No abstract

A small, low-frequency omnidirectional, broad-band hydrophone with relatively good sensitivity and capacitance has been designed, constructed, and tested. The design was of such nature that the hydrophone should withstand vibration and high-velocity shock in addition to meeting other particular requirements. A radially polarized, PZT-5H piezoelectric ceramic tube with end caps and an internal air cavity was cast in a polyurethane compound. This piezoelectric material has a high permitivity for maximum capacitance for permitted physical dimensions; however, two disadvantages are its low upper Curie point and its large variation of capacitance with temperature. A 1-in. outside diam, 18-in. wall thickness, and 1-in. length tube was used as the active part of the hydrophone. Properties of the hydrophone include a capacitance of 0.013 μF, sensitivity of about −95 dB, and omnidirectionality in all planes to about 5 kHz. [The work was partially supported by U. S. Naval Ordnance Laboratory.]

Some 12 transducer elements are assembled in a line array with a spacing of one wavelength. When adjacent elements are excited 180 out of phase, the array radiates two beams at 30 o on either side of the plane that is normal to the line. One-half wavelength from one end element is an acoustically soft reflector, made of Corprene, which reflects one beam to reinforce the other. The construction has cir-4,255,971 43.35.Sx THERMOACOUSTIC MICROSCOPY 0 • Rosencnb, Danvffie, C•ffomJa 94526 ]7 March ]98] (Class 73/606); oeded ] Hovetuber ]978A thermal wave is generated in a material by causing periodic, localized treating at a microscopic spot by focusing intensity modulated light or electromagnetic radiation on the spot. The thermoacoustic signal produced can provide information about material composition or structure. In this invention, the material sample is scanned as a two-dimensional array of microscopic spots to examine surface and subsurface properties. The claims appear to be quite broad.-JVB culaz symmetry so that the radiation pattern is a hollow cone, about 3 ø in thickness. This apparatus was designed and built specifically to measure back scattering from the ocean surface and the sea bottom at a grazing angle of 30 ø. Because the beam is uniform in azimuth, the effects of surface waves and of bottom ripples are averaged out.-LB 4,259,399 43.35.Ty ULTRASONIC NONWOVEN BONDING Betlie R. Hill, assignor to Burlington Industries Incorporated 31 March 1981 (Class 428/288); f'ded 31 August 1978 Ultrasonic energy is used to produce a lightweight fabric from a bart of random, loose thermoplastic fibers. The bart and a carrier of flexible sheet material, such as tissue paper, are progressively fed together between the horn and the anvil of an ultrasonic welding machine, to form the bart into a nonwoven fabric. The carrier is claimed to be an important element of the process.-JVB 4,238,856 43.35.Sx FIBER-OPTIC ACOUSTIC SENSOR Sound can be detected because its acoustic pressure affects the propagation of light through an optic fiber. Light from a laser 9 is transmitted through an optic fiber 10, most of which is wound into a coil 11 on which the sound impinges. The initial amplitude TE o becomes TRE o and TR2E0, respectively, after one and two internal reflections, where T and R are the transmission and reflection coefficients at the ends of the fiber. Ignoring subsequent reflections, the amplitudes T 2 E 0 and T: R: E o of the first two components to reach TREo (DIRECTLY TRANS' MITTED BEAM} ---*T•go (BEAM REFLECTED BACK AND FORTH FROM ENDS OF FIBER} the light detector 12 are compared to detect the sound. Any of three acousto-optical effects may be exploited, and the patent coy-' ers all three. Acoustic pressure varies the length of the optical fiber, and hence varies the phase of the light. If the light is polarized, the acoustic pressure varies the angle through which the plane of polarization is rotated in the fiber. If the light travels by more than one mode of propagation, the acoustic pressure varies the coupling...

This article describes some of the design, construction, and test-performance details of a small, low-frequency, omnidirectional, broad-band hydrophone. The design was of such nature that the hydrophone should withstand high-velocity water-impact shock, have a minimum sensitivity of --100 dB relative to 1 V/tzbar for the frequency range 10 Hz to 2 kHz, have a minimum capacitance of 10 nF, and be omnidirectional in all planes to 2 kHz. A radially polarized PZT-5H piezoelecrtic ceramic tube with end caps and an internal air cavity was cast in a polyurethane compound. This particular piezoelectric material has a high permittivity, so the minimum capacitance could be obtained within the maximum physical dimensions. The mounting of the ceramic tube is described in which two beryllium copper springs are used to aid in positioning and cushioning the brittle ceramic, and to provide electrical contact to the inside and outside silver-filmed electrodes of the tube. Some of the properties of the hydrophone that are shown are the capacitance-temperature relationship, admittance versus frequency for air and water loading, and directivity patterns. The hydrophone was shown to be omnidirectional in all planes up to 5 kHz. I. DESIGN CONSIDERATIONSHE hydrophone described in this article was designed, constructed, and tested, because a commercially available one with the required characteristics could not be found in spite of many different types of hydrophones that have been developed for various purposes. Because of the proprietary nature of most of the hydrophone development, design and fabrication details generally have not been published. For this reason, some of the details with respect to this hydrophone are presented.Some of the requirements of this hydrophone were: (1) minimum sensitivity of --100 dB relative to 1 V/ubar for a frequency range of 10 Hz to 2 kHz; (2) minimum capacitance of 10 nF (0.01 uF); (3) small configuration; (4) omnidirectional in all planes to 2 kHz; and (5) withstand high-velocity water-impact shock and be designed for small-amplitude low-frequency vibration (800 Hz). The maximum allowable configurax R. SOLBERG AND KREISLE Fro. 3. Assembled and cast hydrophone. ceramic. They are fabricated of corprene, a synthetic rubber (chloroprene)-cork composition, which is compliant. A low specific acoustic impedance (pc for lossless materials) of the corprene components is necessary, because of their positions adjoining the aluminum end cap,. hydrophone plate, and piezoceramic, which have high specific acoustic impedances. Lack of acoustic Fro. 4. t-Iydrophone cross section. 1702 Volume 44 Number 6 1968