Light-absorption Variation Research Articles

Colorimetric Sensing of Ascorbic Acid Using Cu-Phen MOFs and Subsequent Digital Image Analysis with Smartphone

Vitamin C, also known as ascorbic acid, is a crucial nutrient involved in a number of enzymatic processes for tissue healing. Additionally serving as an antioxidant, ascorbic acid is crucial for keeping the immune system strong. It is essential to create a quantitative analytical approach to ascertain ascorbic acid concentration in many samples since its consumption from the daily food should be in the proper quantity. Here, we present a colorimetric probe made of synthetic metal-organic frameworks (MOFs) that changes its color only when samples containing ascorbic acid are present. In this study, phenanthroline served as an organic ligand or linker while copper served as the core metal that formed bonds with it. Cu-Phen MOF color fluctuations at 410 nm (from 408 nm to 412 nm) are linearly related to variations in light absorption. Moreover, as a substitute for spectrophotometry UV-visible, we have created a digital image-based colorimetry. The Cu-Phen MOFs’ color change has the maximum slope and linearity when the blue color intensity is used. The detection limit with high precision of 4.2% under ideal circumstances was 0.1 ppm. The established approach allowed for the exact and accurate assessment of ascorbic acid in genuine samples of star fruit (Averrhoa carambola L.).

ASSESSING THE QUALITY OF PHOTOPLETHYSMOGRAPHY SIGNALS FOR ARTERIAL PULSE WAVE SENSING

Objective: Cardiovascular health has an impact on the arterial blood pulse wave features, such as shape and speed. Photoplethysmography (PPG) allows measuring the light absorption variation in the skin due to the blood pulse wave. This study aims at collecting good quality PPG signals for pulse wave sensing. First, the signal quality must be accurately defined and quantified. Then, it must be assessed for several sensor locations during both rest and exercise. Design and method: Based on ECG peaks, the PPG signal is split into beats, which are then fitted to a 4-long piece-wise linear function. Beats are valid only if they follow a specific slope pattern (the second slope has the opposite sign to the other three), and if they have a dichrotic notch. The signal quality is then quantified by the percentage of valid beats. The initial cohort of the clinical trial (NCT05393401, approved by Human Research Review Board (CPP SM I) and Health French Ministry) includes five healthy subjects (1F/4M, age [37-60] years). Their brachial and radial arteries are located by ultrasound. Each subject is monitored with a multi-sensing homemade platform with PPG sensors and ECG; the distance between the LED and the photodiode is 9mm. Measurements are realized with sensors directly above the artery on the elbow, the wrist and the carotid, first at rest and then during a physical exercise. Results: Based on these preliminary results, the quality of PPG signals is best at the wrist whether at rest (48%) or exercise (44%). The second best option is the forearm and the worst is the carotid. The quality during exercise is similar, with a decrease of 4% at the wrist. Conclusions: The signal quality of PPG sensors is strongly impacted by the position along the arteries. The pressure applied on sensors and the extended arm posture also improve the signal quality. Further work should be undertaken to study the feasibility of pulse wave analysis for ambulatory blood pressure monitoring.

Two Promising Methodologies for Dealing with Changes in Optical and Electrical Properties of Polymer Electrolytes (SPEs)

Variation of light absorption, mainly the shift and shape of the absorption edge, are two promising approaches aimed at understanding the fundamental processes of optical transitions in crystalline and amorphous materials. This allows us to better understand the structure of energy bands. Significant advances have been made in understanding the fundamental chemical and physical properties of polymers to improve the efficiency of photovoltaic and optoelectronic devices. However, the relationship between these two properties has not been determined. Characterization of the optical properties of polymers, such as infrared dichroism, light absorption, Raman polarization, and emission spectra, is an important method for studying electronic properties. To consider conductivity and thermal savings in the range (300–500 K), we also investigate the effect of temperature on conductivity. Activation energies found in different cases were used. Ionic conductivity has been found to be temperature-dependent for all SPE formulations. It has been found that the ionic conductivity of the membrane presents two regimes, the first being at relatively low temperatures. The ionic conductivity exhibits a relatively independent behavior of temperature. It was found that the dielectric constant of the SPE polymer electrolytic system increased with increasing temperature. This behavior is typical of pole insulators because the alignment of the dipoles becomes easier with increasing temperature and thus the dielectric constant increases.

