“Smart materials” (also called intelligent or responsive materials) are a class of materials sensitive to temperature, pH, chemical compounds, stress, pressure, moisture, light and vibrations. Smart materials have one or more properties that can be significantly changed in a controlled way by external stimuli. All these properties of smart materials fulfil the requirements of modern sensors and overcome the limits of conventional materials.
Listening, seeing, touching, controlling, feeling and communicating are all different techniques that allow you to animate materials and create a sensual relationship with your environment in the sophisticated medical devices context. It may all sound like science fiction to you. However, it is already a reality.
Would you imagine a pair of pyjamas that we wear every night to go to bed could monitor our health during our sleep, or even control our heart and respiratory rates?
Would you imagine that a simple adhesive plaster stuck on our body could establish the health control of patients and follow their medical parameters using only wireless technologies?
In fact, they do actually exist!
But, what is behind this revolution and this technological success? There is a new generation of materials sensitive to temperature, pressure, and vibrations, which fulfil the needs of current sensors and overcome conventional limits of materials.
The purpose of these materials is not only to capture and relay information but also to be reconfigured to react to environmental changes. In essence, these materials are not simply “smart” but “alive”.
The role of smart materials in the development and enhancement of sensors
When people talk about the “smart” environment, they mean an area with deployed “smart” devices, like wireless digital electrocardiographs (ECGs) and wireless blood pressure monitors, for example.
The technological progress of these devices has always been granted to the digital domain: the computational realm, the realm of bits and smarter computing systems.
However, the hidden face of this progress lies in advances of similar speed and importance in materials science: “smart materials”. The analysis, design and ingenuity put into this field have made it possible to develop a family of materials that are sensitive and detect the environmental changes around them by changing their properties in response to stimuli. These property changes constitute the input data for the sensors. Correspondingly, these materials constitute the cornerstone of the sensors.
But what does this ingenuity bring about? The answer is sensor autonomy. Naturally, a sensor requires electrical energy so that it can process and transmit information in wireless technology. Smart materials can provide that. In fact, in most cases, where sensors have low energy consumption, these materials can produce electrical energy in response to stimuli, thus, serving as input data and sources of power for the sensors .
What are some examples of smart materials?
In simple words, smart materials are those materials which adapt themselves as per required condition. Here is a brief general classification of smart materials without counting all their forms. Smart materials can be:
- polymeric and/or composites
- electrostrictive or
- shape-memory materials
The common property of all these materials is to be adaptive and evolutionary. To date, piezoelectric materials remain the most widespread materials in sensors. To be succinct, the key feature of these materials is to generate electricity as a response to stimuli (thanks to Pierre and Jacques Curie who were at the origin of the piezoelectric discovery).
The use of piezoelectric materials is justified by the recommended sensors criteria, which have been unified in the IDtechEX report 2019-2020: sensors must be self-powered, non-poisonous, bacteria-resistant, and useful in wearables and IoT nodes. To summarise, preferably, we shall shift to one device/material performing multiple tasks.
Piezoelectric materials are divided into two families: natural (such as Rochelle salt, Quartz, and Topaz) and synthetic (such as PZT and PVDF).
Synthetic piezoelectric materials are produced to adapt their properties to the constraints of their corresponding applications, such as performance, dimensions and resistance to failure, for example  .
These advances, in addition to the competitiveness between researchers and developers, have set up customised simulation and synthesis tools from the atomic scale to the macroscopic scale.
These inspiring tools are based on the development of nanotechnology-based processes put to the benefit of chemistry and biology, such as Scanning Tunneling Microscope (STM) or Atomic Force Microscopy (AFM). They allow the manipulation of a material atom by atom and molecule by molecule.
Other tools come from the manufacture of microprocessors, such as optical photolithography, which produces thin layers of materials used in integrated devices. Such miniaturisation results in smaller, lighter and more discreet sensors. All these means pave the way to manufacturing the smart materials of the future.
Beyond Manufacturing: Challenge of Implementation in Sensors
Besides the challenges to produce sensors from smart materials, what remains is the implementation. While each sensor has its requirements, each material has its properties. This requires the development of specific electronics that matches them to one another.
To ensure that, it is necessary to model smart materials through available characterisation and simulation tools. This step is crucial in order to be able to design the low-consumption interface electronics that manage and transmit the data .
In the context of the size and weight reduction, clean room techniques and processes must be used for the integration of the two parts (materials and materials-based electronics), such as MicroElectroMechanical Systems (MEMS). This also constitutes a challenge because each chip has its requirements and must see its development process generated step by step.
Next steps: the 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. 🤓
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