PhD-Level Ultrasonic Engineering • Medical • Manufacturing • Consumer
Is high stress the best?
In order to have the highest electromechanical coupling in a power ultrasonic transducer, you need to place your piezo crystals at the nodal point of the assembly. However, in certain situations you don't want to do that. Because the nodal point is at a high stress location, the piezo will be necessarily undergo large stress for any level of vibration. Here are two points to consider when specifying the placement of your crystal which may actually warrant not placing your crystal exactly at the nodal point:
1. The cyclical stress limit of the piezo ceramic may actually limit the maximum oscillation amplitude which a design can reliably achieve.
2. When the ceramics are not placed at the nodal point, the Q of the assembly increases as now (A) the metal components contain more strain energy per unit of oscillation and (B) you removed component interfaces at the nodal point, which are hubs for power loss.