Characterization techniques for a MEMS electric-field sensor in vacuum

An accurate calibration of an electric-field sensor is difficult to carry out due to challenges involved in generating a uniform electric field over the sensor volume. Additionally, capacitive coupling between the field source and the sensors and related instrumentation tends to distort the measured field further. Sensor characterization includes not only calibration, but also determination of the frequency response (both magnitude and phase), noise power spectral density, dynamic range, and linearity. In this paper, we discuss characterization techniques for an unpackaged microelectromechanical systems (MEMS) electric field sensor in a vacuum chamber. The use of oppositely charged square plates at a spacing of half the plate width is advised by the IEEE 1308-1994 standard for generation of a uniform electric field. Previously, the U.S. Army Research Laboratory (ARL) has shown that by employing guard tubes in the construction of an electric field generating chamber, the fringing fields can be controlled, and the spacing between the endplates can be increased while maintaining a uniform field. A similar, smaller apparatus for generating a uniform axial electric field was constructed to fit into a vacuum bell jar. The considerations and techniques for minimizing error due to fringing and distortion from metal conductors will be presented, along with the techniques and laboratory equipment used for characterizing the sensor.