Small Reflection Coefficient Research Articles

Analysis of submerged breakwater models using ripple tank

A breakwater is an infrastructure that functions to dampen wave energy. To secure the area directly adjacent to the coast, an effective breakwater model is needed based on the analysis of the dissipation coefficient value ( ). This study aims to determine a good breaker model based on the value using a ripple tank. The data analyzed were wave heights before and after passing through the breakwaters of the three concrete models whose arrangement was varied. The results showed that the breaker model that is effective in reducing wave energy is the Grooved cube model with holes arranged horizontally based on the resulting small reflection coefficient ( ) and transmission coefficient ( ) values and large values

Four-wave mixing on thermal and resonant nonlinearities with feedback for object and signal waves

Background. The need to create highly efficient four-wave radiation converters in order to use them in adaptive optics systems, for real-time processing of complex spatio-temporal fields, in interferometry, quantum cryptography, etc. requires along with the use of traditional methods to increase the efficiency of such converters by increasing the interaction length, radiation power density, effective value of the nonlinear susceptibility of the development of new methods. One of these methods is a method based on the imposition of feedback on one or more interacting waves. Aim. The influence of feedback on the amplitude reflection coefficient of the degenerate four-wave radiation converter on thermal and resonant nonlinearities has been considered. Methods. The amplitude reflection coefficient of a degenerate four-wave radiation converter on thermal and resonant nonlinearities in the presence of feedback for both object and signal waves has been analyzed by a numerical method based on the multiple passage of the signal and object waves of the nonlinear layer in the ring resonator. Results. It was shown, that the difference in the reflection coefficients in the presence and absence of feedback for both object and signal waves increase monotonically with a growth in the pumping waves intensity and does not depend on the parameter characterizing the relationship between thermal and resonant nonlinearities at the approximation of a small reflection coefficient. Conclusion. The range of values of the absorption coefficient in which the imposition of feedback for both object and signal waves leads to an increase in the efficiency of the four-wave radiation converter has been established.

A Study on the Acquisition Technology for Weak Seismic Signals from Deep Geothermal Reservoirs

There are rich geothermal resources in China and they are widely distributed. After years of continuous exploration and production, most of the shallow geothermal resources have been explored and the current exploration mainly focuses on deep ones. Among a great many geophysical exploration methods, seismic survey is the most effective means of geothermal resource exploration and production, but its weak seismic reflection signal, low S/N ratio and poor imaging of thermal reservoirs due to the seismic geological conditions restrict the production and utilization of deep geothermal resources. It considers through the analysis of the geophysical characteristics of the thermal reservoir that the main causes for the weak seismic reflection signals from deep thermal reservoirs are (1) the shielding effect of the strong wave impedance interface between the thermal reservoir and the caprocks; (2) the small reflection coefficient inside the thermal reservoir; and (3) the serious absorption and attenuation of high-temperature fluids such as hydrothermal fluids and steam in the thermal reservoirs by seismic waves. Accordingly, a series of seismic data acquisition technologies are proposed based on the high-precision vibroseis low-frequency shooting, high-sensitivity geophones long-spread receiving and small bin size highfold technologies, and their application in the seismic acquisition of dry-hot rocks (HDR) in Gonghe Basin, Qinghai, shows a very good application effect.

A Wideband 5G CubeSat Patch Antenna

This article presents a wideband microstrip patch antenna for Ka-band CubeSat applications. The proposed antenna mainly consists of a square patch antenna printed on a grounded FR4 slab which is used as a building block. Moreover, a parasitic element and slots are added to enhance the impedance bandwidth and improve the gain, respectively. To validate the simulation results, a prototype patch antenna was fabricated and tested inside an anechoic chamber. A good agreement between the simulated and measured results is achieved. The performance of the proposed antenna is compared to the related existing antenna designs. The experimental results confirm that our proposed antenna achieves a wide −10 dB impedance bandwidth of about 20.2% (25.5–31.2 GHz), a small reflection coefficient of −45 dB, high efficiency of 82%, and a measured peak realized gain of 6.9 dB at 28 GHz.

