Jewellery Ultrasonic Cleaner: Automatic Ultrasonic Cleaner works on piezoelectric and so the crystals being used are called as a piezoelectric crystal. Mainly ceramics (lead zirconate) crystals are used in ultrasonic cleaners. It is composed of barium, lead, titanium and zirconium. As crystals become thinner its capacitance rises and its impedance falls.The two crystals are sandwich between aluminum block and mild steel block along with brass shims at the maximum torque of 150 PSI. The brass shims are used to apply the output signal from the generator across the crystal. Their arrangement is such that aluminum block and mild steel are fixed with a mild steel bolt and with the result of this both the crystals will get opposite polarity of excitation at a particular instant of time. Because of this one crystal will expand while the other will contract and for the other half cycle the first will contract and the second will expand. In this fashion expansion of one crystal is compensated by the contraction of the other crystal. The crystal is lead zirconate titanate (PZT-4). It is a ceramic crystal that exhibits the piezoelectric property.