James F. Tressler

Piezoelectric Transducer Designs for Sonar Applications

An electroacoustic transducer is a device that converts acoustic energy (sound) into electrical energy (voltage or current) or vice versa. When the transducer is used to generate sound, it is called a projector, transmitter, or source. When it is used to detect sound, it is called a receiver. Furthermore, when the receiver is employed underwater, it is referred to as a hydrophone. An underwater sonar system consists of projectors, hydrophones, and associated electronics such as amplifiers and data acquisition systems. This chapter, however, will only cover the description and operational principles of the projector and hydrophone components. More specifically, the chapter will focus on piezoelectric ceramic-based transducer designs intended for underwater use that operate in the frequency band spanning from 1 kHz to 1MHz. This span covers weapons sonar (1–100kHz) and imaging sonar (100 kHz to 1MHz) applications. Section 11.2 describes the fundamental parameters and measurement techniques necessary to characterize transducers both in air and in water. The piezoelectric ceramic materials that are most commonly used in sonar transducers and their relevant materials properties are discussed in Sect. 11.3. The most common piezoelectric ceramic-based projector designs for sonar applications are described in Sect. 11.4, where they are grouped according to their operational frequency range. A single transducer cannot operate efficiently over the entire 1-kHz to 1-MHz frequency band – primarily due to impedance matching issues with the associated amplifiers. Consequently, a variety of transducer designs have been developed and optimized for different frequency ranges. The chapter concludes with hydrophone characterization, designs, and some performance results in Sect. 11.5.

Broadband low frequency sonar for non-imaging based identification

A new approach to underwater object identification is presented that aims to capitalize on structural acoustic features found in targets at low frequencies. In order to use these. features for identification purposes, multi-aspect scattering cross-sections must be extracted over a broad range of frequencies. In this paper, we describe a system created to do this. It employs new low frequency source technology based on CYMBAL arrays and an unconventionally large vertical receive array. Data are acquired in a coherent fashion and synthetic apertures are used to extract multi-aspect target scattering cross-sections.

A Comparison of the Underwater Acoustic Performance of Cymbal-Based Projectors to 1-3 Piezocomposite Materials

The performance of two different ‘cymbal’ actuator-based underwater acoustic projector designs is compared. One projector design is a 101 mm by 101 mm Thin Panel potted in polyurethane. The other is a 152.4 mm by 76.2 mm tungsten-backed flat panel embedded in a syntactic foam frame. Both projector designs are characterized in-air and evaluated in-water. The results of the in-water studies are based on a 100 Watt power supply. Comparing to 1-3 piezocomposite materials with the same radiating area and similar thickness, these cymbal-based projectors appear to be best suited for use at frequencies below 4–5 kHz, with particular emphasis in the 1 kHz range. The cymbal-based devices described in this study are strictly prototypes and are not designed for a specific application. Nevertheless, the results indicate that if the acoustic aperture of these projectors were scaled to the appropriate dimensions, they could meet the design goals of many low frequency Navy applications where source levels > 180 dB from a thin package are desired

Thin, lightweight, low frequency acoustic projectors for shallow water environments

Miniature flextensional transducers, called cymbals, have been incorporated into thin, lightweight, large area panels for use a slow frequency acoustic projectors in shallow water. The prototype panels, measuring 100-mm by 100-mm by 6.35-mm thick exhibit a high acoustic output at a relatively low in-water resonance frequency. Furthermore a second resonance frequency that is over an order of magnitude higher suggests that the panel may be used to provide sound output over almost a two decade frequency band. The mass of the unplotted panel is less than 150 grams and the total thickness is 6.35 mm. The cymbal panels are believed to be excellent candidates as acoustic projectors on autonomous and/or unmanned underwater vehicle platforms as well as other shallow water platforms where low frequency, light weight and high acoustic output are desired.

Fabrication and Characterization of Single Crystal Cymbals

Cymbal transducers are made using single crystal relaxor ferroelectric PMN-PT. An electrically conductive adhesive film with uniform geometry and thickness is used to bond the metal cymbal caps to the single crystal. Upon curing, the bond exhibits good mechanical strength under both static and dynamic test conditions. It is found that the capacitance and d 33 of the cymbal drop markedly upon curing as compared to the single crystal disk. It is demonstrated that this is not due to depoling during the adhesive cure stage but rather clamping of the single crystal disk by the stiff metal cymbal caps.

Proper orthogonal decomposition analysis of scanning laser Doppler vibrometer measurements of plaster status at the U.S. Capitol

A large-scale survey (~700 m2) of frescos and wall paintings was undertaken in the U.S. Capitol Building in Washington, D.C. to identify regions that may need structural repair due to detachment, delamination, or other defects. The survey encompassed eight pre-selected spaces including: Brumidis first work at the Capitol building in the House Appropriations Committee room; the Parliamentarians office; the House Speakers office; the Senate Reception room; the Presidents Room; and three areas of the Brumidi Corridors. Roughly 60% of the area surveyed was domed or vaulted ceilings, the rest being walls. Approximately 250 scans were done ranging in size from 1 to 4 m2. The typical mesh density was 400 scan points per square meter. A common approach for post-processing time series called Proper Orthogonal Decomposition, or POD, was adapted to frequency-domain data in order to extract the essential features of the structure. We present a POD analysis for one of these panels, pinpointing regions that have experienced severe substructural degradation.

Piezocomposite Design, Manufacture, and Applications

Publisher Summary This chapter presents an overview of piezocomposite materials. It describes the phenomenon of piezoelectricity, which is the basis of all piezocomposites, and discusses the attributes of the primary piezoceramic materials. The design, manufacturing processes, and primary applications of two commercially available piezocomposite configurations are illustrated. Simple analytical models that are used to describe the properties of these two composite designs are also presented. The chapter then discusses the design issues and manufacturing processes, and describes some important applications for 0-3 and 1-3 type piezoelectric ceramicpolymer composites. The poled ferroelectric ceramics PT and PZT are the materials of choice as the active component in nearly all piezocomposite devices. This is because of their high piezoelectric response and stability. Piezocomposites offer the advantage of easy design flexibility for specific applications, especially in the case of 1-3 connectivity. Although shape apodization, increased band width, and constant beam width transducers can be accomplished with monolithic piezoceramics, it is at a high cost. With piezocomposites, these features can be obtained much more cheaply. In addition, the dice-and-fill and injection molding manufacturing processes have made these, as well as future, advances in product development possible.

Transduction technologies for structural acoustics sonars

This presentation will describe underwater acoustic transduction technologies that the Naval Research Laboratory (NRL) has developed for structural acoustics sonars. The NRL “Skyfish” downward-looking sonar system is deployed on a 21-inch diameter autonomous underwater vehicle (AUV) that features a pair of extendable/retractable wings, each of which houses a thirty-two element cylindrical hydrophone array. The well-behaved acoustic source consists of a pair of transducers, each covering a separate frequency band. The source is designed to provide a fairly wide acoustic aperture for looking both fore and aft as well as in the port and starboard directions. Architectural details of the source and receiver, materials considerations, amplifier design, and experimental data will be presented. [This work supported by the Office of Naval Research & ESTCP.]