Capacitive Omnidirectional Position Sensor Using a Quarter Wave Resonator

An open environment, omnidirectional sensing method is presented that utilizes the mechanics of a quarter wave resonator (QWR). A highly sensitive response to external perturbations is formed as approaching objects alter the stray capacitance around the resonator, causing the system’s frequency to change. The detection range of the experimental system exceeds a 1 m radius around a 150 mm tall device. A theory is presented that predicts the voltage distribution on the QWR and further explores the maximum horizontal distance at which the voltage distribution changes due to an approaching object. The relationship between the excitation voltage versus the distance of various approaching objects is characterized as well as the vertical displacement response, sensor resolution, and the power consumed by the device. Two resonators connected to a classic differential amplifier circuit are used to demonstrate the detection of the velocity and direction of an approaching object. The advantages of the reported approach include low fabrication cost, low power consumption, and omnidirectional detection.