Noncontact excitation of macro and micro cantilevers using ultrasound radiation force excitation

Excitation of vibration of MEMS and other small structures is important for many applications including mass sensing and atomic force microscopy. However, conventional excitation techniques normally require contact, which may not be feasible for small objects. We present a non-contact method that uses ultrasound radiation force in air to produce low-frequency excitation of structures. The excitation was produced using the difference frequency between the two sidebands of a double-sideband suppressed carrier AM (DSB-SC-AM) waveform centered on 500 kHz that was emitted by a focused ultrasound transducer. A laser Doppler vibrometer measured the frequency response and deflection shapes of objects ranging from macroscopic cantilevers to microcantilever arrays. The same transducer was used for excitation of vibrations ranging from less than 100 Hz to over 200 kHz. Also demonstrated was the unique capability to selectively enhance or suppress modes independently by using a phase-shifted pair of transducers. By combining ultrasound radiation force excitation with laser Doppler vibrometry, this demonstrates the capability of performing both excitation and vibration measurement without physical contact.