Electrorheological Fluids as an Electrically Controllable Acoustic Medium: I. Experimental Arrangement and Application to an Absorber of Underwater Sound

Electrorheological fluids (ERF) change their viscoelastic properties in a strong electric field. A new realm of ERF applications could be underwater acoustics where the construction of absorbers with electrically adjustable properties appears possible. An improved impedance tube has been developed for the measurement of the acoustic properties of ERF and hydroacoustic sound absorbers, employing the so-called two-microphone method. Using the new impedance tube, sound velocity and attenuation of ERFs have been measured as functions of frequency, field strength, and temperature. Further, a laboratory model of an absorber for underwater sound, based on the principle of particle velocity transformation with ERF as viscous fluid, has been built and tested. Within certain limits, the absorber impedance can be controlled by changing the electric field strength applied to the ERF.