Characterizing Fundamental Resonance Peaks on Flat-Lying Sediments Using Multiple Spectral Ratio Methods: An Example from the Atlantic Coastal Plain, Eastern United States

ABSTRACT Damaging ground motions from the 2011 Mw 5.8 Virginia earthquake were likely increased due to site amplification from the unconsolidated sediments of the Atlantic Coastal Plain (ACP), highlighting the need to understand site response on these widespread strata along the coastal regions of the eastern United States. The horizontal-to-vertical spectral ratio (HVSR) method, using either earthquake signals or ambient noise as input, offers an appealing method for measuring site response on laterally extensive sediments, because it requires a single seismometer rather than requiring a nearby bedrock site to compute a horizontal sediment-to-bedrock spectral ratio (SBSR). Although previous studies show mixed results when comparing the two methods, the majority of these studies investigated site responses in confined sedimentary basins that can generate substantial 3D effects or have relatively small reflection coefficients at their base. In contrast, the flat-lying ACP strata and the underlying bedrock reflector should cause 1D resonance effects to dominate site response, with amplification of the fundamental resonance peaks controlled by the strong impedance contrast between the base of the sediments and the underlying bedrock. We compare site-response estimates on the ACP strata derived using the HVSR and SBSR methods from teleseismic signals recorded by regional arrays and observe a close match in the frequencies of the fundamental resonance peak (f0) determined by both methods. We find that correcting the HVSR amplitude using source term information from a bedrock site and multiplying the peak by a factor of 1.2 results in amplitude peaks that, on average, match SBSR results within a factor of 2. We therefore conclude that the HVSR method may successfully estimate regional linear weak-motion site-response amplifications from the ACP, or similar geologic environments, when appropriate region-specific corrections to the amplitude ratios are used.

Reflectivity decomposition: Theory and application

Sparse reflectivity inversion of processed reflection seismic data is intended to produce reflection coefficients that represent boundaries between geologic layers. However, the objective function for sparse inversion is usually dominated by large reflection coefficients, which may result in unstable inversion for weak events, especially those interfering with strong reflections. We have determined that any seismogram can be decomposed according to the characteristics of the inverted reflection coefficients that can be sorted and subset by magnitude, sign, and sequence, and new seismic traces can be created from only reflection coefficients that pass the sorting criteria. We call this process reflectivity decomposition. For example, original inverted reflection coefficients can be decomposed by magnitude, large ones removed, the remaining reflection coefficients reconvolved with the wavelet, and this residual reinverted, thereby stabilizing inversions for the remaining weak events. As compared with inverting an original seismic trace, subtle impedance variations occurring in the vicinity of nearby strong reflections can be better revealed and characterized when only the events caused by small reflection coefficients are passed and reinverted. When we apply reflectivity decomposition to a 3D seismic data set in the Midland Basin, seismic inversion for weak events is stabilized such that previously obscured porous intervals in the original inversion can be detected and mapped, with a good correlation to the actual well logs.

Fabrication and characterization of epoxy resin–barium titanate at G-band using waveguide technique

In this paper, fabrication process of epoxy resin-barium titanate nanocomposite and measurement of its complex permittivity are presented. The material is prepared by mechanical mixing of epoxy resin and barium titanate nanopowder. The nanocomposite is intended to be used as high permittivity microstrip antenna substrate, which requires accurate measurement of its electrical characteristics. Thus, characterization of materials is done using waveguide technique, which does not require a precise machining of sample’s width and thickness, and does not utilize small reflection coefficient, which can cause error in measurement. The complex permittivity of the nanocomposite is measured in G-band (4 to 6 GHz). Then, the measured values are compared with prediction method, Lichtnecker and Maxwell-Garnet method. The results show that the measured permittivity of composite materials are in good range with prediction method, while the measurements of loss tangent show that the developed materials are low-loss and suitable to be used as substrate of antenna.

