Showing papers on "Piezoelectric sensor published in 1990"

Theory of laminated piezoelectric plates for the design of distributed sensors/actuators. Part I: Governing equations and reciprocal relationships

Abstract: A piezoelectric laminate theory that uses the piezoelectric phenomenon to effect distributed control and sensing of bending, torsion, shearing, shrinking, and stretching of a flexible plate has been developed. This newly developed theory is capable of modeling the electromechanical (actuating) and mechanoelectrical (sensing) behavior of a laminate. Emphasis is on the rigorous formulation of distributed piezoelectric sensors and actuators. The reciprocal relationship of the piezoelectric sensors and actuators is also unveiled. Generalized functions are introduced to disclose the physical concept of these piezoelectric sensors and actuators. It is found that the reciprocal relationship is a generic feature of all piezoelectric laminates.

Modal Sensors/Actuators

Abstract: A piezoelectric laminate theory that uses the piezoelectric phenomenon to effect distributed control and sensing of structural vibration of a flexible plate has been used to develop a class of distributed sensor/actuators, that of modal sensors/actuators. The one-dimensional modal sensors/actuator equations are first derived theoretically and then examined experimentally. These modal equations indicate that distributed piezoelectric sensors/actuators can be adopted to measure/excite specific modes of one-dimensional plates and beams. If constructed correctly, actuator/observer spillover will not be present in systems adopting these types of sensors/actuators. A mode 1 and a mode 2 sensor for a one-dimensional cantilever plate were constructed and tested to examine the applicability of the modal sensors/actuators. A modal coordinate analyzer which allows us to measure any specific modal coordinate on-line real-time is proposed. Finally, a way to create a special two-dimensional modal sensor is presented.

Simulation of piezoelectric devices by two- and three-dimensional finite elements

Abstract: A method for the analysis of piezoelectric media based on finite-element calculations is presented in which the fundamental electroelastic equations governing piezoelectric media are solved numerically The results obtained by this finite-element calculation scheme agree with theoretical and experimental data given in the literature The method is applied to the vibrational analysis of piezoelectric sensors and actuators with arbitrary structure Natural frequencies with related eigenmodes of those devices as well as their responses to various time-dependent mechanical or electrical excitations are computed The theoretically calculated mode shapes of piezoelectric transducers and their electrical impedances agree quantitatively with interferometric and electric measurements The simulations are used to optimize piezoelectric devices such as ultrasonic transducers for medical imaging The method also provides deeper insight into the physical mechanisms of acoustic wave propagation in piezoelectric media >

Smart skin ice detection and de-icing system

Abstract: The de-icing system of the present invention comprises a piezoelectric sensor means (IAS) and a processor means (CPU). A piezoelectric film is the preferred sensor means and a microprocessor is the preferred processor means. In a preferred embodiment, a strip of piezoelectric film (IAS) placed at a point of model kinetic energy such as the boundary layer transition point or the vortex generator of the aircraft. Such placement of the strip provides adequate airflow to excite the piezoelectric film (IAS) without using a power source, thus providing a passive system. The sensor (IAS) allows measurement of distributed strain and vibrational modes indicative of structural icing. The microprocessor (CPU), which controls the system, processes signals from the sensors (IAS), determines whether ice is present, and indicates (DSP) the presence of ice when appropriate. The film (IAS) may be used in a single piece, which may be as large as the area for which ice detection is desired - for example, the entire leading edge of an aircraft wing - or in multiple pieces, and may be embedded in or attached to a surface. This provides a passive, autonomous system for distributed ice detection over a single sensor or between multiple sensors.

Laminated type piezoelectric apparatus

Abstract: A piezoelectric apparatus includes a piezoelectric device which is biased by a fluid force instead of a spring. Since the fluid force can be maintained within a predetermined value even after the piezoelectric device has been used number of times, and since the fluid force can be modulated by fluid pressure providing means and valve means when the fluid force is decreased from the predetermined valve, the present piezoelectric apparatus can maintain the initial pressure on the piezoelectric device.

