Search

In recent times, the use of Chemical Warfare (CW) agents against civilian and military by terrorists and rogue countries are recurrent. The examples of such attacks are available in open literature. They are highly dangerous due to their acute toxicity nature. They tend to stimulate and paralyze nerve system of the body and cause other toxic side effects. Once these toxic chemicals are released into the atmosphere, timely detection and identification of the same at standoff distances will help the defensive forces to take proper counter measures. Detection techniques such as ion mobility spectrometry, infrared spectrometry, Raman spectrometry, FTIR, LIDAR, etc. have been used widely. Among all these techniques, Raman spectroscopy techniques and LIDAR (LIght Detection and Ranging) is the only active remote detection method that can detect and discriminate the chemical agents at standoff distances. Infrared DIAL (Differential Absorption Lidar) is a versatile technique for remote detection of various chemicals. DIAL technique can provide spatially resolved measurements of these agents with sufficient sensitivity (at few ppm levels) at ranges of several kilometers by exploiting the concept such as scattering and absorption from the atmosphere. The main objective of this review paper is to bring out the details of highly potential chemical warfare agents, their properties and laser based remote detection sensors. LIDAR technique is emphasized in more detail because of their long range detection capability, sensitivity and selectivity. An overview of existing R&D based and commercial systems is also discussed.

Surface acoustic wave (SAW) is one of the most promising technology in the field of gas sensing at low concentrations. Field deployable portable SAW detectors are, however, prone to noise, there by limiting the detection at low concentrations. To meet the current requirements of gas detection at low concentrations, the readout methodology needs to be based on minimal hardware and better noise management. In this paper we describe a readout scheme for portable SAW gas detectors incorporating a field programmable gate array (FPGA). The developed readout system includes a modified reciprocal frequency counter for differential SAW sensor, median noise filtering and moving averages smoothing for noise management, peak detection and interfacing with external display, all implemented in FPGA. The developed readout was tested against VOCs using a lab developed vapour generator and the results have been presented in the paper. The readout system is compact, low power consuming and expandable through software thus ideal for portable handheld applications.

Technological advances and market developments in the wireless communication area have been astonishing during the last decade and the mobile communication sector will continue to be one of the most dynamic technological drivers within comparative industries. This paper extend our previous work for detection and discrimination signals, and deals with a cognitive radio system (CR) to improve spectral efficiency for three signals (WiMAX, Frequency Hopping and CDMA2000) by sensing the environment and then filling the discovered gaps of unused licensed spectrum with their own transmissions. We mainly focused on energy detector spectrum sensing algorithm. The simulation shows that the CR systems can work efficiently by sensing and adapting the environment, and showing its ability to fill in the spectrum holes then serve its users without causing harmful interference to the licensed user.

A significant impact on the spectrum efficiency and quality of service (QoS) of a secondary user (SU) is the ability to capture a frequency slot for transmission in an idle channel. Hence, the SU needs to sense the related spectrum in order to classify a licensed frequency band as occupied or vacant. Spectrum sensing can be a demanding task for a single user due to the random nature of the wireless channel and networks. Cooperative sensing by eight SU nodes have been proposed in this paper to mitigate the effects of channel fading and try to detect the presence/absence of two primary users (PUs). A sensing policy for coordinating the cooperative process is proposed based on two levels hierarchical-fuzzy logic system (H-FLS) by adding a Hopping Sequence (HS) module to the detectors. Two hopping methods are proposed, Random Hopping (RA-H) and Sequential Hopping (SE-H). The simulation results shows enhancement in probability of detection over conventional cooperative sensing.