Smart Materials

Smart Materials: An introduction

A smart material is an object that holds a property that is susceptible to change with the introduction of an external stimulus. This change must be either tangible or visible for the material to qualify for ‘smart’ status.

These changes can include:

• Electrical
• Chemical
• Thermal
• Mechanical
• Magnetic

Definition: Smart Materials

The meaning of smart materials is smart and materials.

A system or material which has a built-in or intrinsic sensor(s), actuator(s), and control mechanism(s) whereby it is capable of sensing a stimulus, responding to it in a predetermined manner and extent, in a short/appropriate time, and reverting to its original state as soon as the stimulus is removed”.

Smart is

• Significant(S),
• Measurable (M),
• Appropriate (A),
• Result Oriented (R), and
• Time oriented (T).

This definition is useful as it covers both the traditional smart materials as well as the more contemporary approach of directly combining materials and contemporary electronics to create material systems that respond to and/or actuate in the presence of environmental stimuli.

The definition of smart materials has been expanded recently to include any materials that may not display a physical change, but do hold electronic functionality.

Smart materials are materials reacting to external stimulations and have one or more properties. We could also call them responsive materials.

These objects can change shape or behaviors with hot water, pressure, chemical, light, or heat. These smart materials could even self-assemble when you touch them.

When a stimulus is applied to such an object, it is possible to transform into a brand-new shape as these materials are reacting to their external environment.

Physical parameters, namely, stress, temperature, moisture, pH, electric, and magnetic fields, are imposed upon these special materials to facilitate their restructuring.

In general, smart materials are materials that react to changed conditions with no need for human intervention.

Examples to summarize:

• When you go to the doctor, he/she measures various vital functions of your body — pulse, blood pressure, and so on. Based on this data, the doctor can tell how your body is doing. Self-reporting materials work similarly. In the future, materials and even entire machines will be able to “report” how they are doing.

• Another example is 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.

In short, a smart material is a compound that has a visible and tangible reaction to external stimuli by undergoing a material property change. These stimuli can include chemical, electrical, mechanical, thermal, and magnetic changes in the environment. The response to these changes is dependent on the material.

Benefits of Smart Materials

When people talk about “smart” environments today, they might mean a home or workplace with a few smart devices embedded in an otherwise static environment, like smart speakers or lightbulbs added to existing systems.

But looking forward, we can imagine a future where everything can be smart.

In such a future, smart clothing knows when it needs to be laundered; it can track your range of motion and adjust its stiffness or breathability to help keep you comfortable and injury-free. In a hospital, smart beds help nursing staff monitor patients’ sleep positioning to avoid the risk of bedsores. The smart buildings you live and work in have walls that can heal themselves whenever cracks form, while factory floors know when there’s been a spill and direct cleaning robots to mop it up. Imagine a smart farm, where seeds can be designed to drill themselves into the soil precisely when environmental conditions are right for them to take root and thrive. And in personal care, imagine a cosmetic foundation that doubles as sunscreen and can change or move depending on the amount of UV light your skin is receiving.

Smart materials offer an opportunity to infuse the world with digital intelligence that blends more naturally and invisibly into our environment.

Smart materials are very beneficial as they:

• Act simultaneously as actuators and sensors
• Perform controlled mechanical actions without any external mechanism
• Adapt to the environmental condition
• Create the potential for new function development within applications.

Smart materials are compelling because they are often an efficient way to fulfill a specific performance objective.

Effective implementation of smart materials can simplify design, reduce the part count, and increase the lifespan of an object.

The uses of Smart Material range from medical and construction to automotive industries. Devices using smart materials might eventually replace more traditional technologies in the construction of buildings, vehicles, and consumer products.

Lower component weight, component size, and complexity combined with improved design flexibility, functionality, and reliability, make smart materials an attractive option.

Also, smart materials offer a level of environmental robustness not easily achieved through other technologies as they are not typically impervious to water, moisture, or dust.

Growing Demand for Smart Materials

The demand for smart materials is driven by the increasing need to reduce weight, component size, and complexity as well as improve design flexibility, functionality, and consistency. Also, smart materials are resistant to water, moisture, dust, and other elements.

Smart Materials: Types and Applications

• Piezoelectric Materials: They can convert mechanical energy into electrical energy and vice versa. For example, they change their shape in response to an electrical impulse or produce an electrical charge in response to applied mechanical stress. They offer a wide range of utility and can be used as actuators (provide a voltage to create motion), sensors, such as many accelerometers, and energy harvesters since the charge generated from motion can be harvested and stored. Common applications for piezo materials are BBQ igniters and actuators for inkjet printer heads. Midé has successfully commercialized energy harvesters, haptic actuators, piezo valve actuators, and flow control devices.

• Magnetostrictive Materials: 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.

