pad and or a joystick is pivotally disposed on the base above the piezoelectric sensors. A biasing element such as a spring, foam or rubber element is positioned between the actuation element and the base to support the actuation device in a neutral position when no face is being applied by a user to also return the activation element to its neutral position after a user's force is removed. Opposing sensors are connected to a bridge circuit such that in the neutral position of the actuation element the output voltage of the bridge is one half of the input voltage. As the user applies a force to the actuation device, the resistance of one or the other (opposing) piezoresistive device will decrease and accordingly drive the output of the bridge circuit either towards the input voltage or ground, depending on which sensor the user is activated. Additionally a piezoresistive device constructed according to the present invention uses a conductive foam overlayed on top of a series of circuit traces which describe open circuits. As the conductive foam is compressed, it will complete the circuit of the circuit traces and provide an output voltage varying with the compression of the foam.

Analysis of beams containing piezoelectric sensors and actuators

Abstract: A one-dimensional theory is developed for modeling the analysis of beams containing piezoelectric sensors and actuators. The equations of motion and associated boundary conditions are derived for the vibrations of piezoelectrically sensored/actuated beams. The effect of coupling between longitudinal deflection and bending deflection is investigated. For the practical applications, in accordance with the proposed beam theory, a one-dimensional finite element formulation is presented. The proposed beam theory as well as the finite element approach can easily be used in developing a formal two-dimensional theory for piezoelectrically actuated composite plates and shells or other physical systems.

Method of manufacturing a piezoelectric device

Abstract: A method for making a piezoelectric device wherein residual stresses in the piezoelectric transducer element of the piezoelectric device are relieved by forming a groove or grooves extending into a thick-walled region of the peripheral wall of a ceramic substrate in the piezoelectric device. The stresses to be relieved are caused by a difference in shrinkage between the ceramic substrate and the piezoelectric transducer as a result of sintering the substrate and the transducer to form an integral product.

Strain Imaging of Lead-Zirconate-Titanate Thin Film by Tunneling Acoustic Microscopy

Abstract: This paper presents a new method for imaging of the piezoelectric property of piezoelectric films with high resolution using tunneling acoustic microscopy. This method is based on detecting fine strains generated by the tip voltage. Such strain is detected either through the surface displacement of the piezoelectric film or through a vibration generated in the film. This method enables us to measure and image the piezoelectric constants, polarization directions, and coercive electric fields of piezoelectric materials.

Application of piezoelectric devices to vibration suppression

Abstract: Embedded piezoelectric devices may be ideally suited for vibration control of space structures, which lack an inertial ground. When subjected to an input voltage, an embedded piezoelectric actuator changes its dimensions, which in turn generates a pair of forces exerted on adjacent structural members. From the direct piezoelectric effect, an embedded piezoelectric transducer generates an electric charge proportional to the structural dynamic response. In this paper, the implementation, testing, and modeling of an active truss structure with piezoelectric sensors and actuators are described. Linear quadratic Gaussian, second-order, and direct-rate feedback control schemes are designed to suppress the vibrations of the active structure. Simulation and test results are presented. It is shown that special model reduction considerations are required to achieve good correlation between test and analysis. Nomenclature The typical symbology for piezoelectric material properties are used in this paper. Except where noted, the piezoelectric variables are with respect to the standard piezoelectric material 1-2-3 Cartesian coordinate frame. The single, or first of the double, subscript denotes the direction of the applied/sensed electrical field. The second subscript represents the direction of the stress/strain in the piezoelectric material. The subscript r represents the radial direction, as measured in a cylindrical coordinate frame. A = cross-sectional area Ac - controller state matrix As - surface area B, BI = input matrix, /th input matrix Bc = controller input matrix

Interaction of structure vibration and piezoelectric actuation

Abstract: A stepped beam model is developed to predict analytically the natural frequencies and mode shapes at different piezoelectric sensor/actuator locations The modal solution obtained by including the inertia and stiffness of the surface-bonded piezoelectric materials is applied to investigate the interaction of structure vibration and piezoelectric actuation under closed circuit condition It is shown that a generalized stiffness from electromechanical coupling is induced by the interaction The generalized stiffness is a function of structure mode shapes and piezoelectric sensor/actuator locations, thus either softening or stiffening system stiffness is achievable in closed circuit condition All analytical predictions are validated by modal testing

Modeling and control of smart structures with bonded piezoelectric sensors and actuators

Abstract: Smart structure has become an increasingly common term describing a structure embedded or bonded with a large number of lightweight active electromechanical sensors and actuators. The authors consider the modeling and control issues related to smart structures bonded with piezoelectric sensors and actuators. They first apply Hamilton's principle to obtain a linearized equation of motion. The natural modes are then found by solving an eigenvalue problem. From the voltage input to current output, the transfer function is shown to be passive, which allows for any strictly passive feedback controller. Issues related to the design of the passive feedback controller in the presence of model non-idealities and performance augmentation with learning-based feedforward control are then discussed.

