We used mid-infrared passive spectroscopic imaging to monitor the composition of components during the fermentation of sake, and to measure the infrared emission peak of glucose of a fruit (Muscat grapes). Monitoring the composition of sake components during fermentation requires the separate analysis of the liquid and gaseous components. In this report, we propose a measurement method for monitoring the liquid and gas components during the sake fermentation process. The proposed method was used to analyze two-dimensional spectral data obtained on site at a sake brewing plant, and the results on the absorption coefficient of ethanol and the luminous intensity of glucose were confirmed by FTIR. Measurements the infrared emission peak of glucose of fruit were also made using passive spectroscopic imaging.
The objective of this study is to visualize tooth hardness by mid-infrared passive spectroscopic imaging with an imaging type 2D Fourier spectrometer. Radiated light in the mid-infrared region (wavelength of approximately 10 μm) is radiated from the surface of an object with a radiation intensity that depends on the temperature of the object. Our proposed device has a multi-slit grating that prevents the cancellation of bright spots. The multi-slit grating enables an inexpensive uncooled microbolometer array sensor to acquire two-dimensional spectral information from the radiated light of the measured target without external irradiation. Because the intrinsic vibration of the molecule itself is detected in this case, the spectral characteristics are the radiation spectra due to the intrinsic vibration peak. Wavelengths that can be confirmed as absorption in active spectroscopy can be confirmed as radiation in passive spectroscopy, resulting in a negative-positive relationship. First, we measured bovine teeth with our spectrometer. A radiation peak assigned to hydroxyapatite, the main component of teeth, was detected. Next, to obtain the relationship between the tooth hardness and spectrum, the micro-Vickers hardness of the tooth surface was measured. By peak deconvolution, we found a negative correlation between the hardness and peak area ratio of the crystalline and amorphous hydroxyapatite phases. The results of this study will be used in the future for non-invasive and simple risk prediction of caries formation.
We developed a one-shot passive Fourier spectrometer to integrate with wearable devices for non-invasive blood glucose measurements. The apparatus was designed with a N.A. of 0.77 for passive spectroscopy of the living body. The field curvature due to the increased N.A. was improved by combining an imaging lens with a phase shifter. Because the apparatus was configured with two lenses, the transmission was high and the optical axis length was 14 mm. In addition, the apparatus was equipped with a multi-slit to prevent loss of interference sharpness. The multi-slit was designed with 5 lines with aperture patterns that enabled the detection of glucose. We measured a blackbody to evaluate the apparatus.
We had already reported that blood glucose levels of internal bodies were able to be measured by the proposed mid-infrared (LWIR: 8-14μm) passive spectroscopic imager from a distance. The mid-infrared passive spectroscopic imager, whose sensitivity is very high because of the proposed multi-slit array technology, is able to detect and analyze radiations from body heats. Expanding the wavelength region to 3 to 20μm will realize the measurement of lactic acids and ketone bodies. Lactic acid levels, whose emission peak are 5.65μm etc., are an indicator of fatigue. Ketone bodies, whose emission peak are 4.65μm etc., are an indicator of metabolic effects of dieting. On the other hand, transmission type lens requires AR(Anti-reflection) coating whose band pass is theoretically narrow around 8 to 14μm. But our passive spectroscopic imager is able to be constructed by the wavelength-independent reflection optics. In this report, we mentioned the broad band, whose wavelength was 3 to 20μm, reflective optics spectroscopic imager using free-form mirror lens units (provided by NALUX Co., Ltd.) with a micro-bolometer array sensor.
We developed a mid-infrared passive spectroscopic imaging apparatus that uses an uncooled micro-bolometer array sensor as a light-receiving device. This apparatus makes it possible to acquire component information such as that of glucose directly emitted from the skin without a light source. However, it is difficult to obtain the background for spectroscopic measurements inside the human body. In this paper, we propose a background correction method for calculating the spectral characteristics from the acquired spectral emission intensity. The proposed method estimates the emitted light through a fitting calculation using Planck’s law as a basis function.
We aim to measure the glucose concentration in the body through passive mid-infrared spectroscopy using a palm-sized imaging two-dimensional Fourier spectrometer. Radiation in the mid-infrared region (at a wavelength of approximately 10 µm) is emitted from the object surface, with the intensity of the radiated light corresponding to the object temperature. Passive spectroscopy acquires component information from the spectral intensity of the radiated light emitted from the object without a light source. Intrinsic vibrations of molecules in the object itself are detected, and the spectral characteristics are thus the emission spectrum of intrinsic vibration peaks. In contrast, conventional active spectroscopy irradiates the measurement target with light and acquires spectral characteristics from the reflected light. Molecular vibrations excited by the light source are measured, and the spectral characteristics are thus absorption spectra of the energy absorbed at the eigenfrequency of the molecule. The wavelengths that are confirmed as absorption wavelengths in active spectroscopy are confirmed as emission wavelengths in passive spectroscopy. Active spectroscopy and passive spectroscopy thus have a negative–positive relationship. The imaging-type two-dimensional Fourier spectrometer (7 to 14 µm) used in past measurement has transmission optics. Using three Ge lenses for the front lens, objective lens, and imaging lens, we constructed reflective optics using reflective mirrors for the objective and imaging lenses. The reflective mirror guarantees flatness and high spectral reflectance over a wide bandwidth (3 to 20 µm), and the measurement bandwidth is thus extended.
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