Acoustic source used for Active Noise Control at low frequency (80 - 250 Hz) is designed and developed by using a piezoelectric ceramic actuator and a flextensional panel diaphragm. In order to reach the vibration magnitude and radiation area needed for high and flat sound pressure level in the low frequency range. Pseudo-Shear Universal (PSU) actuator has been used as the driving part which is a new type of multilayer piezoelectric actuator originated from MRL offering the advantages of large displacement and high blocking force; on the other hand, Carbon Fiber Reinforced Composite has been used as the diaphragm material which provides a more rigid structure than conventional loudspeaker paper. A prototype device was fabricated which has the following characterizations: 40 layers PSU actuator with a compact dimension: 38 mm X 50 mm X 23.6 mm. Two of them are needed for a device. Diaphragm area is 126 mm X 152 mm. At quasistatic condition (5 Hz) and at the 0.84 kV/cm electric field, 344 micrometers displacement could be achieved at the apex of the diaphragm resulted from the flextensional amplifying mechanism with an amplification factor more than 11. The sound passive level in the frequency range 100 - 250 Hz shows better flat behavior than the acoustic sources studied earlier such as Double Amplifier and PANEL air transducers which exhibit a significant reduction of sound pressure level in the low frequency range. By a slight modification, it is likely to make this device in a total thickness of 10 - 15 mm range. High and stable sound pressure level as well as thin flat structure make it much more competitive in the whole area of applications for low frequency active noise control.

A new type of bimorph-based piezoelectric air transducer with the working frequency range of 200–1000 Hz has recently been developed [B. Xu, Q. Zhang, V.D. Kugel, L.E. Cross, Piezoelectric air transducer for active noise control, Proc. SPIE, 2717 (1996) 388–398]. In the present work, basic acoustic characteristics of this device and its piezoelectric elements are analyzed. To model the vibration spectrum of the transducer, a one-dimensional approach is developed where inertia, elastic and damping forces are included. Analytical equations describing mechanical vibrations and electrical impedance of piezoelectric bimorph cantilevers under external forces are derived. In order to describe various losses in the transducer, complex piezoelectric, dielectric, and elastic constants are used. Results of the modeling are in good accord with experimental data. The suggested model can be used for device optimization.

The behavior of piezoelectric, dielectric, and elastic characteristics of soft piezoelectric lead zirconate titanate (PZT) ceramics was investigated under sinusoidal electric field E applied along the poling direction and under mechanical stress-free conditions for a frequency range 10 Hz–10 kHz. Electrical displacement D3 along the poling direction, mechanical strain S1 in the direction perpendicular to the poling direction, and the resonant frequency νr of electromechanically uncoupled bending vibrations of polarized plates were measured. Commercial ceramics PZT5H, 3203HD, and PKI550 with chemical composition near the morphotropic phase boundary were used in the study. It was found that the amplitude and phase of the first harmonic of the relative strain S1(1)/Em and of the relative electrical displacement D3(1)/Em increase similarly with increasing amplitude Em of the electric field if the amplitude is less than coercive field. The corresponding increase in the square of the resonant frequency is more moderate. The dependencies are described well by linear functions except for low electric fields. The functions S1m(1)/Em and D3m(1)/Em demonstrate frequency dispersion as well. Relative amplitude of the second harmonic of the electrical displacement, D3m(2)/D3m(1), which is polar, also increases almost linearly with increasing Em. The relative third harmonic D3m(3)/D3m(1) demonstrates saturationlike behavior. By means of the electric pulse technique, it was found that irreversible changes in the remnant polarization take place even at electric fields much smaller that the coercive field. A mathematical model of a hysteretic transducer, describing the electric field dependence of electromechanical properties of soft piezoelectric PZT ceramics, was suggested. According to this approach, the response depends not only on the instantaneous magnitude of the input signal (e.g., electric field) but also on its past extreme values. It was shown that the experimental Rayleigh law is a particular case of the suggested approach. The model relates directly electric field dependencies of complex piezoelectric coefficient d31(Em) and S1(1)/Em, of complex dielectric permittivity ε33T(Em) and D3(1)/Em, and of the amplitude of elastic compliance s11E(Em) and νr2. Application of the model to experimental data showed that the model describes well the first three complex harmonics of D3 and the irreversible change in the remnant polarization. Physical causes of the observed behavior were analyzed. As an alternative to the model based on the 90° polarization reorientation and tetragonal/rhombohedral phase boundary motion, a new approach was suggested. In this model, the observed hysteretic changes in the electromechanical properties are assumed to be caused by the electric field dependency of the mechanical stress acting at interdomain boundaries in the partly constrained crystallites of these ceramics.

