Reflection Amplitude Research Articles

Reconfigurable Amplitude-Phase-Coding Metasurface with Flexible Beamforming Capability

Recently, reconfigurable coding metasurfaces have attracted extensive attention due to their dynamic and flexible manipulation of electromagnetic (EM) waves, making them an effective solution to connect physical reality and information science. Nevertheless, most previously reported reconfigurable metasurfaces suffer from limited applications, as they solely possess either phase or amplitude modulation. In this article, we propose a reconfigurable coding metasurface that can regulate both phase and amplitude response independently. In the field of the metasurface, the phase response can tailor the wavefronts, and the amplitude response can adjust the redistribution of the energy of the EM waves. Specifically, by integrating a PIN diode into the meta-atom and controlling its bias voltage, the reflection phase can be switched between two opposite phases with a phase difference of about 180°, and the reflection amplitude can be manipulated from 0.02 to 0.98 continuously at 11 GHz. The unit element consists of simple multi-layer structures, reducing its production cost and processing difficulty. By loading 1-bit phase code and multi-bit amplitude code to each unit element severally, this metasurface can modulate the distribution of reflected EM waves in two-dimensional (2-D) space while simultaneously suppressing the sidelobes for any quantity of scattered beams over a wide operating band ranging from 10.5 to 11.5 GHz. This metasurface exhibits promising potential for manipulating the distribution of EM wave energy and shaping of EM beams, which can be expected to facilitate wireless communication technology.

Accurate P-wave reflection and transmission coefficients for non-welded interface incorporating elasto-plastic deformation

P-wave reflection and transmission coefficients for non-welded interface play crucial roles in broad practical engineering productions, involving fracture properties prediction and seismic inversion. However, the existing reflection coefficient equations for non-welded interface in elasto-plastic media are seldom studied, although the elasto-plastic deformation is frequently encountered in the Earth’s subsurface due to artificial and tectonic activities. In this study, we proposed the accurate reflection and transmission coefficients equation for a non-welded interface embedded in an elasto-plastic deformed medium based on the elasto-plastic acoustoelastic and linear-slip theory. In detail, this paper uses elasto-plastic acoustoelastic theory to derive the reflection and transmission coefficients equation. The reflection and transmission coefficients matrix are solved using the linear-slip theory as the boundary condition. Moreover, we use the hardening parameter and plastic deformation to represent the plastic properties of the rock, which is a function of stress and plastic deformation. Through Numerical analysis, the deformation caused by static stress has significantly changed the amplitude and the slope of the reflection and transmission coefficients amplitude. As the stress increases, the rock’s velocity becomes higher, and all reflection and transmission coefficients (i.e., RPP, RPS, TPP, TPS) abruptly change at the critical angle. Furthermore, with the increase in plastic deformation, the critical angle of the incident P-wave and the hardening parameter becomes larger than the unstressed state. The non-welded interface exhibits a low-pass frequency filter for reflected SV-waves and a high-pass frequency filter for reflected P-waves and transmitted P and SV waves. In addition, we can observe that static vertical stress can weaken the anomalous reflections caused by non-welded formations, but the effect is insignificant. On the other hand, the effect of fracture normal compliance to reflection and transmission is detailly investigated. When N<2.5*10-10(MPa-1), The non-welded interface is close to the welded interface, while N>2.5*10-5(MPa-1), the non-welded interface is close to the solid-air interface.

