This paper describes the design and performance of a small, high-frequency, piezoelectric, underwater probe. The probes are fabricated from miniature, thin-wall, lead zirconate titanate ceramic hollow spheres with radii (r) from 0.5 mm to 2.5 mm and wall thickness (t) from 50 mu m to 250 mu m. The experimental results reported in this paper are focused on devices prepared from hollow spheres with an outer radius of 1.38 mm and a mean wall thickness of 75 mu m. As a hydrophone, these devices display a sensitivity of -220.7 dB re 1 V mu Pa-1 at 250 kHz that stays flat to within +/-3 dB over the frequency range from 10 kHz to 450 kHz with an omnidirectional response. Within the accessible range of sphere sizes (r = 0.5-2.5 mm, t = 50-250 mu m), this stable and flat sensitivity behavior could be extended to a range from -212 to -225 dB re 1 V mu Pa-1 and up to 1 MHz. Finite element analysis of this transducer using the ATILA (R) software is also included in this paper, comparing the computational results with the results from the experimental measurements. Based on the excellent agreement obtained, a parametric modeling study was also undertaken and its results are discussed in this paper. The miniature ceramic hollow-sphere transducers fill a gap in the frequency range of 200 kHz to 1 MHz with an omnidirectional response and much higher sensitivity than other ceramic and polymer piezoelectric probes.

In this study new type piezoelectric monolithitic low cost underwater and biomedical transducers based on Class IV flextensional transducer design has been introduced. Transducers were produced by using two techniques: fused deposition and extrusion. Besides, finite element analysis (FEA) was used extensively in order to optimize transducer design to achieve broad bandwidth for both transmitting and receiving and engineered vibration modes. Class IV transducers possess resonance frequencies in the range of above 30 kHz to below 150 kHz. Symmetry and design of the transducer, poling patterns, driving and receiving electrode geometries and driving conditions have strong effect on the vibration modes, resonance frequencies.

The hydrostatic pressure limit that a receiver can withstand without failure is of major importance in underwater sonar systems. In this paper, the hydrostatic pressure tolerance and sensitivity of cymbal receivers were investigated. The failure mode in cymbal transducers under hydrostatic pressure is described. Effects of cavity geometry and material selection on hydrostatic piezoelectric coefficients and pressure limits were evaluated using both experimental data and finite-element analysis (FEA). It was found that cavity depth has a very strong effect on the stability of underwater sensitivity and pressure tolerance of these devices. Cymbals made with soft piezoelectric transducers (PZTs) possess higher figures of merit and better pressure tolerance than those made with hard PZTs. Alternatively, the cymbal sensitivity and pressure tolerance can be improved by changing the cap material.

Traditional flextensional transducers classified in seven groups based on their designs have been used extensively in 1-100 kHz range for mine hunting, fish finding, oil explorations, and biomedical applications. In this study, a new family of small, low cost underwater, and biomedical transducers has been developed. After the fabrication of transducers, finite-elements analysis (FEA) was used extensively in order to optimize these miniature versions of high-power, low-frequency flextensional transducer designs to achieve broad bandwidth for both transmitting and receiving, engineered vibration modes, and optimized acoustic directivity patterns. Transducer topologies with various shapes, cross sections, and symmetries can be fabricated through high-volume, low-cost ceramic and metal extrusion processes. Miniaturized transducers posses resonance frequencies in the range of above 1 MHz to below 10 kHz. Symmetry and design of the transducer, polling patterns, driving and receiving electrode geometries, and driving conditions have a strong effect on the vibration modes, resonance frequencies, and radiation patterns. This paper is devoted to small, multimode flextensional transducers with active shells, which combine the advantages of small size and low-cost manufacturing with control of the shape of the acoustic radiation/receive pattern. The performance of the transducers is emphasized.

