Conversion of Waste Heat into Electrical Power

Heat is a by-product of electrical power, any process that require energy or power produces heat. Conversion of energy or power in to heat is quite natural and is in accordance with the law of thermodynamics but doing the reverse process i.e. conversion of heat in to power is a bit complicated task. A new innovative silicon-based tiny device has been developed by a team at Sandia National Laboratories (SNL) that can convert waste heat in to dc power. A simple illustration is shown in Figure 1. According to Dr. Paul Davids, the principal investigator at SNL for this study, electrical power can be generated from a moderate temperature thermal source by direct conversion of infrared radiation. This infrared power source could replace the radioisotope thermoelectric generators (RTGs) that are used for powering sensors in space applications.

Fig. 1: Conversion of Heat to Power using a tiny silicon chip (Ref. [1])

This tiny device is made of silicon, aluminium and silicon dioxide in which silicon is placed at the bottom and aluminium is placed at the top. These two materials are separated by a very thin layer of silicon dioxide which is about 16,000 times thinner than human hair or is twenty silicon atoms thick. In order to capture the infrared radiations, an antenna pattern is developed on the aluminium top by etching out very thin strips that are 20 times thinner than width of a human hair. With the help of these patterned antennas, infrared radiations channels in to thin layer of silicon dioxide. Inside silicon dioxide, these infrared radiations create very fast electrical oscillations due to which electrons start moving between silicon and aluminium in an asymmetric manner about 50 trillion times a second. This process is called rectification and is responsible for net dc electrical current. This tiny device is named as Infrared Rectenna by the researchers as it involves the process of rectification as well. There are no moving parts in this solid-state device and no direct connection between the heat source and the device. As the process of making this device is similar to that of fabricating integrated circuits, this device is also scalable.

In addition to possibility of powering sensors in space missions of future the device could find use in applications where battery is needed to run reliably for a long time without needing a replacement.

By: Ms. Minaxi Dassi - Assistant Professor (ECE), Chitkara University, H.P.

References

1. Joshua Shank, Emil A. Kadlec, Robert L. Jarecki, Andrew Starbuck, Stephen Howell, David W. Peters, Paul S. Davids. Power Generation from a Radiative Thermal Source Using a Large-Area Infrared Rectenna. Physical Review Applied, 2018; 9 (5) DOI: 10.1103/PhysRevApplied.9.054040
2. https://www.sciencedaily.com/releases/2018/07/180709120135.htm
3. DOE/Sandia National Laboratories