A compact optical ethylene monitoring system

In various fruit storage applications precise and continuous ethylene detection is needed. The aim of this work is the development of a miniaturised mid-infrared filter spectrometer for ethylene detection at 10.6 µm wavelength. For this reason optical components and signal processing electronics were developed, tested and integrated in a compact measurement system. The present article describes the optical components, the integration of the optical system, electronics and results of gas measurements. Next to a Silicon-based macroporous IR-emitter, a miniaturised absorption cell and a detector module for the simultaneous measurement at four channels for ethylene, two interfering gases and the reference signal were integrated in the optical system. Optical filters were attached to fourfold t hermopile-arrays by flip-chip-technology. Silicon-based Fresnel multilenses were processed and attached to the cap of the detector housing. Because of the high reflection losses at the silicon-air surface the Fresnel lenses were coated with Antireflection layers made of Zinc sulphide. For the signal processing electronics a preamplification stage and a Lock-in-board has been developed. First ethylene measurements with the optical system with miniaturised gas cell, Silicon-based IR-emitter, a commercial thermopile detector and the self-developed system electronics showed a detection limit of smaller than 20ppm.