Engineers make tiny, low-cost, terahertz imager chip

December 10, 2012 by Kimm Fesenmaier, California Institute of Technology
Engineers make tiny, low-cost, terahertz imager chip
The new terahertz chips developed by Caltech electrical engineers, shown with a penny for scale. Credit: Kaushik Sengupta/Caltech

(—A secret agent is racing against time. He knows a bomb is nearby. He rounds a corner, spots a pile of suspicious boxes in the alleyway, and pulls out his cell phone. As he scans it over the packages, their contents appear onscreen. In the nick of time, his handy smartphone application reveals an explosive device, and the agent saves the day. 

Sound far-fetched? In fact it is a real possibility, thanks to tiny inexpensive silicon microchips developed by a pair of electrical engineers at the California Institute of Technology (Caltech). The chips generate and radiate high-frequency , called terahertz (THz) waves, that fall into a largely untapped region of the —between microwaves and far-—and that can penetrate a host of materials without the ionizing damage of

When incorporated into handheld devices, the new microchips could enable a broad range of applications in fields ranging from homeland security to wireless communications to health care, and even touchless gaming. In the future, the technology may lead to noninvasive , among other applications.

"Using the same low-cost, integrated-circuit technology that's used to make the microchips found in our cell phones and notepads today, we have made a silicon chip that can operate at nearly 300 times their speed," says Ali Hajimiri, the Thomas G. Myers Professor of Electrical Engineering at Caltech. "These chips will enable a new generation of extremely versatile sensors." 

Hajimiri and postdoctoral scholar Kaushik Sengupta (PhD '12) describe the work in the December issue of IEEE Journal of Solid-State Circuits

Researchers have long touted the potential of the terahertz frequency range, from 0.3 to 3 THz, for scanning and imaging. Such electromagnetic waves can easily penetrate packaging materials and render image details in high resolution, and can also detect the of pharmaceutical drugs, biological weapons, or illegal drugs or explosives. However, most existing terahertz systems involve bulky and expensive laser setups that sometimes require exceptionally low temperatures. The potential of terahertz imaging and scanning has gone untapped because of the lack of compact, low-cost technology that can operate in the frequency range.

To finally realize the promise of terahertz waves, Hajimiri and Sengupta used complementary metal-oxide semiconductor, or CMOS, technology, which is commonly used to make the microchips in everyday electronic devices, to design silicon chips with fully integrated functionalities and that operate at terahertz frequencies—but fit on a fingertip.

"This extraordinary level of creativity, which has enabled imaging in the terahertz frequency range, is very much in line with Caltech's long tradition of innovation in the area of CMOS technology," says Ares Rosakis, chair of Caltech's Division of Engineering and Applied Science. "Caltech engineers, like Ali Hajimiri, truly work in an interdisciplinary way to push the boundaries of what is possible."

Engineers make tiny, low-cost, terahertz imager chip
A bullet and a knife blade hidden inside a toy. Inset: The teraherz image obtained with the silicon chip reveals the hidden objects without needing to cut open the toy. Credit: Kaushik Sengupta/Caltech

Engineers make tiny, low-cost, terahertz imager chip
The toy cut open revealing the hidden bullet and blade. Credit: Kaushik Sengupta/Caltech
The new chips boast signals more than a thousand times stronger than existing approaches, and emanate terahertz signals that can be dynamically programmed to point in a specified direction, making them the world's first integrated terahertz scanning arrays.

Using the scanner, the researchers can reveal a razor blade hidden within a piece of plastic, for example, or determine the fat content of chicken tissue. "We are not just talking about a potential. We have actually demonstrated that this works," says Hajimiri. "The first time we saw the actual images, it took our breath away." 

Hajimiri and Sengupta had to overcome multiple hurdles to translate CMOS technology into workable terahertz chips—including the fact that silicon chips are simply not designed to operate at terahertz frequencies. In fact, every transistor has a frequency, known as the cut-off frequency, above which it fails to amplify a signal—and no standard transistors can amplify signals in the terahertz range. 

To work around the cut-off-frequency problem, the researchers harnessed the collective strength of many transistors operating in unison. If multiple elements are operated at the right times at the right frequencies, their power can be combined, boosting the strength of the collective signal. 

"We came up with a way of operating transistors above their cut-off frequencies," explains Sengupta. "We are about 40 or 50 percent above the cut-off frequencies, and yet we are able to generate a lot of power and detect it because of our novel methodologies."

"Traditionally, people have tried to make these technologies work at very high frequencies, with large elements producing the power. Think of these as elephants," says Hajimiri. "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 researchers also figured out how to radiate, or transmit, the terahertz signal once it has been produced. At such high frequencies, a wire cannot be used, and traditional antennas at the microchip scale are inefficient. What they came up with instead was a way to turn the whole into an antenna. Again, they went with a distributed approach, incorporating many small metal segments onto the chip that can all be operated at a certain time and strength to radiate the signal en masse.

"We had to take a step back and ask, 'Can we do this in a different way?'" says 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."

