Active Electrochromic Thermal Control Devices, 14-R9878

Principal Investigator
Jeffrey L. Boehme

Inclusive Dates:  10/01/09 – Current

Background - Thermal management is critical for optimum functionality of many systems. These may include sensitive electronics with high-power processors or billion-dollar spacecraft orbiting Earth. In general, there are two types of thermal control systems: active and passive. An active system is typically used in addition to the passive system when the passive system is not adequate. Examples of active thermal control systems include heat pipes, heat exchangers, evaporators and louvers.

SwRI researchers are developing novel active thermal control devices based on solid-state, thin-film electrochromic (EC) materials. By proper choice of the electrochromic material, the reflectance (or equivalently, the emissivity (ε)) of the device in the infrared can be modulated by applying an external electrical potential. The emissivity is reversed by changing the polarity of the applied potential.

Approach - The primary objective of this project is to demonstrate the feasibility of fabricating novel active thermal control devices based on thin-film electrochromic materials. The following specific objectives will aid in obtaining the primary objective.

• Develop thin-film electrochromic devices capable of modulating their reflectance in the long-wavelength infrared (8 to 12 µm)
   
• Develop outer IR transparent window and current collector capable of transmitting more than 80 percent of IR radiation
   
• Demonstrate device performance at temperatures ranging from –30 to 90 C
   
• Develop preliminary system design including application schemes, electrical traces and device sealing methods
   
• Assemble devices for client demonstration purposes

Accomplishments - During this program, numerous electrochromic materials (organic and inorganic) were fully characterized. Techniques for fabricating electrochromic devices were developed that operate in the longwave infrared. The current device uses an infrared transparent window upon which a gold grid has been deposited to serve as the current collector. The emissivity of these devices can be modulated between a high and low emissivity state through the application of a small voltage. Lastly, device operation was demonstrated over 10,000 cycles.

Figure 1. Two electrochromic active thermal control devices at high emissivity state.

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