Vibrating superleak second-sound transducers. Theory and experiment

The properties of vibrating superleak second-sound transducers of the type invented by Rudnick and co-workers and Sherlock and Edwards are discussed. Recent theoretical treatments of these transducers are reviewed, and an error in Saslow's theory of the detection process is corrected. The theory is then extended so as to take into account Poiseuille flow of the normal fluid through the superleak. We also describe experiments in which the transducers are used to excite and detect second sound in a resonant cavity containing superfluid4He. Our results indicate that the flow of the normal fluid component through a superleak is very important under the conditions commonly found in experiment involving these transducers. The experimental results are in good general agreement with the theory