Compact Time-domain Research Articles

Highly Compact Time-Domain Borehole Radar With Time-Varying Gain Equivalent Sampling

Highly Compact Time-Domain Borehole Radar With Time-Varying Gain Equivalent Sampling

Rapid Measurement of Magnetic Particle Concentrations in Wildland–Urban Interface Fire Ashes and Runoff Using Compact NMR

Wildfires are increasing in size, frequency, and intensity, releasing increased amounts of contaminants, including magnetic particles, into the surrounding environment. The aim of this paper is to develop a sensing method for the detection and quantification of magnetic particles (MPs) in fire ash and fire runoff using a compact Time-Domain Nuclear Magnetic Resonance (TD-NMR) system. The system is made up of custom NMR electronics with a compact and rugged permanent magnet array designed to enable future deployment as an in situ sensor. A signal-to-noise ratio of 25 dB was measured for a single scan, and sufficient data can be acquired in one minute. A linear relationship with an R <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> value of 0.9699 was established between transverse relaxation rates and MP concentrations in ash samples. This was validated by testing known dilutions of pure magnetite particles and showing that they fit within the same linear curve. The developed approach was then applied to detect MPs in surface water, where changes in the relaxation rates as high as 400% were observed before and after a wildfire event. MPs were removed from the surface water using a magnetic particle separator to confirm that observed changes were solely due to the presence of MPs. The compact NMR system can be used as a simple and rapid approach to track and quantify the concentrations of magnetic particles released from fire ashes and also from other sources such as discharges from coal ash and other combustion ashes.

Compact time-domain diffuse optics system based on CMOS technologies for fast acquisitions of heartbeat-induced absorption changes

Compact time-domain diffuse optics system based on CMOS technologies for fast acquisitions of heartbeat-induced absorption changes

Picosecond pulses with 40 W peak power from a passively mode‐locked tapered quantum well laser

In this letter, the authors present a monolithic edge emitting diode laser intended as a potential key component for the generation of terahertz radiation in a compact time-domain spectroscopy system. The 6 mm long multi-section InGaAsP double quantum well (DQW) laser, featured with a 3.6 mm long tapered (TP) gain section, operates at a wavelength of ∼832 nm and generates pulses at a fundamental repetition rate of ∼6.3 GHz in passive mode-locking operation. Pulses with 2.6 ps width and 40 W peak power are measured. The generated pulses are not bandwidth-limited and should be compressible for further applications.

High-Sensitivity and Compact Time Domain Soil Moisture Sensor Using Dispersive Phase Shifter for Complex Permittivity Measurement

This article presents a time domain transmissometry soil moisture sensor (TDT-SMS) using a dispersive phase shifter (DPS), consisting of an interdigital capacitor that is loaded with a stacked four-turn complementary spiral resonator (S4-CSR). Soil moisture measurement technique of the proposed sensor is based on the complex permittivity sensing property of a DPS in time domain. Soil relative permittivity which varies with its moisture content is measured by burying the DPS under a soil mass and changing its phase difference while excited with a 114-MHz sine wave (single tone). DPS output phase and magnitude are compared with the reference signal and measured with a phase/loss detector. The proposed sensor exhibits accuracy better than ±1.2% at the highest volumetric water content (VWC = 30%) for sandy-type soil. Precise design guide is developed and simulations are performed to achieve a highly sensitive sensor. The measurement results validate the accuracy of theoretical analysis and design procedure. Owning the advantages of low profile, low power consumption, and high sensitivity makes the proposed TDT-SMS a good candidate for precision farming and internet of things (IoT) systems.

A Compact Multi-Distance DCS and Time Domain NIRS Hybrid System for Hemodynamic and Metabolic Measurements.

In this work, we present a new multi-distance diffuse correlation spectroscopy (DCS) device integrated with a compact state-of-the-art time domain near infrared spectroscopy (TD-NIRS) device. The hybrid DCS and TD-NIRS system allows to retrieve information on blood flow, tissue oxygenation, and oxygen metabolic rate. The DCS device performances were estimated in terms of stability, repeatability, ability in retrieving variations of diffusion coefficient, influence of the tissue optical properties, effect of varying count rates and depth sensitivity. Crosstalk between DCS and TD-NIRS optical signals was also evaluated. Finally, in vivo experiments (venous and arterial cuff occlusions on the arm) were conducted to test the ability of the hybrid system in measuring blood flow variations.

Adaptive-glasses time-domain FFOCT for wide-field high-resolution retinal imaging with increased SNR.