Mechanical Behavior of 3D Printed Poly(ethylene glycol) Diacrylate Hydrogels in Hydrated Conditions Investigated Using Atomic Force Microscopy.

Three-dimensional (3D) printed hydrogels fabricated using light processing techniques are poised to replace conventional processing methods used in tissue engineering and organ-on-chip devices. An intrinsic potential problem remains related to structural heterogeneity translated in the degree of cross-linking of the printed layers. Poly(ethylene glycol) diacrylate (PEGDA) hydrogels were used to fabricate both 3D printed multilayer and control monolithic samples, which were then analyzed using atomic force microscopy (AFM) to assess their nanomechanical properties. The fabrication of the hydrogel samples involved layer-by-layer (LbL) projection lithography and bulk cross-linking processes. We evaluated the nanomechanical properties of both hydrogel types in a hydrated environment using the elastic modulus (E) as a measure to gain insight into their mechanical properties. We observed that E increases by 4-fold from 2.8 to 11.9 kPa transitioning from bottom to the top of a single printed layer in a multilayer sample. Such variations could not be seen in control monolithic sample. The variation within the printed layers is ascribed to heterogeneities caused by the photo-cross-linking process. This behavior was rationalized by spatial variation of the polymer cross-link density related to variations of light absorption within the layers attributed to spatial decay of light intensity during the photo-cross-linking process. More importantly, we observed a significant 44% increase in E, from 9.1 to 13.1 kPa, as the indentation advanced from the bottom to the top of the multilayer sample. This finding implies that mechanical heterogeneity is present throughout the entire structure, rather than being limited to each layer individually. These findings are critical for design, fabrication, and application engineers intending to use 3D printed multilayer PEGDA hydrogels for in vitro tissue engineering and organ-on-chip devices.

Seasonal Variations and Source Apportionment of Carbonaceous Components in Luoyang: Implication for Brown Carbon Contribution

A total of 98 samples were collected to analyze the seasonal variation and source apportionment of carbonaceous components, especially brown carbon (BrC), of PM2.5in Luoyang during 2018-2019. The concentrations of organic carbon (OC) and elemental carbon (EC) ranged from (7.04±1.82) μg·m-3to(23.81±8.68) μg·m-3and (2.96±1.4) μg·m-3to (13.41±7.91) μg·m-3, respectively, showing the seasonal variation of being high in winter and low in summer; the carbonaceous fraction and secondary organic aerosol percentages were higher by 8.33%-141.03% and by 0.77%-63.14%, respectively, compared with that in 2015. The light absorption cross section (MAC) values showed different seasonal variations with the concentration of carbonaceous fraction, shown in descending order as autumn (7.67 m2·g-1)>winter (5.65 m2·g-1)>spring (5.13 m2·g-1)>summer (3.84 m2·g-1). The MAC values ranged from 3.84 to 7.67 m2·g-1 at 445 nm, which was lower than that in coal ash. Seasonal variation in light absorption and the contribution of BrC to total light absorption (babs,BrC,405 nm, babs,BrC,405 nm/babs,405 nm) in descending order was winter (31.57 Mm-1, 33%), autumn (11.40 Mm-1, 25%), spring (4.88 Mm-1, 23%), and summer (2.12 Mm-1, 21%). The proportion of carbonaceous components decreased as haze episodes evolved, whereas the contribution of light absorption of BrC increased, highlighting the important contribution of BrC to the total light absorption. The results of PMF and correlation coefficients of babs,BrC,405 nm and PM2.5 components indicated that motor vehicles and secondary nitrate contributed 27.7% and 24.0%, respectively. Our findings have significant scientific implications for the deep controlling of carbonaceous aerosol, especially for BrC, in Luoyang in the future.

PPG Signal and application in the medical field

The ascent of remote health examination is a burgeoning trend in healthcare, aimed at tackling the challenge of hospital overload and streamlining the process of patient monitoring. To achieve these laudable goals, a device that is both efficient and capable of extracting critical health indicators is of paramount importance. Enter photoplethysmography (PPG) technology - a compact and user-friendly device that offers a wealth of health-related information. PPG is an optical, non-invasive method of measuring changes in blood volume in tissue by illuminating the skin and detecting variations in light absorption caused by blood flow. This technique has a multitude of applications, including the measurement of blood oxygen saturation, the estimation of blood pressure, the assessment of vascular aging, and the detection of arrhythmias. Therefore, it presents a promising avenue in addressing the challenge of hospital overload. This article provides an all-encompassing overview of photoplethysmography (PPG) technology, elucidating the underlying principles and highlighting its noteworthy applications. Specifically, the article expounds on the use of PPG in measuring blood oxygen saturation, estimating blood pressure, assessing vascular aging, and detecting arrhythmias. Despite the advantageous applications of PPG, there are still some issues that need to be addressed, such as the limited availability of PPG data sets in certain populations, the sensitivity of PPG signal to motion and ambient conditions, and a lack of clarity about the nature of PPG which leads to the absence of standard criteria in sampling and interpretation of PPG in its applications. And these issues are also thoroughly discussed in the paper.

