TECHNOLOGY UNIVERSITY OF FLORIDAProfessor Kenneth O at the University of Florida has created a microchip-sized radio antenna that is dwarfed by this penny.

Any spy knows that you can make a radio transmitter as small as a button or even a bug, but the antenna, that's a different matter. Radio circuits benefit from the power of modern technology's microminiaturization, but antennas stubbornly do not.

A radio need not be more than a tiny sliver of silicon. Physics, on the other hand, governs the size of antennas, and its laws resist shrinkage better than polyester underwear. Antennas cannot be much smaller than a fraction of a wavelength of the signal they send or receive typically inches long.

Kenneth O (that's his whole name), a professor in the electrical and computer engineering department at the University of Florida at Gainesville, has found a clever way of sidestepping the size issue. He can shoehorn a radio antenna onto the same chip of silicon that holds the radio's circuitry. Better still, he can make the antenna using the same fabrication process as the rest of the chip.

In one deft stroke, he has made complete radio systems tiny enough to tease any secret agent's heart, but he had a shorter-range system in mind.

"We've been working on this for almost eight years, but it is work that has been evolving," explained O. "Our initial goal was to use the on-chip antenna to communicate inside an integrated circuit."

Broadcasting the entire centimeter across a microchip might not seem worthwhile at first. But O's intention was to send essential signals throughout a chip without the need for wires, one of the most expensive parts of manufacturing microcircuits.

About four years ago, O crafted the necessary antenna for inside-the-chip broadcasting. But nothing inherently limited the range of the antenna's signals, so O began to explore longer distances.

Last month, O announced he had pushed the range up to five to 10 meters about 30 feet. Although that still seems like short distance for radio broadcasting, it compares favorably to the Blue Tooth technology that the engineering community favors for linking personal electronic devices.

High means low

The secret to making the antenna smaller is using the shorter wavelengths of higher-frequency signals. O's radio system operates at 24 gigahertz, roughly 10 times the frequency used by home computer networks and micro wave ovens.

Using shorter waves is an obvious idea, which O admits. "In some ways, we could have done this eight years ago. When you do it, it works. It's that simple," said O. "What it needed was someone who is stupid enough to try it."

But high frequencies have a problem: poor propagation. Gigahertz-level signals don't get far because anything between a transmitter and receiver weakens them, including such tenuous stuff as air. For example, the oxygen in the air resonates and strongly absorbs signals at about 60 gigahertz.

"Fortunately there are windows for propagation," said O. "Moreover, if you are talking about short range, the impact is very small."

For his room-size communications, O was able to use relatively weak signals the sort that won't strain a microcircuit of about 10 milliwatts.

"In the kind of applications we are imaging, the average power is even lower, about 40 microwatts," said O. "We get it that low by using short duty cycles." The transmitter sends out only brief pulses, so the average power is minuscule. Chips won't get hot or ravenously consume batteries.

Cheap chips

Although small size is a goal in its own right, one that will earn kudos from the spies planting bugs in your oatmeal, it's not the most intriguing benefit of on-chip-antenna technology. "The key feature is lower cost," said O.

Antennas are expensive add-ons to radios.

They must be built and connected to radio circuits. That means wires and connectors and hands or machines to hook everything together.

The on-chip radio needs no external antenna, no wires and no expensive connectors. The assembly is complete as soon as the radio chip leaves the chip foundry. The cost is hardly higher than the chip alone.

O fabricates his on-chip antenna out of aluminum, a standard metal used for connecting circuits on chips.

Once O had built the on-chip transmitter and antenna, he had to receive its signals to prove that it worked. "It requires a special measurement setup because no one has ever tried to use an on-chip antenna for communication over the air," said O. "It took some time to build a mobile probe station."

In experimenting with sending signals inside integrated circuits, O had built a receiver using the same process as his transmitting antenna. He was able to make a system that can communicate a distance of 40 centimeters, about two feet. He admits that his receiver is not very sensitive, but it is a preliminary model used to prove that the technology is feasible.

O estimates that making a practical radio system using this on-chip antenna is still a year or two off. Commercial products are another year or two down the line.

Rosch is a Shaker Heights free-lance writer.

© 2004 The Plain Dealer. Used with permission.