(262g) Metamaterial and Rectenna Design and Testing for the Conversion of Blackbody Radiation to Electricity Using 5 THz Devices

Metamaterials, a new synthetic set of materials with properties that do not exist on their own in nature, typically consist of various composite materials such as metals and dielectrics. Their repeating geometric structure and material set provide the metamaterial with a negative index of refraction. For this class of metamaterials, the negative index of refraction induces their primary function: their ability to manipulate electromagnetic waves. In this study, metamaterials are designed and fabricated to manipulate incoherent blackbody radiation into a coherent, functional source of electromagnetic waves that are rectified to a DC voltage through a rectenna diode.

The metamaterial-rectenna unit is designed to convert heat into electricity using the optical properties of the blackbody radiation emitted from heat source. In general, as the temperature of the object increases, the wavelength and intensity of the blackbody radiation increase. The metamaterial-rectenna units fabricated in this study are designed to capture electromagnetic radiation with a frequency of 5 THz.

The constructed device uses a rectenna as the rectifying device to convert the alternating current (AC) induced from the electromagnetic waves emitted as blackbody radiation to a direct current (DC). The rectenna, containing a metal insulator-insulator metal (MIIM) tunneling diode, utilizes the ordered electromagnetic radiation from the metamaterial. The metamaterial consists of copper and a photosensitive polymer in an alternating pattern that focuses the electromagnetic radiation over onto the rectenna. The metal of choice, copper, is selected due to its high thermal and electrical conductivity.  The negative photopolymer SU-8 is selected polymer substrate due to its well-characterized optical properties as well as use in photolithography.  The metamaterial is fabricated using various techniques of photolithography, including wet and dry etching of metals and oxides, bilayer lift-off processes, thin-layer deposition of metals using evaporation, and electrodeposition.

In order to test the functionality of the metamaterial, the reflection spectrum of the metamaterial showing a resonance peak at 5 THz was obtained.  The metamaterial-rectenna pair was tested using a thermal source while measuring the electrical response. Matlab and Comsol modeling was used to analyze, as well as, predict the response and characteristics of the devices. Using test pads that have been built into the structure and connected to the rectenna, the diodes are characterized using four-point probe IV measurements. The thermal measurements utilize two of these probes to detect any voltage that is generated by the rectenna-metamaterial device when exposed to a controlled heat source.  In this study, further examination of the metamaterial-rectenna pair is performed with devices designed for 5 THz electromagnetic radiation.