Sweat ducts may act as giveaway 'antennas'
04 April 2008
NewScientist.com news service
Flora Graham



Our skin may contain millions of tiny "antennas" in the form of microscopic sweat ducts, say researchers in Israel. In experiments, they found evidence that signals produced by bouncing electromagnetic waves off the tiny tubes might reveal a person's physical and emotional state from a distance.
The research might eventually result in lie detectors that require no physical contact with the subject.
Human skin contains millions of sweat glands, which are connected to pores at the surface by tiny ducts. These ducts were originally thought of as straight tubes, but detailed images produced in recent years have revealed that they are actually helical.
"When you look at this through the eyes of an electrical engineer, it is very familiar," says Aharon Agranat of the Hebrew University of Jerusalem. "It immediately ignited the thinking that perhaps they also behave as helical antenna."
To function in this way, the ducts would need to conduct a current. And since the ducts are filled with sweat, they do indeed conduct when hit with an electromagnetic wave, although not at the very high frequencies needed.
And yet, experiments performed by the Israeli researchers suggest that they do somehow work as antennas.
Proton hoppingYuri Feldman, who initiated the research, says current may be conducted within the ducts at high frequencies through a mechanism known as "proton hopping," with protons jumping rapidly – in the order of hundreds of femtoseconds – through hydrogen bonds near the surface of cells lining each duct.
Treating the skin as an array of helical antennas could open up a new way of measuring physiological changes from a distance, the researchers say.
This is because perspiration should change the conductivity of each sweat duct. And, since perspiration is linked to other physiological parameters, such as blood pressure and pulse rate, measuring this change would reveal a person's health and mental state.
In experiments, the team beamed electromagnetic waves with a frequency range of about 100 gigahertz at the hands of test subjects.
They measured the frequency of the electromagnetic waves reflecting off the subjects' skin while they relaxed and then after exercise. The reflected signal closely matched their modelled results for skin containing an array of tiny helical antennas.
Remote lie detectorInitially, the experiments were carried out in contact with the subjects' hands, to reduce diffraction effects. But even at a distance of 22 centimetres, the researchers found a strong correlation between subjects' blood pressure and pulse rate, and the frequency response of their skin.
Agranat emphasises that the research is at an early stage, but recognises potential applications. "You could make a lie detector that does not require any connections to the person being tested," he says.
Not everyone is convinced, however. "It's a really interesting idea," says Philip Chadwick, director and researcher at MCL, a company that consults on the effects of electromagnetic fields on humans.
But Chadwick is concerned that the resonance shown in the experimental data seems too sharp to be biological. "People are made of squishy wet stuff, and any resonance will be very damped out," he explains. "This sort of sharp resonance at this frequency has never been observed before."
Agranat admits that his team is reporting a new phenomenon but explains that no-one has considered the shape of the skin ducts before. "The response is governed, not by the chemical composition of the tissue, but by the morphology – because it looks like a coil, it behaves the way it behaves."
Journal reference: Physical Review Letters (vol 100, article 128102)