smart materials[‚smärt mə′tir·ē·əlz]
Materials that can significantly change their mechanical properties (such as shape, stiffness, and viscosity), or their thermal, optical, or electromagnetic properties, in a predictable or controllable manner in response to their environment.
Materials that perform sensing and actuating functions, including piezoelectrics, electrostrictors, magnetostrictors, and shape-memory alloys.
Engineered materials that sense and react to environmental conditions or have properties that can be altered in a controlled fashion by light, temperature, moisture, mechanical force, or electric or magnetic fields. All changes are reversible, given that the materials return to their original states once the external stimulus expires.
The ability of a material to transmit light due to a change in electrical current. The optical properties are reversible, and the material reverts to its original state once the electrical current is removed. As such, electrochromic materials are the primary choice for visual devices, such as smart windows, light shutters, information displays, reflectance mirrors, and thermal radiators. In green architecture, electro-chromic materials are mainly used in “smart windows” for their energy efficiency and thermal comfort. The transparency/opacity level is adjusted by an applied voltage.
Materials that change in size in response to an electric field and produce electricity when stretched are called electrostrictive. These materials are primarily used as precision control systems such as vibration control and acoustic regulation systems in engineering, vibration damping in floor systems, and dynamic loading in building construction.
Smart materials that transform due to a change in light are called light-responsive.
Materials that change their ability to reflect color when exposed to light are called photochromic, and the color change is proportional to their level of UV light absorption. This results in reversible color reflections. When the light source is terminated, the material changes back to a clear state.
Materials that absorb radiation from light and convert it into visible light are called photoluminescent. In green architecture, they are widely used for exit signs and other self-luminous emergency egress indicators, because they do not rely on external energy sources and they require only minimal maintenance.
In a photovoltaic system, an electrical current is produced in a solid material. The physical process of this conversion is called the photovoltaic effect. Currently, there are two types of solar cell technologies: (1) crystalline materials and (2) thin-film materials. In architecture, photovoltaic materials are used in custom panels, shingles, solar tiles, and window film applications.
Changing shape from a rigid form to an elastic state when thermal energy is applied is called shape memory. When the thermal stimulus is removed, the material reverts back to its original rigid state without degradation, which is called superelasticity.
Materials that change color in response to temperature differences are called thermochromic. In architecture, these materials are currently used mostly for interactive visual effects, although they could have additional applications for green architecture in the future. Thermochromic window films alter their color structures as well as reduce solar heat transmission by blocking UV radiation. Thermochromic paints change color and thus heat absorption based on temperature changes in the outdoor environment.
A thermoelectric module is a small, light-weight, and silent solid-state device that can operate as a heat pump or as an electrical power generator with no moving parts. Thermoelectric modules are durable, reliable, silent, lightweight, and compact green materials; they do not include compressed gases, chemicals, or toxic agents.
Thermoresponsive materials are smart materials that transform in response to temperature changes.
Materials that undergo various property transformations in response to heat and temperature changes, including conductivity, transmissivity, volumetric expansion, and solubility. Visibility in thermotropic windows is directly controlled by climatic temperature changes. However, there are no visual changes to the window at low temperatures. Therefore, during the winter these windows allow solar light and heat to penetrate undiminished into the building.