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Anti-Personnel Human Detection System

Screamer Electronic Services has developed and patented a human anti-personnel detection system using a capacitance sensor to detect a human through a wall.

This system is especially useful where other human detection methods such as infra-red or movement cannot be used. Infra-red for instance cannot be used where there are fluctuating temperatures that rise to the level of a human body because it will false alarm.

Similarly, movement detection systems cannot be used where there could be items moved by wind, etc which will again false alarm. Most importantly the sensor does not need to have line of site to the person and can detect human presence through concrete, steel or any other solid object.

How It Works

Every human body is surrounded by an electrical field. Capacitance is entirely dependent on the existence of electric fields. If a human body should approach one plate of a capacitor, the body’s electric field can inter-react with that of the capacitor and can cause the capacitance to increase.

Further, any number of sensor plates may be attached to one plate of a capacitor. These then become an extension of that plate. In this design the plate is attached to the positive plate of a capacitor.

The Detector is dependent on the electric field which surrounds the human body. Because the Detector is based on the principle of body capacitance it has a high degree of immunity to AC fields, as well as being able to function well out of range of such fields.

The Detector is able to act through an insulator – it will work through materials such as glass, wood, plaster, cloth, carpet or even cement. This could prove very useful in certain applications such as detecting the presence over or under a plate hidden in a wall or floor or ceiling .

A special feature of this design is that it may also be cascaded. For instance, it may be used to sense a larger area or more than one area at once. All that is required is separate sensor units, which are then connected in parallel..

  • The circuitry is built into an enclosure measuring +- 72 x 46mm .
  • Input voltage is 12 or 24 volts DC.
  • The output can be interfaced to alarm systems or sirens, immobilizers or a dry contact that in turn can switch mains voltages or higher current DC supplies.
  • One thin cable is attached to the sensor plate which is mounted out of sight or can be encapsulated .

Once installed and activated the Detector will sense the presence of a person who moves across the face area of the hidden sensor plate. The Detector is triggered by the increase in capacitance in the area covered by the sensor plate. Once the Detector is triggered the output is latched and will only be reset by power being removed and the Detector being reset .

The Detector detects above and below the sensor plate and the distance of detection can be calibrated to a maximum of 10.3 meters above and below the sensor plate/s.

A demonstration of it’s practical application

Screamer was approached by a fibreglass canopy manufacturer who wanted to create a canopy which detected if a vehicle was moving while carrying passengers. Screamer supplied the canopy manufacturer with a system which consisted of very thin copper strips of 100cm x 5cm which they laminated into the roof of the canopy. This was then connected to the detector unit that was housed in the corner of the canopy and was in turn connected to the vehicle immobiliser to immobilise the vehicle if the system detected any human presence under or on top of the canopy.

Other human detection systems could not offer the same degree of detection and limited false alarming as well as anti-tampering that the Screamer capacitance system offered.

To see a video of the system in action please click here

To find out more about the system please send an email to gavinh@screamer.co.za