EVALUATION OF HYDRAULIC PERFORMANCE OF WAVE DISSIPATING BLOCK USING POROSITY

The reflection and transmission of wave dissipating work mainly depend on the shape and porosity of wave dissipating block. However, the influence of the shape and porosity of wave dissipating block on the reflection and transmission has not been investigated sufficiently. The purpose of this study is to investigate the influence of the porosity of wave dissipating block on the reflection and transmission coefficients through a series of hydraulic experiments where four kinds of wave dissipating blocks were used. Wave dissipating blocks with smaller porosity provided a larger reflection coefficient and a smaller transmission coefficient as a whole. However, a wave dissipating block provided a smaller reflection coefficient and a smaller transmission coefficient in spite of relatively larger porosity. The measured reflection and transmission coefficients were compared with those estimated by existing equations.Recorded Presentation from the vICCE (YouTube Link): https://youtu.be/lqyzabMw66U

A Wideband Metal-Only Patch Antenna for CubeSat

This article presents a compact wideband high gain patch antenna for CubeSat. The proposed metal-only antenna mainly consists of an upper patch, a folded ramp-shaped patch and shoring pins connecting the antenna with the ground plane. By adjusting the lengths and widths of two arms of the upper F-shaped patch, a second resonant frequency is generated, and hence, the −10 dB bandwidth is increased. Moreover, the effect of arms’ lengths and widths on reflection coefficients, operating frequency and bandwidth is presented. To validate the design and the simulation results, a prototype metal-only patch antenna was fabricated and tested in a Chamber. A good agreement between the simulated and measured results is achieved. The measured results show that the fabricated prototype achieves a −10 dB bandwidth of 44.9% (1.6–2.7 GHz), a small reflection coefficient of −24.4 dB and a high efficiency, i.e., 85% at 2.45 GHz. The radiation performance of the proposed antenna is measured, showing a peak realized gain of 8.5 dBi with cross polarization level less than −20 dB at 2.45 GHz and a 3 dB gain bandwidth of 61.22%.

Monitoring the seasonal changes of an englacial conduit network using repeated ground-penetrating radar measurements

Abstract. Englacial conduits act as water pathways to feed surface meltwater into the subglacial drainage system. A change of meltwater into the subglacial drainage system can alter the glacier's dynamics. Between 2012 and 2019, repeated 25 MHz ground-penetrating radar (GPR) surveys were carried out over an active englacial conduit network within the ablation area of the temperate Rhonegletscher, Switzerland. In 2012, 2016, and 2017 GPR measurements were carried out only once a year, and an englacial conduit was detected in 2017. In 2018 and 2019 the repetition survey rate was increased to monitor seasonal variations in the detected englacial conduit. The resulting GPR data were processed using an impedance inversion workflow to compute GPR reflection coefficients and layer impedances, which are indicative of the conduit's infill material. The spatial and temporal evolution of the reflection coefficients also provided insights into the morphology of the Rhonegletscher's englacial conduit network. During the summer melt seasons, we observed an active, water-filled, sediment-transporting englacial conduit network that yielded large negative GPR reflection coefficients (<-0.2). The GPR surveys conducted during the summer provided evidence that the englacial conduit was 15–20 m±6 m wide, ∼0.4m±0.35m thick, ∼250m±6m long with a shallow inclination (2∘), and having a sinusoidal shape from the GPR data. We speculate that extensional hydraulic fracturing is responsible for the formation of the conduit as a result of the conduit network geometry observed and from borehole observations. Synthetic GPR waveform modelling using a thin water-filled conduit showed that a conduit thickness larger than 0.4 m (0.3× minimum wavelength) thick can be correctly identified using 25 MHz GPR data. During the winter periods, the englacial conduit no longer transports water and either physically closed or became very thin (<0.1 m), thereby producing small negative reflection coefficients that are caused by either sediments lying within the closed conduit or water within the very thin conduit. Furthermore, the englacial conduit reactivated during the following melt season at an identical position as in the previous year.

