SMART SENSORS

 Smart Sensors

 Fiber-Optic-Based Sensors

 The field of sensing technology has been revolutionized in the past decade by the entry of fiber optics. The properties of fiber optics that have made the technology suitable for communications are responsible for it being successful as a sensor as well. Fiber-optic sensors are of two types, namely, extrinsic and intrinsic. In the extrinsic type, the fiber itself acts only as a transmitter and does no part of the sensing. In an intrinsic type, however, the fiber acts as a sensor by using one of its intrinsic properties, such as induced birefringence or electrochromism, to detect a phenomenon or quantify a measurement. Relevant to smart systems, the use of fiber optics in conjunction with optical (sensors) is based on changes in optical effects such as refractive index, optical absorption, luminescence, and chromic properties due to alterations in the environment in which the fiber is embedded. Such alterations refer to strain or other elastic characteristics and thermal and/or electromagnetic properties. Surfaces located with smart fiber sensors are known as smart skins.

Piezoelectric-Based Sensors

The most conventional form of sensing technology is that of piezoelectric materials, which generate an electrical response to a stimulus. In recent times piezoelectric materials have been greatly improved in mechanical strength and sensitivity. Pressure and vibration can be directly sensed as a one-to-one transduction effect resulting from the elastic-to-piezoelectric effect. Bending, on the other hand, can be sensed via piezoabsorption characteristics.

 Magnetostriction-Based Sensors

 The use of metallic glass as a distributive magnetostrictive sensor has been studied. Typically, in the embedded smart sensing applications using the magnetostrictive property, the magnetic field is in the submicrogauss regime, and the nonlinearity associated with the hysteresis of magnetostriction provides a detectable sensor signal. Pressure and force, which cause static or quasi-static magnetic fields, as well as vibrations, which induce alternating magnetic fields, can be regarded as direct magnetostrictive sensor responses. In the bending mode, corresponding magnetostrictive absorption can also be sensed via a reduction in the Q-factor due to absorption losses in a magnetostrictive tunable system.

Shape-Memory Effects-Based Sensors

The latest form of sensing technology utilizes shape-memory materials, namely, Nitinol alloys. The Nitinol sensors are used to measure strain and consist of superelastic Nitinol wires. The basic concept is to measure the change in resistance of a Nitinol wire used as an unbalanced arm of a Wheatstone bridge as a function of the strain. The desirable properties of Nitinol in such a sensing application are its high sensitivity and super[1]elastic nature (which permits strains up to 6% to be accurately and repeatedly measured). The piezoelectric and Nitinol sensing materials can also be used for actuation applications.

 Electromagnetics-Based Sensors

Smart electromagnetic sensors are simple deviations of classic electric/magnetic probes, more properly known as antennas or pickups. Depending on changes in the surroundings is the electromagnetic characteristics, these sensors respond and yield a corresponding signal. Again, environmental changes refer to possible alterations caused by elastic, thermal, optical, magnetic, electric, and/or chemical influences.