The paper is titled "A 0.28 THz Power-Generation and Beam-Steering Array in CMOS Based on Distributed Active Radiators." IBM helped with chip fabrication for this work.

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2.4 / 5 (5) Dec 10, 2012
Maybe this could be applied to US prisons, to replace the tedious and humiliating "frisking" of inmates every time they pass from one section to the next.
2.3 / 5 (4) Dec 10, 2012
I just want it for my cell phone -- look out ladies ;-)
not rated yet Dec 10, 2012
They already know what they've got for Christmas then!
3.5 / 5 (6) Dec 10, 2012
sounds like the tricorder from start treck. Everybody forgets those were used for more than just looking inside people. They could also detect subsances analyze air quality and look through walls. This is that thing.
1 / 5 (2) Dec 10, 2012
Should be possible to use multiples of the device in unison to create "binocular" or "trinocular" 3-d imaging, which could be stored in memory as a model, instead of just 2-d imaging.

Even if the modeling approach is too hard for a hand-held device, it could be incorporated into a medical scanner similar to MRI or CT scanners. I think MRI would not be able to be packaged in the same machine because the magnetism might destroy the circuits, but I'm not sure. Maybe they could figure something out.

Anyway, the idea would be to have more than one Terahertz source and more than one surface to sense the rebounds, so that you get a 3-d perspective of the surface. Sort of like if you had two metal detectors looking at the same object from slightly different angles. This could be all put into a device the size of a phone or so and used in preliminary medical scans for trauma patients or suspected cancer patients.
1 / 5 (2) Dec 10, 2012

Some theoretical improvements or even actual improvements do not scale in the real world practical use in the same manner they do "on paper" in idealized conditions.

Improving the efficiency of an internal combustion engine by a finite amount, like 10%, will not improve the overall efficiency of an automobile by 10%, because of stoppage time and other crap like that. When you are stopped or coasting, the engine is running, wasting fuel, therefore the overall efficiency doesn't improve as quickly as the "on paper" efficiency.

Similarly, real light bulbs might get turned on or off more often in a real house or work place than they do in a laboratory, which can cause them to wear out much more quickly than laboratory results.

I think a full body medical scanner using this technology or something derived from it would be huge boon to diagnosing cancers, infections, and finding foreign objects in the body from accidents or violence, or even in forensics.
5 / 5 (1) Dec 10, 2012
They already use terahertz for airport screening and artwork preservation and analysis (as in being able to detect and see paintings that masters have painted over). The exciting thing about this article is that the cost and size of the imagers are likely to take a big drop down with this technology.
1 / 5 (2) Dec 10, 2012
Law Enforcement is going to love this. Now they'll be able to search you for weapons without having to frisk you. This will avoid the accusation that the cop only searched you to 'cop a feel'... no more need to call in a female cop to search a female suspect...
1.8 / 5 (5) Dec 10, 2012
Should be possible to use multiples of the device in unison to create "binocular" or "trinocular" 3-d imaging..."

The real concern here is whether this sort of radiation is harmful to the subject... needs further study... Also, privacy concerns are an issue in need of consideration. How far will the law allow people to be scanned, where, and under what conditions? Would they allow any store to scan you at the door to see if you've shoplifted anything? Would cops be allowed to scan anyone on a mere suspicion; or would they still need a search warrant or 'probable cause'...? Still a lot of unanswered questions here.
1 / 5 (3) Dec 11, 2012
Another tool for the degenerate. Inventors should think well if you invent is violating the privacy of the women in their own families before starting to make an invention.
This invention will have terrible consequences. Since we can not have privacy and protecting the privacy of our families. And if we try to cover our private parts with metal fiber web, the guards at airports escánners confuse us with terrorists trying to hide something.
Someone invents something to counter attacks against our most basic rights to privacy! Maybe burn or blind sensors let these portable devices using pulsed terahertz emission?Think! Either we stand or we will use the juniors fun of these fascists. There is a limit to everything and this is one of those limits. Your family is at stake. Think, do not be a sheep.
not rated yet Dec 11, 2012
Semiconductors have seemed to be stuck around the 1THz limit for a while. And this seems to be some kind of step forward. The cut off frequency effect also limits speed in computer CPU chips, but no doubt these will use much too much power to be made into anything really large scale.

For a tricorder we also need infrared all the way through to optical as well.
1 / 5 (1) Dec 16, 2012
The real concern here is whether this sort of radiation is harmful to the subject... needs further study... Also, privacy concerns are an issue in need of consideration. How far will the law allow people to be scanned, where, and under what conditions? Would they allow any store to scan you at the door to see if you've shoplifted anything? Would cops be allowed to scan anyone on a mere suspicion; or would they still need a search warrant or 'probable cause'...? Still a lot of unanswered questions here.

How does this most recent Kindergarten school shooting make you fell about this?

I swear, we'd have more freedoms if we didn't have so many "rights".

It would actually be easier to start by banning all firearms with any more capacity than a 6 round revolver, than to literally scan everyone.

Searches and scans on public property are not prevented by the 4th amendment. Nor do they prevent an owner scanning you on their property for their defense, which is THEIR right.

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