Optimal probe geometry for near-infrared spectroscopy of biological tissue

The results of this study clarify the influence of probe geometry on spectroscopic measurements obtained from the surface of a turbid biological tissue. We show that the transition between the measurement of the predominantly backward-propagating and the predominantly forward-propagating photon fluxes is marked by the separation between the source probe and the detector probes at which the dependence of the fluence on small changes in scattering coefficient vanishes. This is the probe separation at which a variable scattering background has the least influence on the measurement of optical absorption in turbid materials. Estimates of the optimum probe spacing for typical values of absorption and scattering coefficients of soft tissue in the near-infrared spectral region (800-2500 nm) are derived from an analytical solution of the diffusion equation. The estimates were verified by Monte Carlo simulations and experiments on particle suspensions with optical properties similar to those of skin tissue.     

气体中痕量水蒸气测量技术进展

气体中水蒸气含量测量在工业生产和科研领域发挥至关重要的作用。随着许多工业生产和科研领域对气体水分含量更加严格的测试要求,对于气体中水蒸气含量测量灵敏度的要求也越来越高。目前测量nmol/mol痕量水分的仪器方法有可调谐二极管激光吸收光谱法、光腔衰荡光谱法、大气压离子质谱仪法;达到这个痕量水平的传感器类测量技术有石英晶体微天平法、冷镜露点法、阻容法、电解法。针对这些测量方法的优缺点以及今后的发展趋势进行了论述分析,通过克服测量过程中的干扰因素,可在一定的程度上提高痕量水含量的测量准确性,对促进痕量水含量准确测量技术的发展有所裨益。     

基于抽象工厂模式的机载总线数据通用化处理方法研究

在机载测试技术中,机载数据总线数据量急剧增加,数据处理越来越趋于复杂化,软件可复用性的要求越来越高。为满足这些需求,将抽象工厂模式的思想应用到航空总线数据处理中,根据抽象工厂的特点和适用场景,将总线数据按照类型进行实例化,形成对外统一的接口,然后对不同的总线接口进行数据处理。该接口只与总线的协议标准和技术特点有关,不依赖于具体信号,因此实现了数据处理的通用化,突破了原来面向各个接口信号分别处理的思想,从而实现了软件可复用的要求,提高了机载总线数据处理的效率和可靠性。     

Regional difference of water content in human skin studied by diffuse-reflectance near-infrared spectroscopy: consideration of measurement depth

Diffuse reflectance (DF) spectra in the 1250-2500 nm region were measured in vivo for the skin of the forehead, cheek, jaw, elbow, volar forearm, palm, knee, and heel of seven healthy volunteers, using a Fourier transform near-infrared (FT-NIR) spectrophotometer with a fiber-optic probe. Apparent regional differences of water content in the skin, as estimated from the diffuse reflectance NIR spectra, are discussed in relation to the influence of measurement depth. The NIR spectra were collected with or without a 300 microm gap between the fiber-optic probe and the skin surface. For comparison, in vitro NIR spectra of stratum corneum sheets equilibrated at 41, 50, 63, and 81% relative humidity, at 25 degrees C, were also obtained. There was a difference in the ratio of the two water bands centered near 1450 nm and 1900 nm between the contact and non-contact measurements. In addition, regional differences of water content calculated from the peak height of the 1900 nm water band, which was normalized to the peak height of the 2175 nm amide band, were compared. The results of Monte Carlo simulation indicated that the apparent regional differences arise at least in part from differences in the measurement depth due to differences in specular reflection at the skin surface and in the thickness of the stratum corneum.     

Polychromatic transmissometer for in situ measurements of suspended particles and gelbstoff in water

The beam attenuation coefficient is an optical parameter that sensitively depends on suspended and dissolved substances in water. Its measurement is not only of interest for an understanding of the radiative transfer in a water column. With appropriate algorithms for data interpretation, it also allows a fast determination of absorbing and scattering matter as time-series measurements or depth profiles that cannot easily be obtained with other methods. An instrument has been developed for measuring spectral attenuation coefficients over a wavelength range from 340 to 785 nm. The optical path length can be set between 0 and 400 mm. This allows application in a wide range of turbidity in coastal and inland (case 2 and case 3) waters and a calibration of the instrument during in-situ measurements. This makes the instrument suitable for long-term applications in which signals from conventional instruments would degrade owing to the biofouling of optical windows. From the data, the amount and the size distribution of suspended particles and the specific absorption of dissolved organic matter are derived in real time. Algorithms based on Monte Carlo methods are available for a classification of transparent particles and phytoplankton.     