The highest three-dimensional (3D) resolution possible in in vivo retinal imaging is achieved by combining optical coherence tomography (OCT) and adaptive optics. However, this combination brings important limitations, such as small field-of-view and complex, cumbersome systems, preventing so far the translation of this technology from the research lab to clinics. In this Letter, we mitigate these limitations by combining our compact time-domain full-field OCT (FFOCT) with a multi-actuator adaptive lens positioned just in front of the eye, in a technique we call the adaptive-glasses wavefront sensorless approach. Through this approach, we demonstrate that ocular aberrations can be corrected, increasing the FFOCT signal-to-noise ratio (SNR) and enabling imaging of different retinal layers with a 3D cellular resolution over a 5∘×5∘ field-of-view, without apparent anisoplanatism.

Light phase detection with on-chip petahertz electronic networks

Ultrafast, high-intensity light-matter interactions lead to optical-field-driven photocurrents with an attosecond-level temporal response. These photocurrents can be used to detect the carrier-envelope-phase (CEP) of short optical pulses, and enable optical-frequency, petahertz (PHz) electronics for high-speed information processing. Despite recent reports on optical-field-driven photocurrents in various nanoscale solid-state materials, little has been done in examining the large-scale electronic integration of these devices to improve their functionality and compactness. In this work, we demonstrate enhanced, on-chip CEP detection via optical-field-driven photocurrents in a monolithic array of electrically-connected plasmonic bow-tie nanoantennas that are contained within an area of hundreds of square microns. The technique is scalable and could potentially be used for shot-to-shot CEP tagging applications requiring orders-of-magnitude less pulse energy compared to alternative ionization-based techniques. Our results open avenues for compact time-domain, on-chip CEP detection, and inform the development of integrated circuits for PHz electronics as well as integrated platforms for attosecond and strong-field science.

Real-Time Dual-Wavelength Time-Resolved Diffuse Optical Tomography System for Functional Brain Imaging Based on Probe-Hosted Silicon Photomultipliers.

Near-infrared diffuse optical tomography is a non-invasive photonics-based imaging technology suited to functional brain imaging applications. Recent developments have proved that it is possible to build a compact time-domain diffuse optical tomography system based on silicon photomultipliers (SiPM) detectors. The system presented in this paper was equipped with the same eight SiPM probe-hosted detectors, but was upgraded with six injection fibers to shine the sample at several points. Moreover, an automatic switch was included enabling a complete measurement to be performed in less than one second. Further, the system was provided with a dual-wavelength (670 and 820 ) light source to quantify the oxy- and deoxy-hemoglobin concentration evolution in the tissue. This novel system was challenged against a solid phantom experiment, and two in-vivo tests, namely arm occlusion and motor cortex brain activation. The results show that the tomographic system makes it possible to follow the evolution of brain activation over time with a 1-resolution.

Stability Condition and Numerical Dispersion of Fourth-Order Compact Precise-Integration Time-Domain Method

In order to mitigate the numerical dispersion errors of the compact precise integration time-domain (CPITD) algorithm, the fourth-order CPITD [CPITD(4)] method is proposed recently which is based on the fourth-order finite-difference scheme and the precise integration technique. Both the stability condition and the numerical dispersion equation have been obtained. In this paper, the numerical dispersion characteristics of the CPITD(4) method, especially the improvement of the numerical dispersion by using the fourth-order finite-difference scheme are discussed in detail. It is found that the numerical dispersion errors of the CPITD(4) method are much less than those of the CPITD, compact finite-difference time-domain (CFDTD), and CFDTD(2,4) methods and can be made nearly independent of the time-step size. Furthermore, the numerical experiments validate the accuracy and the efficiency of the CPITD(4) method, and also verify our analysis of the numerical dispersion characteristics of the CPITD(4) method.

High-Order Symplectic Compact Finite-Different Time-Domain Algorithm for Guide-Wave Structures

Based on higher order symplectic integrator temporal derivatives and compact spatial derivatives, a new high-order symplectic compact finite-difference time-domain (FDTD) algorithm is proposed. The numerical stability criteria and dispersion relation are derived analytically. Compared with the traditional compact FDTD algorithm, the proposed algorithm can significantly reduce the numerical dispersion error and can be made nearly independent of the maximum limitation of the Courant–Friedrich–Levy law. By means of the numerical examples, the proposed algorithm has the benefit of conserving energy for long-time propagation, which can be used to enhance the computational efficiency for the full-wave-analysis of guided-wave structures.

