Reflectometry Approach Research Articles

The Extraction Methodic for GaN Field Transistor input Gate Capacitance in GHz Band

Authors propose new methodic for GaN field transistor input gate capacitance extraction based high-frequency S-parameters measurement and transmission line theory. Input gate capacitance was determined for GaN device (Lg = 0.25 mkm, W = 160 mkm) using proposed methodic for different operating modes at GHz band. This paper contains the dependences of the input capacitance as function of drain voltage (1.0—20.0 V) at 15.0 GHz for Vgs = —3.0 V. It was pointed that input capacitance is decreasing: 460 fF to 340 fF. This capacitance was measured using time-domain reflectometry approach in the same operating modes. Measured results were compared.

Fully Aqueous Self-Assembly of a Gold-Nanoparticle-Based Pathogen Sensor.

Surface plasmon resonance (SPR) is a very sensitive measure of biomolecular interactions but is generally too expensive for routine analysis of clinical samples. Here we demonstrate the simplified formation of virus-detecting gold nanoparticle (AuNP) assemblies on glass using only aqueous buffers at room temperature. The AuNP assembled on silanized glass and displayed a distinctive absorbance peak due to the localized SPR (LSPR) response of the AuNPs. Next, assembly of a protein engineering scaffold was followed using LSPR and a sensitive neutron reflectometry approach, which measured the formation and structure of the biological layer on the spherical AuNP. Finally, the assembly and function of an artificial flu sensor layer consisting of an in vitro-selected single-chain antibody (scFv)-membrane protein fusion was followed using the LSPR response of AuNPs within glass capillaries. In vitro selection avoids the need for separate animal-derived antibodies and allows for the rapid production of low-cost sensor proteins. This work demonstrates a simple approach to forming oriented arrays of protein sensors on nanostructured surfaces that uses (i) an easily assembled AuNP silane layer, (ii) self-assembly of an oriented protein layer on AuNPs, and (iii) simple highly specific artificial receptor proteins.

Insulated rail joint (IRJ) contact characterisation-an ultrasonic reflectometry approach for a cross-material interface

Vehicle–track interaction at insulated rail joints (IRJs) plays a significant role in the wear evolvement and damage of the IRJ components. It is, however, challenging to characterise the contact conditions within the region non-destructively and accurately using experimental tools, especially when the IRJ contact involves both wheel–rail and wheel–endpost contact pairs. This study presents an ultrasonic technique to monitor and characterise static IRJ contacts in a non-invasive manner. The proposed ultrasonic reflectometry technique can realise high-resolution visualisation of contact patch and contact pressure distribution for both wheel–rail contact and wheel–endpost contact, by striking a beam of focused ultrasonic signals at the contact interface. Different data post-processing strategies are applied for the two types of contacts and a deconvolution algorithm is applied to rectify the measurements near the rail–endpost boundary. The ultrasonic measurements are verified through finite element simulations and the results show good agreement with each other in terms of both contact area and contact pressure level. It is expected that the proposed ultrasonic approach can be a reliable tool to assist in revealing the contact behaviour of IRJs more profoundly.

A Wavenumber Domain Reflectometry Approach to Locate and Image Line-Like Soft Faults in Cables

A Wavenumber Domain Reflectometry Approach to Locate and Image Line-Like Soft Faults in Cables

Characterizing Scalar Metasurfaces Using Time-Domain Reflectometry

Two efficient methodologies for the determination of electromagnetic (EM) constitutive properties of scalar metasurfaces are introduced and discussed. In contrast to the available methods, and in line with the recent increasing interest in time-domain (TD) analyses of metasurfaces, we show that the material parameters of a scalar metasurface can be readily achieved directly in the TD merely from the EM reflected pulse shape. The two methodologies are based on an analytical TD reflectometry (TDR) approach and a modern stochastic optimization technique. A number of illustrative numerical examples demonstrating the validity and properties of the proposed techniques are presented.