Distributed structural control using multilayered piezoelectric actuators

Abstract: A method of segmenting piezoelectric sensors and actuators is proposed which can preclude the currently experienced cancelation of sensor signals, or the reduction of actuator effectiveness, due to the integration of the property undergoing measurement or control. The segmentation method is demonstrated by a model developed for beam structures, to which multiple layers of piezoelectric materials are attached. A numerical study is undertaken of increasing active and passive damping of a beam using the segmented sensors and actuators over unsegmented sensors and actuators.

Piezoelectric acceleration sensor

Abstract: The invention relates to a piezoelectric acceleration sensor and to a piezoelectric acceleration device which use a film piezoelectric element (14). Specifically, the piezoelectric acceleration sensor and the piezoelectric acceleration sensor device generate relatively large outputs when acceleration occurs along the sensing axis, but produce relatively small outputs from acceleration perpendicular to the sensing axis. In addition, the sensor and the sensor device are relatively unaffected by temperature fluctuations and are highly impact-resistant.

Piezoelectric sensors and actuators for active vibration damping using digital control

Abstract: Light-weight, rapid, multimode control of a vibrating structure is possible by the use of piezoelectric sensors and actuators and feedback control algorithms. The results of vibration control experiments on a prototype structure such as a cantilever beam using PZT sensors and actuators are presented. Different types of position feedback control and steady-state quadratic optimal control were implemented. Particular attention was paid to the control of low-frequency vibration modes. To extend the applicable range of the control algorithms, signals from the partially distributed sensors and actuators were converted to those from the point concept sensors and actuators. >

Pressure measurement by GaAs piezoelectric sensors

Abstract: A new pressure sensor for pressures up to 100 bar and temperatures of about 200 degrees C is presented. It uses the piezoelectric effect of 111 oriented semi-insulating GaAs. This material allows the monolithic integration of sensor and electronic circuit.

Piezoelectric bridge sound pick-up for string instruments

Abstract: A piezoelectric bridge sound pick-up string instruments has a separate subassembly for each string. Each subassembly has a metal base body (4) with a pocket (4.1) for a piezoelectric sensor element (7), a sensor holder (5) and a pressure piece (8). The pocket is at right angles to the string and is tilted in accordance with the string pressure direction. The sensor element is embedded in an electrically insulating holder, which has a break in its central area (6) and allows a certain deflection of the sensor element. To an electrode on the under surface of the sensor element is fitted a conductor (9) for passing out a signal with positive potential. On an opposite, upper electrode surface is provided a pressure piece with a semi-circular cross-section, which transfers by friction the alternating pressure of the string (14) and functions as an electrical connection of ground potential.

Piezoelectric acceleration sensor and piezoelectric acceleration sensor device

Abstract: The invention relates to a piezoelectric acceleration sensor and to a piezoelectric acceleration device which use a film piezoelectric element. Specifically, the piezoelectric acceleration sensor and the piezoelectric acceleration sensor device generate relatively large outputs when acceleration occurs along the sensing axis, but produce relatively small outputs From acceleration perpendicular to the sensing axis. In addition, the sensor and the sensor device are relatively unaffected by temperature fluctuations and are highly impact-resistant.

A low-cost fiber optic weigh-in-motion sensor

Abstract: A fiber-optic WIM (weigh in motion) sensor, which offers several advantages over the piezoelectric sensor, is proposed. The system consists of a pneumatic tube filled with an incompressible fluid and embedded in a rubber pad, a diaphragm designed to convert pressure into displacement, and an optical displacement sensor. A prototype of the propsed sensor is designed, manufactured, and tested in the laboratory for different load-frequency combinations using an MTS machine. Statistical analyses of data are performed to assess the response of the sensor under varying load frequencies. A piezoelectric cable also is tested under varying load frequencies for the purpose of comaprison with the proposed sensor. The piezoelectric sensor exhibits considerable dependence on the load frequency; whereas, the response of the proposed sensor is much less frequency-dependent, and unlike the piezoelectric cable, has a waveform similar to that of the applied load. This latter property can facilitate significantly the processing of the sesnsor output signal. The linearity of response over the range of applied loads also is better than that of the piezoelectric cable. The proposed sensor is not susceptible to electromagnetic interference, is less expensive, and can be installed on the surface of the pavement, thus eliminating the need to dig the pavement.

