The design variables are independent and have been dictated by the geometric constraints. The equivalent stiffness of the beam is a state variable in this analysis, because it is a function of the thickness of back plate and piezo. The voltage applied to the piezo is also a state variable, a function of the piezoceramic's frequency and capacitance. To avoid depoling, an upper limit of 50 volts has been assigned to the element. Because the cantilever is equivalent to the classic spring-mass system of force being the product of mass, deflection, and frequency, the operating frequency should be raised to increase the shake.
Lower voltage means less power transmitted to the system.
After the harmonic analysis is done, the optimization program recalculates the capacitance and voltage. The modal analysis next computes the stress based on the new voltage. In addition to optimization and actual shake tests, ergonomic research has been done to find the best way of improving the vibration performance of these silent alarms. Although the piezo-vibrator device shook strongly enough to get the wearer's attention in most environmental circumstances, that awareness improved greatly when vibrations were pulsed or interrupted. The duty cycle could be either preprogrammed or selected by the user in the finished product.