IR Cutoff Filter Research Articles

2021 Elijah High-Altitude Balloon Payload

The 2021 WSGC Elijah High-Altitude Balloon Payload Team focused their projects on the upcoming 2024 solar eclipse. These included solar sensing, solar imaging, and the study of cosmic radiation. The solar sensing project involved collecting flight data such as altitude, temperature, and pressure. In addition to this data, quantitative UVA, UVB, light intensity, and solar energy values using various sensors and solar panels. Solar imaging utilized an action camera with solar, IR, and IR cut-off filters in conjunction with a 360-degree camera that captured the entire payload’s flight. The radiation shielding project focused on studying the effectiveness of low-density polyethylene as a radiation shielding material by comparing observations collected by shielded and unshielded Geiger counters. To observe radiation originating from nearby star systems, a particle detector consisting of a scintillator coupled to a silicon photomultiplier was constructed.

Optical Properties of ZnO/Al/Ag/ZnO Multilayers as Near Infrared Cut-off Filters

Various ZnO/metal/ZnO multilayers were fabricated and their optical properties were investigated. Top and bottom ZnO layers were formed by sol-gel method and mid-metal layers were deposited by thermal evaporation for precise control of thickness. After the fabrication of ZnO/Ag/ZnO structure, the transmittance increased to 72%. Adding Al to middle Ag layer, the ZnO/Al/Ag/ZnO structure reduced the near IR transmission in half with 40% optical transmittance in entire visible region. This oxide/double metal/oxide multilayers show the huge potential for building integrated photovoltaics as near IR cut-off filters.

Production of electricity from ethanol and ammonium based wastewater via photo-electrochemical process

A PEC cell is tested with two types of electrolyte (e.g., electrolyte pollutant and alcohols) under irradiation with a Xenon lamp through an IR cutoff filter (IRA-25S). The main objective of this study is to optimize the production of electricity from wastewater containing ethanol and ammonium using a photo-electrochemical (PEC) process. DOE statistical analysis was used to optimize the parameters that influenced the process, namely the active area of photoanode and the concentration of electrolyte. The significance level of the active area of a photo-anode was found to be within 0.5–1.0 cm2, the electrolyte concentrations were found to be 5–20% by volume and the types of electrolytes used included ammonia and an ethanol aqueous solution. For the optimization process, the response surface method (RSM) using central composite design (CCD) was applied to generate a map of the response. The results were statistically analyzed using an analysis of variance (ANOVA) to identify the factors that influence the production of the current density from a PEC cell. An electrolyte containing ethanol was found to produce higher currents than electrolyte containing ammonium. The optimum parameters that produced the maximum current density of 0.77 mA/cm2 were achieved using an ethanol electrolyte with an active area of 0.73 cm2 and a concentration of 20% by volume. Confirmation experiment showed that the current density is about 97% similar to the expected value that is 0.75 mA/cm2.

Color Restoration of RGBN Multispectral Filter Array Sensor Images Based on Spectral Decomposition.

A multispectral filter array (MSFA) image sensor with red, green, blue and near-infrared (NIR) filters is useful for various imaging applications with the advantages that it obtains color information and NIR information simultaneously. Because the MSFA image sensor needs to acquire invisible band information, it is necessary to remove the IR cut-offfilter (IRCF). However, without the IRCF, the color of the image is desaturated by the interference of the additional NIR component of each RGB color channel. To overcome color degradation, a signal processing approach is required to restore natural color by removing the unwanted NIR contribution to the RGB color channels while the additional NIR information remains in the N channel. Thus, in this paper, we propose a color restoration method for an imaging system based on the MSFA image sensor with RGBN filters. To remove the unnecessary NIR component in each RGB color channel, spectral estimation and spectral decomposition are performed based on the spectral characteristics of the MSFA sensor. The proposed color restoration method estimates the spectral intensity in NIR band and recovers hue and color saturation by decomposing the visible band component and the NIR band component in each RGB color channel. The experimental results show that the proposed method effectively restores natural color and minimizes angular errors.

Recovering the Colors of Objects from Multiple Near-IR Images

This paper proposes an algorithm for recovering the colors of objects from multiple near-infrared (near-IR) images. The International Commission on Illumination (CIE) color coordinates of objects are recovered from a series of gray images captured under multiple spectral near-IR illuminations using polynomial regression. The feasibility of the proposed algorithm is tested experimentally by using 24 color patches of the Color Rendition Chart. The experimental apparatus is composed of a monochrome digital camera without an IR cut-off filter and a custom-designed LED illuminator emitting multiple spectral near-IR illuminations, with peak wavelengths near the red edge of the visible band, namely at 700, 740, 780, and 860 nm. The average color difference between the original and the recovered colors for all 24 patches was found to be 11.1. However, if some particular patches with high value are disregarded, the average color difference is reduced to 4.2, and this value is within the acceptability tolerance for complex image on the display.

