AC electric field anomaly detection

AC field sensor monitors the ambient AC field that exists whenever the power line is energized and can detect objects in proximity

Energy Electronics Sensors

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A scientist at the Army Research Laboratory has invented an object detection system.

Schematic diagram of one possible implementation where a vehicle (24) passing through an ambient AC electric field (22), generated by a 60 Hz AC power line (16) fed by an AC voltage source (20), is detected by an AC electric field sensor (18).

The patented technology is available via patent license agreement to companies that would make, use, or sell it commercially.

Current technology advances allow the detection of anomalies in ambient direct current (DC) fields. This is commonly achieved via magnetic field sensors, also known as magnetic anomaly detectors (MAD).

The sensors can detect distortions in the earth’s DC magnetic field caused by ferromagnetic objects but are typically limited by their own dynamic range and geomagnetic noise. Similarly, electric field sensors are used to detect distortions in the earth’s DC electric field caused by conducting objects, such as unarmed intruders or aircraft that do not include any ferromagnetic components. Unfortunately, alternating current (AC) electric fields interfere with these types of sensors and make detection more difficult. There remains a need for a method that can reliably detect and process anomalies in ambient AC electrical fields.

ARL researchers have developed a novel solution to this challenge, utilizing both electric and magnetic AC field sensors. In one possible implementation of the technology shown in the diagram, an AC electric field sensor is placed in an ambient AC electric field generated by an AC power line fed by a stable AC voltage supply. Without power lines, the AC voltage could be supplied to any arbitrary conducting surface to generate an ambient AC electric field. The sensor then generates a signal representative of the ambient AC electric field, which is fed to the mixer of a synchronous demodulation circuit and passes through the high-gain amplifier, after which the demodulated signal is output by the low pass filter.

In a military context, the anomalies detected might be intruders, unknown vehicles and unmanned aircraft, but there are potential civilian applications as well. The sensors can detect when blowing branches or growing trees are in dangerous proximity to power lines.

This data would provide power distribution companies with actionable intelligence on when to cut trees or schedule maintenance on lines. Similarly, truck booms and other large construction equipment can be detected when they’re used too close to energized power lines, thus increasing worker safety.

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