Intensity Of Reflected Signal Research Articles

High resolution, in situ, multispectral, spectroscopic mapping imaging system applied in heritage science

In the current work a setup for the acquisition of high resolution multispectral, spectroscopic mapping infrared images is presented. The idea is based on the Fourier Transform Infrared (FTIR) reflectoscopy since the object is illuminated using the source and the interferometer of an FTIR spectrophotometer and the reflected signal intensity from the object is measured using a high resolution response of a Focal Plane Array (FPA) of InSb sensor. The optical parts like optical fibers, mirrors, beamsplitters, FPA and the FPA lens are selected properly to allow the measurement at a wide frequency range depending on the spectral range of the source interferometer from wavelength 1.3 μm to 26 μm and the spectral range of the FPA which in this case is from wavelength 1.3 μm to 5.5 μm and beyond but with significant attenuation. Moreover, the FPA is triggered through the laser signal that measures the position of the moving mirror of the interferometer and by adjusting appropriately the speed of the scanner mirror and the FPA integration time, the array of interferogramms of a significant region of interest (ROI) can be acquired instantly. This is one of the main contributions of the present work since multispectral images in a non-micrometer level and from an area of a few centimeters by centimeters are acquired by extracting the interferogram, through each sensor of the FPA, in the illuminated ROI and in a time interval less than 1 sec. This is providing to the user the fast acquisition mapping images in a wavelength resolution of the order of less than manometer (based on the spectrophotometers resolution) in a broadband area as stated before. This kind of mapping, multispectral cube images with sub nanometer spectral interval among them, up to now, are acquired by scanning point by point, in an array format, in a ROI of 2 cm by 10 cm, lasting approximately 8.8 hours with 16 averaging per signal. By using this technology in the field of heritage science, the scientists can simultaneously observe, in the case of painted artworks like the ones presented in this manuscript, the overpaintings, pentimenti, defects in the underlayers based on the cube imaging, produced data set, as well as materials identification based on the spectra that are acquired per pixel simultaneously to the cube imaging data set. Using the iTomography system and applying mosaic scanning, the acquisition time of spectroscopic mapping cube images from the hole object, like the icon presented in this work, with dimensions 60 cm × 70 cm, is of the order of 8-10 minutes.

Use of Laser Interferometry to Determine the End Time of the Plasma-Chemical Etching of p-GaN and AlGaN Layers of the p-GaN/AlGaN/GaN Heterostructure with Two-Dimensional Electron Gas

Regularities of the reflected signal intensity changing in time, recorded by the detector of the laser interferometer with the operating frequency of 670 nm during the inductively coupled plasma reactive ion etching in a Cl2/N2/O2 atmosphere of GaN, p-GaN and AlGaN in AlGaN/GaN and p-GaN/AlGaN/GaN heterostructures has been established by laser interferometry and scanning electron microscopy methods due to the changes in refractive indices and etching rates. During inductively coupled plasma reactive ion etching of GaN and p-GaN layers, the intensity of the reflected signal changes according to a periodic law with the thickness change period of about 144 nm, and for AlGaN layers about 148 nm, which is due to differences in their refractive indices and etching rates. During the crossing of the p-GaN/AlGaN and AlGaN/GaN interface, there is an abrupt change in the intensity of the reflected signal within 2.7–9.5 % for 20–40 s, due to changes in the aluminum concentration, refractive indices, and etching rate at the interfaces. The change in the periodicity of the interferogram, which is accompanied by a jump in intensity when passing through the etching front through the p-GaN/AlGaN and AlGaN/GaN interface, makes it possible to determine the end time of the inductively coupled plasma reactive ion etching of the AlGaN and p-GaN layers using laser interferometry in real time in AlGaN/GaN and p-GaN/AlGaN/GaN heterostructures with two-dimensional electron gas. The obtained results can be used to form microwave and power electronics devices elements which are based on the AlGaN/GaN heterostructures.

