TYPES AND WORKING PRINCIPLES

		A thin film sensor, as we define it here, is a thin multi-layer electromechanical arrangement that produces an electrical signal when subjected to a sudden contact force or to a continuously varying stress, strain, or a velocity field. Such an arrangement is obtained by the sequential depositions of electrodes and contact leads upon a sensing element and their lamination into a rugged thin package using suitable polymer films and epoxy resins. Typical applications of electromechanical thin film sensors are of four types. They are the OFF-ON electrical switching and the time-resolved measurements of shock-pressure,-strain, and-material velocity . Thus, there are four types of thin film sensors. They are 1)the switches, 2) the stress gauges, 3) the strain gauges and 4) the electromagnetic velocity gauges. The above thin film sensors rely upon four distinct physical effects for their working principles. They are the sudden electrical contact (switching), the (gradual) change of electrical resistance under the action of stress (piezoresistive) or strain (extensoresistive), the gradual release of electrical charges under the action of stress (piezoelectric) or strain. (extensoelectric), and the generation of a gradual electromotive force across a conductor when, moving in a magnetic field ( EMF velocity effect). The main attribute of a thin film sensor is its capability to generate accurate information without introducing major disturbances or inclusion effects into the experiment. They have of course other attributes. Having over the years developed and produced numerous types of thin film sensors, we have made a conscious effort to incorporate into their model designations letters and numbers that best imply their nature and construction. Furthermore, since most of our sensors are fully packaged (encapsulated) between two protective layers of polymer and only a few deviate from such construction, an appropriate identification prefix that reflects such deviation is added at the beginning of their model # designations.