Cheap, compact chip could expand T-ray scanning potential
By Ben Coxworth
December 12, 2012
Terahertz technology (or T-Ray, for short), sounds like something out of a science fiction movie. It utilizes high-frequency terahertz waves – which are located between microwaves and far-infrared radiation on the electromagnetic spectrum – to see through solid matter without the harmful ionizing radiation of X-rays. Although T-Ray devices have yet to become compact and affordable, that could soon change thanks to new silicon microchips developed at the California Institute of Technology.
Prof. Ali Hajimiri and postdoctoral scholar Kaushik Sengupta developed the tiny T-Ray chips using industry-standard complementary metal-oxide semiconductor (CMOS) manufacturing methods. One challenge that they faced, however, was the fact that the transistors on regular silicon chips simply cannot operate at high enough frequencies to amplify a T-Ray signal. The scientists got around this limitation by tuning and coordinating the frequencies of multiple transistors on one chip, using their combined power to achieve terahertz frequencies.
“Traditionally, people have tried to make these technologies work at very high frequencies, with large elements producing the power. Think of these as elephants,” Hajimiri explained. “Nowadays we can make a very large number of transistors that individually are not very powerful, but when combined and working in unison, can do a lot more. If these elements are synchronized – like an army of ants – they can do everything that the elephant does and then some.”
Even once the T-Ray signal could be amplified, there was still another problem – its frequency was too high to allow it to be transmitted via a normal wire antenna. Once again, the answer lay in spreading the task around. Numerous small pieces of metal were incorporated into the chip, which all worked together to turn the chip itself into the antenna.
The end result: inexpensive chips that are small enough to fit on a fingertip, operate at a speed almost 300 times faster than traditional silicon chips, and that have a directable T-Ray signal over 1,000 times stronger than that of previous technologies. According to Caltech, the chips constitute “the world's first integrated terahertz scanning arrays.”
Using the chips in a scanning device, Hajimiri and Sengupta were able to do things such as imaging a razor blade hidden inside a piece of plastic, and analyzing the fat content of a piece of chicken. Ultimately, it is hoped that such chip-equipped scanners could be used for applications such as luggage inspection, bomb or drug detection, and Star Trek tricorder-like medical imaging.
“We are not just talking about a potential,” said Hajimiri. “We have actually demonstrated that this works.”
A paper on the research was recently published in the IEEE Journal of Solid-State Circuits.
Update: This story was amended on Dec. 13, 2012, to state that X-rays don't generate harmful ionizing radiation, but are ionizing radiation.