Smartphone imaging is pretty advanced these days. You can use the camera to takes videos, high-def photographs and even make panoramic images. One day you might be able to use your camera to see through walls.
That capability could come from a new kind of computer chip that operates in the part of the radio spectrum, known as the terahertz range. In this range, wavelengths of radiation are longer than infrared light and shorter than those of high-frequency radio.
Terahertz radiation can penetrate solids in a way similar to X rays, but because it doesn't carry as much energy, it won't damage tissue. Terahertz frequencies are also better than X rays at seeing inside less dense materials, such as water or flesh, and a terahertz scanner is able to detect whether an embedded object is made of metal or plastic. An X-ray machine can only reveal the shape.
Such devices have been making their way into law enforcement and security. But they are big and expensive to set up. Even the portable versions resemble a bulky professional TV camera.
Electrical engineers Ali Hajimiri and Kaushik Sengupta of the California Institute of Technology have managed to bring the size down to something that could fit into a handheld device. They built a microchip that both broadcasts and receives terahertz radiation.
The chip itself is made with the same technologies used in ordinary cell phones and computers. The challenge was making one that would transmit and receive terahertz frequencies. It turned out that having several transistors on the device operating at the same time was the best way to accomplish that. The transistors are synchronized in such a way that the waves they generate reinforce certain frequencies and cancel out others.
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The researchers still needed had to get past another problem: above a certain frequency, a transistor won't work and thus won't amplify a signal. This is called the cut-off frequency. By operating the transistors in a synchronized way, the engineers were able to get around that problem and make the chip transmit. They also were able to control the direction of the signal.
A third obstacle was putting an antenna on a silicon chip; silicon tends to absorb radio energy. By giving both the antenna and the silicon a certain shape, they made something like the resonator on a guitar that broadcasts terahertz frequencies.
One use for it is data transmission - the higher the frequency of a radio wave, the more information you can cram on it. Since the signal is a higher frequency than Wi-Fi, it could make for faster downloads. "You could use it to download pictures from your digital camera in a few seconds," Hajimiri told Discovery News.
If such a fingernail-sized chip were on a smartphone, it could be used to broadcast terahertz radiation through layers of soft tissue, clothing or the thin walls of a box. The reflected signal would be picked up by an adjacent chip and a computer program would then analyze that information and display an image on the phone's screen. That's what we call a penetrating shot.
Credit: Kaushik Sengupta/Caltech