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Research Papers

Experimental Design and Algorithmics for a Multichannel Spectral Data Acquisition System

[+] Author and Article Information
Konrad Duerr, Rudolf J. Seethaler, Jonathan F. Holzman

Faculty of Applied Science, School of Engineering, University of British Columbia, Kelowna, BC, V1V 1V7, Canada

J. Dyn. Sys., Meas., Control 131(5), 051011 (Aug 19, 2009) (5 pages) doi:10.1115/1.3155014 History: Received August 11, 2008; Revised April 22, 2009; Published August 19, 2009

An optically-encoded mechanical modulation system and an electrical signal extraction algorithm are introduced. The system employs the beam chopping in a highly parallel scheme to impart multiple modulation channels onto the spectrum of a white-light source. The optically-multiplexed beam is directed through an experimental sample, and the absorption of the sample at each of the individual modulation channel wavelengths is resolved. A MATLAB -based parallel frequency-selection algorithm is ultimately used to resolve the signals. The low-noise benefits of optical lock-in detection and the practicality of parallel encoding/extraction are demonstrated in this design.

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Copyright © 2009 by American Society of Mechanical Engineers
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Figures

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Figure 1

The multichannel optical chopper blade. The blade is patterned out of opaque black emulsion on a transparent film, and the film is mounted between two Plexiglas plates. The inset shows the linear focal spot applied across each of the ten channels.

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Figure 2

The spectral acquisition system for the multichannel optical chopper. The broadband optical source is encoded in the source module, and the spectral absorption data are extracted from the sampling module. Cylindrical lenses (CL) and spherical lenses (SL) are used for asymmetric and symmetric focusing, respectively.

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Figure 3

Flowchart for the MATLAB -based algorithm showing the frequency-normalization process and amplitude-normalization process for the multichannel spectral data acquisition system

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Figure 4

Theoretical results for the sampling beam in the (a) time-domain and the (b) frequency-domain. The symmetry of the multichannel optical chopper blade manifests itself through the periodicity in the time-domain signal of (a) and the peaks in the frequency-domain signal of (b).

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Figure 5

Experimental results for the sampling beam in the (a) time-domain and the (b) frequency-domain, and (c) data points corresponding to ten independent spectral measurements acquired with a single-channel lock-in amplifier. The symmetry of the multichannel optical chopper blade manifests itself through the periodicity in the time-domain signal of (a) and the peaks in the frequency-domain signal of (b). The results of the ten independent single-channel measurements in (c) deviate from the multichannel spectral data by at most 2%.

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Figure 6

Experimental results for the sampling beam amplitudes as a function of wavelength for the multichannel optical chopper spectral configuration. The beam from the source module passes through an OG515 optical filter, and the encoded channel data are extracted from the sampling module. Note that only six of the designed ten channels, with spacings of 8 nm, are needed to map the approximately 50 nm rising edge of the OG515 highpass response.

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