LIGA-Based Tunable Optical Filters for Multispectral IR Imagers and Gas Analyzers

The Honeywell Technology Center and the University of Wisconsin have developed microelectromechanical tunable IR filters for IR spectral analysis. The filters and integral actuators are fabricated by the MEMS LIGA process for making high-aspect-ratio metallic microstructures. The tunable IR filter is a mechanically deformable structure consisting of an array of parallel metal plates joined by spring flexures and driven by an integral linear actuator. The plates form an array of identical waveguides whose transmittance properties can be varied by changing the spacing between them. The filter can be coupled with IR detectors or even 2-D imaging arrays such as Honeywells uncooled IR focal plane arrays to form IR detection and imaging systems. In this program, the transmission filter concept was verified and tunable filters were demonstrated. Filters with a tunable range for the transmission wavelength cutoff from 8 micrometers to 25 micrometers were demonstrated. An integral linear electromagnetic actuator technology was developed to drive the tunable filters. Linear actuators with large travel - 1.0 mm and large force 2-3 mN were demonstrated. The initial feasibility of using the tunable IR filters for gas identification and analysis was shown with a laboratory demonstration of a gas point detector.