Smart textiles: E-textiles. Definitions, sensors, energy harvesting

Intelligent textiles emerged at the end of the 20th century, thanks in particular to the chemical and electronics industries, which enabled textile fibers and structures to be functionalized to provide new properties. The miniaturization of electronic components made it possible to integrate them into the heart of garments. Finally, some textiles have now become electronic circuits, thanks to improved manufacturing processes and the integration of conductive materials on a microscopic scale within yarns . All these advances have enabled clothing, home textiles and technical textiles to go beyond their initial roles of environmental protection, mechanical reinforcement and so on. These textile structures have become capable of measuring environmental and/or physiological parameters and analyzing them in order to provide an adapted response or take appropriate action.

The production of e-textile sensors used to measure physiological parameters calls on well-known textile manufacturing techniques that can be easily transferred to the textile industry, such as weaving, knitting, embroidery or coating.

Another focus of smart textiles and e-textiles is energy harvesting, a process by which ambient energy is converted into electrical energy. Energy recovery from sources such as the wind or the sun has been around for a long time. It can produce power measured in megawatts, but is not well suited to micro-environments, where needs are expressed in small, highly localized amounts of power. What's more, the trend towards locally-powered portable devices or connected textiles, without the use of heavy, inefficient batteries, amplifies the need for sources of energy recovery produced by local movements, or the recovery and transmission of existing energy in the form of electromagnetic waves.

Micro-energy recovery includes photonic, mechanical (piezoelectric) and electromagnetic (antennas and metamaterials) sources. The maximum power densities of these three sources are similar. However, the most promising methods at present focus on conversion processes based on piezoelectricity and on the capture and conversion of electromagnetic waves by antennas resonating at frequencies close to those used for data transmission.

The main aim of this article is to introduce engineers and the general public to intelligent textiles and e-textiles in particular, by reviewing the basic concepts and giving examples of concrete applications. New e-textile products and systems are starting to appear on the market as autonomous systems or subsystems...