Using Attenuated Total Reflection (ATR) Apparatus to Investigate the Temperature Dependent Dielectric Properties of Water, Ice, and Tissue-Representative Fats

A novel method of investigating the temperature dependent variation of aspects of the complex refractive index n* in samples in the THz range using continuous, non-polarised, synchrotron radiation is presented. The method relies on the use of ATR apparatus, and retains the advantage of minimal sample preparation, which is a feature of ATR techniques. The method demonstrates a “proof of concept” of monitoring temperature reflectance whilst continuously heating or cooling samples by using a temperature variable Thermal Sample Stage. The method remains useful when the refractive index of the sample precludes attenuated total reflection study. This is demonstrated with the water reflectance experiments. The temperature dependent ATR reflectance of tissue-representative fats (lard and Lurpak® butter) was investigated with the novel approach. Both are within the ATR range of the diamond crystal in a “true” ATR mode. Lard showed no clear temperature variation between −15 °C and 24 °C at 0.7 to 1.15 THz or 1.70 to 2.25 THz. Lard can be regarded as having invariable, constant, dielectric properties within mixtures when biological substances are being assessed for temperature dependent dielectric variation within the stated THz ranges. Lurpak® butter (water content 14.7%) displayed temperature dependent reflected signal intensity features with a steady decline in reflectivity with increasing temperature. This is in line with the temperature-dependent behaviour of liquid water. There is no rapid change in reflected signal intensity even at −20 °C, suggesting that emulsified water retains liquid-water-like THz properties at freezing temperatures.

Effects of Diffuse and Specular Reflections on Detecting Embedded Defects of Foams With a Bifocal Active Imaging System at 0.22 THz

We show the diffuse and specular reflection images of defective foams placed on iron plates, which are obtained by a bifocal active imaging system at 0.22 THz. Foam materials studied are extruded polystyrene boards and acetate copolymer boards with artificially embedded defects. In the field of view of approximately 50 × 90 cm2, the incident angle of the emitting and receiving cochannel system affects the reflected signal intensity and the imaging method. We build a light reflection model, which corrects the angle-dependent intensity behavior, to make the imaging results more intuitive. Experimental results show that large-angle imaging, which collects mainly diffuse reflection light, can be used to detect defects and is actually more suitable for detecting small defects than small-angle imaging, which mainly collects specular reflection light.

Point-Focusing of Shear-Horizontal Wave Using Fan-Shaped Periodic Permanent Magnet Focusing Coils EMAT for Plate Inspection

Ultrasonic guided wave testing method is very effective in safety monitoring of complex structures, such as large-scale tank floor and industrial metal plate. The fundamental shear horizontal (SH) wave mode with the Lorentz force mechanism has the advantage that the propagation velocity does not change with the frequency. However, it is hard to recognize the dispersed ultrasonic signal accurately due to the bidirectional propagation characteristics of the SH guided wave. Therefore, a new transducer structure with a fan-shaped periodic permanent magnet (PPM) and centripetal conductor has been designed to achieve guided wave focusing and signal enhancement. Compared with the traditional transducers, the new-designed transducer has been proved to be more effective in energy focusing on the simulation and experimental verification. For the new structure of the transducer, the aperture angle, focusing radius, and coil rotation angle are studied in detail in this paper. The results show that, as the aperture angle and the coil rotation angle decrease, the signal intensity becomes higher at the focusing position. Moreover, as the focal radius increases, the amplitude of the ultrasonic signals on the focusing side and the divergent side will decrease, while the difference between the two sides will increase exponentially. In the defect detection in this paper, the reflected signal intensity of the new-designed fan-shaped PPM focusing coils electromagnetic acoustic transducer (EMAT) is approximately two times that of the traditional parallel PPM parallel coils EMAT. Therefore, the newly designed EMAT is of great significance for the signal enhancement.

A heuristics-based method for obtaining road surface type information from mobile lidar for use in network-level infrastructure management

Road surface type is a key input to most asset management and maintenance management models and analyses, such as deterioration prediction models, life cycle cost analysis, and need estimates. However, surface type changes in space and time due to the use of varying pavement types and the application of different surface treatments. In recent years, the transportation and municipal industry has begun to use mobile lidar (Light Detection and Ranging) systems to collect roadway condition and inventory data, including surface type. This paper provides a heuristics-based method for detecting road surface type based on statistical analysis of laser reflected signal intensity. The studied surfaces are open graded asphalt, dense graded asphalt, seal coated asphalt, concrete, and roadside vegetation. This method will improve the availability and quality of surface type data, especially for large roadway networks, by automating the process of obtaining this information from mobile lidar measurements.

Numerical study of three-dimensional sound reflection from corrugated surface waves

When a sound wave propagates in a water medium bounded by a smooth surface wave, reflection from a wave crest can lead to focusing and result in rapid variation of the received waveform as the surface wave moves [Tindle, Deane, and Preisig, J. Acoust. Soc. Am. 125, 66-72 (2009)]. In prior work, propagation paths have been constrained to be in a plane parallel to the direction of corrugated surface waves, i.e., a two-dimensional (2-D) propagation problem. In this paper, the azimuthal dependence of sound propagation as a three-dimensional (3-D) problem is investigated using an efficient, time-domain Helmholtz-Kirchhoff integral formulation. When the source and receiver are in the plane orthogonal to the surface wave direction, the surface wave curvature vanishes in conventional 2-D treatments and the flat surface simply moves up and down, resulting in minimal temporal variation of the reflected signal intensity. On the other hand, the 3-D propagation analysis reveals that a focusing phenomenon occurs in the reflected signal due to the surface wave curvature formed along the orthogonal plane, i.e., out-of-plane scattering.

