Variable Compliance Split Ring Transducer

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. The proposed work will investigate two different modifications to the split ring structure that allow its resonance frequency to be adjusted under active control so that it is always operated at or near its resonance. Because the transducer is always operated at resonance, the phase of its input impedance is approximately constant, vastly 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 first concept for a variable compliance transducer would replace a section of the shell near the hinge with a magnetostrictive portion; the compliance would be adjusted using the "Delta E" effect which changes modulus of the active material with stress and magnetic state and thus shifts the transducer resonance. The second concept utilizes stiffening members located near the hinge of the ring; the stiffening members are selectively actuated to change the compliance of the ring and shift the transducer resonance. Both these concepts are broadband, efficient transducers that can reach source levels in excess of 210 dB, resonant frequency less than 1 kHz, and bandwidth greater than 200 Hz.