Detection of Delaminations in Composite Beams Using Piezoelectric Sensors

Abstract: This paper investigates the feasibility of a proposed technique for detecting delamination using piezoelectric layers or patches embedded or bonded to a composite structure Variations in the voltage generated in the piezoelectric layers indicates the presence and location of delamination, when the structure is excited either externally or via actuators The theoretical foundations of a method for predicting the dynamic response of delaminated composite beams with piezoelectric layers are described The governing equations are presented for the case of external vibroacoustic excitation, as well as, for the case of locally induced vibrations by some of the embedded piezoelectric elements An exact solution is developed within the limits of linear laminate theory Applications illustrate the feasibility of delamination detection in cantilever beams The results illustrate that the proposed technique may provide accurate detection of the presence, size, and location of a delamination

Piezoelectric Sensor for Detecting Force Gradients in Atomic Force Microscopy

Abstract: This paper presents a piezoelectric sensor for detecting force gradients in the noncontact atomic force microscope (AFM). To simplify the force gradient detecting system of the noncontact AFM, the direct sensing cantilever with a ZnO piezoelectric film has been developed. The signal related to the vibration amplitude of the cantilever end is measurable by detecting the charge induced by the piezoelectric effect. The gradient of the force between the tip of the vibrating cantilever driven by an external oscillator and the sample modifies the vibration amplitude of the lever, hence inducing a change of the piezoelectric charge signal. We have adapted the transfer matrix method for calculating the change of the piezoelectric charge due to the gradient of the force. The piezo-electric signal trace has been recorded as a function of sample displacement. We have converted the recorded data to force gradients using a transfer matrix.

Identification of Foreign Object Impact in Structures Using Distributed Sensors

Abstract: An impact load identification method using distrib uted built-in sensors for detecting foreign object impact is pro posed. The method consists of a system model and a response comparator. The system model characterizes the dynamic response of the structure subjected to a known impact force. The comparator compares the measured sensor outputs with the estimated mea surements from the model and predicts the location and the force history of the impact. The method has been developed for beams containing distributed piezoelectric sensors.

Chemical sensing by analysing dynamics of plasma polymer film-coated sensors

Abstract: A chemical sensing system that incorporates unique sensor films and uses pattern recgonition of their dynamic responses is presented. This system consists of a sensor array of quartz-crystal microbalances coated with plasma polymer films. The films, synthesized by radio-frequency sputtering, are useful because of their high density of radical sites and unsaturated bonds. When this sensor array is exposed to a gas, the adsorption and desorption of the target gas causes a dynamic frequency response in each piezoelectric sensor. The sensor response is analysed by an autoregressive model typically to estimate the parameters of dynamic systems. This model's coefficients reflect the sensor dynamics, providing pattern vectors that characterize the target gas. Based on this model, classification maps for single gases can be created with these pattern vectors. Thesse maps show that the dynamic sensor response provides useful information for gas classification. This model also confirms that our sensing system can identify the components of a gas mixture.

Governing equations and finite element models for multiaxial piezoelectric beam sensors/actuators

Abstract: Governing equations and finite element models for multiaxially active laminated piezoelectric beam sensor/ actuator elements capable of simultaneously sensing/actuating all four components (axial extension, biaxial bendings, and tonional twisting) of beam deformation are presented and used in special sensor/actuator pair designs as well as fiinite element analysis for transient responses of adaptive frame structures partially composed of these active beam elements

Bidirectional road traffic sensor

Abstract: A bidirectional road traffic sensor include several respective lengths of coaxial piezoelectric cable each having a conductive core, a conductive polymer surrounding the core, a conductive sheath therearound and an electrically non-conductive jacket therearound. The cables are spliced together such that conductive core and conductive sheath of one length of piezoelectric cable is spliced respectively to the conductive sheath and conductive core of another piezoelectric cable. The splices are encapsulated in an electrically non-conductive material so that the spliced lengths of piezoelectric cables respectively constitutes positive, neutral and negative piezoelectric sensors. Pressure changes in the piezoelectric sensors are caused by vehicle passage thereover. In such a manner, electrical pulses are responsively produced by passage of vehicles traversing respective detection zones defined by the sensors and moving in respective particular directions so that such passage of such vehicles may be registered.