Effect of temperature, high pressure and freezing/thawing of dry-cured ham slices on dielectric time domain reflectometry response

Dielectric Time Domain Reflectometry (TDR) is a useful technique for the characterization and classification of dry-cured ham according to its composition. However, changes in the behavior of dielectric properties may occur depending on environmental factors and processing. The effect of temperature, high pressure (HP) and freezing/thawing of dry-cured ham slices on the obtained TDR curves and on the predictions of salt and water contents when using previously developed predictive models, was evaluated in three independent experiments. The results showed that at temperatures below 20°C there is an increase of the predicted salt content error, being more important in samples with higher water content. HP treatment caused a decrease of the reflected signal intensity due to the major mobility of available ions promoting an increase of the predicted salt content. Freezing/thawing treatment caused an increase of the reflected signal intensity due to the microstructural damages and the loss of water and ions, promoting a decrease of the predicted salt content.

An Optical Fiber Formaldehyde Biosensor Based on a Modified Single Sol–Gel Film of Alcohol Oxidase and Chlorophenol Red in Flow System

An optical fiber formaldehyde biosensor based on a modified single sol–gel film consisting of alcohol oxidase (AOX) and chlorophenol red (CPR) was developed. The modification relies on addition of poly(vinyl alcohol) (PVA) into sol–gel matrix, in order to increase the function of AOX. The biosensing element on a sol–gel film has been placed inside the flow-cell for the flow system measurements. In the presence of a constant AOX, a color change of the CPR was measured in term of its reflected signal intensity at the wavelength 555 nm. This color change could be related to the formaldehyde concentration in the sample solutions. The performance of optical formaldehyde biosensor in the flow system has been optimized. The formaldehyde biosensor exhibited a dynamic linear response range in the formaldehyde concentration range of 0–10 mg/L with linear correlation (r ) was 0.996. The detection limit of the biosensor was 0.035 mg/L while reproducibility was < 1% RSD (relative standard deviation). Tofu as real food sample were analysis using the biosensor revealed that it was promising for food analysis of formaldehyde.

Infant Skin Microstructure Assessed In Vivo Differs from Adult Skin in Organization and at the Cellular Level

Functional differences between infant and adult skin may be attributed to putative differences in skin microstructure. The purpose of this study was to examine infant skin microstructure in vivo and to compare it with that of adult skin. The lower thigh area of 20 healthy mothers (ages 25-43) and their biological children (ages 3-24 months) was examined using in vivo noninvasive methods including fluorescence spectroscopy, video microscopy, and confocal laser scanning microscopy. Stratum corneum and supra-papillary epidermal thickness as well as cell size in the granular layer were assessed from the confocal images. Adhesive tapes were used to remove corneocytes from the outer-most layer of stratum corneum and their size was computed using image analysis. Surface features showed differences in glyph density and surface area. Infant stratum corneum was found to be 30% and infant epidermis 20% thinner than in adults. Infant corneocytes were found to be 20% and granular cells 10% smaller than adult corneocytes indicating a more rapid cell turnover in infants. This observation was confirmed by fluorescence spectroscopy. Dermal papillae density and size distribution also differed. Surprisingly, a distinct direct structural relationship between the stratum corneum morphology and the dermal papillae was observed exclusively in infant skin. A change in reflected signal intensity at approximately 100 mum indicating the transition between papillary and reticular dermis was evident only in adult skin. We demonstrate in vivo qualitative and quantitative differences in morphology between infant and adult skin. These differences in skin microstructure may help explain some of the reported functional differences.

On the control of thin film growth by angular reflectometry near the brewster angle

The method of angular reflectometry is used to analyze the formation dynamics of layered structures on transparent substrates. This method is highly sensitive to changes in the parameters of a film structure at the early stage of formation thereof. It is based on the angular dependence of the reflected signal intensity near the Brewster angle and is almost independent of the state of the measuring facility. Experimental data obtained for multiferroic thin films on an isotropic crystalline Al2O3(001) substrate are presented. The films on the Al2O3(001) substrate are obtained by sputtering a Bi0.95Nd0.05FeO3 target for 5–600 s in an rf glow discharge initiated in oxygen.

