Vienna Uni develops silicon-based electric field sensor

Researchers at Vienna Technical University have developed a sensor for measuring the strength of electric fields in a variety of products; the sensor is much smaller, simpler and less prone to distortion than comparable devices.


Vienna Uni has developed a tiny electric field sensor for measuring the strength of electric fields – image courtesy of Vienna TU.

Accurately measuring electric fields is important in a variety of applications and devices manufactured in the automotive, medical, electronic, communication and defence industries.

In a break from the design principle that has been followed by all other measuring devices to date, a research team at Vienna TU has now developed a silicon-based sensor as a microelectromechanical system (MEMS).

MEMS is a process technology used to create tiny integrated devices that combine mechanical and electrical components; these devices can sense, control and actuate on the micro scale, and generate effects on the macro scale.

Current MEMS devices include accelerometers for airbag sensors, inkjet printer heads, computer disk drive read/write heads, projection display chips, blood pressure sensors, optical switches, microvalves, biosensors and many other products that are all manufactured and shipped in high commercial volumes.

Devised in conjunction with the Department for Integrated Sensor Systems at Danube University Krems, this new developed sensor has the major advantage that it does not distort the very electric field it is currently measuring.

Distorting measuring devices

Andreas Kainz from the Institute of Sensor and Actuator Systems (Faculty of Electrical Engineering, Vienna TU), said: “The equipment currently used to measure electric field strength has some significant downsides.

“These devices contain parts that become electrically charged. Conductive metallic components can significantly alter the field being measured; an effect that becomes even more pronounced if the device also has to be grounded to provide a reference point for the measurement.”

Schematics of the sensor: the moveable and the fixed grid – image courtesy of Vienna TU.

Such equipment also tends to be relatively impractical and difficult to transport. The sensor developed by the team at Vienna TU is made from silicon and is based on a very simple concept: small, grid-shaped silicon structures measuring just a few micrometres in size are fixed onto a small spring.

When the silicon is exposed to an electric field, a force is exerted on the silicon crystals, causing the spring to slightly compress or extend.

These tiny movements now need to be made visible, for which an optical solution has been designed: an additional grid located above the movable silicon grid is lined up so precisely that the grid openings on one grid are concealed by the other.

When an electric field is present, the movable structure moves slightly out of perfect alignment with the fixed grid, allowing light to pass through the openings. This light is measured, from which the strength of the electric field can be calculated by an appropriately calibrated device.

Prototype achieves impressive levels of precision

The new silicon sensor does not measure the direction of the electric field, but its strength. It can be used for fields of a relatively low frequency of up to one kilohertz.

Kainz said: “Using our prototype, we have been able to reliably measure weak fields of less than 200 volts per metre. This means our system is already performing at roughly the same level as existing products, even though it is significantly smaller and much simpler.

“Other methods of measurement are already mature approaches – we are just starting out. In future it will certainly be possible to achieve even significantly better results with our microelectromechanical sensor.”