Abstract
Control systems are becoming increasingly dependent on digital processing and so require sensors able to provide direct digital inputs. Resonator sensors, configured to have a mechanical resonance frequency or relative phase of oscillation dependent on the measured parameter, are a subject of considerable practical interest. The author reviews the wide range of devices which have been proposed and developed, including sensors for liquid or gas density and viscosity, liquid level, mass and mechanical force, and fluid flow rates. Techniques cover the frequency range from audio, for sensors based on vibrating vanes or tubes, to 100 MHz or more for surface acoustic wave devices. Resonator sensors based on single crystal materials such as quartz and silicon are of particular interest because they combine high accuracy and repeatability and low cost of manufacture and potentially very low power consumption.