Thermal Modeling of Resonant Scatterers and Reflectometry Approach for Remote Temperature Sensing

Thermal modeling of different transmission lines (TLs) based on resonant scatterers is presented. The coplanar strip (CPS) and microstrip (MS) TLs are used to model resonators and to introduce the thermal dependence. A reflectometry approach is employed to validate the model by detecting the scatterers’ resonance frequency and comparing it with analytical expressions. The observable shift in the resonance frequency of the scatterers with temperature variations is due to the thermal expansion of metals and temperature dependence of the substrate permittivity. Since all the measurements are done remotely with no direct line of sight, it is shown how such a reflectometry approach can be used for remote temperature sensing using a passive label composed of resonators. Unlike previous works in this domain where the thermal dependence is considered empirically, the introduced model is used to take into account all thermal effects affecting the resonant scatterers allowing to link rigorously the variations of the measured resonance frequency with the temperature without any lookup table. Temperature sensing using very simple TLs based on resonant scatterers was demonstrated in a real environment. A temperature error of less than 3 °C is obtained. Once the temperature has been determined, it is possible to go back to the TL parameters, such as the effective permittivity and the physical length.

Fast Chirp Frequency-Modulated Continuous-Wave Reflectometer for Monitoring Fast Varying Discontinuities on Transmission Lines

A portable fast chirp frequency-modulated continuous-wave (FMCW) reflectometer is presented to locate and monitor fast varying discontinuities or faults on transmission lines. This frequency-domain reflectometry (FDR) approach exploits and adapts the advantages of the closely related and frequently employed FMCW radar principle to transmission line reflectometry and overcomes the limitations of commonly used time-domain reflectometry (TDR) methods. The signal generation is based on direct digital synthesis (DDS) and frequency multiplication in order to exploit the advantages of DDS technology, e.g., fast and agile sweep time, and to overcome the drawbacks of analog signal sources related to nonlinearities, temperature sensitivity, or phase noise. By this means, the presented reflectometer provides highly linear, broadband, and fast swept chirp pulses with a duration on the order of microseconds with an initial frequency in the lower UHF-band and a bandwidth of 5.2 GHz. The system concept, its hardware realization, and performance specifications are introduced. The first laboratory test results for static transmission lines and a dynamic measurement setup are presented. The results demonstrate the effectiveness, versatility, and fine ranging capabilities on the order of 2 cm of this approach.

Review of Novel and Emerging Proximal Soil Moisture Sensors for Use in Agriculture.

The measurement of soil moisture in agriculture is currently dominated by a small number of sensors, the use of which is greatly limited by their small sampling volume, high cost, need for close soil–sensor contact, and poor performance in saline, vertic and stony soils. This review was undertaken to explore the plethora of novel and emerging soil moisture sensors, and evaluate their potential use in agriculture. The review found that improvements to existing techniques over the last two decades are limited, and largely restricted to frequency domain reflectometry approaches. However, a broad range of new, novel and emerging means of measuring soil moisture were identified including, actively heated fiber optics (AHFO), high capacity tensiometers, paired acoustic / radio / seismic transceiver approaches, microwave-based approaches, radio frequency identification (RFID), hydrogels and seismoelectric approaches. Excitement over this range of potential new technologies is however tempered by the observation that most of these technologies are at early stages of development, and that few of these techniques have been adequately evaluated in situ agricultural soils.

Demonstrating the Potential of Low-Cost GPS Units for the Remote Measurement of Tides and Water Levels Using Interferometric Reflectometry

AbstractA low-cost [$30 (U.S. dollars)] consumer grade GPS receiver with a sideways-mounted antenna has been applied to measure tidal water levels at a mesotidal coastal site using an interferometric reflectometry approach. The proof-of-concept system was installed approximately 16 m above mean sea level in close proximity to a conventional bubbler tide gauge that provided validation data. The received signal-to-noise ratios (SNR) for the satellites in view were recorded for several months during two successive years and the observed frequencies of the interferometric oscillations used to calculate the difference in elevation between the receiver and the water surface. Comparisons with concurrent and historic in situ tide gauge data at the site initially helped to identify a calibration issue with the in situ gauge. The GPS-based measurements were shown to be in excellent agreement with the corrected in situ gauge, exhibiting a root-mean-square difference of 5.7 cm over a tidal range exceeding 3 m at spring tides and a daily averaged RMS of 1.7 cm. The SNR data from the low-cost GPS receivers are shown to provide significantly higher-quality data for this purpose compared with high-end geodetic grade receivers at similar sites. This low-cost, widely available technology has the potential to be applied globally for monitoring water levels in a wide variety of circumstances and applications that would otherwise be cost or situation prohibitive. It could also be applied as an independent cross check and quality control measure for conventional water-level gauges.