Wideband microwave multiport-based system for low gas concentration sensing and its application for acetone detection

A microwave system dedicated to low gas concentrations sensing at room temperature is proposed. An optimized transmission line type sensor coated with a thin film, that changes electrical properties under target gas exposure is developed. The sensor’s response, namely its reflection coefficient is measured using a novel wideband multiport reflectometer. The instrument exhibits an advantageous measurement uncertainty, which can be adjusted to precisely measure small reflection coefficient changes over a wide bandwidth. Broadband data is used to extract the system’s response to gas defined as the reflection coefficient’s phase slope over frequency. The developed sensor covered with acetone-sensitive copper-oxide film together with a reflectometer operating over 1.5 GHz – 4.5 GHz band were incorporated in a gas measurement system to test its response to low acetone concentrations in the range of 0.5 ppm – 5 ppm. Due to high sensor’s sensitivity, optimum measurement conditions provided by the dedicated reflectometer and wideband analysis of the collected data, a robust and low-noise signal proportional to acetone concentration is achieved. The tested concentrations result in measured system’s response in the range of 0.02°/GHz – 0.29°/GHz @ 20 °C and 50 % of relative humidity derived with uncertainty of ±0.022°/GHz being 3 times lower than for a commercial instrument. Additionally, humidity dependence, stability, repeatability, reproducibility, and selectivity are investigated.

Investigation of Pore Pressure on Seismic Amplitude Response: A Well-Based Modeling Case Study of Sojuko Field, Niger Delta

The Sojuko field was discovered in 2001 in the eastern shallow offshore area of the Niger Delta, Nigeria. Three (3) exploration wells have so far been drilled in the field, two (2) of which are reasonably vertical and the third highly deviated. Three (3) key reservoirs which are laterally continuous across the wells have been identified with proven oil and gas reserves. Pore pressure data from repeat formation test (RFT) measurements acquired in the deviated well show that the wells are entirely hydrostatic to true depth (TD). This research focuses on investigating how seismic amplitudes change with offset/angle of incidence in relation to varying pore pressure regimes at the shale-hydrocarbon sand and shale-brine sand interfaces using well data. The aim is to aid quantitative interpretation in an on-going field-wide exploration drive to de-risk hydrocarbon exploration in the deeper plays in the area which are below TD, and are expected to be overpressured. The study is hinged on end-member shale elastic parameter substitution in which the shales are subjected to varying overpressure regimes while keeping the reservoirs (sands) at in situ (hydrostatic) condition. The end-member shale property substitution simulated shale compaction dis-equilibrium as the main overpressure generation mechanism in this study. The results show that top gas sands, top oil sands and top brine sands would be visible on seismic in the deeper plays where pore pressures are expected to be very high, but with distinctive seismic amplitude with offset/angle behavior. The top gas sands are visible as blue loop with small positive reflection coefficients at the near offsets/angles, but with polarity reversal to red loop with negative reflection coefficients which become more and more negative at the far angles at hard overpressure regimes. Top oil sands are recognized as blue loop with large positive reflection coefficients at the near angles; the coefficients becoming less and less positive at the far angles/offsets. The top oil sands may not be detected on seismic at the far angles/offsets unless at very hard overpressures. Brine sands have similar seismic response as oil sands at hard overpressures, but can be distinguished from oil sands based on their much higher amplitudes over the entire offset/angle range. The study is also aimed at removing uncertainty in seismic-based pore pressure quantification at the deeper targets where there is absence of well data for calibrating pore pressure effects at varying conditions.

