A family of materials with an ability to modify some of its original properties by applying external stimuli such as stress, temperature, humidity, pH, electric and magnetic fields called Smart Materials. Some of the materials that also in this class of materials, piezoelectric materials, magneto-rheostatic materials, electro-rheostatic materials, thermo-responsive materials, pH-sensitive polymers, halochromic materials, electro chrome materials, thermo chrome materials and photo-chrome materials. Smart materials inanimate materials, assimilate various functions such as sensing, actuation, and control logic to adaptively respond to changes in their environment which they are exposed, in a constructive and most recurrent way.
To quote a few illustrative examples of intelligent materials in transition in their property because of the impact of any external stimuli, we will consider piezo electric materials. Piezo electric materials are materials that create tension resulting from the use of stress. The reverse effect on the production of stress when voltage is applied across the piezo electric material also holds good. Therefore, we find extensive use of piezo electric materials as sensors in different environments. They are mainly used to measure fluid compositions, fluid density, fluid viscosity, or the strength of an effect. An example from our daily lives would be an airbag sensor in automobiles, where piezo electric material senses the force of an impact on the car and sends an electrical charge that by triggering airbag inflation.
Another example of piezo electric material will be electro-and magneto-rheostatic rheostatic materials undergo change in their viscosity. These are liquids that almost switch to a solid from a thick fluid within a millisecond when exposed to a magnetic or electric field. Electro-rheostatic liquids undergo changes viscosity when exposed to an electric field whereas magneto-rheostatic liquids undergo similar changes when exposed to a magnetic field. Some common electro-rheostatic fluid milk chocolate or cornstarch, while magneto-rheostatic liquids minute iron particles suspended in oil.
Thermo-responsive materials such as shape memory alloys or shape memory polymers are smart materials that change their shape with changes in temperature. Magnetic shape memory alloys experience shape due to significant changes in magnetic field. pH-sensitive polymers enlarge or collapse when they experience change in pH of surrounding medium. Halochromic materials change their color in response to changes in acidity. One of the most common use of these materials will be in the paint, which is undergoing change in their color as an indication of corrosion of the material beneath them. Chromogenic systems change their color due to the impact of electrical, optical or thermal changes. Electro chrome materials change their color or opacity as a result of the use of voltage, thermal materials, chrome color change based on changes in temperature and photo-chrome materials change their color in response to a change in light. An application of electro-chrome material will be liquid crystal displays and an application of photo-chrome materials will be in sunglasses, which darken on exposure to strong sunlight.
Smart materials find a wide range of applications because of their different responses to external stimuli. The various applications can be in our daily lives, aerospace, engineering applications and mechatronics to name a few. The scope of smart materials include solving engineering problems with unattainable efficiency and allows for creation of new products that generate revenue. Sensual equipment that can sense their environment and produce information for use in health and usage monitoring systems (hums) find application in aerospace industry with the purpose of flight control. An airline requires umpteen number of people power which conduct routine, ramp, intermediate and main control to check health and use of the fleet. This control covers a wide range of tasks requiring a lot of time. Therefore, a plane designed by a sensual structure has an advantage of self-checking its performance to a greater extent than the current data recording and provide ground crews with enhanced health and usage monitoring. This will reduce the costs associated with the hums and thus such an aircraft can fly for several hours without human intervention.
These sensual structures also find application in the field of civil engineering. They are used to monitor civil structures to evaluate their durability. They are also used in food packaging to keep track of safe storage and preparation. However, smart materials and structures is not limited to sensing but also to adapt to their surrounding environment, and these materials have an ability to move, vibrate and display various other actions beyond the sensual aspects. Few applications of such adaptive materials include the ability to control aeroelastic shape of aircraft wing to reduce the pull and improve operational efficiency in order to check vibrations of the satellites' light constructions, etc.
