Smaller sensors on the way?

Certain bands of the electromagnetic spectrum are useful for specific sensing applications, whether chemical detection or thermal imaging. Terahertz frequencies, for instance, can readily penetrate clothing and paper and so are finding use at airports in the form of full-body scanners. These systems are relatively big though; shrinking both the radiation source and detector size would make them potentially more mobile. Tao et al. have combined a micromechanical cantilever system with a metamaterial-engineered split-ring resonator. The cantilever array is made from a bilayer of two metals, the different thermal properties of which cause a cantilever to move when it absorbs heat. That heat can also be provided in form of absorbed photons. As the split-ring metamaterial can be tuned by design to operate at any desired wavelength, the authors chose its geometry to confer sensitivity to absorption in the microwave and terahertz frequency range. Moreover, they incorporated a reflector on each cantilever across the array to facilitate simple optical readout of any deflection of the cantilevers. The approach offers a relatively cheap and flexible route to designer sensor imaging arrays.