High isolation circularly polarized (CP) antennas using compact soft surface

ABSTRACTA compact soft surface is proposed to improve an isolation of circularly polarized patch antennas in this article. The soft surface is generally made up of a periodically alternating perfect electric conductor and perfect magnetic conductor. The perfect magnetic conductor is implemented by the corrugation with a depth of quarter wavelength. The proposed compact soft surface is designed by a folded corrugation with a length of a quarter wavelength and the folded part is located below perfect electric conductor plane. Thus, the compact soft surface can be designed without any additional area above the ground plane. To verify its feasibility, mutual coupling and axial ratio of two circularly polarized antenna elements without and with the compact soft surface have been compared. This improved isolation results in small active reflection coefficient and wide beamwidth of active element pattern which would help to design wide scanning angle array.

Design and Characterization of Ultra-Wideband Horn Antenna in Quasi-TEM Mode

This paper describes the ultra-wideband horn antenna design operating in quasi TEM mode. The antenna consist of a triangular plate with an inclination angle above a ground plane and directly feed by a coaxial cable. Broadband characteristics, radiation pattern, high gain and small reflection coefficient were achieved. Its performance analysis and main parameters effects were obtained by using ANSYS HFSS software. In the numerical analysis, an optimized model was obtained in 1.57 to 12.85 GHz bandwidth a 11 to 14 dBi gain. The proposed antenna was manufactured and the measured reflection coefficient results show an operation frequency range between 1.48 and 10.12 GHz, agreeing very well with simulations.

Multifrequency Transformer With Arbitrary Frequency and Real Impedance Transform Ratio

In this letter, the modified small reflection theory is further extended to the design of a multifrequency transformer with an arbitrary frequency and real impedance transform ratio, by mapping small reflection coefficients between $2N+m$ - and $2N$ -section transformers. Due to the introduced mapping, the dominated equation of the $2N+m$ -section transformer is reduced to that of the $2N$ -section transformer without introducing an additional matching frequency among the desired frequency ratio range. For verification, a penta-frequency transformer is implemented and measured. The measured results agree closely with the calculated and simulated results.

Front to Back Ratio Bandwidth Enhancement of Resonance Based Reflector Antenna by Using a Ring-Shape Director and Its Time-Domain Analysis

An uni-directional antenna designed by resonance-based reflector has the merits of compact size, low-profile, and ultra-wide impedance bandwidth. However, its front to back ratio (FBR) bandwidth is narrow owing to the small reflection coefficient values at the high frequencies of the RBR in-phase band. To solve this problem, a ring-shaped director (RD) was placed above a resonance-based reflector-based antenna to guide the high frequencies. Then, the FBR bandwidth was enhanced. The proposed antenna achieves a wide measured impedance bandwidth from 2.17 to 3.76 GHz (53.6%). Its FBR band (FBR >7 dB) covers the whole operational band and the FBR >10-dB band covers 2.17–2.58 GHz (17.3%). The proposed antenna consists of a bow-tie element, a ring-shaped resonance-based reflector under the bow-tie element and an RD above the bow-tie element to form a sandwich configuration. The profile of the proposed antenna is only $0.16~\lambda $ at the lowest frequency of 2.17 GHz. To further evaluate the performances of the proposed antenna, the time-domain characteristics of the antenna were analyzed in terms of group delay, waveform response, correlation coefficient, and pulsewidth stretch ratio. Good time-domain characteristics were observed.