Piezoelectric actuators are being increasingly used in smart systems like vibration suppression and acoustic noise canceling devices. In this work, a novel piezoelectric bending actuator CRESCENT was developed. CRESCENT is a stress-biased ceramic-metal composite actuator. The technology involves the use of the difference in thermal contraction between the ceramic and the metal plates bonded together at a high temperature by a polymeric agent to produce a stress-biased curved structure. The electromechanical performance of this device in the cantilever configuration was investigated. The tip displacement, blocking force and electrical admittance were chosen to characterize the performance of the actuator under quasistatic conditions. The device fabricated at optimum temperature exhibits large tip displacement and blocking force and possesses superior electromechanical characteristics to conventional unimorph actuators.

The PANEL (Piezoelectric Acoustic Noise ELiminator) transducer was developed for air acoustic noise cancellation in the frequency range of 200–1000 Hz. It has a thin panel structure, occupies less volume, and is lighter than an equivalent electromagnetic transducer. This device consists of a U-shaped configuration of piezoelectric bimorph and unimorph actuators bridged by a triangular amplifying diaphragm, which acts as an effective source of the sound radiation into air. The role of the diaphragm is twofold: it amplifies by a factor of 5–20 the tip displacement of the piezoelectric actuators and it also increases the sound emitting area. Amplitude of the vibrations and usable frequency range of the transducer depend on the dimensions and material of the actuators and diaphragm. The overall dimensions of the device fabricated were 52×50×24 mm. Soft PZT ceramics were used. The diaphragm was made of a carbon fiber reinforced composite. The diaphragm vibrations reach 500 μm rms well below the fundamental resonant frequency of bending vibrations which lies between 200 and 500 Hz. Above resonance, the amplitude of vibrations gradually decreases to 25 μm rms at 1000 Hz. The experimental results indicate that the transducer developed is promising as a sound transmitter for acoustic noise canceling devices.

During the last several years novel piezoelectric bending actuators have been developed: RAINBOW, CERAMBOW, CRESCENT, d33 bimorph and THUNDER. A comparative experimental investigation of electromechanical characteristics of these devices along with conventional d31 bimorph and unimorph actuators was conducted in this work. All transducers were fabricated from soft piezoelectric ceramics. The experimental results show the d33 bimorph and unimorph elements have superior quasistatic characteristics as compared to other type of bending-mode actuators. All these piezoelectric devices demonstrate a significant dependence of electromechanical performance on the magnitude of the driving electric field. It was found that the decrease in the mechanical quality factor and resonant frequency of bending vibrations in d31 unimorph, RAINBOW, CRESCENT (CERAMBOW) and THUNDER with increasing electric field is much smaller than that in bimorph and d33 unimorph actuators. The dependence of the behavior of these devices on the operating conditions governs the selection of a particular device for a specific application.

Piezoelectric actuators have significant potential for use in smart systems like vibration suppression and acoustic noise canceling devices. In this work, a novel piezoelectric bending actuator CRESCENT was developed. CRESCENT is a stress-biased ceramic-metal composite actuator. The technology involves the use of the difference in thermal contraction between the ceramic and the metal plates bonded together at a high temperature by a polymeric agent to produce a stress-biased curved structure. An extensive experimental investigation of this device in the cantilever configuration was carried out. The tip displacement, blocking force and electrical admittance and were chosen to characterize the performance of the actuator under quasistatic conditions. The device fabricated at optimum temperature exhibits large tip displacement and blocking force and possesses superior electromechanical characteristics to conventional unimorph actuators.

