Using the theory of sandwich transducer,the author analyzes the combination coupling vibration of longitudinal vibration transducer and thin disk.The equivalent circuit diagram of this coupled transducer is drawn.The equivalent elastic constant is deduced and then the resonant frequency equation of coupled transducer is deduced.Resonant frequencies of the transducer which have the mentioned size are calculated by computer.This resonant frequencies' difference is compared with that of single pendulum.The res...