Multilayer piezoelectric ultrasonic transducer for medical diagnostics - uses cascaded discs for bandwidth enlargement and optional barker code generation, forming rectangular pulse train

摘要

Whereas bandwidth can be increased by making the piezo-electric disc thin, this reduces the power output. A method for maintaining power while increasing bandwidth is to stack a number of discs of equal width with some elastic bonding medium between them, and to polarise alternate discs, or only some of the discs in opposite directions, either by providing electrodes at inversion points or by stacking discs with their inherent polarity orientations (ceramic transducer discs) in such a manner that groups of various effective thicknesses are produced within the stack. Groups of discs having unidirectional orientation may be replaced by a single disc of equivalent thickness. If a steep pulse is applied to such a composite stack the same responds by a sequence of tensional reactions which at the output end produce a coded ultrasonic signal whose sequential pulse length characteristic closely corresponds to the disc thickness sequence in the transducer stack. If the phase orientation of the consecutive layers is selected in accordance with a Barker code the factors which normally limit bandwidth are reduced to a minimum.