Remote Lie Detection Possible

April 2, 2008 -- A new way to remotely monitor blood pressure, pulse rate and sweating could be used to screen for health signs as well as to administer lie detection tests on people without their knowledge or consent.

While researchers stress their work remains only proof-of-concept, a commercial version using sub-terahertz waves could theoretically help remotely monitor medical patients, evaluate athletic performance, diagnose disease and detect lies.

The key is in the surprising shape of human sweat ducts.

Recent advances in imaging technology revealed that sweat ducts, the tiny tubes that connect sweat glands to the outside of the skin, are helical -- or shaped like cork screws. That's a similar to the shape of some antennas.

"At this point it's not clear why nature chooses to create sweat ducts shaped like antennas," said physicist Aharon Agranat of the Hebrew University of Jerusalem and a co-author on a study about the work in the March 28 edition of Physical Review Letters. "We are simply exploiting it."

When Yuri Feldman, also a physicist at the Hebrew University of Jerusalem and a study author, saw these sweat gland images, they reminded him of the helical antennas often used in basic engineering classes.

By measuring certain factors like the number of twists, any beginning electrical engineering student can calculate which wavelength of energy the antenna would interact with, say the physicists.

The wavelength of human sweat glands falls in the sub-terahertz, or sub T-ray, range.

Full T-rays have recently been used in a variety of other applications, from uncovering hidden artwork to finding concealed weapons. T-rays, unlike their energetic cousins X-rays, are harmless.

By creating a machine that generates and detects sub T-rays, the scientists say they can look at which wavelengths interact with the millions of tiny "antennas" buried within the body's largest organ, the skin. While sweating doesn't produce T-rays, sweat production changes the wavelength that is bounced back off the sweat duct antenna.

By measuring these wavelengths, scientists can, in turn, calculate how much and where a person is sweating.

Different parts of the body sweat depending on the reason. Eating a spicy chili pepper causes sweat beads to break out on the forehead. Sunbathing causes sweat glands on the chest and back to be activated.

Various diseases and medical conditions activate other sweat glands, while also changing blood pressure and pulse rate. Eventually, with development of an accurate sweat map and other studies, the physicists hope to create a tool that can diagnose diseases based on where a person is sweating.

In subsequent tests the researchers were also able to also measure blood pressure and pulse rate remotely. They did this by monitoring the kinds of sweating that are directly linked to changes in blood pressure and pulse.