Measurement of the chief ray angle of mobile phone camera

The chief ray angle (CRA) of a mobile phone lens is related to the acceptance angle of the IR cutoff filter and micro lens array. The CRA of a lens need to be within an allowed value, otherwise image blurring or vignetting occurs. However, because of the compact size of mobile phone camera lenses, it is not easy to measure the CRA accurately. In this paper, we suggest a new method to measure the CRA of high-quality mobile phone camera lenses accurately using a laser beam as a light source and a plane mirror to collimate the beam in a double pass configuration. When the plane mirror is tilted to the same angle as the lens CRA, the spot center does not change, irrespective of the longitudinal position of the plane mirror. We manufactured the reference optics, which consisted of four spherical lenses, to verify our method. We found that our new CRA measurement method has 0.65° of measurement uncertainty for 15° CRA, which satisfies phone camera makers’ requirements.

IR Cut-Off Filter가 차단하지 못한 미량의 적외선이 디지털화상에 미치는 영향 분석

분광특성의 차이로 필름은 자외선에 민감한데 반해 디지털 카메라의 센서는 적외선에 굉장히 민감하다. 이에 따라 CCD 또는 CMOS를 사용하는 모든 디지털 카메라에는 IR Cut-Off Filter가 센서전면에 장착되어 있다. 이상적으로 100% 적외선을 차단하여야 하지만 실험 결과 완전히 적외선을 차단하지 못하고 있었으며, 각 카메라마다 적외선 투과량 또한 달랐다. 따라서 본 연구는 디지털 카메라에 장착되어 있는 IR Cut-Off Filter의 기계적 특성에 의해 투과되는 미량의 적외선이 디지털 화상이미지에 끼치는 영향을 분석하는 데 그 목적이 있다. UV필터를 장착한 상태(적외선 투과상태)와 UV-IR필터를 장착한 상태(적외선미투과상태)를 비교분석한 결과, 잡음(Noise)과 색 재현력 평가에서는 그 차이가 미세하거나 거의 동등한 수준이지만, 동적 폭(Dynamic Range)과 해상도에는 IR Cut-Off Filter를 통해 투과되는 미량의 적외선이 어느 정도 영향이 있음을 확인할 수 있었다. Films are sensitive to ultraviolet rays and in contrast, digital camera sensors are extremely sensitive to infrared rays due to the differences in spectral characteristics. As a result, all digital cameras that use CCD or CMOS are equipped with IR Cut-Off Filter on the overall sensor. Complete block out of infrared rays is ideal, but the actual experiment results showed that infrared rays were not being blocked out completely. Infrared permeability was also different for each camera. Therefore, this study aims to analyze the effect of the minute quantities of infrared rays, which get transmitted due to mechanical properties of IR Cut-Off Filters that are installed on digital cameras, on digital picture images. The results obtained by carrying out a comparative analysis of a UV Filter (infrared transmitting state) and a UV-IR Filter (infrared blocked out state) are as follows. It was confirmed that the minute quantities of infrared rays do affect dynamic range and resolution to some extent, despite the little or no difference in noise and color reproduction.

디지털 자외선 사진을 위한 적정 디지털 카메라 시스템

자외선 사진은 범죄수사, 고고학, 피부의학 등 다양한 분야에서 활용되고 있다. 과거 자외선 사진은 일반적인 흑백필름을 이용하여 촬영하는 경우가 대부분이었는데, 그 이유는 필름의 감광유제로 사용되는 할로겐화은(AgX)성분이 카메라의 센서인 CCD(Charge Coupled Device)혹은 CMOS(Complementary Metal-Oxide-Semiconductor)에 비해 자외선에 민감하기 때문이다. 이에 본 논문에서는 보급형 디지털 카메라를 사용하여 자외선 사진의 화질을 개선시키고, 자외선 사진을 위한 최적의 디지털 카메라 특성을 찾는 것을 목적으로 하였다. 이를 위해 디지털 카메라의 적외선 차단 필터를 제거하고, 자외선 투과필터의 개조를 통해 자외선 사진의 화질향상 여부를 검증하였다. 또한 센서의 종류와 크기, 화소수에 따른 자외선 사진의 재현성을 화질측정 요소들을 통해 분석하였으며, 이를 통해 디지털을 이용한 자외선 사진에 가장 적합한 카메라 특성을 찾고자 하였다. 나아가 본 논문을 통해 일반 디지털 카메라를 활용한 자외선 촬영 시스템을 구축할 수 있을 것이며, 이는 결국 디지털 자외선 사진의 폭넓은 활용에 기여할 것으로 기대된다. Reflected-Ultraviolet photography is applied to the evidence of crime, Archaeology, and Dermatology. In the past, Ultraviolet photography was done with standard black-and-white film. Because emulsion of film is more sensitive to near UV light than CCD(Charge Coupled Device) or CMOS(Complementary Metal-Oxide-Semiconductor)of digital camera. In this research, we purpose to improve qulity of ultraviolet photographs and to find out the best alternative digital camera by utilizing a cunsumer digital camera. To achieve theses, we removed IR cutoff filter from digital camera. And by using modified UV pass filter, we verified the increase of image resolution of digital ultraviolet photographs. Also, we analyze reproducibility of digital ultraviolet photographs according to type, size, pixel of image sensor. Furthermore, this research resulted in the development of an practical digital camera system by utilizing a cunsumer digital camera. Eventually, it will contribute to practical use in the various field of digital ultraviolet photographs