Ground penetrating radar investigations of buried remnants at ancient capital cities of Panchala and Vatsa kingdoms spread along Ganga-Yamuna doab of India from 600 BCE to 1100 CE

Ahichhatra and Kaushambi, ancient settlements located in Uttar Pradesh, comprise differential cultural deposits and architectural remnants from 2500 BCE to 1200 CE. These settlements flourished as the capital cities of once-prosperous urban kingdoms known as Panchala and Vatsa Mahajanapadas but remain abandoned in the present day. To provide ancillary data for the simplification of traditional archaeological explorational practices, a few portions located in and around the fortified areas of both settlements were considered for subsurface investigations using Ground Penetrating Radar (GPR). In Ahichhatra and Kaushambi, 2D and 3D GPR survey was carried out in the open areas devoid of vegetation for the understanding of the spatial alignment of the buried features within the fortified walls. The subsurface investigations at Ahichhatra have shown high amplitude reflections referring to buried wall structures, residential complexes, raised platforms, past-used surfaces and structural continuity. Also, the partial excavation carried out at Ahichhatra has revealed walls and compacted floors validating our findings. From Kaushambi, the findings include wall structures and interconnected chambered structures. The anomalies obtained in the data collected from considered survey sites located in Ahichhatra are 1–2 m wide and 2–4 m deep whereas in Kaushambi they are 0.5–1 m wide and 2–4 m deep. These findings helped us to determine the progressive urban relics of the ancient kingdoms which were known for their second phase of urbanism in Ganga Valley that prevailed until their abandonment. For a better understanding of the cultural history, detailed mapping of the contemporary sites can be carried out using integrated survey methods.

Measuring seismic attenuation in polar firn: method and application to Korff Ice Rise, West Antarctica

Abstract We present seismic measurements of the firn column at Korff Ice Rise, West Antarctica, including measurements of compressional-wave velocity and attenuation. We describe a modified spectral-ratio method of measuring the seismic quality factor (Q) based on analysis of diving waves, which, combined with a stochastic method of error propagation, enables us to characterise the attenuative structure of firn in greater detail than has previously been possible. Q increases from 56 ± 23 in the uppermost 12 m to 570 ± 450 between 55 and 77 m depth. We corroborate our method with consistent measurements obtained via primary reflection, multiple, source ghost, and critically refracted waves. Using the primary reflection and its ghost, we find Q = 53 ± 20 in the uppermost 20 m of firn. From the critical refraction, we find Q = 640 ± 400 at 90 m depth. Our method aids the understanding of the seismic structure of firn and benefits characterisation of deeper glaciological targets, providing an alternative means of correcting seismic reflection amplitudes in cases where conventional methods of Q correction may be impossible.

A Broadband X-Ray Study of the Dwarf Nova SS Cyg during Quiescence and Outburst

We present a broadband X-ray study (∼0.3–50 keV) of the dwarf nova SS Cyg highlighting the changes in the accretion during two phases, the quiescence and the outburst states. The investigation was based on simultaneous observations carried out with the XMM-Newton and NuSTAR telescopes in two epochs, involving medium- and high-resolution spectroscopy. Spectra were harder during quiescence (kT high ∼ 22.8 keV) than the outburst (kT high ∼ 8.4 keV), while the mass accretion rate increased by ∼35 times in the outburst (1.7 × 1016 g s−1) as compared to quiescence. The bolometric luminosity (0.01–100.0 keV) during the outburst was dominated by a blackbody emission (kT BB ∼ 28 eV) from the optically thick boundary layer (BL), and the inner edge of the accretion disk resides very close to the white-dwarf (WD) surface. X-rays from the BL are consistent with the WD having mass . Our study conclusively confirms the presence of the reflection hump in the 10–30 keV range for both phases, which arises when X-ray photons hit colder material and undergo Compton scattering. We estimated a similarly strong reflection amplitude during quiescence (∼1.25) and the outburst (∼1.31), indicating both the WD surface and disk are contributing to reflection. The neutral Fe K α line, which is correlated with Compton reflection, also showed similar strength (∼80 eV) in both phases. Finally, X-rays also revealed the presence of a partial intrinsic absorber during the outburst, possibly due to an outflowing accretion disk wind.

