Everyone is familiar with heaters. Although the simplest forms of heaters are sunlight and fire, both are not easy to handle or control. Therefore, people prefer using electricity for generating heat, as this is easy to control, requiring only a switch to shut off or turn on.
An electric heater generates heat by driving current through a resistive element. The power this arrangement consumes is the product of the resistance of the element and the square of the current flowing through it. The resistance radiates a part of the power it consumes as heat. This heat reaches other nearby surfaces through conduction, convection, or radiation, and transfers its energy to them, increasing their temperature.
Controlling an electric heater is a convenient way to keep the heated surface at a specific temperature or at least below a temperature that would cause damage. Initially, the resistive element of these heaters used simple nickel-chrome wires, as these could withstand high temperatures without melting. The heaters generally wrapped the wires around a mass and connected the ends to a power source. However, this arrangement, although effective, was not a practical solution for all applications.
Heaters have now evolved into flexible types, ones designed on flexible material, suitable for attachment to both flat and non-flat surfaces. Usually, temperature-sensing devices accompany these heaters, allowing constant monitoring and adjustments depending on the changes in the ambient surroundings. Flexible heater materials are commonly of two types—polyimide and silicon rubber—with flexible polyimide heaters being more popular.
Designers need to choose the conductor or the resistive element very carefully when designing a flexible heater. Flexible circuits commonly use copper as the standard cost-effective material, and this comes as a pre-laminated material. However, as copper is a good conductor, its resistivity is low. Therefore, heaters designed with regular copper require a lot of surface, and is suitable only for very low resistive designs.
Flexible heaters meant for producing high heat within small areas need a different material than regular copper for higher resistance. Designers thus use different types of nickel-copper alloys, such as Constantan or Inconel instead, which allow much higher resistive circuits within smaller areas. However, as nickel-copper alloys pre-laminated on a polyimide substrate are not commonly available, flexible heaters are more expensive.
The resistance of a heater depends on the target temperature of the material it is heating. After calculating the required resistance, the designer creates a pattern of interlocking serpentine traces of the correct width and length that emit consistent heat across the surface.
Some equipment, exposed to conditions of varying temperatures, use flexible heaters to keep their components at a consistent temperature. In cold countries, automobile manufacturers use flexible heaters for warming the steering wheel or the seat in their cars. Flexible heaters often keep biological samples at typical body temperature of a human or animal for better analysis. Flexible heaters keep batteries and electronics of aircraft warm when they have to operate at high altitudes. Flexible heaters keep critical components within ATMs and handheld electronic devices operating accurately in cold climates. This makes flexible heaters an important element in the electronic industry.
