Abstract. In line with the emergence of decentralized e-Systems and the everincreasing needs for effective interaction and collaboration, a rising challenge is how to enable communication and gather information on the real-time state of distributed agents in an e-Work network. That is, each agent (e.g., machine agent; resource agent; product agent), as an autonomous and intelligent element of a collaborative e-System, must be able to detect and process useful information from its environment and share it with other peers. The supporting technologies for this critical need are sensor and RFID (Radio Frequency Identification) networks. In this chapter, fundamentals of each technology are discussed and some real-life applications are reviewed.
SensorsA sensor is an instrument that responds to a specific physical stimulus and produces a measurable electrical signal. Sensors have different types ranging from mechanical to electrical, electromechanical, magnetic, optical, chemical or even biological. Indeed, any device that is directly altered in a predictable and measurable manner by changes in a real-life parameter is known as a sensor for that parameter. Sensors play a significant role in any e-System due to the need to gather, process, and share information relevant to specific tasks. Recent advances in micro-device technology, micro-fabrication, chemical processes, and digital signal processing have enabled the development of economically affordable micro-/nano-sensors. Micro-sensors have a variety of applications in many practical areas such as medical and space devices, military equipment, telecommunication, and manufacturing (Luo, 1996;Luo et al., 2002). Compared to conventional sensors, micro-sensors provide some unique advantages such as interfering less with the environment they measure, requiring less manufacturing cost, being used in narrow spaces and harsh environments, etc. Successful design and implementation of micro-sensors depends highly on sensors' capability, cost, and reliability.
Sensing PrinciplesAccording to their working principles, sensors are technically classified into different types (Table 8.1). Sensors may measure physical phenomena by capturing resistance change, capacitance change, inductance change, thermoelectric effect, piezoelectric effect, photoelectric effect, Hall effect, and so on (Wilson, 2004;Fraden, 2003). Among these effects, majority of sensors utilize the resistance change or resistivity of a conductor. Considering uniform current density in the insulator, the resistance R of a conductor of cross-sectional area A can be computed as , ρ ⋅ = l R A ( 8 . 1 ) where l denotes the length of the conductor, and ρ is the electrical resistivity of the material. Resistivity is a measure of the material's ability to oppose electric current. Therefore, the change of resistance can be measured by detecting physical deformation (l or A) of conductive materials or by sensing resistivity (ρ) of conductor. A strain gage, for example, is a sensor that measures resistance by deformation ...