• Photoactive Materials: There are several types: electroluminescent emit light when they are fed with electrical impulses, fluorescents reflect light with greater intensity and phosphorescents can emit light after the initial source has ceased.

• 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. Hydrogels can absorb up to 1,000 times their volume in water. After this water has been absorbed, it can be released when its surroundings are dry. Changes in temperature or pH can also cause the hydrogel to release water. Therefore, hydrogel granules are added to soil to help retain water for plants.

• Shape Memory Materials: They can change the shape, even returning to their original shape, when exposed to a heat source, among other stimuli. Further classified into Shape Memory Alloys and Shape Memory Polymers.

• Chromoactive Materials: They change color when subjected to a certain variation in temperature, light, pressure, etc. Nowadays, they are used in sectors such as optics, among others.
• Light-Sensitive Materials (Photochromic): Photochromic pigments change color in the presence of light. Depending on their chemistry, pigments can vary across various color ranges at different rates. Elena Cochero’s fantastic work with photochromic pigments demonstrates how a designer can take great advantage of elegant material properties within some unexpected applications. Elena’s work has focused on UV-sensitive pigments, a subset of photochromic pigments. She has harnessed the pigment’s ability to “see” invisible but potentially harmful UV light. She has used these pigments to make badges for children that change color on exposure to UV to help give a tangible indication of sun exposure. Recently she’s used these pigments to make a pendant that transforms from translucent to bright pink to indicate your sun exposure.

• Temperature-Sensitive Materials (Thermochromic): Similar to photochromic pigments, thermochromic materials change color based on temperature. They also have a range of responses to heat or cold, with the designer being able to specify different colors and responses to suit design requirements. LCR Hallcrest’s line of thermochromic thermometers is an excellent example of where the appropriate use of a smart material can dramatically simplify design and in the process, make it more scalable. These passive thermometers are applied widely across machinery, factories, and even medical patients. These devices provide a simple, visual indication of the temperature of its mounting location. The combination of robust operation and low-cost opens up a diverse range of applications: whether a part may be too hot to touch, whether food is stored at the correct temperature, or to monitor a patient’s temperature during a surgical procedure easily.

• Chemical-Sensitive Materials (Chemochromic): Smart materials can play a role in even more mission-critical applications where there is no reasonable alternative. Chemochromic materials change color in the presence of certain chemical compounds. Like photochromic and thermochromic materials, chemochromic materials can be specified to react in specific ways to different chemical compounds. NASA’s design for a Hypergol Leak Detection Sensor is an elegant response to the challenge of detecting potentially dangerous leaks of hypergolic propellants. In simpler terms, leaking rocket fuel is an extraordinarily dangerous situation, and operators must spot leaks fast. NASA’s design uses chermochromic pigments, which change color in the presence of hypergolic to alert workers to the presence of a leak. The pigment is deployed as tape directly to a pipe, so the sensor can take the shape of the surface. Once attached, the tape changes color from yellow to black to visually indicate the presence of the fuel. This system has an elegantly simple design with minimal components, no electronics, and no moving parts making it fundamentally robust and scalable.
• Self-Healing Materials: Self-healing materials are a class of smart materials that have recently captured the public’s imagination. From self-healing glass, textiles, and paint, it’s exciting to imagine that the materials around might have some of the self-repair capability of a biological system. But of course, the mechanism behind self-healing materials isn’t biology, but polymers. Polymers, which, when fractured, are chemically promoted to rebond or to rebound. Out of many possible applications, the first comes from an unexpected place: self-healing paint for high-end vehicles. Finding a small scratch on the otherwise perfect surface of a new car is frustrating, but self-healing polymers make it possible for the surface to repair itself. The first commercial roll-out of such a material was by Kawasaki Motorcycles. The 2019 H2 motorcycle comes with what Kawasaki describes as a “Highly-Durable Paint,” which will self-repair certain types of scratches over time.

Examples of Smart Materials

Muscle Wire is a shape memory alloy that contracts between 3 and 7% when current runs through it. While this material is not strong enough for heavier applications — like rolling up heavy blinds or pulling any significant weight — it allows us to create motion in a noiseless and smooth way for several other applications in which the use of motors is not perfect.

Electrotextiles include thread, fabrics, and yarn with electrical properties. They are made by blending or coating textiles with metallic fibers and are available in many different weaves and textures. We’re only just discovering uses for these materials — but some of the most interesting, in my opinion, is for making a large array of sensors like the ones developed by Kobakant and pictured above: a zipper slider, a crochet squeeze sensor, a piezoresistive touchpad, an embroidered potentiometer, a knit accelerometer, and a tilt sensor. Conductive fabrics have also been used both by hobbyists and product designers to make objects like roll-up keyboards, jackets with controls for smartphones, and electronics-enhanced garments.

