Mainly used in the field of power ultrasonic and underwater acoustics, a sandwich piezoelectric transducer composed of metal blocks on both end faces of a piezoelectric ceramic disc is used.

Since the transducer of this structure was proposed by French physicist Lang Zhiwan, it is sometimes called the Langevin transducer.

The advantage of this transducer structure is that it utilizes both the longitudinal effect of the piezoelectric ceramic vibrator and the lower resonance frequency. On the other hand, due to the characteristics of the piezoelectric ceramic itself, that is, the tensile strength is poor, at high power. It is prone to cracking under working condition. Prestressing is applied to the piezoelectric ceramic disc by using metal blocks and pre-stressed bolts, so that the piezoelectric ceramic disc is always in a compressed state during intense vibration, thereby avoiding cracking of the piezoelectric ceramic sheet. .

	Type	Resonant Frequency	Resonant Resistance	Capacitance	Maximum electric power	Applications
	PTC50K154TLL	49KHz-51.1KHz	≤35Ω	2750pF±10%	20W	Used in the portable equipment for collar cleaning.
	Type	Resonant Frequency	Resonant Resistance	Capacitance	Maximum electric power	Applications
	PTC45K152BLG	44.1KHz-45.9KHz	≤100Ω	1375pF±10%	10W	Used in the portable equipment for collar   cleaning.
	Type	Resonant Frequency	Resonant Resistance	Capacitance	Maximum electric power	Applications
	PTC40K252LLG	39KHz-40.5KHz	≤45Ω	4900pF±10%	100W	Used in High-Power ultrasonic cleaning equipment.