The new “radio frequency (RF)/ultrasound hybrid imaging system,” the brainchild of Assistant Professor Amin Arbabian and Research Professor Pierre Khuri-Yakub, was designed for remote detection of embedded objects in a number of different kinds of matter, including water, soil and tissue.
It was developed by the Stanford electrical engineering team as part of the Defense Advanced Research Projects Agency (DARPA) project aimed at developing a system to detect plastic explosives (IEDs) hidden underground that metal detectors are unable to pick up.
The main task of the team, who recently presented their research at International Ultrasonics Symposium in Taipei, was to create a detection mechanism that would not touch the surface, so as to avoid triggering an explosion.
To make their “tricorder” technology “hear” hidden objects, researchers developed a technology based on basic principles of physics – namely that electromagnetic stimulation makes material expand and contract, and that this “expansion and contraction” generates ultrasound waves that can be detected at the surface.
“In a potential battlefield application, the microwaves would heat the suspect area, causing the muddy ground to expand and thus squeeze the plastic. Pulsing the microwaves would generate a series of ultrasound pressure waves that could be detected and interpreted to disclose the presence of buried plastic explosives,” Stanford said in the press release.
To make it possible for the detection process to be carried out from a distance, the Stanford team built “capacitive micromachined ultrasonic transducers” to differentiate the difference in sound waves transmission in solid objects and air.
“What makes the tricorder the Holy Grail of detection devices is that the instrument never touches the subject,” Arbabian said.“All the measurements are made through the air, and that’s where we’ve made the biggest strides.”
The scientists believe that the ability to detect objects remotely will greatly advance methods for detecting tumors in patients. So far their experiments have shown great potential.
The Stanford team used microwave pulses to heat a flesh-like tissue – with an implanted sample “target” –from about a foot away. The heat caused the target to contract and to send out ultrasound waves that were then measured by scientists without touching the “flesh.”
“We think we could develop instrumentation sufficiently sensitive to disclose the presence of tumors, and perhaps other health anomalies, much earlier than current detection systems, non-intrusively and with a handheld portable device,” Arbabian said.
The team believes that their technology will eventually be more portable and less expensive than all other alternatives.
“We’ve been working on this for a little over two years,” Khuri-Yakub said. “We’re still at an early stage but we’re confident that in five to ten to fifteen years, this will become practical and widely available”.