Light Diffusing Acrylic is infused with colorless light-diffusing particles. While regular acrylic only diffuses light around the edges, this material illuminates across its entire surface. On the example pictured above, we wrapped a strip of RGB LEDs around a piece of this material and made it cycle through several colors to demonstrate its light-diffusing properties. Light-diffusing acrylics are currently used for interior design and multi-touch applications.

Conductive Inks are paints infused with conductive particles like silver and carbon. They are used to create both hand-painted and printed electrical traces on paper and are at the base of one of the most promising branches of material science: printed electronics. Printed electronics allow us to create cheap, flexible, and recyclable circuits using standard paper, a slightly modified document printer, and conductive ink.

Applications of Smart Materials

Shape memory polymers could be inserted inside the body and react to the changes and stimulation of the body. Indeed, it could allow the creation of brand new antibiotics reacting, for example, to the body temperature changes.

Possible use of shape memory materials would be on solar panels that would be working as sensors for detecting the sun. This way, solar panels could be auto-rotating in the right direction. Combined with robotics, it could allow the creation of solar panels optimized to get the maximum solar energy.

Combining traditional construction materials with smart material could be a great solution to get structures able to grow, self-repair, or adapt quite quickly to their environment.

Airbus SAS is starting to use a 4D-related “smart” material that reacts to temperature to cool jet engines and a wing that morphs according to aerodynamic conditions to decrease air resistance.

Applications in Various Fields

Smart materials offer differentiated functionalities resulting in smart applications. Primarily limited to space and defense applications earlier, use cases of smart materials are increasing rapidly in industries such as aerospace, automotive, manufacturing, electronics, and construction.

Defense and Space: Smart materials have been developed to suppress vibrations and change shape in helicopter rotor blades. Shape-memory-alloy devices are also being developed that are capable of achieving accelerated breakup of vortex waves of submarines and similarly different adaptive control surfaces are developed for airplane wings. Besides, the present research is on its way to focus on new control technologies for smart materials and design methods for the placement of sensors and actuators.

Nuclear Industries: Smart technology offers new opportunities in the nuclear industrial sector for safety enhancement, personal exposure reduction, life-cycle cost reduction, and performance improvement. However, the radiation environments associated with nuclear operations represent a unique challenge to the testing, qualification, and use of smart materials. However, the use of such smart materials in nuclear facilities requires knowledge about the material’s response to irradiation and how this response is influenced by the radiation dose.

Self-Repair: One method in development involves embedding thin tubes containing uncured resin into materials. When damage occurs, these tubes break, exposing the resin which fills any damage and sets. Self-repair could be important in inaccessible environments such as underwater or space.

Bio-Medical: In the field of biomedicine and medical diagnostics, still investigations are being carried out. Certain materials like poly-electrolyte gels are being experimented with for artificial-muscle applications, where a polymer matrix swelled with a solvent that can expand or contract when exposed to an electric field or other stimulation. Besides, due to the biodegradability of these materials, it may make it useful as a drug-delivery system.

Health: Biosensors made from smart materials can be used to monitor blood sugar levels in diabetics and communicate with a pump that administers insulin as required. However, the human body is a hostile environment, and sensors are easily damaged. Some research on barrier materials is going to protect these sensors. Nowadays different companies are developing smart orthopedic implants such as fracture plates that can sense whether bones are healing and communicate data to the surgeon. Small-scale clinical trials of such implants have been successful and they could be available within the next five years. Other possible devices include replacement joints that communicate when they become loose or if there is an infection. Current technology limits the response of these devices to transmitting data but in the future, they could respond directly by self-tightening or releasing antibiotics. This could reduce the need for invasive surgery.

Reducing Waste: All over the world, electronic wastes are the fastest-growing component of domestic waste. During the disposal and processing of such wastes, hazardous and recyclable materials should be removed first. Manual disassembly is expensive and time-consuming but the use of smart materials could help to automate the process. Recently fasteners constructed from shape-memory materials are used that can self-release on heating. Once the fasteners have been released, components can be separated simply by shaking the product. By using fasteners that react to different temperatures, products could be disassembled hierarchically so that materials can be sorted automatically.

Food: Food makes up maximum waste among all others. Most of the food grown for consumption is thrown away without consumption due to their reaching of the expiry date. These dates are conservative estimates and actual product life may be longer. Manufacturers are now looking for ways to extend product life with packaging by utilizing smart materials. As food becomes less fresh, chemical reactions take place within the packaging and bacteria build-up. Smart labels have been developed that change color to indicate the presence of an increased level of a chemical or bacteria in it. Storage temperature has a much greater effect than time on the degradation of most products. Some companies have developed ‘time-temperature indicators’ that change color over time at a speed dependent on temperature.

Research and Innovation

Aviation

An airplane skin that self-heals to remove dings and dents, thereby maintaining optimal aerodynamics, was considered impossible in the isotropic age; however, it becomes a possibility in the anisotropic age.

