(This article is sponsored by The Boston Group)

There is a growing need for detection of hazardous substances (toxic gases, chemicals) in a hostile environment for security and industrial applications. Most current technology for such purpose use optical techniques which are expensive, bulky and need cumbersome manual operation. Hence they are not suitable for use in most hostile environments. Solid State sensors offer a convenient alternative due to their low-cost of manufacturing, portability, and low power consumption. CMOS technology in particular enables integration of the physical sensor, and circuitry for measurement and analysis on the same chip or a package, thereby lowering cost through mass production. Currently, solid-state sensors are heavily used in the industrial and automotive markets.

Detection Using Distributed Sensor Network

Detection of gases and chemicals in hazardous environments requires remote measurement without manual intervention. If the contaminant is sparsely distributed in the atmosphere, multiple deployments of sensors are needed. In such situations, one uses a distributed sensor network for data gathering. Such network consists of a massive array of intelligent low-cost sensor motes physically distributed in an atmosphere for detection (Fig. 1). Each network node contains a sensor, its interface electronics, DSP, and a RF transceiver. The computer at the receiving end performs signal processing of the distributed data to extract accurate sensor information.


Figure 1. An example of distributed sensing using N redundant sensors. AD and DA represent A/D and D/A converters, PA is the power amplifier, and LNA is a low-noise amplifier. An advantage of a distributed network is accurate detection through averaging and redundancy inherent in the network.

It can be shown that such a distributed ah-hoc network offers a very high signal to noise ratio in monitoring the enviorment, and an average low cost of deployment. The most critical design parameters for such a distributed network are 1) The number of sensors 2) Energy/bit of transmission, 3) Life-time of a battery for an individual sensor 4) Selectivity and Sensitivity of individual sensors which depends on the physical sensor and the electronics. In this article, we will focus on some of the recent and newly developed techniques for implementing highly selective and sensitive sensor systems. Such a sensor system consists of an improved solid-state physical sensor and a highly sensitive measurement circuitry built on chip.

Majority of current sensors have an active film (such as oxide, polymer or metal) coated on the surface. To achieve high selectivity, the film needs to be prepared with specific receptors that respond only to certain types of analytes. Some of them are ISFET, ENFET and MOSFET and will be discussed in the next issue.

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