**Generation of Linear Traveling Waves in Piezoelectric Plates in Air and Liquid**

**Alex Díaz-Molina 1,\*, Víctor Ruiz-Díez 1, Jorge Hernando-García 1, Abdallah Ababneh 2, Helmut Seidel 3 and José Luis Sánchez-Rojas 1**


Received: 5 April 2019; Accepted: 25 April 2019; Published: 27 April 2019

**Abstract:** A micro- to milli-sized linear traveling wave (TW) actuator fabricated with microelectromechanical systems (MEMS) technology is demonstrated. The device is a silicon cantilever actuated by piezoelectric aluminum nitride. Specifically designed top electrodes allow the generation of TWs at different frequencies, in air and liquid, by combining two neighboring resonant modes. This approach was supported by analytical calculations, and different TWs were measured on the same plate by laser Doppler vibrometry. Numerical simulations were also carried out and compared with the measurements in air, validating the wave features. A standing wave ratio as low as 1.45 was achieved in air, with a phase velocity of 652 m/s and a peak horizontal velocity on the device surface of 124 μm/s for a driving signal of 1 V at 921.9 kHz. The results show the potential of this kind of actuator for locomotion applications in contact with surfaces or under immersion in liquid.

**Keywords:** traveling waves; piezoelectric; microactuator; MEMS