经验模态分解和空间滤波在两相流速度测量中的应用

在利用空间滤波和电容传感器测量两相流速度时,需要准确测量电容传感器输出信号的带宽.针对此问题提出一种利用经验模态分解算法来测量传感器带宽的方法.文章首先介绍电容传感器的空间滤波效应和经验模态分解的基本原理,并给出固体速度和电容传感器输出信号带宽之间的关系.然后将经验模态分解和平滑滤波器结合对测量信号进行平滑处理,测量处...     

Direct and chemically-mediated absorption spectroscopy usingoptical fiber instrumentation

This paper shows various applications of optical fiber sensors to absorption spectroscopy. Sensors for the monitoring of chromium in sewage water and for the colorimetry of gasoline samples are presented together with sensors for radiation dosimetry in radiotherapy and for lighting control in museum environments. In all these sensors, a combination of broadband and multi-band spectral measurements are collected using the same custom instrumentation unit consisting of LED light sources and an optical fiber microspectrometer. Extensions of the unit to implement other sensors making use of visible spectral range are discussed. The custom instrumentation implemented to address these sensors is their key unifying feature. It opens the possibility of addressing other sensors making use of absorption-based optrodes which present an analyte-modulated absorption spectrum in the visible spectral range     

Tunable laser diode system for noninvasive blood glucose measurements

Optical sensing of glucose would allow more frequent monitoring and tighter glucose control for people with diabetes. The key to a successful optical noninvasive measurement of glucose is the collection of an optical spectrum with a very high signal-to-noise ratio in a spectral region with significant glucose absorption. Unfortunately, the optical throughput of skin is low due to absorption and scattering. To overcome these difficulties, we have developed a high-brightness tunable laser system for measurements in the 2.0-2.5 microm wavelength range. The system is based on a 2.3 microm wavelength, strained quantum-well laser diode incorporating GaInAsSb wells and AlGaAsSb barrier and cladding layers. Wavelength control is provided by coupling the laser diode to an external cavity that includes an acousto-optic tunable filter. Tuning ranges of greater than 110 nm have been obtained. Because the tunable filter has no moving parts, scans can be completed very quickly, typically in less than 10 ms. We describe the performance of the present laser system and avenues for extending the tuning range beyond 400 nm.     

测量围护结构含水率的同面散射场式电容传感器设计

目前常用的测量含水率的方法有微波法、红外线法和电容法.由于基于电容法的传感器具有分辨力高、响应速度快、体积小、结构简单等优点,被广泛应用.针对围护结构含水率测试深度的要求和测试特点,本文通过仿真和实验,对同面电容传感器探头的结构尺寸进行了优化设计,并采取了保护电极以提高其抗干扰能力;运用改进的充放电电容检测电路,设计出一种测量围护结构含水率的新型同面散射场式电容传感器,该传感器具有宽范围的测试深度和较高的测试灵敏度.     

Noncontact Material Identification and Distance Measurement Using Effective Capacitance With CdS Cells

We propose a novel noncontact sensing method for material identification and for detection of the distance between the sensor and the surface of a material by using its electrical and optical properties. In the proposed method, capacitance between the terminals of a pair of CdS cells, called the effective capacitance, is measured, and several capacitance values are obtained by changing the emission strength of the light emitting diode, thus changing the resistance value of the CdS cells. From these values, it is possible to identify the materials and to detect the distance between the CdS cells and the material. In this paper, we compare four kinds of effective capacitance measurement methods using a pair of CdS cells and describe the proposed measurement method. In addition, this paper discusses the measurement accuracy of effective capacitance values in the proposed method and demonstrates its ability to identify six material samples-clear, white, and black acrylic, clear vinyl chloride, brown bakelite, and aluminum-and to detect the distance between the CdS cells and the material.     

Optical properties of apple skin and flesh in the wavelength range from 350 to 2200 nm

Optical measurement of fruit quality is challenging due to the presence of a skin around the fruit flesh and the multiple scattering by the structured tissues. To gain insight in the light-tissue interaction, the optical properties of apple skin and flesh tissue are estimated in the 350-2200 nm range for three cultivars. For this purpose, single integrating sphere measurements are combined with inverse adding-doubling. The observed absorption coefficient spectra are dominated by water in the near infrared and by pigments and chlorophyll in the visible region, whose concentrations are much higher in skin tissue. The scattering coefficient spectra show the monotonic decrease with increasing wavelength typical for biological tissues with skin tissue being approximately three times more scattering than flesh tissue. Comparison to the values from time-resolved spectroscopy reported in literature showed comparable profiles for the optical properties, but overestimation of the absorption coefficient values, due to light losses.     