How do bubbles affect light absorption in photoelectrodes for solar water splitting?

This study quantified the optical losses due to gas bubbles present on the surface of photoelectrodes in a photoelectrochemical cell by simulating the area-averaged and local variation in light absorption.

6\u2009nm super-resolution optical transmission and scattering spectroscopic imaging of carbon nanotubes using a nanometer-scale white light source

Optical transmission and scattering spectroscopic microscopy at the visible and adjacent wavelengths denote one of the most informative and inclusive characterization methods in material research. Unfortunately, restricted by the diffraction limit of light, it cannot resolve the nanoscale variation in light absorption and scattering, diagnostics of the local inhomogeneity in material structure and properties. Moreover, a large quantity of nanomaterials has anisotropic optical properties that are appealing yet hard to characterize through conventional optical methods. There is an increasing demand to extend the optical hyperspectral imaging into the nanometer length scale. In this work, we report a super-resolution hyperspectral imaging technique that uses a nanoscale white light source generated by superfocusing the light from a tungsten-halogen lamp to simultaneously obtain optical transmission and scattering spectroscopic images. A 6-nm spatial resolution in the visible to near-infrared wavelength regime (415–980 nm) is demonstrated on an individual single-walled carbon nanotube (SW-CNT). Both the longitudinal and transverse optical electronic transitions are measured, and the SW-CNT chiral indices can be identified. The band structure modulation in a SW-CNT through strain engineering is mapped.

Row orientation affects the uniformity of light absorption, but hardly affects crop photosynthesis in hedgerow tomato crops

Abstract Light distribution within canopies is important for plant growth. We aimed to quantify the influence of row orientation on inter- and within-row variation of light absorption and photosynthesis in a hedgerow crop. An experiment with two row orientations of a tomato crop was conducted which was then used to calibrate a functional–structural plant model (FSPM). The FSPM was used to analyse light absorption and photosynthesis for each of the row facing directions in the double-row trellis system (e.g. north- and south-facing rows for the east–west row orientation). The measured leaf area decreased by 18 % and specific leaf area by 10 %, while fruit dry weight increased by 7 % for south-facing compared to north-facing rows, but total plant dry weight did not significantly differ. Model simulations showed a 7 % higher light absorption for the south-facing rows than north-facing rows, while net photosynthesis was surprisingly −4 % lower, due to local light saturation. When in the model leaf area was kept equal between the rows, light absorption for the south-facing rows was 19 % and net photosynthesis 8 % higher than for north-facing rows. We conclude that although south-facing rows would be expected to have a higher photosynthesis than north-facing rows, plants can adapt their morphology such that differences in light absorption and photosynthesis between north- and south-facing rows are minimal. Rows oriented north–south were more uniform in light absorption and photosynthesis than east–west rows, but the overall crop light absorption and photosynthesis were minimally affected (both 3 % lower compared to east–west orientation).

Substantial decreases of light absorption, concentrations and relative contributions of fossil fuel to light-absorbing carbonaceous aerosols attributed to the COVID-19 lockdown in east China.

