Making Integrated Terahertz Imaging a Reality
The terahertz (THz) applications include: high data-rate, communication, high-resolution imaging radar and spectroscopy. Among these, imaging radars are developed as a reliable and cheap measurement technique for short-range remote sensing applications. Terahertz radiation has several distinct advantages over other wavelengths of light such as: 1) many dielectric materials are transparent to Terahertz radiation; 2) Terahertz radiation is nonionizing and consequently safe for biological tissues unlike X-ray, 3) Terahertz images have a relatively high lateral resolution ≈1 mm. These advantages make the terahertz imaging intriguing. There are optical devices for these applications however, they are bulky and expensive solutions. A silicon chip can cover THz advantages at a lower price and a more scalable scheme. However, there are challenges on fully integration of a radar system on silicon. These challenges includes efficient power generation, low sensitivity of the Rx. front end, generation of ultra-wideband signals, long image acquisition time and finally putting together all the building blocks of a radar transceiver in a single chip. In this thesis, we have demonstrated three integrated radars at THz frequencies, which exhibits the feasibility of low cost, low power and fully integrated silicon-imaging instrumentation for future 2D and 3D practical imaging applications, such as biomedical hydration sensing, security screening and industrial quality control. We have demonstrated systems, which are capable of practical biomedical hydration sensing applications. The system is tested for contactless detection of skin burn with a high resolution. In chapter 1, A 320 GHz fully integrated transmission-based THz imaging system is reported. The system is composed of a phase locked high-power transmitter and a coherent high-sensitivity subharmonic-mixing receiver. To enhance the imaging sensitivity, a heterodyne coherent detection scheme is utilized. To obtain frequency coherency, fully integrated phase-locked loops are implemented on both the transmitter and receiver chips. In chapter 2 a 170GHz, fully integrated single-chip heterodyne FMCW imaging radar is reported. We have propose a design methodology to maximize the tuning range of the VCO. A co-design of the VCO, coupler and antenna is performed to minimize the chip area and the DC power consumption. The prototype is capable of forming 2D and 3D images with a range resolution of 7.0mm. The structure is quite compact with a total Si area of only 0.7mm^2. In chapter 3, 4,an ultra-wideband fully integrated imaging radar at THz frequencies is presented which demonstrates a fine lateral resolution without using any focal lens/mirror. We have achieved a lateral resolution of 2mm for an object at 23cm distance as well as a range resolution of 2.7 mm. To achieve the decent range resolution, in a FMCW radar configuration, a state-of-the-art chirp bandwidth of 62.4GHz at a center frequency of 221.1GHz is generated and efficiently radiated. By optimal design of the passive embedding around the core transistor the tuning bandwidth of the radiator is maximized. At the receiver side to maximize the IF level a sub-harmonic mixer is utilized which is designed for the lowest conversion loss. Finally, to obtain the fine lateral resolution, we have implemented near-field beamforming algorithm based on the ISAR systems. In chapter 5, an array implementation of the FMCW radar is reported. Using the array structure electrical beam forming becomes practical. In the proposed array structure, 8 pixels at the receiver side are used that are capable of digital beam steering. The array is used in focal plane and plane wave imaging schemes. We have shown that by using the signals from all the pixels we can lower the number of mechanical movements significantly by a factor of 16 while the image quality is not degraded. This makes the imaging faster by almost the same factor.
Electrical engineering; Biomedical engineering; FMCW; Hydration sensing; Imaging radar; Remote sensing; Synthetic aperture radar; Terahertz
Hysell, David Lee; Molnar, Alyosha Christopher
Electrical and Computer Engineering
Ph. D., Electrical and Computer Engineering
Doctor of Philosophy
dissertation or thesis