Polarized light diffuse reflectance FT-NIR MEMS spectrometer enabling the detection of powder samples through a thin plastic layer

Abstract

Polarized scattered light Fourier transform infrared (FTIR) spectroscopy is used for measuring the absorbance of highly scattering materials overcoming the multiple scattering effect. It has been reported for in vivo for biomedical applications and in-field for agricultural and for environmental monitoring. In this paper, we report a polarized light microelectromechanical system (MEMS)-based FTIR in the extended near infrared (NIR) that utilizes a bistate polarizer in a diffuse reflectance measurement setup. The spectrometer is capable of distinguishing between single backscattering from the uppermost layer and multiple scattering from the deep layers. The spectrometer has a spectral resolution of 64cm−1 (about 16 nm at a wavelength of 1550 nm) and operates in the spectral range of 4347cm−1 to 7692cm−1 (1300 nm to 2300 nm). The technique implies de-embedding of the MEMS spectrometer polarization response by normalizing its effect; this is applied on three different samples: milk powder, sugar, and flour in plastic bags. The technique is examined on different scattering size particles. The scattering particles diameter’s range is expected to vary from 10 µm to 400 µm. The absorbance spectra of the samples are extracted and compared to the direct diffuse reflectance measurements of the samples, showing good agreement. By using the proposed technique, the calculated error for the flour was decreased from 43.2% to 2.9% at 1935 nm wavelength. The wavelength error dependence is also reduced.