THE HYDRODYNAMIC CHARACTERISTICS OF AN INCLINED SUBMERGED POROUS PLATE WITH ROCK FILLED STRUCTURE

In this paper, we investigate the hydrodynamic efficiency of normal incident waves interacting with an absorbing system. The wave absorbing system consists of a submerged permeable structure filled with rock, a solid back wall, and a submerged horizontal or slightly inclined porous plate. Using a linear wave theory assumption, a multi-domain BEM (MBEM) model was created to calculate and discuss the reflection coefficients, free surface wave profiles, total wave force on the solid wall, and the horizontal and uplift forces acting on the porous plate of the water waves from several properties of the breakwater. The numerical model was calibrated using previous numerical studies to act as limiting cases for a partially submerged impermeable structure and a horizontal porous plate with a solid back wall. The accuracy of the solution is demonstrated by comparing the numerical values with those obtained from other analytical solutions. From the numerical results, the wave dissipation effect from the permeable rock-filled structure was found to perform better than expected when compared to an impermeable structure. In the case of a horizontal porous plate, the smaller submergence depth of the plate results in a smaller reflection coefficient. The larger the porous effect parameter, the smaller the value of the reflection coefficient and the larger the porous effect parameter, the greater the ability of the porous plate to reduce the uplift forces.

Optimisation of external cavity parameters of a weak absorption laser spectrometer

We consider some peculiar features of the optimisation procedure of external optical cavity parameters of a laser spectrometer, caused by the use of a three-beam measurement scheme and the presence of losses in the mirrors. It is found that the maximum sensitivity to the absorption of an intracavity medium can be achieved only at a certain choice of the value and the ratio of the reflection coefficients of the mirrors. For example, registration of the spectra of the methane impurity in the atmosphere shows that in accordance with the calculation model, for the same resonator -factor the use of an input mirror with a smaller reflection coefficient allows the measurement sensitivity to be increased by approximately two times.

Synthesis of microporous Ni/NiO nanoparticles with enhanced microwave absorption properties

The fabrication of microporous metal materials with many potential applications is challenging due to their high chemical activities and the difficulty in controlling the pore size. By adjusting the reaction condition and the composition of the Ni–Al nanoparticle precursor, we have successfully produced the microporous Ni nanoparticles (NPs) of 22 nm by chemical dealloying method. During the passivation process, the microporous Ni NPs covered with NiO shell are generated as the result of surface oxidation. The micropores range from 0.6 to 1.2 nm in diameter with a large surface area of 68.9 m2/g. Due to the elimination of Al atoms during dealloying process, the crystalline size of the microporous Ni NPs is sharply decreased to 2–5 nm. The specific architecture offers the microporous Ni/NiO NPs a small microwave reflection coefficient (RC) and a wide absorption bandwidth (RC ≤ −10 dB) of −49.1 dB and 5.8 GHz, much better than the nonporous counterpart of −24.1 dB and 3.7 GHz. The enhanced microwave absorption performance has been interpreted in terms of the micropore structure, core/shell structure and nanostructure effects.

G-Band 도파관 산란 계수 정밀 측정

본 논문에서는 (서브)밀리미터파 대역에서 산란 계수 정밀 측정이 어려운 요인 및 보다 정확한 측정을 하기 위한 방안을 기술하였으며, G-band(140~220 GHz)에서의 측정 사례를 제시하였다. 우선 마이크로파 대역과 (서브)밀리미터파 대역에서 사용되는 산란 계수 측정시스템(벡터회로망 분석기)의 동작 원리에 대한 차이점을 파악하고, (서브)밀리미터파 대역 산란 계수 측정시스템을 보다 잘 운영하기 위한 방안을 기술하였다. 그리고 더 좋은 도파관 전송 특성 및 연결 반복도를 얻기 위한 방안과 반사 계수 크기가 작은 피측정기를 정밀 측정하기 위한 방안을 기술하였다. This paper discusses difficulties in precise measurements of the scattering parameters in (sub-)millimeter-wave range and tips for more accurate measurements, and provides measurement examples in the G-band(140~220 GHz). First, one investigates the differences in operating principles of scattering parameters measurement systems used in microwave and (sub-)millimeter-wave ranges and describes tips for better operation of the (sub-)millimeter-wave scattering parameters measurement system. In addition, one describes tips for better transmission properties and connection repeatability of waveguides and a precise measurement method for devices with small reflection coefficients.