Applications for Microwaves - Research Proposal Example

Electronic Intrusion Detection Systems Name Institution Date Electronic Intrusion Detection Systems 1) Microwave Sensor Technologies Principle of Operation There are several applications for microwaves; perimeter protection is one of the major uses of this technology. Microwave sensors are devices that use electromagnetic fields and devices that operate at frequencies from about 300 MHz up to the terahertz range. Microwave sensors are devices for motion detection that operate by flooding a given space with an electronic field. In the event of any movement or acceleration within the area disturbs this field and generates an alarm. These sensors are usually used for motion detection in long, narrow, flat perimeter zones (Barnard & Barnard, 1988). The microwave signals are transmitted in the “X” band. The signals are generated by diodes that operate within limits preset by the manufactures so that they cannot harm humans or other animals. The effective detection area (width and height) of any such system will greatly depend on the height of mounting of the antennas. This height is the distance from the antenna aperture to the ground. When the devices are properly aligned, maximum detection width and height can be achieved at the midrange. It is important to adjust this height during installation to achieve maximum signal monitoring while the signal is monitored at the receiver (Polovka, 2007). Most common applications use either the bistatic or monostatic configurations. The bistatic configuration consists of a transmitter at one end of the area to be monitored with the receiver module at the opposite end. A modulated, low power microwave frequency signal is emitted from the transmitter, while at the receiver; the signal is combined in a vector summation with the reflected signals from nearby objects and ground and the direct line of sight signal. The receiver continuously monitors this signal for any changes that may occur in the surrounding due to movements within the detection zone. The sensor is preset so that any changes that exceed the threshold trigger an alarm (Polivka, 1995). The sensor is also equipped with an automatic circuitry that allows for compensation for extremely slow changes in the signal that may result from environmental conditions. The detection zone is determined by the antennas, the frequency of transmission and the distance between the transmitter and receiver. The detection zone for a bistatic microwave usually resembles an oblate spheroid, as shown below: Figure 1: detection zone for a bistatic microwave Strengths and weaknesses and how to overcome them Extreme weather conditions may cause the microwave sensors to generate false alarms. These sensors are usually affected in the first few seconds of a hard rain. When the rain persists for some time however, the sensor recognizes this and adapts to the rain. It is also possible that large puddles of water will cause such alarms especially when the detection area is extended to the ground. The sensor can detect the ripples on waters surfaces which are interpreted as intrusion to raise the alarm. Proper drainage must be ensured within the detection zone for running water. Microwave sensors have the advantage of overcoming challenges from falling debris, cardboards, tumbleweeds and paper since these objects are not reflective. Concerns exist, however, when these objects are wt or icy, since in this form, they may be able to reflect waves and therefore, cause false alarm. These sensors are also sensitive to size and a small animal like a mouse or a bird will not cause any alarm. It is highly likely, however, that larger animals like a rabbit or a flock of flying birds will be detected (USNRC, 2011). Due to the nature of the detection area, it is possible that creeping intruders close to the transmitter or receiver may not be detected. It is therefore necessary to ensure that the sensors are properly overlapped so that the area to be detected is fully covered. Figure 2 below illustrates possible layouts to ensure proper coverage while figure 3 shows a corner setup that provides overlap to minimize possibility of intruder crawling beneath the beams. Figure 2: Possible microwave sensor layout Figure 3: corner setup for effective overlap The microwave is used in most weather conditions and is appropriate for long, flat and narrow zones. It is capable of functioning even in snow conditions as long as the antenna is not blocked (Garcia, 2007). 2) Active infrared sensors Principle of operation These are infrared beam-break sensors that work by detecting the loss or considerable reduction of the infrared signal transmitted from the transmitter to receiver. The emitter and detector could stand as a single unit that operates at the same wavelength, or the system could be photoelectric, working together with reflective surfaces. Infrared sensors can be classified into two: the retro-reflective sensors, and the diffuse reflective sensors. The former can be effectively used in harsh environment, and are built with significantly large detection range than the latter. Infrared sensors operate with a pin photo-detector and an X circuit to Y as shown in figure 4 below. The sensors detect changes in object distance using the radiations. The transmitter emits a pulsed light beam and sends it out to the receiver which reflects it back to the field of scan. When the beam is interrupted by an object, the light beam returns back to the receiver at an angle. This causes the receiver to send a high output signal which activates an alarm (Garcia, 2007). The triangulation method is shown in figure 5 below: Figure 4: Infrared internal circuit Figure 5: Infrared sensor object detection The sensor consists of an infrared transmitter and a receiver at the other end. In most applications, the system is composed of two columns with several infrared transmitters on one side and several receivers on the other. With this arrangement, it is possible to achieve a detection volume is significant height. The effective volume of detection is defined by all the beams with the diameter equal to that of the transmitter and receiver optical lens. Depending on the type of infrared used, the distance between the columns could be up to 152 meters or more. It is advisable to keep the firs beam about 6 inches from the ground to detect crawling intruders; the beams higher than this could be spaced further (Garcia, 2007; Fay, 2007). A multibeam arrangement is shown in figure 4 below: Figure 6: Multibeam active infrared sensor columns Strengths and weaknesses and how to overcome them The sensor is activated when any or all of the beams is blocked for a preset period of time. The sensitivity of the sensor can be adjusted so that shorter measured interruptions of the beams are ignored by the system. This helps to reduce nuisance alarms from small bird or rolling debris. Other sensors adjust the beam interruption time automatically depending on the number of beams interrupted. Recent developments have enabled these sensors to accommodate a huge variety of applications and the ability to withstand harsh environments. Models have been developed that can communicate with a remote computer so that they can be remotely adjusted according to the prevailing