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Perimeter Security

In today's world, the term “perimeter security” has taken on many, often confusing shapes. Players from the IT world, looking to capitalize on the convergence hype, are using this term to describe a means to secure a network, while traditional security industry players look at it from a physical standpoint – perimeter means either a solid means of protecting an area, such as bollards, fences, etc., or perimeter intrusion detection systems (PIDS). PIDS come in many flavors – buried cable, fence mounted cable, tensioned cable, acoustic (microphonic) cable, magnetic cable, seismic, infrared, radar and microwave.

Traditionally, PIDS are divided into two categories – bi-static (transmitter/receiver) and mono-static (transceiver) sensors. Bi-static sensors come in several categories, with detection zones ranging from 30 feet in the traditional type, to 2,500 feet in some of the modern millimeter wave systems, creating both long and narrow zones. This transmitter/receiver style of detection gives you an ability to establish an “invisible fence,” where the detection field serves to identify human and/or vehicular intrusion. Intruders create a “void” in a detection zone, which is then analyzed by the system through the use of complex algorithms. These algorithms compare this void to a matrix, populated with parameters equaling various human “shapes.”

Mono-static sensors are also known as volumetric sensors, named for their mass sensing ability. Traditionally, these devices were used to protect enclosed spaces, such as rooftops, garbage dumps, etc. Modern applications are a lot more diverse, with an ability to protect individual objects, such as vehicles, aircraft, etc. Since these objects have a constant mass, the sensor begins its detection process only when that mass changes, which could be the case during an intrusion.

If the parameters of the object causing the change in mass match those of a human, an alarm is created. Usually, these sensors are based on the Doppler effect, which has a drawback – objects moving at speed across the detection zone or directly towards the detector may go undetected. This problem is solved with detectors using Line Frequency Modulation (LFM), which constantly probes segments of the zone, thus eliminating the aforementioned concern.

Mobile rapid deployment intrusion detection systems are an important category of sensors that are based on a classic transmitter/receiver series. In the past, this would be restricted primarily to military and law enforcement use.

Today, they are used in a wide variety of applications, anywhere from aircraft and cargo protection to concert crowd control. These sensors employ the same principles of operation as their stationary counterparts, but do so in a lighter, more compact, fashion. They are often deployed with the use of tripods, long lasting batteries and wireless alarm transmission. Another type of rapid deployment systems is based on seismic sensors. They feature exceptional battery life (one to five years, depending on the manufacturer) along with an ability to form a wireless mesh network for reliable delivery of alarm signals. There are multiple accessories available, such as break wire and magneto-metric (ferromagnetic) sensors, allowing, for example, the detection of armed humans within a protected perimeter.

Modern detectors have the ability to adapt to changing terrain conditions, consume less power and compensate for uneven terrain while also being immune to electromagnetic interference (EMI). Sensors are more robust and easier to install and use, while false alarms are minimal. Microwave intrusion has finally come of age.