Detection-Localization-Identification of Vibrations Over Long Distance SSMF With Coherent $\Delta \phi$-OTDR

We propose a novel interrogation technique for Distributed Acoustic Sensing (DAS) and demonstrate the detection and recognition of multiple vibration events over 50 km of SSMF. A differential-phase optical time-domain reflectometry ( $\Delta \phi -$ OTDR) approach is used. At the transmitter side, a continuous ultra-narrow-linewidth laser is modulated with polarization-multiplexed orthogonal binary sequences and at the receiver side, the back-scattered signal is captured through a polarization-diversity coherent mixer in a self-homodyne configuration. The detection of the full optical field vector and the use of an ultra-narrow-linewidth laser source enhance the sensitivity of the interrogating solution. A comparison of the experimental results to a simulation model is developed to better understand the noise limits. A low-complexity localization technique based on a multi-resolution approach is also presented. Major results include the identification of an engine noise, paving the way for numerous smart-city/industrial monitoring applications over deployed telecom fibres.

A new thermo-time domain reflectometry approach to quantify soil ice content at temperatures near the freezing point

Soil ice content (θi) is an important property for many studies associated with cold regions. In situ quantification of θi with thermo-time domain reflectometry (TDR) at temperatures near the freezing point has been difficult. The objective of this study is to propose and test a new thermo-TDR approach to determine θi. First, the liquid water content (θl) of a partially frozen soil is determined from a TDR waveform. Next, a pulse of heat is applied through the thermo-TDR sensor to melt the ice in the partially frozen soil. Then, a second TDR waveform is obtained after melting to determine the θl, which is equivalent to the total water content (θt) of the partially frozen soil. Finally, θi is calculated as the difference between θt and θl. The performance of the new approach was evaluated in sand and loam soils at a variety of θt values. The new approach estimated θt, θl, and θi accurately. The root mean square errors (RMSE) of estimation were 0.013, 0.020, and 0.023 m3 m−3 for sand, and 0.041, 0.026, and 0.031 m3 m−3 for loam. These RMSE values are smaller than those reported in earlier thermo-TDR studies. Repeating the thermo-TDR measurements at the same location on the same soil sample caused decreased accuracy of estimated values, because of radial water transfer away from the heater tube of the thermo-TDR sensor. Further research is needed to determine if it is possible to obtain accurate repeated measurements. The use of a dielectric mixing model to convert the soil apparent dielectric constant to θl improved the accuracy of this approach. In our investigation, application of a small heat intensity until the partially frozen soil temperature became larger than about 1 °C was favorable. The new method was shown to be suitable for estimating ice contents in soil at temperatures between 0 °C and − 2 °C, and it could be combined with the volumetric heat capacity or thermal conductivity thermo-TDR based methods, which measured ice content at colder temperatures. Thus, the thermo-TDR technique could measure θi at all temperatures.

Potential clinical applications of terahertz reflectometry for the assessment of the tear film stability

Terahertz reflectometry technique is applied for noninvasive precorneal tear film assessment. The results of the receiver operating characteristic analysis show a good applicability of the proposed method. The direct comparison of the results obtained by reflectometry approach and results of Norn testing shows a good correlation. The in vivo measurement of the dynamic of tear film thinning could be useful for clinical diagnosis of dry eye syndrome.

Structural evolution of a Ni/NiOx based supercapacitor in cyclic charging-discharging: A polarized neutron and X-ray reflectometry study

Ni/Ni-oxide based supercapacitors with their excellent stability and long cycle lifetime are favorable due to their cost effectiveness and practicality. And yet, the full picture of their cyclic charging-discharging process is not well understood, and the influential factors on the cycle life of a supercapacitor are complicated. Using a combined polarized neutron and X-ray reflectometry approach, we have studied the structural evolution of a layered Ni/NiOx supercapacitor electrode, operated in an alkaline electrolyte for cyclic charging-discharging. For the lower thousands of cycles, oxidation of Ni current-collecting backbone and dissolution of outer Ni oxide electroactive materials contribute to a total thickness consumption of 2 nm. Upon higher thousands of cycles, the two-dimensional NiOx surface-layer evolves into a three-dimensional porous network as a result of the “hole drilling” depletion behavior of Ni oxide, i.e., dissolution of the “more porous” part and preservation of the “more compact” part in the NiOx layer. The extra surface area of the Ni/NiOx supercapacitor generated after cyclic charging-discharging gives rise to an increased capacitance. Evidenced by the increased derived density, the crystal defects of inner-layer NiOx are also eliminated with cycling, probably through Ni atom rearrangement, filling of oxygen vacancies within NiOx, or both.