conditions. In some applications, the lowest beam can be turned off, for example, in the event that snow cover rises to its level while the other beams are left to operate normally. Such sensors can therefore be used in colder and snowy weather and still operate effectively. Nuisance alarms may be caused by any movements or blockage or significant obstruction of the infrared beam. Nuisance alarms may be as a result of large animals obstructing the lowest beam, but this has been minimized by having the sensors installed between two fences. Small birds will usually not cause any alarms but a flock of birds may result to the nuisance alarms. Debris blown over the ground surface that blocks the bottom beam could result to nuisance alarms. Accumulated snow to the level of the beam will also cause constant alarm and this must be cleared or the lower beam disabled. Disabling this beam however, may result to intruders crawling under the sensor undetected (American Society of Civil Engineers, Environmental and Water Resources Institute (U.S.), 2011). These sensors operate within line of sight an on the principle of beam-break (not field disturbance) and they do not take into account any motions around them. They can therefore be used in narrow and confined areas or areas with much activity nearby. They can also be used as complementary sensors to other sensors with good crawl detection because of their detection height and uniformity (USNRC, 2011). 3) Ported coaxial Cable Systems Principle operation This sensor is terrain-following, covert, volumetric detection system that is made up of two ported coaxial cables that are buried to the ground, with a control unit. Within the processor is a transmitter, several amplifiers and filter circuits, a receiver, and a microprocessor with hardware and software. The sensor utilizes electromagnetic energy and two identical “leaky” coaxial cables arranged side by side in the ground. The sensor transmitter is fixed to one of the cables while the receiver, connected to the other (Barnard & Barnard, 1988; Mays, 2004). The outer conductor of both cables is ported and contains small holes that are closely spaced so that radiofrequency (RF) energy can radiate. This cable structure allows any electromagnetic energy transmitted through the cables to be radiated into the surrounding environment so that the energy is coupled to the receiver cable through its ported shield. In this way, there is established a static field of coupling between the pair of cables. Any form of intrusion into the established field pertubes the coupling so that a change is introduced in the received signal. This change is processed and assessed for action. If the change detected in the electromagnetic field is beyond the preset threshold, then an alarm is activated (Mays, 2010). Figure 6: The zone of detection for a ported coax sensor These sensors are sensitive to changes in the dielectric properties or the conductivity within the detection zone, but they are insensitive to seismic noise (Garcia, 2005). The detection zone for these sensors is elliptical and can be up to 1 metre high and 3-4 metres wide. Intrusion detection is achieved both above and to some extent, below the ground. Field tests have revealed, however, that both the size of the detection zone and the sensitivity of the sensor vary along the length of the cables. The variance may result from a number of causes, including cancellations of phase, metallic objects buried in the ground, variation if distance between the cables or the depth of burial, and the composition of the soil where the cables are laid. These factors greatly affect the sensors probability of detection and must therefore be taken into consideration. It is therefore critical that areas of low sensitivity be identified and necessary adjustments to the sensitivity made so that the system achieves the desired detection volume (Barnard & Barnard, 1988). Figure 7: Detection envelop for a typical installation Strength and weakness and how to overcome them Several soil characteristics have significant effect on the strength of ported coax receiver signal. The systems, however, have shown great performance results at sites with considerably large attenuation. Variations in soil mixture may also contribute to its vulnerability to defeat since they affect the attenuation of the coax signal. Wet soil conducts easily compared to dry or frozen soil; seasonal changes, therefore, may be accompanied by significant changes in ported coax sensitivity of detection. It is usually necessary to conduct recalibration so that these seasonal changes are accounted for. Ported coax sensors have a relatively low nuisance alarm rate in properly designed and carefully installed systems (Barnard & Barnard, 1988). However, several environmental factors as well as certain installation factors are able to affect the rate. Surface water from melted ice or rain water is the main source of nuisance. This means that it is essential to ensure that the area of installation is properly drained. Both standing water and that which is flowing and produces ripples when wind blows will result to disturbances that are detectable by the sensor. Alarms may also be raised by moving metallic objects or dielectric objects. Smaller animals of below 4 kilograms do not generally cause any alarms unless the walk across the cables in large groups. The sensor type will also determine the nuisance alarm rate, the method of installation, maintenance practices, and the setting of level of the sensitivity. These sensors find extensive use in places where aesthetic considerations demand that the sensor technology be unseen by the general public. They also function very effectively for detection of crawling intruder and is usually used to complement other sensor technologies that may have a weakness to crawling incomers. As Purpura (2013) says, the vulnerability to defeat of these sensors is low. References Purpura, P. (2013). Security and Loss Prevention: An introduction. Oxford: Butterworth- Heinemann Mays, L.W. (2010). Transmission and Distribution. Denver, CO: American Water Works Association Mays, L. (2004). Water Supply Systems Security. New York : McGraw Hill Professional Polivka, J.. (1995). Microwave Radiometry and Applications. International Journal of IR/MM Waves. Vol.16, No. 9, pp.1593-1672 Barnard, R. L. & Barnard R. (1988). Intrusion Detection Systems. Texas: Gulf Professional Publishing Polovka, J. (2007). An Overview of Microwave Sensor Technology, High Frequency Electronics. Santa Barbara, CA: Summit Technical Media, LLC. pp 34 – 42 Garcia, M. L. (2007). Design and Evaluation of physical Protection Systems. Oxford: Butterworth-Heinemann USNRC. (2011). Intrusion Detection System and Subsystems: Technical Information for NRC Licensees. NUREG – 1959 Fay, J. (2007). Encyclopedia of Security Management. Oxford: Butterworth-Heinemann American Society of Civil Engineers, Environmental and Water Resources Institute (U.S.). (2011). Guidelines for the Physical Security of Water Utilities, ANSI/ASCE/EWRI 56-10: Guidelines for the Physical Security of Wastewater/stormwater Utilities, ANSI/ASCE/EWRI 57-10. Reston, VA: ASCE Publications Garcia M. L. (2005). Vulnerability Assessment of Physical Protection Systems. Oxford: Butterworth-Heinemann Read More