Developing a self-diagnostic system for piezoelectric sensors

Abstract: Measurement techniques for developing a self-diagnostic system for piezoelectric sensors are presented. The self-diagnostic system uses two types of measurement techniques based on passive and active evaluation of the piezoelectric element. Both hard and soft failures can be detected by this system. Hard failures such as loss of sensor signal and change in sensor output resistance are determined by monitoring the sensor's output resistance, voltage or current. These are passive measurements of the sensor's output condition. Soft failures include changes in sensor calibration and mounting conditions. Soft failures are detected by measuring structural/electrical impedance of the piezoelectric sensor. Active measurement techniques are used to calculate changes in piezoelectric element properties related to soft failures. This paper describes the general operating principles of a self-diagnostic system and discusses the design of an active/passive measurement technique required for this system to function. Experimental results using two types of piezoelectric accelerometers are presented.

Piezoelectric device operable in the thickness shear vibratory mode and manufacturing method therefor

Abstract: A piezoelectric device operable in the thickness shear vibratory mode, and a method for manufacturing the piezoelectric device. In the piezoelectric device, a rectangular piezoelectric plate is polarized to have its polarization axis inclined to both the long and short sides thereof. This is accomplished by applying a predetermined electric field to the piezoelectric plate in the direction of the long side thereof, after applying a predetermined electirc field to it in the direction of the short side thereof. A pair of electrodes are formed on the piezoelectric plate so that the piezoelectric device is operable in the thickness shear vibration mode.

Noise in piezoelectric sensors

Abstract: Piezoelectric sensor noise generation mechanisms will be reviewed. The sensor needs to be considered as part of a sensor‐preamplifier system whose output signal‐to‐noise is to be maximized. When the preamplifier noise is dominant (as is often the case), an appropriate figure‐of‐merit for the piezoelectric sensor material is the gd product, where g and d are the appropriate piezoelectric coefficients, i.e., the signal‐to‐noise ratio produced by a given volume of piezoelectric sensor material is proportional to gd. On the other hand, if Johnson noise produced in the sensor resistance is dominant, the appropriate figure‐of‐merit is gd/tan δ, where δ is the dielectric loss angle of the piezoelectric sensor material, i.e., the sensor resistance is introduced via the tan δ factor. The figures‐of‐merit of a number of piezoelectric hydrophone materials will be compared.

Detector for pressure distribution

Abstract: PURPOSE:To measure a continuous change of a pressure distribution by continuously reading out voltage data from a piezoelectric sensor elements arranged in the matrix state and cumulatively calculating them for each piezoelectric element separately. CONSTITUTION:A piezoelectric type pressure sensor 10 includes the sensor elements 11 arranged in the matrix state, and electric charges corresponding to the pressure change are accumulated in capacitors 14 on the sensor elements 11. The outputs from the sensor elements are read as the voltage values corresponding to the amount of the pressure change, and the read out data are cumulatively calculated fro every piezoelectric sensor element separately. The voltage data are cumulatively added to the pressure change for each sensor element by arithmetic means; therefore, if the pressure change is not existent on each pizeoelectric sensor, constant voltage data are obtained, and if pressure change is existent, the pressure data at the time of the measurement can be obtained. The continuous change of the pressure distribution can be thereby measured.

Spinning piezoelectric beam of a dual-axis angular rate sensor and method for its adjustment

Abstract: A method for adjusting a piezoelectric beam of a dual-axis angular rate sensor, in which the piezoelectric beam is excited in a direction at right angles to the lengthwise direction of two piezoelectric sensors and to a rotary shaft; detected voltages of the two piezoelectric sensors are measured by a signal measuring circuit; a bending portion of at least one of the two piezoelectric sensors is ground so that the levels of the two measured signals and the difference therebetween become small; the piezoelectric beam is excited again in the lengthwise direction of the piezoelectric sensors at right angles to the rotary shaft; detected voltages of the two piezoelectric sensors are measured by the signal measuring circuit; and a weight mounted on the free end of at least one of the two piezoelectric sensors is ground so that the levels of the two measured signals and the difference therebetween become small. Thus, acceleration components applied to the piezoelectric beam, in the detected voltages of the two piezoelectric sensors, have the same phase and the same amplitude. On both sides of each piezoelectric sensor there are formed electrodes which are spaced 1.5 times the thickness of the sensor from support washers.