Strong pulsed electron emission has been observed from 12/65/35 lead lanthanum zirconate titanate ceramic composition in two different nonswitched phases at room temperature and at the temperature 100 degrees C. The electron emission parameters of this composition appear to be independent of phase for the two phases investigated. Fast photography acid direct observation show that the strong electron emission occurs from the surface discharge pfa;sma. The new experimental data make it possible to demonstrate the validity of the Child-Langmuir law for this electron emitter. A pulsed plasma lead lanthanum zirconate titanate ceramic cathode with burst frequency up to 100 KHz and collector current density up to 10 A/cm(2) is developed. (C) 1996 American Institute of Physics.

Characteristics of cantilever shear mode piezoelectric actuator have been investigated. In this actuator configuration, soft PZT ceramic plate was poled along length and driven across its thickness, with one end mechanically clamped and the other free. Experimental results indicated that relative large tip displacement can be obtained through nonlinear piezoelectric response at high driving field. Due to lateral shear force, mechanical bending also contributes to the tip displacement of shear mode actuator. The fundamental bending resonant frequency was observed in the frequency range from 150 Hz to 600 Hz, depending on thickness and length of actuator. We also found that the resonant frequency of bending vibration is dependent on the driving field because of elastic nonlinearities. Two layer and multilayer shear mode actuators were also developed to reduce the driving voltage, while shifting the bending resonance to higher frequency range by increasing the total thickness of actuator

Our experimental data show that a rather thin layer with inverted polarization at the +c-face strongly suppresses the pyroelectrically induced electron emission from LiNbO3 crystals. We assume that the microscopic electric field of pyroelectric positive surface charges increases a potential barrier to polarons moving toward the vacuum. The pyroelectrically induced electron emission provides a novel method of detecting thin surface layers with inverted polarization.

A new type of piezoelectric air transducer has been developed for active noise control and other air acoustics applications. The transducer is based on the composite panel structure of a bimorph-based double amplifier, that is, two parallel bimorphs or bimorph arrays with a curved cover plate as an active face attached to the top of the bimorphs. The electro- mechanical and electro-acoustic properties of the double amplifier structure and the transducer are investigated in this paper. The displacement of the cover plate of the double amplifier structure can reach millimeter scale with a relatively low driving voltage, which is more than ten times larger than the tip displacement of bimorphs. The sound pressure level (SPL) of the transducer can be larger than 90 dB (near field) in the frequency range from 50 to 1000 Hz and be larger than 80 dB (far field) from 200 Hz to 1000 Hz, with the largest value more than 130 dB (near field). Because of its light weight and panel structure, it has the potential to be used in active noise control.

A piezoelectric bimorph transducer utilizing piezoelectric d33 coefficient was developed. This bimorph consists of piezoelectric segments bonded by a polymeric agent and was fabricated by a dicing and layering technique. The transducer has superior piezoelectric characteristics compared to standard piezoelectric d31 bimorphs. Piezoelectric coefficients, electrical admittance, mechanical compliance, and losses of the actuator were found to increase with increasing driving electric field.

Polarization switching in triglycine sulfate crystals with one of the polar surfaces covered by a thin dielectric film (1 μm) has been found to be highly diminished in a 50 Hz electric field. We assume that the depolarization field caused by the film significantly moderates the process of the nucleation and (or) sideways motion of 180° domain walls. When crystals with both conductive electrodes were connected to the Sawyer–Tower circuit through the capacitor, which was equivalent to the dielectric film, the polarization reversal did occur. We assume that in the case of the conductive electrode, a nonuniform distribution of the electrical charge at the electrode/ferroelectric interface and an injection current through the interface trigger off polarization reversal. Analysis of the energetic state of the crystals has been performed.

