Imagine all the things you could do with a smartphone app that lets you peek inside objects without opening them. Security guards could find weapons hidden in pillows or stuffed toys. Health-conscious shoppers could see how much fat is in that chicken breast that’s on sale. And curious kids could spy on the contents of their Christmas presents without ever picking up or shaking a package.
It sounds like something from a science-fiction movie, but researchers at the California Institute of Technology (Caltech) have found a way to do that all in real life.
“We are not just talking about a potential,” said electrical engineering professor Ali Hajimiri. “We have actually demonstrated that this works. The first time we saw the actual images, it took our breath away.”
The secret to the new spy-worthy technology are electromagnetic waves in the high-frequency, terahertz range. Lying between microwaves and far-infrared radiation, terahertz waves can penetrate many materials without the ionizing damage caused by X-rays.
While scientists have known about the potential for terahertz-wave “spying” for a long time, the technology up until now has typically meant bulky and expensive systems requirng lasers and, sometimes, ultra-low temperatures. Using complementary metal-oxide semiconductor technology, though, Hajimiri and postdoctoral researcher Kaushik Sengupta found a way to shrink the terahertz technology onto a silicon microchip.
Their innovation combines many transistors working in unison to amplify the silicon chip signal into the terahertz range. They also incorporated multiple tiny metal segments into the chip to turn the whole thing into an antenna capable of transmitting a terahertz signal.
“Traditionally, people have tried to make these technologies work at very high frequencies, with large elements producing the power,” Hajimiri said. “Think of these as elephants.”
He continued, “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.”
The resulting terahertz-transmitting microchip sends out electromagnetic waves that can penetrate materials to show high-resolution images of objects hidden inside. They can also detect the chemical fingerprints of drugs, explosives or biological weapons.
“We had to take a step back and ask, ‘Can we do this in a different way?'” said Sengupta. “Our chips are an example of the kind of innovations that can be unearthed if we blur the partitions between traditional ways of thinking about integrated circuits, electromagnetics, antennae, and the applied sciences. It is a holistic solution.”