Abstract: A sensing system computes an amount of moisture on a surface of a substrate, such as a window of a vehicle. The sensing system includes a transmitter which produces a wave to propagate through the substrate. A receiver receives the wave which propagated through the substrate. A phase shift detection circuit measures a phase shift between signals representing the transmitted and received wave. A temperature sensor senses a temperature of the substrate. A controller, in communication with the phase shift detection circuit and the temperature sensor, calculates the amount of moisture on the surface based on the phase shift and the temperature of the substrate. A wiper motor and wiper blade may then be actuated automatically based on the amount of moisture calculated to clear the moisture on the substrate.

Abstract: Silicon and glass micromachined (MEMS) acoustic sensors incorporating trapped-liquid architectures are disclosed. The trapped liquid serves as an acoustic transmission medium allowing the input port to the system to be physically separated from the sensing location. The trapped liquid interacts with a conductive, flexible sensing membrane. Sound pressure waves enter the trapped liquid through an input membrane, travel to the sensing membrane, and excite vibrations of the sensing membrane. The vibrations of the sensing membrane are measured using on-chip capacitive sensing. The capacitive sensing structure is formed by the conductive sensing membrane and a fixed conducting top electrode. As the gap between the conductive sensing membrane and the fixed top electrode varies, the capacitance varies, leading to an electrical signal which is the electrical output of the system.