A structure called an Interdigital Transducer (IDT), with alternate positive and negative electrodes, is implemented on the surface of the quartz substrate so that a wave-like vibration is emitted across the surface. The oscillation frequency is inherent in interval between the electrodes (  ) and the propagation speed of sound (V) within the substrate. This type of quartz cut and structure is able to produce much higher frequencies than a tuning fork crystal or AT cut crystal. Like all of Epson’s timing and sensor products, a quartz substrate is used for its piezo-electric property, high reliability and stable characteristics over temperature.