Micromachined ac/dc electric field sensor with modulated sensitivity

• This electric field sensor possesses adjustable sensitivity, enabling wide measurement range, from sub-1 V/m to over MV/m.
• This micromachined sensor possesses a smaller size than traditional dc electric field mills.
• The sensor operates by monitoring the displacement of a membrane, avoiding maintenance issues of rotating field mills.

This paper presents a compact ac/dc electric field sensor with adjustable sensitivity and measurement range. The sensor is fabricated using an SOI micromachining process, and consists of a metallized membrane supported by micro-springs. The sensor operates by monitoring membrane displacement due to incident electric fields. Unlike field mills, this sensor does not have rotating parts, avoiding associated wear and maintenance issues. High sensitivity is achieved by using a laser position monitoring system. Modulation of the incident electric field with a bias voltage on the sensing membrane is used to give the sensor a wide measurement range, from sub-1 V/m to MV/m. Bench top experimental measurements with both dc and ac fields demonstrated a resolution of 0.1 V/m and sensitivity of 180 mV/(V/m), with the sensor operating at resonance. Measurements under 20 kV simulated power line 75 cm from the sensor demonstrated a resolution of 17 V/m and sensitivity of 360 mV/(kV/m).