To prevent spreads of Coronavirus disease-2019 (COVID-19), China adopted the lockdown measures in late January 2020, providing a platform to study the response of air quality and atmospheric chemical and physical properties to strict reduced emissions. In this study, the continuous measurements of aerosol light absorption were conducted in Nanjing, east China, from January 3 to March 31, 2020. Our results showed that the contribution of black carbon (BC) to light absorption at the different wavelengths was more than 75% and the rest light absorption was contributed by brown carbon (BrC), which was mainly originated from primary emissions. Secondary BrC absorption, which was mainly produced by photochemical oxidation, constituted a minor fraction (2–7%) of the total absorption. Compared with the sampling in the pre-lockdown, the significant decreases of BC (43%) and secondary BrC absorption (31%) were found during the lockdown period, resulting in a substantial decrease of solar energy absorbance by 36% on a local scale. The control measures also changed the diurnal variations of light absorption. Due to the reduced emissions, the relative fraction of fossil fuel to BC also dropped from 78% in the pre-lockdown to 71% in the lockdown. The concentrations of BC, PM2.5 and NO2 decreased 1.1 μg m−3, 33 μg m−3 and 9.1 ppb whereas O3 concentration increased 9.0 ppb during the COVID-19 lockdown period. The decreased concentrations of BC, PM2.5 and NO2 were mainly contributed by both emission reduction (51–64%) and meteorological conditions (36–49%). Our results highlighted that the balance of control measures in alleviation of particulate matter (PM) and O3 pollution, and meteorology should be seriously considered for improvement of air quality in this urban city of China.

Dissolved organic matter from tropical peatlands reduces shelf sea light availability in the Singapore Strait, Southeast Asia

Shelf seas provide valuable ecosystem services, but their productivity and ecological functioning depend critically on sunlight transmitted through the water column. Anthropogenic reductions in underwater light availability are thus a serious threat to coastal habitats. The flux of light-absorbing coloured dissolved organic matter (CDOM) from land to sea may have increased world-wide, but how this has altered the availability and spectral quality of light in shelf seas remains poorly known. We present time-series data from the Sunda Shelf in Southeast Asia, where the monsoon-driven reversal in ocean currents supplies water enriched in CDOM from tropical peatlands for part of the year, resulting in 5- to 10-fold seasonal variation in light absorption by CDOM. We show that this terrigenous CDOM can dominate underwater light absorption at wavelengths up to 500 nm, and shift the underwater irradiance spectrum towards longer wavelengths. The seasonal presence of terrigenous CDOM also reduces the 10% light penetration depth by 1-5 m, or 10-45%. We estimate that on average 0.6 m, or 25%, of this terrigenous CDOM-mediated shoaling might be attributable to the enhanced input of dissolved organic matter following peatland disturbance. The seasonal change in the light environment is correlated with changes in phytoplankton absorption spectra that suggest a photo-acclimation response, and we infer that terrigenous CDOM likely contributes to limiting the depth distribution of photosynthetic corals. The results reveal an ecologically important but largely overlooked impact of human modifications to carbon fluxes that is likely increasingly important in coastal seas.

Evaluation of the Light Environment of a Plant Factory with Artificial Light by Using an Optical Simulation

Good lighting designs can establish suitable light environments in plant factories with artificial light (PFALs). This study used optical simulations to investigate the effects of lighting designs in PFALs on the coefficient of variation of light absorption (Φp; CV) of individual plants and the coefficient of utilization for the lighting system (U). Three-dimensional models of canola plants were constructed using a scanner, and a 3D model of the cultivation shelf was also created. The photosynthetic photon flux density (PPFD) distribution in the cultivation spaces, with or without the canola plants, was estimated first. The PPFD on the canola leaves was then estimated when the lighting design parameters, such as number, distance, height, radiant flux, and light distribution of the light-emitting diode lamps, were modified. The optical simulation showed good accuracy when estimating the PPFD distributions on the cultivation shelf and the leaves of the canola plants. The results showed that while the PPFD distribution across the growing area was uniform, it was not on a plant canopy. By appropriately controlling the layout of the lamps and their directionality, lighting designs that reduce Φp; CV and improve U in PFAL could be possible, and optical simulations could help to develop them.

Photogenerated Oxygen Vacancies in Hierarchical Ag/TiO2 Nanoflowers for Enhanced Photocatalytic Reactions.

Oxygen vacancy (Vo) creation and morphology controlling make significant contributions to the electronic and structural regulation of metal oxide semiconductors, yet an investigation about convenient approaches for fabricating hierarchical catalyst with abundant oxygen vacancies still has significant challenges. Here, we report a unique method to create abundant oxygen vacancies in hierarchical Ag/TiO2 nanoflowers during photocatalytic reaction, which is accompanied by light absorption variation and surface plasmon resonance (SPR) enhancement. Its high efficiency of photocatalytic H2 evolution (the highest apparent quantum yield reaches 3.2% at 365 nm) and rhodamine B degradation can be considered as benefits from the synergistic effects of the well-arranged hierarchical structure, the photogenerated oxygen vacancies, and the SPR of cocatalyst Ag. This work proposes an effective strategy to optimize the synthesis of regular hierarchical structures and enriches the research on the vital function of oxygen vacancies in photocatalytic reactions.