Estimation of chest-wall-induced diffused wave distortion with the assistance of ultrasound

The chest-wall layer underneath breast tissue consists of muscles and bones, which induce distortion in near-infrared diffused waves measured at distant source--detector pairs when reflection geometry is used. A priori information on chest-wall depth obtained from coregistered real-time ultrasound can be used to assist in the removal of distant measurements. We applied Monte Carlo simulation to a simple two-layer model consisting of breast tissue and a chest wall to investigate chest-wall-induced distortion. The Monte Carlo method indicates that, when more than 50% of the received photons travel through the breast tissue layer before being detected, the detected signal may be useful for image reconstruction. The results of phantom experiments obtained from the two-layer model further validate the distortion problem and demonstrate imaging improvement after distant measurements have been filtered out. Clinical examples have shown similar imaging improvements on reconstructed absorption maps. Clinical data obtained from 20 patients with the chest-wall depths of less than 2 cm from the skin surface suggest that the cutoff distances of distorted measurements are largely related to the chest-wall depth and are relatively independent of the optical properties of tissue.     

In vivo noninvasive measurement of blood glucose by near-infrared diffuse-reflectance spectroscopy

This paper reports in situ noninvasive blood glucose monitoring by use of near-infrared (NIR) diffuse-reflectance spectroscopy. The NIR spectra of the human forearm were measured in vivo by using a pair of source and detector optical fibers separated by a distance of 0.65 mm on the skin surface. This optical geometry enables the selective measurement of dermis tissue spectra due to the skin's optical properties and reduces the interference noise arising from the stratum corneum. Oral glucose intake experiments were performed with six subjects (including a single subject with type I diabetes) whose NIR skin spectra were measured at the forearm. Partial least-squares regression (PLSR) analysis was carried out and calibration equations were obtained with each subject individually. Without exception among the six subjects, the regression coefficient vectors of their calibration models were similar to each other and had a positive peak at around 1600 nm, corresponding to the characteristic absorption peak of glucose. This result indicates that there is every possibility of glucose detection in skin tissue using our measurement system. We also found that there was a good correlation between the optically predicted values and the directly measured values of blood samples with individual subjects. The potential of noninvasive blood glucose monitoring using our methodology was demonstrated by the present study.     

Photothermal Characteristics of Novel Flexible Black Silicon for Solar Thermal Receiver

In this article, a novel type of flexible black silicon used for enhancing the absorption of a solar thermal receiver is reported. The optical absorption properties of this kind of flexible black silicon with three different sizes of conical microstructure are analyzed using the finite-difference time-domain (FDTD) method and the heat transfer properties are studied using the COMSOL multiphysics heat transfer solver. The results show that flexible black silicon with small-size microstructure has the highest optical absorptance and heat transfer speed. A commercial silicon-on-insulator wafer is irradiated by an auto-scanning femtosecond laser system and then split by etching out its middle layer in 52?% hydrofluoric acid to fabricate the flexible black silicon. The obtained flexible black silicon presents very good flexibility, and its photothermal characteristics are investigated. The optical absorption spectrum test results indicate that the absorptance of the flexible black silicon is as high as 97?% in the visible spectral region and is higher than that of anodized aluminum in a broad spectral range from 250?nm to 2500?nm. The light radiation heating experiment results show that the energy absorption efficiency of the water covered with flexible black silicon is improved 13?% compared with that of the water covered with anodized aluminum. It is confirmed that as a light-absorbing and heat-transferring layer the flexible black silicon has an important potential application in exploring solar energy.     

可调谐半导体激光吸收光谱测温谱线选择

可调谐半导体激光吸收光谱(Tunable Diode Laser Absorption Spectroscopy,TDLAS)作为非接触光学测量手段,在燃烧诊断、推进系统研发中应用广泛,而吸收谱线对的选择是采用TDLAS技术进行燃气温度测量的基础和关键一步。在扫描波长-直接吸收法测量H_2O温度的实验中,首先系统地研究了谱线选择的基本原则和实现步骤,对选择原则中各指标的量化进行了重点分析;然后对中心频率在7000～7500 cm~(-1)范围内的水分子吸收谱线进行研究和筛选;最后结合数值模拟进行分析,选择了7022. 7091,7444. 3707 cm~(-1)和7185. 5962,7444. 3707cm~(-1)两对谱线,为TDLAS温度测量系统设计提供依据。     

Hyperspectral remote sensing for shallow waters. 2. Deriving bottom depths and water properties by optimization