Device for measuring an electric field

Abstract: A device for measuring an electric field comprises three optical fiber sensors, which each have a piezoelectric sensor element, as well as an interferometer for generating a sensor signal. The optical fiber sensors have piezoelectric sensor elements that exclusively detect with the aid of the inverse piezoelectric effect a predetermined directional component, assigned in each case, of the electric field. The directional components of the different sensor elements are each aligned perpendicular to one another. An evaluation circuit determines the absolute value and direction of the electric field from the sensor signals generated. The sensor elements are preferably formed by a single piezoelectric body, on whose faces the sensor fibers are fixed.

Piezoelectric sensors and actuators for active vibration damping using digital control

Abstract: All air‐borne, water‐borne, and space structures suffer from undesirable vibrations. Conventional methods of passive damping would require addition of masses comparable in many cases to that of the structure itself; the control is not broadband and significantly alters the performance of the structure. Light‐weight, rapid, and multimode control of the vibrating structure is possible by the use of piezoelectric sensors and actuators and digital feedback algorithms. The results of vibration control experiments on prototype structures, such as clamped cantilever beams, truss structures, such as T beams, Y beams, shafts undergoing torsional vibrations, etc., using PZT sensors and actuators will be presented. Different types of digital control methods have been implemented, each with its own advantages and disadvantages. The damping ratio with and without control is calculated and compared with experimental results. Damping is increased anywhere from 0.3 to 3 orders of magnitude. Different poling arrangements ...

Method for adjusting a spinning piezoelectric beam of a dual-axis angular rate sensor

Abstract: A method for adjusting a spinning piezoelectric beam of a dual-axis angular rate sensor, in which the spinning piezoelectric beam is excited in a direction at right angles to the lengthwise direction of two piezoelectric sensors (22a, 22b) and to a rotary shaft (21); detected voltages of the two piezoelectric sensors (22a, 22b) are measured by a signal measuring circuit (30); a bending portion of at least one of the two piezoelectric sensors is ground so that the levels of the two measured signals and the difference therebetween become small; the spinning piezoelectric beam (20) is excited again in the lengthwise direction of the piezoelectric sensors (22a, 22b) at right angles to the rotary shaft (21); detected voltages of the two piezoelectric sensors are measured by the signal measuring circuit (30); and a weight mounted on the free end of at least one of the two piezoelectric sensors is ground so that the levels of the two measured signals and the difference therebetween become small. Thus, acceleration components applied to the spinning piezoelectric beam, in the detected voltages of the two piezoelectric sensors, are rendered to have the same phase and the same amplitude. On both sides of each piezoelectric sensor there are formed electrodes which are spaced 1.5 times the thickness of the sensor from support washers (24).

Linear piezoelectric step motors

Abstract: The design of a linear step motor using piezoelectric material is presented. The principle of operation is based on the characteristics of piezoelectric ceramics, which have a relationship between pressure and voltage. This motor can achieve a very-high-precision positioning. The resolution can be as high as 0.1 mu m to 10 AA, depending on the operating voltages and the dimension of the piezoelectric ceramic for a specific application. Due to the slow response of the mechanical clutches, the system cannot be driven very fast. It takes 10/sup 4/ s to generate a 2.74 cm displacement. >

Device for magnifying displacement of piezoelectric element and method of producing the same

Abstract: A device for magnifying displacement of a piezoelectric element at a printing head is proposed. The displacement of a column shaped piezoelectric element due to applied voltage is transmitted to a contact member and is magnified via a displacement magnifying mechanism to drive a printing wire connected to the displacement magnifying mechanism. A temperature compensating member is disposed between a frame supporting the piezoelectric element and the piezoelectric element and/or between the contact member and the piezoelectric element, and gives a preload to the piezoelectric element to support in a fixed manner the piezoelectric element between the frame and the contact member. The temperature compensating member is plastically deformed to compensate for the deformation of the piezoelectric element due to temperature change.

Piezoelectric sensors for use as a DNA probe

Abstract: It will be shown that a quartz crystal coated with single strand DNA can act as a sensor for hybridization in liquids. The method used is based on the change in oscillating frequency resulting from the increase in mass on the crystal surface which is accompanying the hybridization. Specifically, it will be shown how an AT - cut quartz crystal oscillating at 5 MHz would operate as a DNA probe. Also a theoretical model will be presented which will show what the key physical parameters are, their interrelationships as well as their effect on measuring the inimobilization of DNA on a piezoelectric crystal.

