ONLINE MAGAZINE ISSN 2150-5128
By karen robertsCollege of Engineering
Dennis Prather (left), and Yao Peng in the millimeter wave photonics laboratory in the Department of Electrical and Computer Engineering, where they have invented the world's first millimeter wave photonic detection module that spans through 200 GHz.
According to U.S. military statistics, improvised explosive devices (IEDs) are the number-one killer in the Middle East, particularly in Afghanistan and Iraq. They are the largest cause of casualties to U.S. troops and NATO forces combined.
"It's a huge issue. We believe IEDs are going to impact all types of warfare scenarios because they are easy to make, hard to detect and tremendously destructive because you never know where they will turn up," says Dennis Prather, Alumni Professor of Electrical and Computer Engineering at the University of Delaware.
To help overcome this problem, Prather and his research team have developed a highly sensitive, low-cost application for accurately detecting and identifying IEDs using millimeter waves (MMWs). The approach involves using high-frequency photonic modulators, which convert millimeter waves, found in the electromagnetic spectrum between infrared and microwaves, into an optical signal that can be more easily imaged.
"Imaging in the millimeter wave spectrum offers many of the advantages common to infrared imaging, but allows for the ability to see through obscurants, such as blowing sand, fog, dust, smoke and light rain. It also offers the ability to see through certain types of materials, like outer garments, fiberglass, drywall and others," Prather notes.
Prather has extensive experience in the development and application of photonic devices and their integration into systems for imaging, communications and photonic applications. He is also a commander in the U.S. Naval Reserves and the United States representative on the NATO Technical Group for High-Performance Millimeter Wave Imaging.
Over the past few decades, imaging in the infrared spectrum has allowed us to see through the darkness or "in the absence of light" because objects at non-zero Kelvin give off radiation (think hot, glowing coals in a fireplace).
By contrast, Prather's system uses passive radiation and requires just 400 watts to operate, about the same energy needed to run a high-end personal computer. It does not illuminate objects; rather it looks for radiation given off from systems that emit heat, using the sky temperature as a reference.
This means that while humans see blue sky during the day and black sky at night, millimeter waves always see the absence of millimeter wave radiation, or black. As luck would have it, anything metal on earth also reflects millimeter waves. Since many IEDs are metallic in nature, Prather's device uses millimeter waves to "see" through the sand and other environmental conditions and detect IEDs buried underground.
"This system requires much less power than typical active systems like infrared, and because it never has to illuminate anything, it is entirely covert — a huge advantage for the military," he says.
Another benefit of millimeter waves is that they are a great discriminator of false alarms because they use the sky temperature, not radiation, to visualize targets. While IEDs typically look "hot" under infrared, so do rocks and mounds of sand and dirt. When viewed with millimeter waves, only IEDs are visualized.
"You don't see this in optics or infrared at all, which change based on the environmental conditions, making this wavelength a good tool for tracking and discerning IEDs," says Prather. "The tradeoff, however, is that you don't get the same high resolution as in the visible or infrared spectrum, so in that regard, it is not the most optimal solution for target acquisition."
When imaging conditions hinder the ability to see in visible and infrared, so- called VIS-IR blind, these technologies lose sight of what they are tracking. The millimeter wave system is never blind, making it advantageous when used in combination with other types of technology.
"It's called image fusion — where you take visible, infrared and millimeter waves and put them together to create a high-quality, information-based image in all conditions," Prather says. "We're just beginning to think about applications on that level."
Funded through grants from the U.S. Office of Naval Research (ONR), the Air Force Office of Scientific Research (AFOSR), the Defense Advanced Research Projects Agency (DARPA) and the Army Research Laboratory, Prather's millimeter wave system is now being tested in laboratory scenarios. The current system measures 60 cm x 60 cm x 20 cm and weighs 27.6 pounds. According to Prather, it needs to be smaller — by about 15 cm in depth.
"In the military, SWaP – size, weight and power – is the mantra," explains Prather. "That's what we're working on now, making it small enough to be mounted to a Humvee or secured to an unmanned aerial vehicle (UAV)."
Prather is also working with partners including Lockheed Martin, Heico, Systems Integration Organization and Phase Sensitive Innovations to investigate scalability and manufacturing scenarios that would help transition the technology to industry. — Karen B. Roberts
