Modern Sensors as Elements of Intrusion Detection and Perimeter Protection

Outdoor protection is becoming increasingly important not only to secure equipment and assets stored outside, but also to capture intruders before they access critical parts of a site. The development of outdoor technology and the greater accessibility of such technology makes early detection easier to afford and to deploy. CCTV and intrusion alarm systems have benefitted from these additional outdoor triggers that can operate even in the most challenging lighting conditions. A number of sensing technologies are available, and the choice depends on the site configuration and environment. They range from passive and active infrared (PIR and AIR) sensors to intelligent LiDARs and radar sensors, as well as fibre optic sensors.

When it comes to short-range residential or commercial applications, ‘traditional‘ outdoor PIRs will probably be the right solution. They capture the thermal electromagnetic waves emitted by all ‘bodies’ that have a temperature. Passive Infrared (PIR) sensors detect slight temperature changes created by a person or object entering or moving in a secured area.
When installing a PIR, it is important to mask sources of heat or reflection (such as surfaces reflecting sunlight, heating or air conditioning unit blowing hot air) from the detection area. If this isn’t possible, it is wise to consider using dual-technology sensors combining passive infrared and microwave technologies. Short-range PIRs can usually cover an area up to 15m with a wide angle and 24m with narrow angle.
A number of additional features are worth considering when choosing which sensors to use: selecting one that has small animal tolerance will prevent the sensor being triggered when a cat or a small dog is entering the detection area. Another feature, the double conductive shielding, adds extra protection against sunlight or car headlights making the sensors more stable. Manufacturers also have their own detection algorithms that might suit certain environments and applications better.
With the right optical configuration and algorithm, passive infrared sensors can also be designed for long-range detection. Most long-range PIRs offer a detection range between 30 and 50m, and a few can detect up to 100m. Long-range motion sensors will typically be connected to a CCTV system to provide a volumetric detection, securing a wide area such as a car park, building sites, retailers yards, or the approach to a building. The sensor’s detection zone is usually set to match the cameras field of view and provides security staff with a good view of what is happening in the intrusion area.

The Right Technology for the Right Application
Active infrared technology is very well suited to protect perimeter lines, ranging from just a few meters (ideal for protecting a driveway or loading bay) up to 200m with a single pair of beams. Longer distances can be achieved by using a series of beams, protecting larger sites. The way the technology works is simple: one beam (the transmitter) emits an infrared radio signal continuously to another beam (the receiver) which captures the signal using a photodiode, also known as a photoelectric cell. If the beam is broken, it means someone or something has interrupted the signal, and an alarm is generated.
A key factor in successfully deploying active infrared technology is to make sure the transmitting and receiving beams are aligned and have a clear line of sight. Any vegetation between the two beams may cause disruption, and any weak alignment may compromise the signal transmission in adverse weather conditions. If the IR beams are installed in an environment where wildlife or animals are likely to pass through, there are options to adjust the interruption time to ignore, for example, flying birds, or use a selection of twin and quad beams to detect different size objects.
Active infrared technology is not thermal-based and therefore can be deployed in hot countries where the ambient temperature can be very similar to the human body temperature.
Some environmental factors, such as strong sunlight on the photodiode could impact the performance of this technology, but this can be avoided by using a number of different features. In many models of standard beams, the photodiodes are also fitted with additional filters to receive the same wavelength as the one emitted by the infrared signal from the transmitter. Some models will also feature an additional layer of protection through a technology known as ‘double modulation’. The technology generates a more sophisticated pulse pattern and so discriminates against interference created by sunlight, or other external light sources.
There are a number of potential applications where IR beams can be used: they can be mounted on top of a wall to detect people climbing over it, or on top of a flat roof as a ‘virtual perimeter’. Wireless beams offer very easy to deploy perimeter protection in remote areas that have limited power sources, such as farm land or fields.
When stacked in towers, IR beams can create a complete virtual perimeter around a wider area. In this instance, beams with multi frequency channels should be used to make sure there will be no cross-talk or interference between the beam transmitters and beam receivers.

Specific Applications Require Specific Technologies
PIR and AIR sensors have evolved in recent years to offer more sophisticated algorithms, making them a very useful outdoor intrusion trigger. In parallel, other sensing technologies from other industries (especially the military) are bringing another level of customisation and built-in analytics allowing a higher level of protection and new range of potential applications.
One of them is based on laser technology also referred to as LiDAR. The sensor’s rotating head, or rotating mirror, emits a constant laser beam that scans the area of detection. Each time the beam hits an object, the signal is reflected back to the sensor which then calculates the time it took for the signal to be returned. This is called ‘Time of Flight’ technology and it means the sensor can detect the distance, size and speed of moving objects.
Laser sensors can offer a wide range of detection angles – 90, 180 and 360 degrees – and the detection distance can range from a few centimeters up to over 250m. Two-dimensional LiDARs can be installed for horizontal or vertical applications, creating a thin layer of detection, a virtual plane or wall. They are extremely versatile, and can create an invisible fence around a perimeter, a building facade or detect anyone approaching walls, doors and windows on multiple storeys. Horizontally, they can protect flat roofs, creating a ceiling detecting access though skylights or hatches. They can be deployed as outer perimeter pre-warning zones detecting people or vehicles approaching specified areas.
Some LiDARs feature self-learning features which means they will understand how a detection area has changed – whether that’s snow building up on the ground or a tree branch that has grown into the area. Configuration software provides greater flexibility when it comes to settings – the detection area can be customised using the area masking feature, and a number of detection zones can trigger different outputs. The system can be easily set to detect moving objects bigger or smaller than a defined size.
While many applications will be required to detect people, some will be specified to detect vehicles and others much smaller objects. The technology and settings’ flexibility make the laser sensors a highly reliable trigger for security with very low false alarm rates.
The laser technology can also be used in conjunction with fibre optics to create a powerful intrusion detection sensor directly mounted on to a wall topping or fence. An alarm processing unit will send a laser pulse over the fibre optics cable and analyse the change in the interference pattern along the cable to determine what kind of disturbance is happening. This allows it to detect if anyone is climbing over, lifting or cutting through the fence. Vibrations caused by the wind, nearby traffic or small animals can be identified and filtered out. This solution has the benefit of being reliable with systems having been installed for more than 20 years and are still very stable. It can protect perimeters from less than 100 meters to many kilometres.

Radar Systems are Getting Stronger
 Radar technology, such as those used in aviation or in modern cars, are now also used in commercial security technology. Fixed radars allow the monitoring of wide, open areas at distances reaching well over one kilometre. The radar analyses the reflection of masses, and to differentiate between people from potential nuisance alarms, a number of criteria such as direction, speed and movement will be analysed. In some radars, built-in analytics will be able to categorise objects such as people, vehicles or even drones.
The integration of outdoor sensors in video and wider management systems help further improve the reliability and performance of security systems in a wide variety of applications. Using a combination of sensing technologies ensures the deployment of multi-layered protection – from the outer perimeter to the building itself. As for any security system, it is key to understand the customer’s requirements and site configuration to choose the right technologies to use. One size, as they say, rarely if ever fits all!