The crystal diaphragm 60 is a cemented laminate of two piezoelectric crystals 101 and 103 which may be formed of a material, such as quartz or thin discs of a piezoelectric material or piezoelectric ceramic material, such as discussed in the aforenoted ASME Publication entitled Application of the Piezoelectric Effect for Energy Converters of the Artificial Heart Program by G. M. Benson and Nichol