Porous silicon as an intermediate buffer layer for GaN growth on (100) Si

We report preliminary results on the growth of GaN on (100) Si substrate using porous silicon (PS) as an intermediate buffer layer. The growth was in situ monitored by laser beam reflectivity. Analysis of the evolution of the reflectivity signal indicates a change from relatively flat surface to rough one as the growth temperature (Tg) is increased. At a temperature of about 1050°C, the growth rate is very low and the reflected signal intensity is constant. When the growth temperature is varied, no drastic change of the porosity of the intermediate layer was detected. Scanning electron microscope (SEM) observations of the GaN/SP/Si structure revealed a good surface coverage at 500°C. When Tg increases, the structure morphology changes to columnar like structure at 600°C, and well-developed little crystallites with no preferential orientation appear at 800°C. These observations agree well with the X-ray diffraction (XRD) analysis. A preferential hexagonal growth is obtained at low growth temperature, while cubic phase begin to appear at elevated temperatures.

Radiative transfer in a layer of magnetized plasma with random irregularities

The problem of radio wave reflection from an optically thick plane uniform layer of magnetized plasma is considered in the present work. The plasma electron density irregularities are described by a spatial spectrum of arbitrary form. The small-angle scattering approximation in invariant ray coordinates is proposed as a technique for the analytical investigation of the radiation transfer equation. The approximate solution describing the spatial and angular distribution of radiation reflected from a plasma layer is obtained. The solution obtained is investigated numerically for the case of ionospheric radio wave propagation. Two effects occur as a consequence of multiple scattering: a change in the reflected signal intensity and an anomalous refraction.

Position sensing apparatus for an object to be measured

A position sensing apparatus includes an ultrasonic wave transmit-receive element for transmitting and receiving ultrasonic waves to and from an object whose position is to be sensed and a manipulator for changing the relative positions between the object and the ultrasonic wave transmit-receive element, and a signal processor utilizing changes in the reflected signal intensity in the vicinity of the center of the object to be measured, thereby sensing the position of the object.

Surface models including direct cross-radiation: a simple model of furrowed surfaces

Abstract In the interpretation of measured reflectance data it is important to consider those surface radiation effects which make a significant contribution to the overall irradiation pattern. A model was constructed for furrowed bare soil surfaces which includes the direct cross-radiation effect between the surface elements. According to the model computations performed the direct cross-radiation plays a significant role in the measured, reflected signal intensity. The computational method developed is suitable for including the direct cross-radiation effect in surface radiation models in the optical region.

An ultrasonic fatigue crack growth monitor and load controller

The design of an ultrasonic crack follower which continuously monitors the position of a fatigue crack in a 36 mm thick C.K.S. type specimen is described. An open-bottomed ‘tank’ containing a mobile immersion probe is mounted on the top surface of the sample. The probe is used to measure the position of the crack tip by normal ultrasonic techniques; as the crack grows the probe is automatically advanced to keep the reflected signal intensity constant. The probe drive mechanism is geared to two potentiometers, one of which produces an output proportional to the probe position, the other is used to attenuate the load control signal so as to keep the stress intensity range constant. The unit was capable of detecting crack growth increments of 450 μm. The automatic nature of the measurement greatly simplified the collection of fatigue crack growth data.

Oblique echoes from over-dense meteor trails

Ray paths are computed for waves refracted by meteor trails having a Gaussian radial distribution of ionization density. From the spreading of initially parallel rays as they pass through the trail, a measure of reflected signal intensity vs. scattering angle is obtained; the results are presented in polar scattering diagrams, valid in the limit of large trail size. Equivalence theorems are derived relating both intensity and scattering angle for rays incident upon the trail at an arbitrary angle to the intensity and scattering angle for rays incident in the plane normal to the trail. Curves are presented showing the dependence of echo duration on forward-scatter-angle with trail orientation as parameter; it is found that the sec 2 φ law developed for under-dense trails applies to over-dense trails only if the plane of propagation contains the trail axis. If not, the effective secant exponent may be as small as 0·3. The theory is compared with McKinley and McNamara's duration measurements. It is found that although the general agreement is satisfactory, the details of their experimental results depend on the way that winds change the trail orientation. The ray theory is also compared with Keitel's wave theory solution. Unfortunately, he could not get wave solutions for dense trails of age greater than 0·357 per cent of the minimum echo duration. Even so, the ray solutions agree with Keitel's results for scatter angles up to 155°, thus including all angles available to ground-based stations.