Active Acoustic System Research Articles

Piezocomposite actuator designs for an active underwater acoustic control system coating

The design and development of piezocomposites for use as the actuating device in an underwater acoustic control system coating will be discussed. Both flexible piezoceramic and 1–3 piezocomposite designs are explored as actuator candidates in the thin‐walled polymer matrix encapsulant coating. The actuators will be presented in single layer form for the absorption of normally reflected acoustic pressure waves. A bilaminate design will be shown for the absorption of both the normally reflected and transmitted acoustic waves. Experimental measurements will be used for performance comparison of different composite and lamination designs.

Model of a bilaminar actuator for active acoustic control systems

To increase levels of sound attenuation, it is often necessary to utilize active acoustic control methods. A complete active acoustic control system typically consists of sensing devices, an electronic control circuit, and an actuating device. Each component is designed to cause destructive interference of the impressed acoustic pressure field. A piezocomposite actuator is presented for active underwater attenuation control of an impressed acoustic field. The actuator is composed of bilaminate plates for absorption of both the reflection and the transmission of normally incident acoustic waves independent of the backing impedance. An electromechanical model of the bilaminate piezocomposite design with an analytical discussion is presented. An illustrated numerical example and discussion of system implications are included.

GAPEX: A Ground-Based Atmospheric Profiling Experiment

Abstract During the week 29 October–4 November 1988, a Ground-based Atmospheric Profiling Experiment (GAPEX) was conducted at Denver Stapleton International Airport. The objective of GAPEX was to acquire and analyze atomspheric-temperature and moisture-profile data from state-of-the-art remote sensors. The sensors included a six-spectral-channel, passive Microwave Profiler (MWP), a passive, infrared High-Resolution Interferometer Sounder (HIS) that provides more than 1500 spectral channels, and an active Radio Acoustic Sounding System (RASS). A Cross-Chain Loran Atmospheric Sounding System (CLASS) was used to provide research-quality in situ thermodynamic observations to verify the accuracy and resolution characteristics of each of the three remote sensors. The first results of the project are presented here to inform the meteorological community of the progress achieved during the GAPEX field phase. These results also serve to demonstrate the excellent prospects for an accurate, continuous thermodynamic ...

Large area sensors for active acoustic control systems

The design and development of a composite piezoelectric polymer (PVDF) sensor for use in an active acoustic control system is presented. Large area PVDF plates are encapsulated in a polymer matrix to detect both the incident and reflected signals in an underwater pulse tube at low frequencies. These signals are amplified, phase shifted, and then used to drive an absorbing transducer to negate reflections. The results of this system are compared with earlier data [X.-Q. Bao et al., J. Acoust. Soc. Am. Suppl. 1 84, S49 (1988)] that utilized piezoceramic spherical hydrophones.

Large area sensors for active acoustic control systems

The design and development of a composite piezoelectric polymer (PVDF) sensor for use in an active acoustic control system are presented. Large area PVDF plates are encapsulated in a polymer matrix to detect both the incident and reflected signals in an underwater pulse tube at low frequencies. These signals are amplified, phase shifted, and then used to drive an absorbing transducer to negate reflections. The results of this system are compared with earlier data [X.-Q. Bao, V. K. Varadan, and V. V. Varadan, J. Acoust. Soc. Am. Suppl. 1 84, S49 (1988)] that utilized piezoceramic spherical hydrophones. [Work supported by the Research Center for the Engineering of Electronic and Acoustic Materials.]

An Electret Loudspeaker for Active Acoustic Systems

A push-pull electret loudspeaker has been developed which can be used for an active acoustic wall lining.

The measurement and analysis of active system acoustic impedance

A considerable part of the structure borne vibration in small aircraft is caused by both mechanically and acoustically induced vibration from the aircraft engine. The measurement method suggested within this work obtains the acoustic impedance of an active acoustic source; particular emphasis will be placed on the measurement procedure and apparatus for acquiring the source impedance characteristics of an internal combustion engine. The acoustic impedance is directly used to identify a mismatching impedance and when physically implemented with the acoustic source eliminates much of the acoustic energy output. This project utilized a two sensor sampling technique for obtaining the acoustic impedance of an active acoustic system. The two sensor method of analysis incorporates a Digital Signal Analyzer system to calculate incident‐reflected acoustic properties. The laboratory method of experimentation includes exposure of the engine to a broadband random noise while performing sensor signal analysis using a transfer function technique. [Work supported by Nelson Industries, Inc.]

Reverberation Received by a Hydrophone Separated From an Active Acoustic Source

Reverberation equations have customarily been derived only for a source and receiver at the same point as in the familiar sonar situation. However, the study of interference between two similar active acoustic systems requires a knowledge of the characteristics of the reverberation received at a point separated from the source. A simplified expression for volume reverberation is derived for directional projectors oriented in the same direction but displaced along the beam axis. Reverberation decay curves are presented with source-to-receiver separation as a parameter. The variation of the volume reverberation index, Jv (usually considered a constant), is also discussed.