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Chemical Sensors Comprehensive Sensor Te... > CHAPTER 1. INTRODUCTION TO CHEMICAL ... - Pg. 1

CHAPTER 1 I NTRODUCTION TO C HEMICAL S ENSOR T ECHNOLOGIES G. Korotcenkov B. K. Cho 1. DEFINITIONS AND CLASSIFICATIONS The Oxford English Dictionary defines a sensor as "a device which detects or measures some condition or property, and records, indicates, or otherwise responds to the information received." Accordingly, sensors have the function of converting a stimulus into a measurable signal (Figure 1.1). The stimulus can be a physical stimulus such as temperature, pressure, or acceleration; alternatively, the stimulus can be a concentration of specific chemical or biological materials. While the measured signal is typically electrical, it may alternatively be pneumatic, hydraulic, or optical. Sensors are based on a broad range of underlying physical operating principles. One can usually separate three basic components of a sensor: (1) a sensor element; (2) sensor packaging and connections; and (3) sensor signal processing hardware. While they can be used in all three phases of matter, sensors for gas and liquid environments are the most common (Shieh et al. 2001). Generally, sensors can be divided into three major categories: (1) physical sensors; (2) chemical sensors; and (3) biosensors. In this volume we consider chemical sensors. Chemical sensors are widely used in many different applications, and chemical sensing technology has become a basic enabling technology in many fields (see Table 1.1). As will be shown here, interest in chemical sensors has grown as production applications, such as intelligent manufacturing processing, have proliferated. Sensors are also of great importance in safety-related areas, with applications ranging from assessing the integrity of 1