Smart material is an object that holds a property that is susceptible to change with the introduction of an external stimulus.

For example, we can talk about sportswear with ventilation valves that react to temperature and humidity by opening when the wearer breaks out in a sweat and closing when the body cools down, about buildings that adapt to atmospheric conditions such as wind, heat or rain, or about drugs that are released into the bloodstream as soon as a viral infection is detected.

Types of smart materials -

Piezoelectrics :

Piezoelectric materials are materials that produce an electric current when they are placed under mechanical stress. The piezoelectric process is also reversible, so if you apply an electric current to these materials, they will actually change shape slightly (a maximum of 4%).

There are several materials that we have known for some time that posses piezoelectric properties, including bone, proteins, crystals

Imagine walking down the street and charging your phone as you walk, charging your laptop by typing, or powering a nightclub by dancing on a piezoelectric floor! The concept of piezoelectricity has been around since the 1880s and was discovered by Jacques and Pierre Currie. Despite already being used in things like lighters to create the spark that ignites the gas, using it as an everyday energy source is still a long way off.

Shape Memory material:

Shape memory materials (SMMs) are featured by the ability to recover their original shape from a significant and seemingly plastic deformation when a particular stimulus is applied. This is known as the shape memory effect (SME).

Electrostrictive Materials:
This material has the same properties as a piezoelectric material, but the mechanical change is proportional to the square of the electric field. This characteristic will always produce displacements in the same direction.

Thermoresponsive Materials:
Thermoresponsive is the ability of a material to change properties in response to changes in temperature. They are useful in thermostats and in parts of automotive and air vehicles.

Magnetostrictive:

Similar to piezoelectric materials that respond to changes in electrical fields, this class of materials responds to changes in magnetic fields and can perform as an actuator, or sensor if deformed. While they can work well, they exhibit a large hysteresis which must be compensated when using the material in sensor applications.

Electrochromic materials:
Electrochromic materials, also known as chromophores, affect the optical color or opacity of a surface when a voltage is applied. Among the metal oxides, tungsten oxide (WO3) is the most extensively studied and well-known electrochromic material. Others include molybdenum, titanium and niobium oxides, although these are less effective optically.

Fullerenes:
These are spherically caged molecules with carbon atoms at the corner of a polyhedral structure consisting of pentagons and hexagons. These are usually used in polymeric matrices for use in smart systems. They are used in electronic and microelectronic devices, superconductors, optical devices, Superconductors, Medical.
Hydrogels:

Hydrogels can be tailored to absorb and hold water, or other liquids, under certain environmental conditions. Hydrogels have been around for a long time, specifically in disposable diapers. A key feature however is the gels can be tailored chemically to respond to different stimuli. Midé has also patented a method to embed the gels into a foam which enables systems to be built with the gels, such as the Hydrogel Activated Bulkhead Shaft Seals.

Electroactive Polymers:

There are many forms of electroactive polymers and many are still being refined. They have great potential as the flexibility of how they can be used provide advantages over some of the metals and ceramics mentioned above. Most typically applications include energy harvesting and sensing (see Stretchsense development kit) however some researchers are looking at high voltage, low current actuators.

Bi-Component Fibers:

Adaptive thermal insulation can enable smart clothing that can change its thermal properties based on the environment. Midé has developed bi-component fiber technology where two different materials are co-extruded together to enable shape change depending on ambient temperature.

Advantages -

A few of the key drivers for smart materials are listed as follows:
Sustainability, including advances in recycling and reuse
Other environmental concerns, including extending service life or improved energy efficiency
Performance benefits
There is an increasing need for products that are able to react to changing operating conditions and user demands to achieve high-level performance. Extended system functionality is the major factor driving the demand for smart materials, globally.

Application-

Barriers -

A few of the barriers affecting the smart materials market are as follows:

Lack of market pull for material suppliers
High research costs
Problems associated with intellectual property rights in the necessary multidisciplinary research projects
Lack of economy of scale
Processing problems
Environmental issues (e.g., possible regulations against the use of lead in PZT ferroelectrics)

Future of smart materials -

The era of smart materials is just starting. Based on all that has been described above and especially the evolution observed, we can imagine implantable chips capable of replacing failing organs in our body, such as virtual hearing, pacemakers, and artificial retinas.

We can imagine smart pills that will be controlled and intended for specific locations in our bodies to diagnose and treat internal diseases without resorting to surgical procedures. So, let’s dream of a more exciting tomorrow.

Smart materials have the power to overcome limitations and fulfil the future challenges of the sensors. I am convinced that the era of smart materials is just starting. These materials will be the cornerstone of future technological progress.