Flexible heaters are suitable for a wide range of uses that require variable heating options. While providing optimal heat transfer, they also offer the right temperature for products like foodservice, medical devices, sensors, instrument panels, and electronics.

We are accustomed to thinking of heaters in standard shapes like square, round, and rectangular. However, customized flexible heaters are available in a wide variety of shapes that have the requisite shape to wrap around specific objects like inserts and pipes. They may also have different temperature zones for applications that generate their own heat in some places while requiring heating in others.

Designers make flexible heaters from polyimide and silicone rubber, and their size depends on the resistive element necessary. For very thin flexible heaters, etched foil heaters are the most suitable, and both polyimide and silicone materials can use them. Etched foil heaters are also suitable for smaller flexible heaters, as they can be as small as 1-inch square, or as large as 18 x 24 inches for silicone rubber, and 10 x 70 inches for polyimide. For larger sizes, designers prefer wire-wound resistive elements.

If necessary, designers can make flexible heaters in odd and non-symmetrical shapes as well. However, the specific needs of the application almost always define the shape, requiring laser cutters and mechanical equipment for creating the outline of the desired shape. Recent developments ensure that internal cutouts are also possible, such as in rectangular, square, circular, and other shapes, without sacrificing the reliability and heating capacity of the flexible heater.

Etched foil elements allow quick thermal transfers and faster warmups for heaters made from both polyimide and silicone rubber. However, wire wound heaters are notably slower, and there may be a delay in heat transfer when the heater element is wire-wound. Wire wound heaters are not suitable for polyimide heaters.

Some applications do not require heating equally throughout the surface. For instance, some electronic circuitry may create its own heat, protecting itself from external or internal temperature changes. Such applications do not require additional heating. However, outside this protected zone, the rest of the circuitry may require suitable temperature control for proper operation. Engineers provide suitable heating with cut-outs along the heater material. Flexible heaters with multiple heating zones are the answer for applications that require heating but at different temperatures.

Flexible heaters made from polyimide or silicone rubber are the most suitable for such applications. Multiple zone heating is necessary if some part of the electronics requires heating at a certain temperature, while another part needs raising to a different temperature.

Making heaters with multiple heating zones requires designers to place different heating elements at suitable places, with separate controls for these zones. However, other simpler options are also available, requiring one heater and a single controller. One of the options involves using elements with variable widths.

The width of the conductor of foil etched heaters impacts the watt density in specific areas of the flexible heater. When the width of the conductor is low, its resistance increases resulting in lowering the thermal output at that zone, creating multiple heating zones.

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.