Research And Development Of NIR Spectrometers Based On AOTF Technology

The near infrared spectroscopy (NIR) analysis method, as a new highly efficient analytical technique, was used in many trades such as petrochemical, chemical industry, agriculture, food, pharmacy, clinic, papermaking, etc, with its advantage of better accuracy and repeatability, shorter time of testing, simpler operation and easy actualizing on-line analysis. The near infrared region of the spectrum extends from 750nm to 2500nm. Most organic materials have excellent reflectance or transmittance properties at these wavelengths. The absorption of NIR radiation by organic molecules is due to overtone and combination bands primarily of O-H, C-H, N-H and C=O groups whose fundamental molecular stretching and bending absorb in the mid-IR region, the amount of information is extremely abundant. The technology of the near infrared spectrum, got the extensive concern in practical application in recent years quickly, known as "the spectrum of the world in future ".In this paper, there are four main parts: optical system, optic-electrical detect module, AOTF (Acousto-optic tunable filter) RF drivers. AOTF is a special optical filter that is based on the theory of the interaction between acoustic and optical waves in an aniaxial birefringent crystal. The output wavelength change of the AOTF depends on the refractive index change of the medium, which is caused by the frequency change of incident ultrasonic wave onto the medium. AOTF has many advantages such as high speed, wide (unable wavelength range and large incident angle aperture without higher order of diffraction, and so on. The technology of AOTF has been more and more applied in the online analyze of the production.Whether system is considering portable instrument characteristic of instrument fully to design, adopting several new techniques and new design methods to realize.1 , An optical fibers with collimation system is used as the light source so that the parallelism of the light beam is improved.2, A MCU(Micro Controlling Unit) controls DDS(Direct Digital Synthesizer) to realize the frequency synthesis, a keyboard controls the continuous or single step frequency scanning, the wavelength and related frequency are displayed on the display monitor.3, Artificial intelligence algorithms were developed for calibration through the regression of spectral data against corps moisture content measurements.The spectral range of the spectrometer is from 800nm~1700nm and the spectral resolution is about I nm~5.5nm. Because the whole system design have consulted the modern portable spectrometer, this spectrometer has smaller size, lighter weight, lower power dissipation, easier way to control than most...