Adaptive sensor materials

The advantages of miniaturization are now being exploited in areas beyond microelectronics. Adaptation of materials and processes originally devised for semiconductor manufacture has allowed fabrication of sensors (for example, pressure meters and accelerometers used in the automotive industry) (6,7), complex optical (8) and micromechanical (6,7,9) assembHes, and devices for medical diagnostics (6,7,10) using Hthographic resists. 

W.E. Morf and N.F. de Rooij, Micro-adaptation of chemical sensor materials. Sens. Actuators B. 51, 89-95 (1995). 

With more than 150 publications on LAPS devices, a wide range of possible applications for LAPS has been demonstrated in the past. However, since LAPS devices belong to the family of field-effect-based sensors, results and studies on, e.g., ISFETs and EIS sensors can be easily adapted to LAPS. This includes especially the transfer of alternative sensor materials, which were initially developed for ISFET and EIS devices and will further extend the range of possible applications for LAPS. 

To build up functional or protective layers, various methods from other technical industries have been adapted to the specific needs of ceramic sensor materials. Important criteria for the selection of the various technologies are the shape of the ceramic substrate (e.g., thimble or planar design), if it is co- or post-fired, if the layer material is expensive (e.g., noble metals) or inexpensive (e.g., alumina, magnesia spinel), and if the geometry and thickness need to be controlled precisely. 

The design of smart materials and adaptive stmctures has required the development of constitutive equations that describe the temperature, stress, strain, and percentage of martensite volume transformation of a shape-memory alloy. These equations can be integrated with similar constitutive equations for composite materials to make possible the quantitative design of stmctures having embedded sensors and actuators for vibration control. The constitutive equations for one-dimensional systems as well as a three-dimensional representation have been developed (7). 

At the same time, many practical issued associated with the use of optical oxygen sensors in food packs still remain. These have to be addressed to adapt the existing sensing materials and prototype systems for real-life applications, achieve the required sensor specifications, operational performance and safety. Considerable technological developments and effort in eliminating current problems and bottlenecks are required, to facilitate widespread use of the oxygen sensors by food and packaging industry. 

The human body, for instance, has sensors (eyes, ears, touch receptors in the skin, and so forth), a controller (the brain), and actuators (muscles) to react and respond to commands. These are the same basic concepts as the adaptive systems discussed in this chapter. Robots today, such as the welding machines used in industry or the toy dogs sold as pets, are extremely Umited in mobility and adaptability compared to humans. Yet smart materials, along with a design based on the sensory, nervous, and muscular systems of the body, could one day create an agile and adaptable robot. 

Expert systems are easy to program and to understand because they usually resemble instructions in English. The time and cost for developing these systems is relatively small. The primary problem usually turns out to be interpreting the sensors. Because first and second derivatives of sensor data are used to find trends and patterns, noise can be a major problem. The rules allow the controller to adapt to the condition of the material and to the geometry of the part. Expert systems make it relatively easy to change to backup plans when sensor or equipment failures occur. In fact, rule-based systems can be quite general and handle a number of materials with little material specific data. 

Smart and adaptive or intelligent materials adjust their mechanical properties upon the receipt of an external stimulus. In engineering language, they act as integrated sensors, processors, and actuators. For example, some polymers can be considered to be smart since they change their shapes with a change of temperature [3] this property has been exploited in the development of all-... 

As has been indicated, the sensor can be adapted to almost any process application. The sensor is designed to withstand pressures to 300 psi and can be designed to withstand process temperatures as high as 450° C using sapphire window materials. Accuracies between 0.01 an 0.5 % are typical. Sensitivities to 0.01% have been obtained and are primarily limited by the sophistication of the network analyzer utilized. 

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