Professor Kenneth K. O. and his colleagues at The University of Texas at Dallas and Oklahoma State University have developed an innovative and affordable terahertz imager microchip that can enable devices to detect objects and create images through obstacles that include fog, smoke, dust, and snow.
Tech Briefs: What got you started in this area of research?
Professor Kenneth K. O: For 15 years, my research group has been trying to figure out new opportunities for the silicon integrated circuits industry. When we started, although we were working on terahertz applications, our main focus was on radar operating at 77 GHz.
Tech Briefs: What are some differences between your terahertz imaging and 77 GHz radar?
O: The fundamental difference is just the frequency — it's a factor of roughly five times higher — so the wavelength is about five times smaller. That means that an imager with the same form factor can give five times better resolution by going to 430 GHz. Our system is essentially made of pixel arrays of radars running at 430 GHz. But the performance of these pixels is worse than at 77 GHz. So, in order to address that problem, we have designed the chips to work with a reflector. With the help of the reflector, we can potentially achieve the same kind of range — about 200 meters — as radar running at 77 GHz.
Tech Briefs: How does it contribute to power reduction?
O: You can think of it as a lens — it focuses the signal and sends it to a particular point in space. Therefore, all the power that's radiated from a pixel gets focused to that point instead of being dispersed as it propagates.
Tech Briefs: How does your radar deal with the frequency limits of CMOS technology?
O: The problem is that we cannot use CMOS amplifiers to provide gain for the receivers at terahertz frequencies. So, we use frequency multiplication to generate the RF signal and also use a technique called harmonic mixing to down-convert the signal without an amplifier in front. This degrades the sensitivity of the receiver, so we have to overcome that. Those are two challenges in going up to higher frequencies compared to 77-GHz radar.
Tech Briefs: So, you're saying that you somehow need more gain to increase the amplitude of the reflected signal?
O: Yes, that's exactly right. We need to make sure that the signal we transmit recaches the target we're trying to detect and that the signal power level that reaches the targets is the same as at 77 GHz. The way we do that is by using the reflector along with our focal plane array. This reflector gives us that gain in power and then it reflects back and once again gives us gain for the receiver. So, even with the poor sensitivity, we can still detect the reflected signal.
Tech Briefs: You've said that this radar can penetrate atmospheric obstacles like snow and dust and fog. But those are all particles; can it penetrate solids?
O: Some. It can penetrate nonconductive materials like plastic containers. Industrial applications include monitoring the dryness of printing on paper and fabrics. You can also think of industrial settings, where you have a steam environment. You need to monitor what's behind the steam. A really significant application is to see through smoke and fire — an amazing application for fire fighters to help them search for people.
An edited version of this interview appeared in the May 2022 issue of Tech Briefs.