Unconditional $$L^{\infty }$$ L ∞ -convergence of two compact conservative finite difference schemes for the nonlinear Schrödinger equation in multi-dimensions

This paper is concerned with the unconditional and optimal $$L^{\infty }$$ -error estimates of two fourth-order (in space) compact conservative finite difference time domain schemes for solving the nonlinear Schrodinger equation in two or three space dimensions. The fact of high space dimension and the approximation via compact finite difference discretization bring difficulties in the convergence analysis. The two proposed schemes preserve the total mass and energy in the discrete sense. To establish the optimal convergence results without any constraint on the time step, besides the standard energy method, the cut-off function technique as well as a ‘lifting’ technique are introduced. On the contrast, previous works in the literature often require certain restriction on the time step. The convergence rate of the proposed schemes are proved to be of $$O(h^4+\tau ^2)$$ with time step $$\tau $$ and mesh size h in the discrete $$L^{\infty }$$ -norm. The analysis method can be directly extended to other finite difference schemes for solving the nonlinear Schrodinger-type equations. Numerical results are reported to support our theoretical analysis, and investigate the effect of the nonlinear term and initial data on the blow-up solution.

A spread spectrum approach to time-domain near-infrared diffuse optical imaging using inexpensive optical transceiver modules.

We introduce a compact time-domain system for near-infrared spectroscopy using a spread spectrum technique. The proof-of-concept single channel instrument utilises a low-cost commercially available optical transceiver module as a light source, controlled by a Kintex 7 field programmable gate array (FPGA). The FPGA modulates the optical transceiver with maximum-length sequences at line rates up to 10Gb/s, allowing us to achieve an instrument response function with full width at half maximum under 600ps. The instrument is characterised through a set of detailed phantom measurements as well as proof-of-concept in vivo measurements, demonstrating performance comparable with conventional pulsed time-domain near-infrared spectroscopy systems.

Compact and Passive Time-Domain Models Including Dispersive Materials Based on Order-Reduction in the Frequency Domain

In this paper, compact time-domain (TD) models featuring materials with frequency-dependent electromagnetic (EM) properties are derived. The considered frequency-dependent material models include multiterm Debye and Lorentz models for the electric permittivity and the magnetic permeability and a multiterm Drude model for the electric conductivity. The TD models are based on finite-element systems in the frequency domain (FD). To render the model compact and computationally efficient, the dimension of the FD system is compressed with the help of projection-based model-order reduction. In contrast to older approaches, the TD transformation is performed on the FD model itself rather than on the transfer function. The result is a state-space representation, which may either be solved by custom time integrators or imported into commercial circuit simulators. The advantages of the new approach include provable passivity of the FD model, provable causality of the TD model, and the ability to reconstruct the transient EM fields.

Abstract P041: New Biomarkers for Detecting and Subtyping Insulin Resistance

Introduction: The metabolic abnormalities that precede type 2 diabetes progress slowly and in stages. Current evidence-based diabetes prevention programs target individuals in Stage 2 (impaired glucose tolerance or prediabetes). However, by that stage, 70% of pancreatic beta-cell insulin secretory capacity has been lost irreversibly. Thus, it is imperative to identify individuals in Stage I (early insulin resistance syndrome) in order to preserve pancreatic insulin secretion and prevent both diabetes and prediabetes. Early insulin resistance syndrome is characterized by compensatory hyperinsulinemia, dyslipidemia, sub-clinical inflammation and acid-base abnormalities. The nature of the association between these elements is unclear, and different subtypes of insulin resistance syndrome may exist. Hypothesis: We have developed two novel and unconventional biomarkers for characterizing insulin resistance in non-diabetic subjects. One approach is based on dynamic light scattering (DLS) of human serum. The second approach measures the T 2 relaxation time of water in human plasma using compact time-domain NMR relaxometry (TD-NMR). We hypothesize that these methods can detect subtypes, i.e. , insulin resistance with or without inflammation, hypercholesterolemia, or acid-base abnormalities. Methods: Seventy-two asymptomatic non-diabetic human subjects were recruited through an IRB-approved biomarker discovery protocol. Medical histories, anthropomorphic measurements and fasting blood samples were obtained, and over 1300 blood biomarkers were measured on each subject along with DLS and TD-NMR parameters. Bi-variate correlation analyses and multiple regression models were used to analyze continuous variables, and categorical variables were established for insulin resistance, inflammation, acid-base abnormalities and lipid abnormalities. Multiple means comparisons were performed using one-way ANOVA and Tukey-Kramer testing. Results: Plasma water T 2 from TD-NMR was strongly correlated with markers of early insulin resistance syndrome. Multiple regression analysis showed independent contributions from markers of hyperinsulinemia, hypercholesterolemia and inflammation. Multiple means comparisons showed significant differences for insulin resistance with and without inflammation. By contrast, DLS parameters were strongly correlated with insulin markers, but could not distinguish the inflammatory subtypes. Conclusions: Both TD-NMR and DLS are able to detect early insulin resistance in individuals who do not meet the criteria for prediabetes or metabolic syndrome. However, TD-NMR has the unique ability to distinguish inflammatory vs. non-inflammatory subtypes of insulin resistance. Subtyping and risk stratification are important for the design of personalized interventions to prevent diabetes, prediabetes and cardiovascular disease.

