A terahertz endoscope. Pulses travel down one wire and come back the other, with the returning pulses conveying information about the target they reflected off of.

Wave on a Wire

After decades of tinkering with fiber optics, metal tubes, and plastic ribbons, scientists have discovered that all you need to detect an elusive form of electromagnetic ray is a bare metal wire. The simple technology may one day help doctors better explore the human body.

Terahertz rays bridge the gap between microwaves and infrared light in the least-explored portion of the electromagnetic spectrum. These beams can penetrate walls, boxes, and other barriers, helping scientists detect what's inside, yet they are safe for biological use. Labs worldwide are successfully pioneering terahertz emitters for medical diagnostics, wireless communications, and security imaging, but researchers have struggled to invent devices that can pick up the waves and guide them to a receiver. Neither the metal tubes used as microwave waveguides nor the optical fibers used for the near infrared are able to guide terahertz rays over long distances.

In the 18 November issue of Nature, physicists Kanglin Wang and Daniel Mittleman of Rice University in Houston, Texas, show that plain stainless steel wires work just fine, with terahertz pulses even traveling down bends in the lines. Mittleman says that the waves are able to roam free on the wire without dispersing. That means terahertz pulses can be kept short, which is crucial to imaging. The researchers also show that a pair of metal wires can act as terahertz endoscopes. In their instrument, terahertz waves travel down one wire and back up the other, conveying information about targets in the body much as ultrasonic pulses do in echolocation.

"The simplicity of the whole idea, and the fact that no one has really demonstrated this before, is remarkable," says semiconductor physicist David Citrin of the Georgia Institute of Technology in Atlanta. He expects many further studies into how the wires can be optimized.

Related sites
Daniel Mittelman's Web page
Information on guiding electromagnetic waves