Bottom simulating reflectors in the Manila Trench forearc and its implications on the occurrence of gas hydrates in the region

Gas hydrate occurrence and stability in active plate margins have been reported in various localities, with investigations focusing on its potential as an alternative energy resource or the threat it poses due to dissociation and methane release into the atmosphere. The Manila Trench forearc, proximal to active margins and probable methane-rich sediments, can be an analog for gas hydrate formation and geologic preconditions constrained by tectonics and sedimentation processes. The possible occurrence of gas hydrates in offshore western Luzon Island is reported for the first time based on bottom simulating reflectors (BSRs) in multi-channel seismic reflection datasets. Results indicate a prevalence of BSRs on the frontal wedge seaward of the North Luzon Trough (NLT) and in the West Luzon Trough (WLT) basin fill. Continuous, discontinuous, double, and pluming BSRs in the forearc encompass a total area of approximately 15,400 km2 at depths of 223–553 mbsf in the frontal wedge and 486 to 1428 mbsf within the basins. Enhanced amplitude reflectors (EARs) above and below the BSRs indicate possible gas hydrate and free gas accumulations, respectively. Gas chimneys associated with the upward migration of methane-rich fluids appear to be controlled by deep structural features. The accretion of continent-derived sediments along the northern segment of the frontal wedge promotes the formation of fluid migration structures, enhancing fluid migration and gas hydrate formation at shallower depths. Estimated geothermal gradient values for the frontal wedge range from 28 to 92 °C/km, consistent with previously reported in-situ measurements from offshore SW Taiwan. In contrast, arc-derived sediments within the NLT and west-ward fluid migration along the landward-tilted sequences limit gas hydrate accumulation within the basin. To the south, the preferential formation of gas hydrates within the WLT basin points to deep gas sources within the forearc basin sediments, with upward movement of methane-rich fluids along normal faults. Estimated geothermal gradient values in the basin are lower, ranging from 12 to 45 °C/km, reflecting lower thermal conditions. The absence of BSRs seaward of the WLT signifies widespread gas hydrate dissociation in the frontal wedge slope.

Low-Sidelobe Dual-Beam Antenna Based on Metasurface With Independently Regulated Amplitude/Phase

A method to design low-sidelobe dual-beam antennas is proposed based on metasurface with independently regulated amplitude/phase. This method includes the following steps. Firstly, a standard horn antenna is modeled and the amplitude and phase of the radiation field at the interface are obtained. Next, the phase compensation technology based on the actual radiation phase of the feed is employed to control directions of the main lobe. Finally, the reflection amplitude of metasurface is controlled by combining Schelkunoff polynomials and actual radiation amplitude of the feed. Specifically, by mapping the angles of the dual beams to the complex coordinate system, the sidelobe level (SLL) of the dual-beam antenna is reduced. Meanwhile, a compensation factor is introduced to offset the gain loss caused by amplitude modulation.

Effects of scattering parameters on seismic observables of PKP precursors and apparent D″ reflections – A parameter study

The lowermost mantle has been studied with a variety of seismic waves which show that different structures on many length-scales exist there but it is possible that several seismic phases could be generated by one structure. Specifically, we use a randomly distributed scattering layer that is able to generate precursors to the core phase PKPdf as well as waves that resemble reflections off the D″ layer (PdP wave) and here we present a parameter study to understand how scattering parameters in this layer affect the two tested seismic waves and whether it is possible to discriminate between a reflector or a scattering layer as cause for apparent D″-reflected waves. We compute synthetic data for several source-receiver combinations and vary the parameters of the heterogeneity model above the core-mantle boundary: correlation length, velocity (and density) perturbation, taper to soften the transition, thickness, location of the scattering layer and the randomness of the models. We measure the effects on the amplitudes and arrival times of the seismic waves, and in addition for the apparent D″ reflection, we also record the number of reflected waves, their polarity and slowness. We find that the precursor and reflection amplitudes are influenced by all scattering parameters and that trade-offs exist. One conclusion therefore is that it is difficult to match local scattering parameters to fit observations with a unique model since several combinations of scattering parameters result in similar amplitudes and travel times. Interestingly, amplitudes for different correlation lengths are affected differently for larger and smaller epicentral distances, therefore testing the amplitudes of precursors at different distance ranges could potentially help to distinguish between correlation length and perturbation effects. We were not able to further narrow down the scattering parameters of the layer when using a combination of PKP precursors and PdP-like reflections due to the non-uniqueness. Analyzing the effects on PdP arrivals that arrive between P and PcP, we find influences on all seismic observables albeit without clear trends. But based on our modeling it seems prudent to assume that the waves are caused by a scattering layer if 1) the observations show strong scatter in arrival time, slowness and amplitude and 2) if more than one arrival is present between P and PcP.

