Researchers from Cornell University have developed a novel method of generating terahertz signals using an inexpensive silicon chip. This new method has a broad range of potential applications including ones in medical imaging, security and wireless data transfer.
Terahertz radiation is the portion of the electromagnetic spectrum which exist between microwave and infrared light. Terahertz radiation can penetrate through clothing and even through some of the outer layers of the skin itself but unlike X-Rays which are considered harmful to the human body.
Using Terahertz radiation can be useful in many areas. For example, Terahertz scanning can identify
tiny skin cancers which are too small for the naked eye to detect. Terahertz scanning can also detect and identify a large number of complex organic chemicals used in explosives
. Another unrelated but potentially useful property of Terahertz radiation has to do with its use of higher frequencies which can carry more bandwidth making it an ideal close range ultra-high speed wireless networking solution.
So far most methods for generating Terahertz radiation involved lasers, vacuum tubes and special circuits which had to be cooled down to near absolute zero. This is costly, complicated and for the most part extremely cumbersome – often requiring room-sized apparatus costing thousands of dollars.
Recently, Cornell Electrical and Computer Engineering Professor Ehsan Afshari and his team developed a new method for using inexpensive CMOS chip technology for generating power levels high enough for some medical applications. Professor Afshari believes that with further research, higher power will be possible, enabling devices such as handheld scanners for military and law enforcement.
Generating high frequencies out of solid state devices is not a simple task and depends on , how fast electrons can move back and forth inside a transistor. To confront this issue engineers make use of what is known as “harmonics”, basically signals that naturally appear at multiples of the fundamental frequency of an oscillator. The base frequency is typically set by a circuit that uses a variable capacitor known as a varactor, but at terahertz frequencies the varactors don’t tune very sharply. Professor Afshari was able to come up with a novel way of tuning by coupling a number of oscillators in a ring, resulting in what is known as a high-quality signal, where all the power goes into a very narrow frequency band.
Professor Afshari was able to create a CMOS chip which was about 10,000 times more powerful (at Terahertz frequencies) than any previous silicon chip. Since the signal created by the device emerges along the axis of the ring, it might be possible to scan large areas with a narrow, high-power Terahertz beam.
According to Professor Afshari the power could be increased even further by adding more oscillators to the ring or using multiple rings, and Professor Afshari is also working with Cornell University experts on gallium nitride, a material that can handle both higher frequencies and higher power. However at this stage the focus is actually on making the production of the chip from less-expensive silicon. According to Professor Afshari: “The goal is to make a complete device on one CMOS chip,” he said. “I can envision a tiny thing you could put in a cell phone.”
More information can be found on the Cornell University website