Variable compliance split-cylinder transducer using Galfenol for frequency control.

Abstract

The size of conventional split ring transducers is much smaller than a wavelength at operating frequency leading to a high Q resonance and limited operating bandwidth. This work investigated modifying the split ring structure to allow its resonant frequency to be adjusted under active control so that it is always operated at or near its resonance. Because the transducer is operated at resonance, the phase of its input impedance is approximately constant, simplifying the design of the transmit power amplifier and reducing the size and weight of the system. A high Q system is desirable for an actively tuned system resulting in very high efficiency and allowing the use of less expensive shell materials. The two variable compliance designs studied involve the use of Galfenol stiffener bars located at the nodal point/hinge point of the shell. By activating all or a portion of these bars, the compliance (stiffness) of the shell can be varied with a corresponding shift in resonance frequency. Two methods of compliance control are being investigated, one that switches the stiffness “on” and “off,” and one that allows continuous control using the “delta‐E” effect in Galfenol.