Dual-frequency transducers fabricated using partially poled vinylidene fluoride-trifluoroethylene copolymer

Transducers capable of generating two ultrasonic frequencies have been fabricated from partially poled vinylidene fluoride/trifluoroethylene copolymer disks. The observed resonances correspond to the fundamental and second harmonic of the thickness vibration mode of the disk. The resonance frequencies depend on the thickness of the disk, but not on the thickness of the poled region. The second harmonic is stronger than the fundamental when the thickness of the unpoled region is larger than half of the thickness of the disk.