A micromachined airflow sensor based on RF evanescent-mode cavity resonator

This paper presents an RF airflow sensor based on an evanescent-mode cavity resonator. The frequency loading is achieved by a capacitive post in the center of a cylinder cavity. As a sensing mechanism, an elastic membrane with a sensing beam is utilized to generate a strain on the top of the cavity. The airflow deflects the sensing beam, changing the parasitic capacitance of the cavity and hence, the resonant frequency of the resonator. The cavity resonator is fabricated by micro-molding of thermal-plastic polymers enabling a low cost batch fabrication. The coplanar waveguide (CPW) feeding structure is formed simultaneously during the molding process by using a metal transfer technique. The resonant frequency of the resonator as a function of the sensing beam deflection angle is demonstrated, and a wind tunnel test is performed to demonstrate an equivalent sensitivity of 0.36GHz/(m/s) for the air flow velocity measurement.