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Enhanced Metamaterials for Reconfigurable mm-Wave and THz Systems
Sanphuang, Varittha

2016, Doctor of Philosophy, Ohio State University, Electrical and Computer Engineering.
Millimeter-wave (mm-Wave) and Terahertz (THz) technology have become attractive due to emerging applications in wireless, satellite communication, imaging and sensing, and material characterization. Although, several THz applications have been proposed, the lack of electronic components is an ensuing issue. In this dissertation, we examine materials and mm-Wave/THz filters for sensor applications. Both bandpass and reconfigurable filters are considered and specific designs are provided. Specifically, we introduce metamaterials to improve spatial filters in the Ka (26.5 – 40 GHz) and THz (0.3 – 10 THz) bands for sensor and detector applications. Periodic structures are presented to design narrowband and broadband frequency selective surfaces (FSSs). For the Ka band design, both the narrowband and broadband FSS designs are studied. Experimental results show excellent agreements with the simulations for all the designs. In addition, a low loss FSS transparent window is designed, for the 1st time ever, to enhance the THz spectroscopic measurement system, especially for THz imaging of biological samples. The proposed metamaterial designs provide up to 136% of bandwidth hence the THz image quality was improved by 30%.

Reconfigurability of mm-Wave and THz is also introduced to enhance the sensitivity of associated detectors and sensors. In contrast to traditional RF MEMS used for reconfiguration in THz applications, we introduced material-based switching: bimaterial and phase-change materials (PCMs) actuators. First, we develop reconfigurable filters operating in the THz band that subjected to the temperature gradient of the surrounding medium by employing bimaterial actuator. The filter was fabricated and the equivalent circuit was extracted and demonstrated. Measurement and simulation results show good agreement with excellent transmittance (>80%).

Next, vanadium dioxide (VO2) is considered here as PCMs, which shows insulator-to-metal transition (IMT) properties with large conductivity change on the order of ~10K at relatively low temperature of Tc ~68°C. Importantly, VO2 films can be monolithically integrated onto array structure (such as FSSs) using a microfabrication process compatible with mm-Wave and THz devices. In this dissertation, a successful VO2 deposition process is provided to achieve the largest possible conductivity change. The reconfigurable filters are made of FSS and heater is integrated for VO2 excitation. A broadband ON/OFF filter at 0.35 THz is demonstrated with 20 dB change in transmission between the ON and OFF states. Additionally, a reconfigurable stopband FSS filter with tunable rejection rate of more than 90% from 0.75 to 0.55 THz is presented. The two states of both filters are achieved at relatively low temperature of 68°C, making them suitable for practical applications. Comparisons between simulation and measurement show excellent agreement. The developed equivalent circuits of PCMs based on VO2 thin films for reconfigurable FSSs are also developed.

The proposed bimaterials and PCM switching mechanisms are employed in specific FSS structures that are fabricated and tested. Experimental results are provided to verify the successful operation of the filter and detector devices. The proposed reconfigurable metamaterials in this work can enhance the performance of applications of devices such as spatial filter, detector and absorber in mm-Wave and THz systems to provide frequency selectivity in practical realization.
John L. Volakis (Advisor)
Niru K. Nahar (Advisor)
Siddharth Rajan (Committee Member)
170 p.

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Sanphuang, V. (2016). Enhanced Metamaterials for Reconfigurable mm-Wave and THz Systems . (Electronic Thesis or Dissertation). Retrieved from https://etd.ohiolink.edu/

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Sanphuang, Varittha. "Enhanced Metamaterials for Reconfigurable mm-Wave and THz Systems ." Electronic Thesis or Dissertation. Ohio State University, 2016. OhioLINK Electronic Theses and Dissertations Center. 25 Nov 2017.

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Sanphuang, Varittha "Enhanced Metamaterials for Reconfigurable mm-Wave and THz Systems ." Electronic Thesis or Dissertation. Ohio State University, 2016. https://etd.ohiolink.edu/

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