TABLE OF CONTENTS Microsensors offer three major advantages over their macroscale counterparts, all of which are associated with their size. Firstly, the high surface area to volume ratio at the microscale means that microsensors tend to have unprecedented levels of sensitivity. For example, in gas sensing, the gas to be detected interacts with a surface to produce a signal. The amplitude of the signal is therefore proportional to the active area of the device. The underlying substrate serves no purpose in detection, and is only a source of noise. Therefore, sensors with a high surface to volume ratio will also have a good signal to noise ratio, and many high sensitivity gas sensors have been demonstrated using this technology [24]. Secondly, the small size of microsensors makes it possible to obtain local measurements of a particular effect in remote locations, such as the use of flow meters to measure fluid flows in microfluidic systems [25] or the proposed use of sensors in biomedical applications [26]. Thirdly, microsystems allow the integration of a degree of signal processing into a sensor with a resulting improvement in signal to noise ratio [27]. The unique opportunities offered by microsensors are making this an area of rapid development. However, most of theses sensors use one of a limited number of sensing principles, and these will be briefly reviewed in this section.
Mechanical sensors have arguably become the most commercially successful of all the microsystem devices with applications...