New Type Piezoelectric Gas Sensor Using Temperature Characteristics of Quartz Crystal

Abstract: A new type quartz piezoelectric sensor coated with a sputtered Pt film was proposed for the detection of inflammable gases, i.e., H2, CO, and iso-butane diluted with air. The sensing signal of the new sensor is provided by an increase in resonance frequency of the crystal (ΔF) due to a temperature increase upon contact with sample gases in the temperature range 100°-400°C. The frequency change of the sensor was found to be opposite in direction to that of a conventional adsorptiontype piezoelectric gas sensor operating at ambient temperature. The temperature change of the present sensor resulted from the oxidation of the inflammable gas on the surface of the catalyst film. A linear relationship between ΔF and H2 concentration (0-0.4vol%) was observed at the temperatures examined. The 90% response time of the present sensor to 0.3vol% H2 was about 20s at 200°C. The sensitivity of the sensor to H2 in air increased sharply with increasing temperature above 100°C. Furthermore, the gas selectivity to H2 was very high especially at 100°-200°C.

An experimental study of the use of PVDF piezoelectric sensors in active structural acoustic approaches

Abstract: An experimental investigation was performed to determine the feasibility of implementing polyvinylidene fluoride (PVDF) piezoelectric distributed sensors on the surface of a structure as error sensors in an adaptive lms control approach to minimize acoustic radiation. A simply supported rectangular plate was chosen as the test structure and was excited by a point‐force steady‐state harmonic disturbance. Structural inputs achieved by three piezoceramic actuators bonded to the surface of the panel. Two narrow strip PVDF sensors were positioned on the plate such that the dominant observed response was due to the odd modes (i.e., the more efficient radiators). The error sensors in effect act as spatial wavenumber filters and only observe those components that contribute significantly to far‐field sound radiation. Both position and number of piezoceramic actuators were varied during the test to determine the effects on control performance. A variety of test cases was studied for controlling sound radiation due to a disturbance both on and off resonance. Results from these experiments indicate that PVDF sensors and piezoceramic actuators (i.e., an “intelligent” structure) show much promise for controlling acoustic radiation from structures, to a large degree overcoming the need for error microphones in the far field. [Work supported by ONR/DARPA.]

Piezoelectric linear motor

Abstract: PURPOSE: To obtain a piezoelectric linear motor, which operates with high accuracy, suitable for miniaturization and causes no fluctuation in quality even when mass produced, by constituting a clamping piezoelectric element of a bimorph piezoelectric element having high manufacturing accuracy and operational accuracy. CONSTITUTION: A bimorph piezoelectric actuator 6 bends upon application of a voltage and unclamped, and only a bimorph piezoelectric actuator is clamped. A straight advance multilayer piezoelectric actuator 3 elongates upon application of a voltage and the piezoelectric actuator 6 moves in x direction. When voltage is removed from the piezoelectric actuator 6, it is recovered and clamped again. When a voltage is applied on a piezoelectric element 4, the piezoelectric element 4 bends and unclamped and only the piezoelectric element 6 is clamped. When voltage is removed from the piezoelectric element 3, it is recovered entirely and contracts thus moving the piezoelectric element 4 and a movable part 11 in x direction. COPYRIGHT: (C)1992,JPO&Japio

Electric field measuring instrument

Abstract: PURPOSE: To detect the magnitude and the direction of a field simultaneously by providing at least two optical fiber sensors and directing respective directional components arranged in a piezoelectric sensor perpendicularly to each other CONSTITUTION: A non-piezoelectric support 1 is fixed with three piezoelectric sensor elements 2a-2c which are fixed, respectively, with sensor elements 3a-3c having a specified length and a longitudinal part The elements 3a-3c are connected, respectively, with detectors 4a-4c which detect a variation in the length of corresponding elements 3a-3c detected through the elements 2a-2c by means of an interferometer and delivers corresponding output signals The output signals are transmitted from the output sides 5a-5c of detectors to an evaluation circuit 6 The circuit 6 determines the magnitude and the direction of a field E from the sensor signals and Presents them in a desired form for example on a display The determined amount may be transmitted to a monitoring station depending on the application