Behavior of piezoelectric actuators (bimorph, unimorph, RAINBOW, and shear-mode) fabricated from soft ceramics has been investigated in a wide electric field and frequency range. The electrical admittance, mechanical displacement, and blocking force of these transducers have been found to be highly dependent on the magnitude of driving field. The resonant frequency and mechanical quality factor of bending vibrations for all but shear-mode actuators decreases significantly with increasing driving field. Analysis shows that despite a large variation in the quasi-static electrical admittance and reduced tip displacement of bimorph, unimorph, and RAINBOW cantilevers with driving field, their ratio is almost a constant, which characterizes the ratio of dielectric permittivity epsilon(33)(T), to piezoelectric coefficient d(31).

In the last few years the technology of using piezoelectric actuators for applications requiring large displacements such as loudspeakers and noise-cancelling devices has undergone significant development. RAINBOW (Reduced and INternally Biased Wafer) is a novel high displacement actuator and knowledge of its dynamic response is indeed essential for these applications. In an attempt to characterize the RAINBOW, measurements were made of important lumped mechanical and electrical parameters. Cantilevers of different dimensions were cut from RAINBOW discs. The data include measurements of the mechanical displacement (under both quasistatic conditions and electromechanical resonance), hysteresis, mechanical quality factor and the electrical impedance of RAINBOW cantilevers. These measurements demonstrate the macroscopic effects of the sinusoidal applied electric field and indicate significant non-linearities in the RAINBOW device

Bimorph based double amplifier actuator is a new type of piezoelectric actuation structure which combines both bending and flextensional amplification concepts. As a result the displacement of the actuator can be more than ten times larger than the tip displacement and can be used in air acoustic transducers as an actuation element. This paper studied the dependence of displacement on actuator parameters and optimum design issues for the cover plate (the flextensional part of the actuator) theoretically and experimentally

It was discovered recently that a large electric-field-induced strain can be obtained in several polyurethane elastomers which show promises for the applications in the transducers and actuators. In this study, electrostrictive properties of a polyurethane elastomer were investigated systematically. The elastic, dielectric and DSC spectroscopy analysis indicated the existence of two transition processes in the polyurethane from -50 degrees C to 80 degrees C, The field-induced strain coefficients exhibited large increases at the transition regions, indicating that the transition processes have significant effect on the field-induced strain response. From the elastic and dielectric constant data, the contribution of uniform Maxwell stress was calculated. It was found that the contribution of the Maxwell stress effect to the measured strain coefficient increased from about 10 % below the glass transition temperature, T-g, (similar to.25 degrees C) to about 50 % and 35 % for the frequencies of 10 Hz and 100 Hz, respectively, at similar to 40 degrees C, which is above T-g. The difference between the measured strain response and the calculated Maxwell stress effect indicates a significant contribution from other mechanisms such as electrostriction.

Pyroelectric properties of LiNbO3 crystals are studied by SEM. It is shown that various diffusion treatments of these crystals causing changes both of the domain configurations and crystal conductivity give rise to a strong variation of the pyroelectric potential.

Basic switching parameters (switching transient current, switching time, etc.) observed during electrical polarization reversal of undoped ferroelectric triglycine sulfate crystals with free surface are asymmetric. A comparison of the experimental data with the theoretical models of Fatuzzo [Phys. Rev. 127, 1999 (1962)], Pulvari, and Kuebler [J. Appl. Phys. 29, 1742 (1958)] shows that the classic models cannot to the fullest describe this type of polarization reversal. It is suggested that the asymmetric switching is caused by the difference in the field electron emission from a metal switching electrode and a ferroelectric crystal.

Pyroelectrically induced electron emission (EE) is studied from LiNbO3 crystals with a layered domain structure fabricated under various diffusion treatments. It is observed that the appearance of a thin oppositely polarized surface layer at the +C-surface suppresses EE. For bidomain configuration with equal thicknesses of the inverted and the original domains EE occurs from the boundary between two domains. It is proposed that a potential barrier for emitted electrons depends strongly on the spontaneous polarization direction at a free polar surface,