Feasibility study of phase-sensitive imaging based on multiple reference optical coherence tomography

Multiple reference optical coherence tomography (MR-OCT) is a recently developed, low-cost and compact time-domain OCT solution for primary care and consumer level applications. A combination of a voice coil actuator and a partial mirror (PM) extends the scan range for imaging depths of approximately 1 mm in biological samples. Our previous research on MR-OCT is based only on intensity information obtained from the depth-resolved interference signal. In this Letter, we extract the phase information from the MR-OCT signal and, hence, provide an additional contrast modality. The phase sensitivity of the system is measured to be approximately 0.2 and 1.5 rad for the first and twelfth orders of reflection when using a mirror as the sample. This Letter describes first results of phase-sensitive data measured on a phantom obtained with MR-OCT. Data from a chick embryo chorioallantoic membrane (CAM) is used to demonstrate the feasibility of MR-OCT for in vivo phase-sensitive imaging.

Simulation and Measurement Methods for RCS Estimations of a Scale Model Airplane

In a military context, the radar cross section (RCS) of an airplane is a very important subject. For an RCS estimation object, a scaled-down model is often employed for ease of measurements. Recently, electromagnetic simulations of the RCS has become very convenient because of developments in high-speed calculation methods such as MLFMM and HOBF in electromagnetic simulators employing the MoM algorithm. As for the measurements, high-resolution measurements via the time domain analysis are promising. In this paper, important estimation expressions for use with a scale model are briefly explained. In terms of calculations, comparisons are drawn between the actual calculation abilities of MoM, MLFMM, and HOBF at 18 GHz for a 1/48-scale model. In terms of measurement, a high-resolution measurement system employing a compact range and time domain analysis that is used in this study is explained. Next, the calculated and measured results are compared in order to show the accuracy of the obtained results. The results in vertical and horizontal planes of a scale model are shown at vertical and horizontal polarizations. Moreover, using the calculation method to determine estimates at higher frequencies is also investigated in order to obtain the practical RCS value of a real-sized airplane

Wave Equation-Based Compact FDTD Algorithm for Longitudinally Magnetized Ferrite-Loaded Structures

In this paper, a compact finite-difference time-domain (FDTD) algorithm involving only the transverse components of the magnetic field and the magnetic induction is proposed for the dispersion analysis of longitudinally magnetized ferrite structures. Details of the implementation are presented as follows: 1) discretization; 2) boundary treatment; 3) the treatment of interfaces; and 4) the treatment of conductors. The constitutive relation of ferrite is simplified then suitably discretized using approximating formulas obtained from the Mobius transform technique. Some examples are presented to validate the algorithm with numerical results; good agreement is obtained by comparison with other frequency domain methods. A significant reduction in memory space requirements compared with other FDTD methods is also achieved.

Rational Modeling of Nonhomogeneous Systems

Nonhomogeneous transmission systems occur in several practical configurations such as nonideally transposed overhead lines, cross-bonded cables, and river crossings of overhead lines. In the past, a compact and efficient representation of nonhomogeneous system (NhS) was only possible in the frequency domain as the chain matrix (matrix transfer function) was used to obtain an equivalent nodal admittance matrix. Time-domain representation of a NhS demands explicit representation of each homogeneous section, thereby not being an efficient solution. This work proposes to represent nonhomogeneous systems using a rational approximation which allows for a compact and accurate time-domain realization. In this approach, we exploit the fact that a NhS can be seen as a particular case of a frequency-dependent network equivalent. The frequency dependence of the NhS is included via the rational modeling of the admittance matrix using the so-called Vector Fitting algorithm. Two test cases are considered to illustrate the gain of the proposed solution. The first one is the modeling of a nonideally transposed transmission line, and the second one is a case of river crossing. To asses the accuracy of the modeling, the results are compared against the ones obtained either using the Numerical Laplace Transform and PSCAD.

2D CPITD method for extracting attenuation constant of longitudinally invariant lossy transmission lines

Owing to the fact that the conventional compact two-dimensional (2D) precise integration time-domain (CPITD) method ignores the attenuation along the propagation direction for lossy invariant transmission lines, the calculation results are unsatisfactory. To extract the exact attenuation constant, a novel CPITD method that considers the attenuation constant along the propagation direction and describes an iterative process to seek out the attenuation constant is proposed. Compared with previous research related to the compact 2D finite-difference time-domain (CFDTD) method, the analytical or approximate analytical solution of the attenuation constant as the initial input value is used followed by the golden division method to find the interval of the exact attenuation constant in the iterative process. Numerical experimentations validate that the results of the novel method are much more accurate than those of the conventional CPITD method. Furthermore, the proposed method is of higher computational efficiency than the CFDTD method.