Analysis of organic multilayer structures using a combined grazing incidence X-ray fluorescence/X-ray reflectometry approach

Organic light-emitting diodes (OLEDs) continue to attract research interest due to their application in bright displays and solid-state lighting. The highest efficiency values are reached with multilayer devices. The morphology of these layers is important for device performance. A current field of development is the application of solution-based deposition techniques. In general, solution processed devices do not yet reach the performance of OLEDs with vapor deposited materials. In this study, we used typical OLED materials with a sulfur based small molecule host, which can be vapor deposited as well as solution processed, to prepare single and multilayer samples. Samples consisted of the host layer deposited on a hole transport and a buffer layer and were investigated with a combination of grazing incidence X-ray fluorescence (GIXRF) and X-ray reflectometry (XRR). Measurements were performed using a diffractometer with an added fluorescence detector. The angle curves obtained have been evaluated with the software package JGIXA. Significant differences between differently prepared samples have been observed for single layer and multilayer samples. Sulfur could be detected in the layers beneath the solution processed host layer, but not in the layers below the vapor deposited host. The obtained results demonstrate the combination of GIXRF and XRR as a suitable nondestructive analysis method for the characterization of organic thin films with little to no sample preparation required.

Improved thermo-time domain reflectometry method for continuous in-situ determination of soil bulk density

Quantifying the dynamics of surface soil bulk density (ρb) is important for characterizing water, heat, and gas exchanges in agricultural and environmental applications. Unfortunately, very few approaches are available for continuous in-situ monitoring of ρb. The soil heat capacity-based (C-based) thermo-time domain reflectometry (thermo-TDR) approach has been used to measure ρb in-situ, but this approach gives ρb estimates with relatively large errors. In this study, we present a new soil thermal conductivity-based (λ-based) thermo-TDR approach for continuous and automatic determination of ρb variation in-situ. An error analysis, literature data, and field experiments were used to evaluate the performance of the C-based and λ-based approaches. The error analysis undertaken on hypothetical soils indicated that the new λ-based approach was less sensitive to errors in the measurement inputs than was the C-based approach when the same relative errors occurred, except on very dry soils. Thermo-TDR measurements reported in the literature on seven soils showed that the new λ-based approach provided more accurate and precise ρb estimates, with coefficient of determination (R2) of 0.70 and root mean square error (RMSE) of 0.103 Mg m−3, than did the C-based approach which gave ρb with R2 of 0.32 and RMSE of 0.178 Mg m−3. Two field experiments were conducted to test the performance of the new λ-based thermo-TDR approach for monitoring ρb dynamics. The results showed that following tillage surface ρb increased by about 35% within 40 days. The ρb obtained by the λ-based thermo-TDR approach agreed well with independent core sampling measurements, with an average RMSE of 0.122 Mg m−3. The C-based approach failed to give acceptable ρb estimates in most cases because of probe deflection and environmental factors. We conclude that the new λ-based thermo-TDR approach is a promising method for continuous in situ measurements of ρb.

Experimental location of damage in microelectronic solder joints after a board level reliability evaluation

Abstract Reliability evaluation of integrated circuit (IC) packages to assess drop impact is critical, especially in the case of handheld electronic products. The objective of this study is to experimentally identify the location of damage in solder joints in electronic packaging after a board level reliability (BLR) evaluation. The BLR drop test is a useful way to characterize the drop durability of different soldered assemblies onto a printed circuit board (PCB). It is also of great importance when there is a need to evaluate the solder joint between the chip package and PCB through a daisy-chained structure during the evaluation period. However, there is no detailed information available on a pattern ground with a hatched copper PCB layout for high speed responses that are closely related to actual working conditions. In this paper, a fault location on a daisy-chained structure with a pattern ground is shown through a non-destructive analysis using a time-domain reflectometry (TDR) approach. The results obtained in this project indicate that the TDR approach can be used to detect the location of a crack in the string based on changes in the waveform response. The fault location in critical solder balls as predicted by TDR correlate well with experimental observation by cross-section.

