The paper deals with a novel setup of a Hadamard transform spectrometer (HTS) which encoding mask is realized by a micro mirror array. In contrast to other applications of an HTS the mirrors of the array are not statically switched but dynamically driven to oscillate at the same frequency. The Hadamard transform is obtained by shifting the phase shift of oscillation. The paper gives a brief introduction in the entity of the Hadamard transform technique. The driving and detection circuits are presented and first measurement results are discussed.
A novel characterization method for MEMS devices based on the combination of measurement and simulation results is introduced on the example of an electrostatically actuated micro mirror array. The aim of this method is to determine geometrical parameters and built-in mechanical stress on the base of the measured eigenfrequencies. A Laser Doppler interferometer and a signal analyzer are used to determine the frequency response function (FRF) of the micro mechanical structure and the eigenfrequencies are calculated. For the numerical simulation of the micro mirrors behavior the finite element (FE) model is used and a series of nonlinear coupled-field analysis and pre-stressed nonlinear modal analysis have been performed. Hence the dependence of the eigenfrequencies on geometrical parameters and built-in mechanical stress is obtained. The comparison to the measured frequencies yields in values for the searched parameters that are mean values for the entire micro mechanical structure. The presented method is very efficient because it determines several characteristics of a MEMS device on the base of only one measured frequency response function. The article demonstrates that a sufficient accuracy is achieved and stress values are calculated that are hardly ascertainable using common measurement methods.
The paper presents a novel kind of Hadamard transform optic. First investigations are made with a micro mirror array in a Hadamard transform spectrometer (HTS) whereby the usually used detector array is replaced by the micro mirror array. All the mirrors are imaged onto a single detector. The measurement is performed using a Hadamard matrix, i.e. while each detector reading a certain combination of mirrors given by the matrix is reflecting the light towards the detector. All the rest of them are reflecting the light beside it. The consequence is an improvement of the signal to noise ratio (SNR). The novelty of the realized spectrometer is that in contrast to other applications the mirrors are not statically switched but they are forced to oscillate at their resonant frequency. By this way a special Hadamard matrix can be used that improves the SNR best.