In the wake of the news that the Star Trek material “transparent aluminum” is now a reality comes news of another SciFi technology from that same show that has taken its first step toward reality: the tricorder.
In Star Trek, when Dr. Leonard “Bones” McCoy needed to diagnose an ill member of the Starship Enterprise, he simply pointed his tricorder device at their body and it identified their malady without probing or prodding. Similarly, when Capt. Kirk beamed down to an alien world, his tricorder quickly analyzed if the atmosphere was safe to breathe.
Now engineers at Stanford University have taken the latest step toward making such a device reality. The work grows out of research designed to detect buried plastic explosives, but could also provide a new way to detect early stage cancers.
The careful manipulation of two scientific principles drives both the military and medical applications of the work, researchers say.
First, all materials expand and contract when stimulated with electromagnetic energy, such as light or microwaves. Second, this expansion and contraction produces ultrasound waves that travel to the surface and can be detected remotely.
The basic principle of this interaction was first revealed in 1880 when Alexander Graham Bell was experimenting with wireless transmission of sound via light beams. Bell used light to make sound emanate from a receiver made of carbon black, which replicated a musical tone.
Engineers built on the principles demonstrated in Bell’s experiment to develop a device to “hear” hidden objects.
The new work, published in the journal Applied Physics Letters, was spurred by a challenge posed by the Defense Advanced Research Projects Agency (DARPA), best known for sponsoring studies that led to the internet. DARPA sought to develop a system to detect plastic explosives buried underground—improvised explosive devices (IEDs)—that are currently invisible to metal detectors. The task included one important caveat: The detection device could not touch the surface in question, so as not to trigger an explosion.
All materials expand and contract when heated, but not at identical rates. Ground, especially muddy ground soaked with water, absorbs more heat than plastic.
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.
HOLY GRAIL OF DETECTION DEVICES
Sound waves propagate differently in solids than air, with a drastic transmission loss occurring when sound jumps from the solid to air. That’s why, for instance, ultrasound images of babies in utero must be taken through direct contact with the skin.
Researchers accommodated for this loss by building capacitive micromachined ultrasonic transducers, or CMUTs, that can specifically discern the weaker ultrasound signals that jumped from the solid, through the air, to the detector.
“What makes the tricorder the Holy Grail of detection devices is that the instrument never touches the subject,” says Amin Arbabian Arbabian, assistant professor of electrical engineering. “All the measurements are made through the air, and that’s where we’ve made the biggest strides.”
On the next page, check out the video of how this tricorder concept will work…