Optical fiber fuel level sensor for aeronautical applications

An optical fiber fuel level sensor for aeronautical applications is developed and tested. The sensor is based on an array of total internal reflection point sensors multiplexed on a single fiber by optical couplers and simultaneously interrogated by an Optical Time Domain Reflectometry approach. Unlike conventional sensors based on total internal reflection, the new design permits to be sensitive to common jet fuels (JetA-1, JP4, JP5, JP7), and also to correctly operate when the sensor is partially or totally exposed to condensed water on the sensor surface. The sensor does not require aircraft calibration or temperature compensation.Experimental results show that an accuracy of±1.5mm could be achieved. The sensor is also able to measure the free water level in the fuel tank.

Study of dielectric behavior of ternary mixtures of epoxy/titanates (MgTiO3, CaTiO3, SrTio3and BaTiO3) with carbon black

The aim of this paper is to study and to model the dielectric behavior of various ternary composites prepared with epoxy resin (RE), one type of titanates (magnesium titanate MgTiO 3 , calcium titanate CaTiO 3 , strontium titanate SrTiO 3 , and barium titanate BaTiO 3 ) with carbon black (CB). The study has therefore been focused on the effect of adding carbon black to titanate included in an epoxy matrix. The effects have been quantified according to the volume fraction of carbon black. In this work, we present a method based on nonlinear optimization for determining the permittivity of the every constituent, in order to minimize systematic errors and mount the effect of carbon black. The time domain reflectometry (TDR) approach is used to characterize the samples under test in the range from DC to 10 GHz. The conductivity behavior study is performed at a low frequency of 400 MHz, throughout this work. We explain the carbon black effect on the ternary mixtures by using the substitution principle for predicting their dielectric behavior. The experimental results confirm the concordance with the modified Lichtenecker mixture law. To predict the electromagnetic behavior of the ternary composites in quantitative manner, we use a numerical optimization method for identification the parameters of the theoretical model. Finally, these materials find their interest in the miniaturization of electronic components used in microelectronic and telecommunication applications.

Relaxation dynamics and thermophysical properties of vegetable oils using time-domain reflectometry

Dielectric relaxation studies of vegetable oils are important for insights into their hydrogen bonding and intermolecular dynamics. The dielectric relaxation and thermo physical properties of triglycerides present in some vegetable oils have been measured over the frequency range of 10MHz to 7GHz in the temperature region 25 to 10°C using a time-domain reflectometry approach. The frequency and temperature dependence of dielectric constants and dielectric loss factors were determined for coconut, peanut, soya bean, sunflower, palm, and olive oils. The dielectric permittivity spectra for each of the studied vegetable oils are explained using the Debye model with their complex dielectric permittivity analyzed using the Havriliak-Negami equation. The dielectric parameters static permittivity (ε 0), high-frequency limiting static permittivity (ε ∞), average relaxation time (τ 0), and thermodynamic parameters such as free energy (∆F τ), enthalpy (∆H τ), and entropy of activation (∆S τ) were also measured. Calculation and analysis of these thermodynamic parameters agrees with the determined dielectric parameters, giving insights into the temperature dependence of the molecular dynamics of these systems.

Mobile Surface Reflectometry

AbstractWe present two novel mobile reflectometry approaches for acquiring detailed spatially varying isotropic surface reflectance and mesostructure of a planar material sample using commodity mobile devices. The first approach relies on the integrated camera and flash pair present on typical mobile devices to support free‐form handheld acquisition of spatially varying rough specular material samples. The second approach, suited for highly specular samples, uses the LCD panel to illuminate the sample with polarized second‐order gradient illumination. To address the limited overlap of the front facing camera's view and the LCD illumination (and thus limited sample size), we propose a novel appearance transfer method that combines controlled reflectance measurement of a small exemplar section with uncontrolled reflectance measurements of the full sample under natural lighting. Finally, we introduce a novel surface detail enhancement method that adds fine scale surface mesostructure from close‐up observations under uncontrolled natural lighting. We demonstrate the accuracy and versatility of the proposed mobile reflectometry methods on a wide variety of spatially varying materials.