In earlier studies of passive remote sensing of shallow-water bathymetry, bottom depths were usually derived by empirical regression. This approach provides rapid data processing, but it requires knowledge of a few true depths for the regression parameters to be determined, and it cannot reveal in-water constituents. In this study a newly developed hyperspectral, remote-sensing reflectance model for shallow water is applied to data from computer simulations and field measurements. In the process, a remote-sensing reflectance spectrum is modeled by a set of values of absorption, backscattering, bottom albedo, and bottom depth; then it is compared with the spectrum from measurements. The difference between the two spectral curves is minimized by adjusting the model values in a predictor-corrector scheme. No information in addition to the measured reflectance is required. When the difference reaches a minimum, or the set of variables is optimized, absorption coefficients and bottom depths along with other properties are derived simultaneously. For computer-simulated data at a wind speed of 5 m/s the retrieval error was 5.3% for depths ranging from 2.0 to 20.0 m and 7.0% for total absorption coefficients at 440 nm ranging from 0.04 to 0.24 m(-1). At a wind speed of 10 m/s the errors were 5.1% for depth and 6.3% for total absorption at 440 nm. For field data with depths ranging from 0.8 to 25.0 m the difference was 10.9% (R(2) = 0.96, N = 37) between inversion-derived and field-measured depth values and just 8.1% (N = 33) for depths greater than 2.0 m. These results suggest that the model and the method used in this study, which do not require in situ calibration measurements, perform very well in retrieving in-water optical properties and bottom depths from above-surface hyperspectral measurements.     

Fluorescence spectra provide information on the depth of fluorescent lesions in tissue

The fluorescence spectrum measured from a fluorophore in tissue is affected by the absorption and scattering properties of the tissue, as well as by the measurement geometry. We analyze this effect with Monte Carlo simulations and by measurements on phantoms. The spectral changes can be used to estimate the depth of a fluorescent lesion embedded in the tissue by measurement of the fluorescence signal in different wavelength bands. By taking the ratio between the signals at two wavelengths, we show that it is possible to determine the depth of the lesion. Simulations were performed and validated by measurements on a phantom in the wavelength range 815-930 nm. The depth of a fluorescing layer could be determined with 0.6-mm accuracy down to at least a depth of 10 mm. Monte Carlo simulations were also performed for different tissue types of various composition. The results indicate that depth estimation of a lesion should be possible with 2-3-mm accuracy, with no assumptions made about the optical properties, for a wide range of tissues.     

Multispectral polarization imaging for observing blood oxygen saturation in skin tissue

We propose a new technique that combines two-dimensional (2D) multispectral imaging and polarization gating for observing the blood oxygen saturation (SpO2) level in human skin tissue. The spectral decomposition of the skin tissue image provides the principal information on blood oxygenation. The polarization gating selects the measurement depth according to the relative orientation of the two polarizers that are placed on a camera and a light source. The combination of these two methods yields multispectral images of the superficial and deep layers of the skin tissue separately. In order to evaluate the blood oxygen, we focus on the multispectral images of the deep site. The SpO2 levels at each image pixel are calculated by means of the partial least squares regression with respect to each reflectance spectrum. The reassignment of the predicted responses retrieves an image whose pixel values represent the relative SpO2 levels. A demonstration experiment for acquiring the multispectral polarization images is performed in the spectral range of 500 to 680 nm, and the SpO2 distributions are obtained.     

Optical diffuse reflectance accessory for measurements of skin tissue by near-infrared spectroscopy

An optimized accessory for measuring the diffuse reflectance spectra of human skin tissue in the near-infrared spectral range is presented. The device includes an on-axis ellipsoidal collecting mirror with efficient illumination optics for small sampling areas of bulky body specimens. The optical design is supported by the results of a Monte Carlo simulation study of the reflectance characteristics of skin tissue. Because the results evolved from efforts to measure blood glucose noninvasively, the main emphasis is placed on the long-wavelength near-infrared range where sufficient penetration depth for radiation into tissue is still available. The accessory is applied for in vivo diffuse reflectance measurements.     

Multiply scattered aerosol lidar returns: inversion method and comparison with in situ measurements

A novel aerosol lidar inversion method based on the use of multiple-scattering contributions measured by a multiple-field-of-view receiver is proposed. The method requires assumptions that restrict applications to aerosol particles large enough to give rise to measurable multiple scattering and depends on parameters that must be specified empirically but that have an uncertainty range of much less than the boundary value and the backscatter-to-extinction ratio of the conventional single-scattering inversion methods. The proposed method is applied to cloud measurements. The solutions obtained are the profiles of the scattering coefficient and the effective diameter of the cloud droplets. With mild assumptions on the form of the function, the full-size distribution is estimated at each range position from which the extinction coefficient at any visible and infrared wavelength and the liquid water content can be determined. Typical results on slant-path-integrated optical depth, vertical extinction profiles, and fluctuation statistics are compared with in situ data obtained in two field experiments. The inversion works well in all cases reported here, i.e., for water clouds at optical depths between ~0.1 and ~4.