Layer-by-Layer Printing of Photopolymers in 3D: How Weak is the Interface?

Additive manufacturing or, as also called, three-dimensional (3D) printing is considered as a game-changer in replacing traditional processing methods in numerous applications; yet, it has one intrinsic potential weakness related to bonding of layers formed during the printing process. Prior to finding solutions for improvement, a thorough quantitative understanding of the mechanical properties of the interface is needed. Here, a quantitative analysis of the nanomechanical properties in 3D printed photopolymers formed by digital light processing (DLP) stereolithography (SLA) is shown. Mapping of the contact Young’s modulus across the layered structure is performed by atomic force microscopy (AFM) with a submicrometer resolution. The peakforce quantitative nanomechanical mapping (PF-QNM) mode was employed in the AFM experiments. The layered specimens were obtained from an acrylate-based resin (PR48, Autodesk), containing also a light-absorbing dye. We observed local depressions with values up to 30% of the maximum stiffness at the interface between the consecutively deposited layers, indicating local depletion of molecular cross-link density. The thickness values of the interfacial layers were approximately 11 μm, which corresponds to ∼22% of the total layer thickness (50 μm). We attribute this to heterogeneities of the photopolymerization reaction, related to (1) atmospheric oxygen inhibition and (2) molecular diffusion across the interface. Additionally, a pronounced stiffness decay was observed across each individual layer with a skewed profile. This behavior was rationalized by a spatial variation of the polymer cross-link density related to the variations of light absorption within the layers. This is caused by the presence of light absorbers in the printed material, resulting in a spatial decay of light intensity during photopolymerization.

Diurnal Variation of Light Absorption in the Yellow River Estuary

Considering the influence of river discharge and strong winds, the diurnal variability of ocean optical absorption properties in the Yellow River Estuary (YRE) is quantified, using in-situ measurements. The study finds that terrestrial sources due to the Yellow River discharge can cause high diurnal variation of water absorption because of the movement of river plume in the YRE, but such an influence diminishes far away from the Yellow River plume. The diurnal variability of water absorption, affected by strong winds, is found to be strengthened with a rapid increase of particles and colored dissolved organic matter (CDOM) arising from re-suspended sediment induced by wave forcing. The diurnal variability of particle absorption is controlled by non-algal particle absorption in the YRE, and the ratio of non-algal particle absorption (aNAP) and total particle absorption for most wavelengths is more than 0.56. The diurnal variation of spectral slope of non-algal particle absorption (SNAP) is found to vary within a narrow range, although large variability in the aNAP spectrum is observed. The CDOM is correlated negatively with salinity, and such negative correlation becomes weaker with the decreasing influence of riverine input. The spectral slope of CDOM absorption (Sg) may reflect the formation and constituents of CDOM with weak relationship to its concentration, and its relationship with the absorption of CDOM at 440 nm may be associated with the source of CDOM. The value of Sg, which is affected by re-suspended bottom sediment, is much lower than that derived from CDOM affected by Yellow River runoff. Disregarding the absorption of pure water, the diurnal variability of total water absorption stems principally from changes in non-algal particle matter rather than CDOM and Chl-a. By the observations of hourly GOCI (Geostationary Ocean Color Imager) data, the major diurnal variations of remote sensing reflectance at 680 nm are observed in near-coastal waters and the estuary of the Yellow River, which are mainly influenced by the flow discharge of Yellow River and strong winds. Finally, the seasonal differences of diurnal variations of water absorption caused by strong winds and river discharge are determined.

Absorptance determinations on multicellular tissues.

The analysis of the variation of the capacity and efficiency of photosynthetic tissues to collect solar energy is fundamental to understand the differences among species in their ability to transform this energy into organic molecules. This analysis may also help to understand natural changes in species distribution and/or abundance, and differences in species ability to colonize contrasting light environments or respond to environmental changes. Unfortunately, the challenge that optical determinations on highly dispersive samples represent has strongly limited the progression of this analysis on multicellular tissues, limiting our knowledge of the role that optical properties of photosynthetic tissues may play in the optimization of photosynthesis and growth of benthonic primary producers. The aim of this study is to stimulate the use of optical tools in marine eco-physiology, offering a succinct description of the more convenient tools and also solutions to resolve the more common technical difficulties that arise while performing optical determinations on highly dispersive samples. Our study focuses on two-dimensional (2D-) parameters: absorptance, transmittance, and reflectance, and illustrates with correct and incorrect examples, specific problems and their respective solutions. We also offer a general view of the broad variation in light absorption shown by photosynthetic structures of marine primary producers, and its low association with pigment content. The ecological and evolutionary functional implications of this variability deserve to be investigated across different taxa, populations, and marine environments.

