This paper describes interface circuits for a multiphase disk-shaped piezoelectric generator. By using quarter-circle shaped electrodes, similar to an ultrasonic motor, multiple output voltage phases are obtained from a single resonating disk. A lumped circuit model for the piezoelectric transducer is derived, which is accurate for the traveling wave excitation. Interface circuits that take advantage of the multiple output phases have been designed, implemented, and tested. A time-interleaved AC-DC converter with low output voltage ripple serves as an example of these interface circuits. In addition, a new energy recycling technique, which exploits the relative phase difference between adjacent electrodes, is explored. Measured results show a greater than 10% increase in total energy harvesting ability with the use of the proposed energy recycling technique.