Airplane components are made of a composite material that has been coated with a thin layer of nanosensors. This coating serves as a “nervous system,” allowing components to sense various parameters, such as pressure and temperature, among others.

When the airplane’s wings sense damage, it sends a signal to microspheres of uncured material within the nanocrystal coating. This signal instructs the microspheres to release their contents in the damaged area and then start curing, much like putting glue on a crack and letting it harden.

Airbus is researching the field of smart materials at the University of Bristol’s National Composites Center, thereby propelling the adoption of smart materials by the aviation industry.

Automobile

The automotive industry, meanwhile, can use smart materials to manufacture cars that not only sense damage and self-heal but also collect data about the performance, which can be fed back into the design and engineering process.

The Hackrod project brings technology partners together with a team of automotive enthusiasts in Southern California. The project aims to design the first car in history with smart materials and engineered using artificial intelligence.

In another example, Paulo Gameiro, coordinator of the EU-funded HARKEN project and R&D manager for the Portuguese automotive textiles supplier, Borgstena, are developing a prototype seat and seatbelt that use smart textiles with built-in sensors to detect a driver’s heart and breathing rates, to alert passengers if the driver is showing tell-tale signs of drowsiness.

Health

One of the most important innovations of Smart Materials is Arterial stents made from Shape-Memory Alloys (SMAs). A clogged or collapsed artery is a significant health risk and can directly contribute to the death of a patient. The challenge is how to remove the restriction to blood flow in a fast and minimally invasive way. Thankfully, a smart material with a shape memory function, known as NiTiNOL, and some clever engineering provides a solution that has been used in thousands of patients.

NiTiNOL has a shape memory that is retained over time and it is possible to switch between states by varying the temperature of the material.

The arterial stent takes advantage of the temperature differential between the human body and the surrounding environment. Outside of the body, the NiTiNOL bulb is collapsed. The actuation of the device occurs when it is inserted into the body, the warmth of the patient expands the device to hold the artery open. The continual heat of the patient’s body ensures that the device will remain expanded, promoting healthy blood flow.

Arterial stents use NiTiNOL’s unique properties to make a device that collapses when inserted, then expands in the presence of body heat, keeping the artery open.

Future Scope

Aerial Industry

The application of smart materials will enable the wings of aircraft to be more flexible thanks to shape-memory alloys. The outer elements of an aircraft will become more skin-like in that they will have to be strong, hard, and rigid, yet flexible.

The theory behind this design stems from Da Vinci’s flying machine, an example of a historic smart material theory being realized with tomorrow’s modern technology. The ‘skin’ of the plane will also have self-healing properties, even when the aircraft is in flight; thanks to the introduction of self-healing plastics.

Energy Sector

The implementation of printed photovoltaic cells will allow the energy sector to take solar panels to the next level. Photovoltaic cells can be painted onto any surface, in any shape. These cells can transform sunlight and heat into electricity. This will undoubtedly have a positive impact on residential properties and, while this solution is not yet commercially-ready, the industry is certainly getting closer.

Mobile Industry

There are LG devices that already contain self-healing materials, restoring any scratches that occur on the back of the device. However, research is currently taking place to move this on to another level. The aim is to invent self-healing glass (for screens) and lithium batteries that can be housed within mobile devices.

Automotive Industry

Windscreen chips become cracked due to water molecules within the air mixing with the chip in the glass, breaking it down and worsening the condition. Crack-resistant glass is currently in development that reacts well with airborne water molecules, resulting in the glass healing over time instead of deteriorating.

As material scientists continue to study intelligent materials, further future applications will be discovered. The opportunity within the energy, automotive, medical, and even military sectors are sure to benefit from the technological advances available through the incorporation of smart materials.

Conclusion

The technology of smart materials by its nature is a highly interdisciplinary field. Starting from the field of basic sciences such as physics, chemistry, mechanics, computing, and electronics it also covers the applied sciences and engineering such as aeronautics and mechanical engineering. This may explain the slow progress of the application of smart structures in engineering systems, even if the science of smart materials is moving very fast. In the present scenario, the most promising technologies for lifetime efficiency and improved reliability include the use of smart materials and structures. Understanding and controlling the composition and microstructure of any new materials are the ultimate objectives of research in this field and are crucial to the production of good smart materials.

Summary and Topics Covered

In this blog, we covered all one needs to know about Smart Materials. The need to invest in Smart Materials is something that we stressed upon while explaining the ideas. We’ve explained how Smart Materials have evolved over the years in terms of technology to create better designs and applications. We’ve also added the research conducted regarding Smart Materials and also explained the widely used applications of it in different industries.

Authors: Aniruddha Kulkarni, Khushi Bhartiya, Abhita Lakkabathini, Saket Kolpe.

Image Source: Google Images

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