Believe it or not, researchers at the University of Wollongong (New South Wales, Australia) have discovered that peeling adhesive tape emits unpolarized terahertz radiation. The researchers found that the mechanism of this emission is most likely triboelectric charging, or tribocharging for short–a transfer of electric charge (most likely ions) between two materials; the same process that allows a person to build up a static charge by scuffing one’s feet on carpet, only to experience a rapid discharge or “shock” after touching a conductive material.
When certain adhesive tapes (Scotch Magic 810, for example) were unwound in a fixture and measured with a Fourier-transform spectrometer with a spectral resolution of 0.12 THz and signal-to-noise ratio of 1000:1, a broad peak was observed at 2 THz, then a dip, and then a steady rise to 18 THz. Heating effects were ruled out as the emission mechanism, especially since the terahertz emission did not correlate with the adhesive strength of the tape used. The non-monotonic spectrum (initial peak) in the terahertz output was consistent with the tribocharging mechanism, followed by “bremsstrahlung” radiation upon discharge. In the bremsstrahlung process, the charges decelerate, which, together with the absorption of the surrounding atmosphere, results in the observed spectrum. The researchers say that a further understanding of this mechanism could lead to the development of inexpensive terahertz sources emitting at wavelengths from 1 to 20 THz. Contact Roger A. Lewis at [email protected].
