Novel far infrared imaging sensor based on the use of titanium-nickel shape memory alloys

In this paper we describe a novel imaging sensor design¹ that uses the thermo-mechanical properties of nickel-titaniu (NiTi) shape memory alloys (SMAs) for detecting far infrared radiation (FIR). A thin NiTi SMA cantilever is coated with a FIR absorbing layer on one surface, while the other is coated with a highly reflecting metallic layers such a s gold. Upon absorption of FIR, the temperature of the cantilever changes. This causes the tilt angle of the cantilever to change as well. The deflection is very large if the temperature change coincides with the temperature range of the phase transformation of the NiTi SMA. The detection of the mechanical movements in the cantilever is achieved by illuminating the reflective side using a visible laser beam. A Michelson interferometer is used to covert the reflected light into optical modulation. In doing t his, very small displacement in the cantilever can be visualized as laser intensity variation. A single element device has been fabricated for this purpose and our initial experimental result have demonstrated the successful detection of FIR. An estimati n of angular deflection per unit change of temperature suggests that our approach can offer sensitivity higher than the reported design based on the use of bi -material strips. We envisage that a tw -dimensional array of such devices can lead to the possibi lity of realizing a practical lo -cost infrared imaging device operating under room temperature conditions.