: The main objective of this work is to take traditional high-power, low frequency transducers and miniaturize them to expand the operating range, reduce fabrication costs, and improve performance. This effort began with the development of the and moonie miniature flex-tensional transducers. This project improved upon the cymbal design, explored modifications and developed new designs based on other low-frequency technology, such as the hollow sphere and more complex flex-tensionals miniaturized through extrusion and Fused Deposition of Ceramics (FDC) technology. Transducer development has been supported heavily by finite element analysis. Applications for cymbals, cymbal modifications, BB miniature hollow spheres, and monolithic multimode transducers has been explored. Emphasis is placed on Navy needs and biomedical applications.

Cymbal transducers have been found as a promising structure for piezoelectric energy harvesting under high force (∼ 100 N) at cyclic conditions (∼ 100–200 Hz). The thicker steel cap enhances the endurance of the ceramic to sustain higher ac loads along with stress amplification. This study reports the performance of the cymbal transducer under ac force of 70 N with a pre-stress load of 67 N at 100 Hz frequency. At this frequency and force level, 52 mW power was generated from a cymbal measured across a 400 kΩ resistor. The ceramic diameter was fixed at 29 mm and various thicknesses were experimented to optimize the performance. The results showed that the PZT ceramic of 1 mm thickness provided the highest power output with 0.4 mm endcap. In order to accommodate such high dynamic pressure the transducer and cap materials were modified and it was found that the higher piezoelectric voltage constant ceramic provided the higher output power. Electrical output power as a function of applied ac stress magnitude was also computed using FEM analysis and the results were found to be functionally coherent with experiment. This study clearly demonstrated the feasibility of using piezoelectric transducers for harvesting energy from high magnitude vibration sources such as automobile.

Miniature versions of high-power, low-frequency transducers are being optimized to produce broadband transmit and receive responses, engineered vibration modes and optimized acoustic beam patterns.

The effects of materials on the performance of the cymbal-type flextensional transducers were investigated under in-air and water-loaded conditions by finite element analysis (FEA) methods. At the initial stage, FEA and experimental studies were conducted in parallel to gain experience with the FEA models. Later, all calculations were carried out by computational methods: resonance frequencies, projector TVR, receiver FFVS, effective coupling coefficient (keff), and mechanical quality factor (Q m ) were calculated. Ceramic and endcap materials have strong effects on the TVR/FFVS performance of cymbal transducers. It is possible to tailor a wide range of flexural resonance frequencies by optimizing the ceramics used as the driver and the metals used as the endcaps.

Twinned crystals are normally classified according to twin-laws and morphology, or according to their mode of origin, or according to a structural basis, but there is another classification that deserves wider acceptance, one that is based on the tensor properties of the orientation states. An advantage of such a classification is the logical relationship between free energy and twin structures, for it becomes immediately apparent which forces and fields will be effective in moving twin walls. The domain patterns in ferroelectric and ferromagnetic materials are strongly affected by external fields, but there are many other types of twinned crystals with movable twin walls and hysteresis. These materials are classified as ferroelastic, ferrobielastic, and various other ferroic species. As explained in the next section, each type of switching arises from a particular term in the free energy function. Ferroic crystals possess two or more orientation states or domains, and under a suitably chosen driving force the domain walls move, switching the crystal from one domain state to another. Switching may be accomplished by mechanical stress (X), electric field (E), magnetic field (H), or some combination of the three. Ferroelectric, ferroelastic, and ferromagnetic materials are well known examples of primary ferroic crystals in which the orientation states differ in spontaneous polarization (P(s)), spontaneous strain (x(s)), and spontaneous magnetization (I(s)), respectively. It is not necessary, however, that the orientation states differ in the primary quantities (strain, polarization, or magnetization) for the appropriate field to develop a driving force for domain walls. If, for example, the twinning rules between domains lead to a different orientation of the elastic compliance tensor, a suitably chosen stress can then produce different strains in the two domains. This same stress may act upon the difference in induced strain to produce wall motion and domain reorientation. Aizu suggested the term ferrobielastic to distinguish this type of response from ferroelasticity, and illustrated the effect with Dauphine twinning in quartz. Other types of secondary ferroic crystals are listed in Table 16.1, along with the difference between domain states, and the driving fields required to switch between states.