Theory and applications of cylindrical sandwich shells with piezoelectric sensors and actuators

Abstract: Cylindrical sandwich shells with piezoelectric axial and ring elements bonded to the outer and inner surfaces are considered. Thermal effects are included in the analysis. Governing equations of motion and the boundary conditions derived in this paper can be applied to the shells with piezoelectric sensors or actuators or to the shells with a feedback control including both sensors and actuators. Detection of delaminations using axial sensors is used as an example of application of the theory.

PZT-polymer composites fabricated with YAG laser cutter

Abstract: Piezoelectric composites have been constructed by YAG laser cutting of PZT ceramics and back-filling with silicone rubber. Composites containing 46–76 vol.% PZT have been prepared with several different rod sizes. The measured dielectric constant ranges from 310 to 598, d33 from 297 to 305 pC/N, and g33 from 87 × 10−3 to 62 × 10−3 V m/N. The influence of the new fabrication method on the piezoelectric properties of the composite is evaluated, and it is confirmed that an elastomer with low elastic modulus increases g33 and suppresses the radial mode vibration in resonance. For the PZT-silicone rubber composites made by YAG laser cutting, g33 can be enhanced in 1–3 composites to about three times the value for solid PZT. The piezoelectric properties are compared with those of 1–3 composites made by ultrasonic cutting. The g33 values of composites fabricated by ultrasonic cutting are larger than those fabricated by laser cutting. These results indicate that to get higher values of g33 it is necessary to perforate PZT with ditches of the same width.

Loudspeaker system with closed housing for improved bass reproduction

Abstract: Loudspeaker system with closed housing for improved bass reproduction The loudspeaker system operates utilizing pressure control in the closed loudspeaker housing This pressure control suppresses pressure changes of the air inside the housing The control circuit comprises a pressure sensor, a controller, a power amplifier and an electrodynamic transducer inside the housing The membrane of the transducer is covered with piezoelectric material and conducting coatings forming piezoelectric sensors to measure the changes of the air pressure upon the surface The piezoelectric material consists of polyvinylidene fluoride, PVDF The sensors are specially shaped to avoid distortions They differ in thickness for the elimination of acceleration-dependent signal terms

Dither-motor design with concurrent sensing and actuating piezoelectric materials (Ring laser gyroscope)

Abstract: The authors present an analytical model to predict the model parameters of a dither-motor structure in a ring laser gyroscope in which the piezoelectric sensor and actuator are employed as driving mechanisms to avoid the problem of so-called lock-in effects It is shown that the natural frequency of a dither motor is strongly influenced by: (1) the inertia and stiffness of piezoelectric elements and bonding layers, (2) the location of piezoelectric elements, and (3) the interaction between structural vibration and piezoelectric actuation Conventionally piezoelectric elements are used for sensor and actuator independently A technique for utilizing each of the piezoelectric elements concurrently for dither rate sensing and dither motion actuation is also developed Experimental results show that the system performance and reliability can be significantly increased by accurately predicting the fundamental structural frequency and by implementing the concurrent sensing/actuating technique

Piezoelectric sensor and coordinate input apparatus employing the same

Abstract: A piezoelectric sensor for detecting elastic plate vibrations in an object such as the transmission plate in a coordinate input apparatus is prismatic in shape and is fixed to the surface of the object. The prismatic sensor is arranged so that it is parallel to the direction of propagation of the vibrations and has an electrode surface perpendicular to the surface of the object. The arrangement of the prismatic sensor permits the thickness of the object in which the plate vibrations propagate to be substantially reduced and reduces the manufacturing cost of coordinate input apparatus using the prismatic sensor.

Finite element modeling of a finite piezoelectric sensor/actuator embedded in a fluid-loaded plate

Abstract: The sensor response of a piezoelectric transducer embedded in a fluid loaded structure is modeled using a hybrid numerical approach. The structure is excited by an obliquely incident acoustic wave. Finite element modeling in the structure and fluid surrounding the transducer region is used and a plane wave representation is exploited to match the displacement field at the mathematical boundary. On this boundary, continuity of field derivatives is enforced by using a penalty factor. Numerical results are presented for the sensor response and it is found that the sensor at that location is not only non-intrusive but also sensitive to the characteristic of the structure.