Fluorescence Imaging with UV-Excitation for Evaluating Freshness of Rice

To measure the freshness of rice quickly and conveniently, we used a fluorescence imaging method with UV-excitation. The system consists of two UV-A fluorescent lamps and a blue LED with a band-pass filter, a cooled CCD camera with an IR cutoff filter to capture the fluorescence image on a PC, and image processing software for measuring the fluorescence intensity of the image. In a darkened box, sample materials are placed on a stage painted with non-fluorescent, flat black paint to minimize background scattering. Testing stored samples of unhulled rice and brown rice, we found a high correlation between the fluorescence intensity and conventional indices such as free fat acidity and guaiacol reaction. The fluorescence intensity increased as the storage temperature rose or the storage period lengthened. Eating quality decreased significantly as the fluorescence intensity rose. These results show that this system can estimate the loss of eating quality that occurs during storage of rice. Thus, fluorescence intensity could provide an effective and convenient way to evaluate rice quality.

Control of Spectral Photosensitivity in Stacked Color Sensors: Proposal and Theoretical Analysis

To capture a realistic and pleasing full-color two-dimensional representation of a scene, we propose and analyze stacked color sensors that incorporate a distributed Bragg reflector (DBR) with a phase-compensation layer between a blue absorption layer and a green absorption layer. Because incident light on color sensors is not coherent, photosensitivity is calculated for partially coherent light. In the blue absorption region, it is found that the peak wavelength mainly depends on the thickness of the blue absorption layer, and the spectral width is dominantly controlled by the Bragg wavelength λB of the DBR when λB > 0.4 µm. It is also revealed that the phase-compensation layer plays an important role in controlling the spectral shape of the photosensitivity. From the viewpoint of a measure of the goodness, the Bragg wavelength λB and the thickness of each absorption layer are optimized for bare color sensors and color sensors capped with an IR cutoff filter.

Cathodic electrodeposition of oxide semiconductor thin films and their application to dye-sensitized solar cells

Cathodic electrodeposition of titanium dioxide (TiO 2) and zinc oxide (ZnO) thin films has been studied in the aim of developing cost-effective alternative routes to the photoelectrode materials for dye-sensitized solar cells (DSCs). Preparation of porous anatase TiO 2 thin film modified by cis-dithiocyanato bis(4,4′-dicarboxylic acid-2,2′-bipyridine)ruthenium(II) (N3) dye has been achieved by a three-step process: cathodic electrodeposition of a Ti hydroxide thin film from an acidic aqueous solution containing TiOSO 4, H 2O 2 and KNO 3, heat treatment of the film at 400 °C and chemical adsorption of dyes from solution. The photocurrent action spectrum measured at the N3-modified TiO 2 thin film electrode in contact with I −/I 3 − redox electrolyte solution revealed incident photon to current conversion efficiency (IPCE) of 37% in the visible range. While TiO 2 needed heat treatment for crystallization, direct electrodeposition of crystalline ZnO was possible from an aqueous solution of Zn(NO 3) 2. Addition of N3 to the deposition bath made it possible to synthesize porous ZnO/N3 hybrid thin film in one step. IPCE of 24% has been achieved for this film. A sandwich cell using the electrodeposited ZnO/N3 hybrid thin film photoelectrode measured I sc=0.61 mA/cm 2, V oc=0.46 V, F.F.=0.46 and η=0.13% under illumination by an artificial light source (500-W Xe lamp equipped with a <420-nm and an IR cutoff filters, intensity=100 mW cm −2), being the first example of a real working DSC fabricated without any heat treatment.

Shallow water bathymetry using integrated airborne multi-spectral remote sensing

An integrated low cost airborne multi-spectral remote sensing system is described and evaluated for remote sensing for shallow water bathymetry. The system consists of: two 35mm motor driven reconnaissance cameras using colour and colour infrared film. Three optically filtered (including removable internal IR cut-off filters), electronically shuttered CCD progressive scan cameras (Sony XC-7500) integrated into an airborne direct digital recording system using a PC processor, a 32-bit RGB analogue to digital conversion card and Zip disk storage. Two CCD based imaging spectrometers providing approximately 10nm bandwidth spectral data across the CCD spectrum (400nm to 1000nm). These CCD cameras were used with a variable interference filter fixed in front of the sensor surface. This provided a 'rainbow' image of the ground varying across the image from 400nm to 700nm (visible) and 700nm to 1000nm. Field studies were undertaken to evaluate the performance of digital multi-spectral (DMV) imagery, supplementary reconnaissance photography (SRP) and VIFIS imaging spectrometry for mapping shallow water bathymetry. The results indicate good performance in shallow water and suggest that with further refinement the system could be used to give a quick comprehensive estimate of shallow water depths

Infrared filters and analyzers of the composition of substances based on them

Results of investigations on designing band dispersion and dispersion-interference filters for the 4–30 μm IR range and cutoff filters for the 50–300 μm region are presented. Analyzers of the composition of a substance that are designed on the basis of band IR filters and analysis procedures are described.