Large elasto-optic effect and reversible electrochromism in multiferroic BiFeO3.

The control of optical fields is usually achieved through the electro-optic or acousto-optic effect in single-crystal ferroelectric or polar compounds such as LiNbO3 or quartz. In recent years, tremendous progress has been made in ferroelectric oxide thin film technology—a field which is now a strong driving force in areas such as electronics, spintronics and photovoltaics. Here, we apply epitaxial strain engineering to tune the optical response of BiFeO3 thin films, and find a very large variation of the optical index with strain, corresponding to an effective elasto-optic coefficient larger than that of quartz. We observe a concomitant strain-driven variation in light absorption—reminiscent of piezochromism—which we show can be manipulated by an electric field. This constitutes an electrochromic effect that is reversible, remanent and not driven by defects. These findings broaden the potential of multiferroics towards photonics and thin film acousto-optic devices, and suggest exciting device opportunities arising from the coupling of ferroic, piezoelectric and optical responses.

Efficient Photocatalytic Oxygen Production over Nitrogen‐Doped Sr4Nb2O9 under Visible‐Light Irradiation

AbstractPhotocatalytic water splitting is an appealing process for solar energy conversions yet it is often limited by the slow oxidation of water to oxygen half‐reaction. Here we performed an investigation on N‐doped Sr4Nb2O9 as a water oxidation photocatalyst. Our results show that N doping is an effective approach to improve the visible‐light response of Sr4Nb2O9. Efficient photocatalytic oxygen production was observed after N doping, and the highest production rate of ∼27 μmol h−1 under visible‐light irradiation corresponds to an apparent quantum efficiency of ∼0.31 %. Clear anodic photocurrent can be generated under visible‐light illumination, and the flat‐band potential was determined to be ∼−1.25 V vs. Ag/AgCl at pH 7. Theoretical calculations reveal that N doping introduces additional valence bands and is responsible for the visible‐light response. Variations in light absorption and photo‐oxidation performance can be controlled by modifying these valence band positions using different nitridation temperatures.

Linking canopy leaf area and light environments with tree size distributions to explain Amazon forest demography.

Forest biophysical structure - the arrangement and frequency of leaves and stems - emerges from growth, mortality and space filling dynamics, and may also influence those dynamics by structuring light environments. To investigate this interaction, we developed models that could use LiDAR remote sensing to link leaf area profiles with tree size distributions, comparing models which did not (metabolic scaling theory) and did allow light to influence this link. We found that a light environment-to-structure link was necessary to accurately simulate tree size distributions and canopy structure in two contrasting Amazon forests. Partitioning leaf area profiles into size-class components, we found that demographic rates were related to variation in light absorption, with mortality increasing relative to growth in higher light, consistent with a light environment feedback to size distributions. Combining LiDAR with models linking forest structure and demography offers a high-throughput approach to advance theory and investigate climate-relevant tropical forest change.

Motion Artifact Compensation for Wristwatch Type Photoplethysmography Sensor

Heart beat measurement is useful not just for medical use but also for daily healthcare monitoring and for sports. Photoplethysmography is an optical pulse measurement method that measures the variation of light absorption of the blood flow in capillary. Fingertip and earlobe, which are suitable places for this method, are not suitable for wearing sensors in daily life. Measurement at wrist will be more favorable. Technical difficulties of applying photoplethysmography measurement on wrist are: a) blood flow variation and change of sensor orientation caused by body motions, and b) low sensitivity compared to measurement at fingertips or earlobes because of the low capillary density in the tissue. We derived a transfer function that expresses the relationship between body acceleration and change in capillary blood flow based on a simple fluid dynamics model of artery and capillary. Preliminary experiments have shown that motion the artifacts can be reduced by subtracting the change of blood flow estimated from body acceleration. This method is different from conventional frequency filtering methods that do not consider the relationship between the body motion and the changes in the capillary blood flow. Furthermore, sensor head suspension mechanism has been employed in order to stabilize the sensor orientation with respect to the skin as well as the applied force on the skin.