It is also possible that large puddles of water will cause such alarms especially when the detection area is extended to the ground. The sensor can detect the ripples on waters surfaces which are interpreted as intrusion to raise the alarm. Proper drainage must be ensured within the detection zone for running water. Microwave sensors have the advantage of overcoming challenges from falling debris, cardboards, tumbleweeds and paper since these objects are not reflective. Concerns exist, however, when these objects are wt or icy, since in this form, they may be able to reflect waves and therefore, cause false alarm.

These sensors are also sensitive to size and a small animal like a mouse or a bird will not cause any alarm. It is highly likely, however, that larger animals like a rabbit or a flock of flying birds will be detected (USNRC, 2011). Due to the nature of the detection area, it is possible that creeping intruders close to the transmitter or receiver may not be detected. It is therefore necessary to ensure that the sensors are properly overlapped so that the area to be detected is fully covered.

Figure 2 below illustrates possible layouts to ensure proper coverage while figure 3 shows a corner setup that provides overlap to minimize possibility of intruder crawling beneath the beams. Figure 2: Possible microwave sensor layout Figure 3: corner setup for effective overlap The microwave is used in most weather conditions and is appropriate for long, flat and narrow zones. It is capable of functioning even in snow conditions as long as the antenna is not blocked (Garcia, 2007). 2) Active infrared sensors Principle of operation These are infrared beam-break sensors that work by detecting the loss or considerable reduction of the infrared signal transmitted from the transmitter to receiver.

The emitter and detector could stand as a single unit that operates at the same wavelength, or the system could be photoelectric, working together with reflective surfaces. Infrared sensors can be classified into two: the retro-reflective sensors, and the diffuse reflective sensors. The former can be effectively used in harsh environment, and are built with significantly large detection range than the latter. Infrared sensors operate with a pin photo-detector and an X circuit to Y as shown in figure 4 below.

The sensors detect changes in object distance using the radiations. The transmitter emits a pulsed light beam and sends it out to the receiver which reflects it back to the field of scan. When the beam is interrupted by an object, the light beam returns back to the receiver at an angle. This causes the receiver to send a high output signal which activates an alarm (Garcia, 2007). The triangulation method is shown in figure 5 below: Figure 4: Infrared internal circuit Figure 5: Infrared sensor object detection The sensor consists of an infrared transmitter and a receiver at the other end.

In most applications, the system is composed of two columns with several infrared transmitters on one side and several receivers on the other. With this arrangement, it is possible to achieve a detection volume is significant height. The effective volume of detection is defined by all the beams with the diameter equal to that of the transmitter and receiver optical lens. Depending on the type of infrared used, the distance between the columns could be up to 152 meters or more. It is advisable to keep the firs beam about 6 inches from the ground to detect crawling intruders; the beams higher than this could be spaced further (Garcia, 2007; Fay, 2007).

A multibeam arrangement is shown in figure 4 below: Figure 6: Multibeam active infrared sensor columns Strengths and weaknesses and how to overcome them The sensor is activated when any or all of the beams is blocked for a preset period of time. The sensitivity of the sensor can be adjusted so that shorter measured interruptions of the beams are ignored by the system. This helps to reduce nuisance alarms from small bird or rolling debris.

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