Chip-based microwaves may replace X-rays for medical imaging, security

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Washington, May 30 : A team of two researchers from different educational institutions in the U.S. has proposed a method of generating high-power signals at frequencies of 200 GHz and higher on an ordinary silicon chip - something they believe may enable microwaves on a chip to replace X-rays for medical imaging and security purposes.

Assistant Professor Ehsan Afshari of Cornell University and Assistant Professor Harish Bhat of the University of California-Merced believe that a phenomenon called nonlinear constructive interference may make it possible.

A research article in the journal Physical Review E says that linear constructive interference occurs when two signals that are in phase-that is, with their peaks ad valleys matched-produce a new signal as large as both added together.

However, the report adds, if the signals are travelling through an uneven medium, the waves can become distorted-with some getting delayed and some moving ahead-to produce a "nonlinear" result that combines many small waves into fewer large peaks.

Afshari says that this effect is quite similar to the breaking of waves on the seashore.

Waves in the open ocean travel as smooth undulations, he adds, but they encounter an uneven surface at varying depths near shore and become distorted into breakers.

To create this effect on a chip, Afshari and Bhat propose a lattice of squares made up of inductors-the equivalent of tiny coils of wire-with each intersection grounded through a capacitor.

The researchers say that an electrical wave moves across the lattice by alternately filling each inductor, and then discharges the current into the adjacent capacitor.

A capacitor temporarily stores and releases electrons, and these capacitors, made of layers of silicon and silicon dioxide, are designed to vary their storage capacity as the voltage of the signal changes, creating the equivalent of the varying depths of an ocean beach and distorting the timing of the electrical signals that pass by.

When low-frequency, low-power signals are applied simultaneously to both the vertical and horizontal wires of the lattice, the waves they produce interfere as they meet across the lattice, combining many small waves into one large peak.

The process produces harmonic signals at multiples of the original frequency, and a high-power, high-frequency signal can be read out somewhere in the middle of the lattice.

Afshari and Bhat say that computer simulations created by them suggest that the process can be implemented on a common complimentary metal-oxide silicon (CMOS) chip to generate signals at frequencies well above the ordinary cut-off frequencies of such chips, with at least 10 times the input power.

They believe that frequencies up to around 1.16 THz are possible.

ANI

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