Is microwave radiation the nondestructive imaging technology of the future? Microwaves with frequencies from a few hundred gigahertz (GHz) up to slightly over 1 terahertz (THz), penetrate just a short distance into surfaces without the ionizing damage caused by X-rays. The technology could be used to detect skin cancer or image dental flaws beneath the enamel. It could also be a valuable tool for airport security, to detect objects hidden under clothing.
Most of these applications require inexpensive portable hardware that can generate signals in the GHz to THz range with more than 1 watt of power. However, transistors on a standard silicon chip have been limited to a few milliwatts at up to about 100 GHz.
Now a method of generating high-power signals at frequencies of 200 GHz and higher on an ordinary silicon chip has been proposed by Ehsan Afshari, Cornell assistant professor of electrical and computer engineering, and Harish Bhat, assistant professor of mathematics at the University of California-Merced. The researchers present a mathematical analysis of the new method in the May issue of the journal Physical Review E.
Afshari and Bhat propose to use a phenomenon known as nonlinear constructive interference. Linear constructive interference occurs when two signals that are in phase that is, with their peaks and valleys matched produce a new signal as large as both added together. But if the signals are traveling through an uneven medium, the waves can become distorted, some delayed, some moving ahead to produce a "nonlinear" result that combines many small waves into fewer large peaks. Afshari likens the effect to the breaking of waves on the seashore. In the open ocean, waves travel as smooth undulations. But near shore the waves encounter an uneven surface at varying depths and become distorted into breakers.
To create this effect on a chip, the researchers propose a lattice of squares made up of inductors the equivalent
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Cornell University Communications