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"At present, there are some obvious flaws in the equipment used to measure the strength of the electric field," explains Andreas skantz of the tuvin Institute for sensor and actuator systems. "These devices all contain live parts. When measuring, the conductive metal composition will significantly affect the measured electric field; if the equipment needs to be grounded to provide the measurement reference value, the influence will be further amplified. "As a result, such electric field measuring devices are generally relatively impractical and difficult to transport.

MEMS sensors are made of silicon material and are based on a very simple principle: a micro spring and a micro grid silicon structure fixed on the spring, which are used to measure micro scale motion. When the silicon structure is in the electric field, a certain force will be generated on the silicon crystal to make the spring slightly elongate or compress.

A. The measuring principle of this kind of MEMS electric field sensor is: the mass (m) is suspended on the elastic element (rigid K), and the elastic element is fixed on the fixed frame of conducting electricity. When placed in an electric field (E), electrostatic induction produces a force (FES) on the mass. Under the action of this force, the mass will produce a certain displacement (δ x), and then the displacement is measured by optical principle;

b. A cross-sectional view of the device shows that the light emitted by the LED can be projected onto the photodiode below through the gap between the gate silicon structure and the hole. The movement of the mass block changes the gap between the opaque area and the hole, thus changing the light input of the LED which can reach the photodetector;

C. 3D view of the MEMS electric field sensor; SEM image of the MEMS electric field sensor.

How to measure the fine displacement of mass? The researchers have designed an optical solution: a layer of mesh structure is set above the movable mesh silicon structure, the holes of the upper and lower layers of the mesh structure are arranged precisely, and the upper opening is precisely aligned with the lower opaque area. In other words, LED light cannot penetrate the two-layer silicon structure when the lower layer of the network silicon structure is not moving. When the sensor is placed in the electric field, the lower mesh silicon structure is displaced under the action of electrostatic force, which makes the gap between the upper and lower reticular structures, and the LED light can reach the lower photodetector through the gap. By measuring the amount of incident light, the intensity of the electric field can be calculated using appropriate calibration equipment.

The accuracy of the prototype is exciting.

The electric field sensor of MEMS can not measure the direction of electric field, but can measure the intensity of electric field accurately. It can measure the electric field strength from low frequency to 1kHz. "With our prototype sensor, we can measure weak electric fields below 200 V / m with high reliability," Andreas kanz said This means that our system has the same performance as existing products, and our sensors are smaller and simpler. In addition, there is still much room for improvement. Other measurement methods are relatively mature solutions, and our MEMS electric field sensor has just been designed and formed. Of course, it can be improved in the future.