A miniature flextensional transducer, the “cymbal,” is an emerging underwater transducer technology for large area and restricted volume transmit and receive arrays. The performance of the device is being evaluated for a number of applications requiring a large number of elements. Simple design, low cost and the ability to tailor performance to the desired application are attractive features of the cymbal. Analysis of the fabrication and performance of the cymbal has revealed that the benefits of the cymbal's flexible design also present production concerns. Asymmetry in the cavity depth or epoxy layer can result in unwanted resonances that can detract from the in-water performance. To avoid these spurious resonances, tolerances in cavity depth could be as low as 5 μm, resulting in low production yields. These and other fabrication concerns have been analyzed through experiment and finite element modeling software using the ATILA code. We were able to identify ways of improving manufacturing yields and minimizing variances to accommodate large array production. The origins of the spurious resonances are discussed along with the performance of a prototype array.

A single-beam interferometer capable of resolving displacements on the order of 10 −4 Å was used to examine the field-induced displacement in several low-permittivity dielectric materials. The experimental principle and procedures of the single-beam interferometer are described in this article. The importance and the accuracy of the Maxwell stress and the thermal stress corrections are also discussed. We present in this article the field-induced strains and the apparent electrostrictive coefficients of several common dielectric materials, including Al 2 O 3 , BeO, MgO, AlN ceramics, and SiO 2 glass. Under application of an electric field, these common ceramic materials become thicker in the field direction, while glasses and glass-ceramics get thinner. The magnitude of the displacements varies between 10 −2 to 10 −3 Å under 1 MV/m electric field. By comparison, the field-induced displacements in these common electronic materials are approximately 3 to 5 orders of magnitude smaller than those observed in relaxor materials, such as PMN and PVDF, and soft polymers.

Smart electromeehanical systems consist mainly of sensors, actuators, and data processing units. Actuators are the responding units of many smart systems including those for active vibration control and noise control. Increased demand for actuators with high-displacement, high generative force, and quick-response time has led to a search for new actuator materials and new designs. The performance of traditional piezoelectric transducers with newly designed flextensional transducers is compared.

A new type of cymbal transducer, called the concave cymbal, has been developed to increase the pressure tolerance and reliability of the transducer under high hydrostatic pressure. The main feature of the new design is a lead zirconate titanate ceramic ring sandwiched between two concave metal endcaps. It shows much improved pressure performance and can withstand a pressure of up to 6 MPa while maintaining high effective hydrostatic piezoelectric coefficients. When incorporated into a planar array with a radiating area of 5.5 cm/spl times/5.5 cm and weight of only 30 g, a transmitting voltage response of around 125 dB re 1 /spl mu/Pa/V@1 m was obtained over a frequency range between 20 and 50 kHz.

Different transmission electron microscopy techniques have been compared for the detection and size measurements of ordered regions on a nanometer scale in a disordered matrix phase. As a model system, the perovskite lead magnesium niobate doped with varying amounts of La has been chosen for the present study. While selected area electron diffraction can reveal the existence of ordered structures, dark‐field contrast micrographs are usually used to reveal the spatial distribution and the size of ordered regions. However, for small ordered regions, a few nanometers in diameter, the measurements are no longer accurate because of superposition in projection. High‐resolution transmission electron microscopy (HRTEM) combined with image processing is shown to be a suitable technique to provide a quantitative measurement of such localized ordering. The detection limit of this method is discussed in detail, using the experimental results and HRTEM image simulations.

This paper reviews the current trends and historical development of piezoelectric sensors and sensor materials technology. It begins with a discussion of the bases of piezo- and ferroelectric activity, followed by an overview of the most commonly used piezoelectric ceramic: lead zirconate titanate (PZT). A discussion of the properties and applications of piezoelectric crystals and additional piezoelectric ceramics is followed by a description of several sensor configurations prepared from bulk ceramics. An extensive review and comparison of piezoelectric ceramic—polymer composite sensors based on the connectivity of the constituent phases is also presented. We conclude our discussion of sensor configurations with recent examples of piezoelectric ceramic—metal composite sensors, and expected future developments in the area of piezoelectric sensors.