Integrated optical longitudinal strain sensor on a micromachined silicon longitudinal mode transducer

We present a silicon-based ultrasonic actuator with an integrated grating to measure ultrasonic strain and phase optically. This sensing technique will enable remote closed-loop control of silicon-based high-intensity ultrasonic actuators. This capability might allow the use of silicon-based high-intensity actuators in new applications where precise ultrasonic energy is required, which requires close-loop control over the resonator amplitude while maintaining a high quality factor. Our technique requires defining a grating on the surface where strain is to be measured. The longitudinal strain results in the grating line/space modulation, which changes the angle of the diffracted orders. We present results of this concept by presenting data on strain measurement of a micromachined silicon longitudinal mode transducer in the shape of a bar.