Well‐log integration and seismic‐to‐well tie off George V Land (Antarctica)

AbstractCenozoic sediments from the continental rise off the George V Land consist of silty/clayey facies variably rich in diatom ooze; these sediments hold a record of the glacial history of the Wilkes Subglacial Basin and are important for estimating the contribution of the East Antarctic Ice Sheet to global sea level changes during past transition to warmer climates. This is fundamental to predict future scenarios related to the global warming. The petrophysical properties of Antarctic marine sediments are influenced by the ice sheet dynamics and may affect the amplitude of seismic reflections. Through a seismic‐to‐well tie procedure, we investigate the origin of high amplitude reflections from Miocene‐early Pliocene deposits identified in two seismic lines crossing at the Integrated Ocean Drilling Program Expedition 318 drill site U1359. Downhole and core log measurements are preconditioned and merged to obtain complete velocity and density records from the sea floor to the bottom of the deepest of the four wells drilled at this site. We generate a synthetic trace by convolving the reflectivity series with the seismic wavelet obtained from the sea‐floor reflection and match the synthetic trace to the seismic data with a time variant cross‐correlation procedure. This procedure established a robust time‐depth relationship, not achievable from the available small‐offset seismic data. To our knowledge, this is the first seismic‐to‐well tying in the George V Land area. Based on results from synthetic data, the anomalous high amplitude seismic package can be linked to changes in density of sediments. Such changes are interpreted as representative for the alternation of diatom‐rich (warm climate) and silty‐clay layers with ice‐rafted debris (cold climate) inside the deposits. We suggest that the analysis of the characteristics and the distribution of similar seismic anomaly around Antarctica can give insight into the modality of past Antarctic ice sheet dynamics.

Irradiation of ultrasonic sensors and adhesive couplants for application in light water reactor primary loop piping and components

The Electric Power Research Institute (EPRI) Nuclear Sector and US Department of Energy Light Water Reactor Sustainability Program are committed to engaging in research and development endeavors to address materials aging issues specific to long term operation of light water power reactors. To this effect, EPRI launched an industry initiative to develop nondestructive evaluation systems for online monitoring of existing cracks in light water reactor primary coolant loop piping and components. One of the goals of this initiative is to develop a sensor system (or systems) that can determine nondestructively if cracks are growing or arrested and, in the case of the former, to characterize their growth rates. A missing component of this initiative is an experimental assessment of how sensors and adhesive couplants will perform in service when exposed to chronic energetic neutron radiation, particularly at the primary coolant loop hot and cold leg dissimilar metal welds, which join the primary loop piping to the reactor pressure vessel and reside in the vicinity of the reactor core. The objective of this experimental study was to determine how ultrasonic transducers and adhesive couplants perform when exposed to irradiation in a test reactor to simulate and accelerate in-service exposure. To achieve this objective, the signal stability of piezoelectric transducers and performance of adhesive couplants as a function of accumulated fast neutron fluence were characterized by collecting ultrasonic data in-situ during irradiation. Of particular interest were the ultrasonic signal quality and time decay of the amplitude of acoustic reflections as a function of fast neutron fluence. The results of the study showed that, of the 8 transducer/substrate sample assemblies tested, only 3 generated usable ultrasonic signals through the conclusion of the irradiation campaign. It was found that high temperature epoxy tends to ultrasonically couple the sensors to the substrates better than three types of refractory ceramic cements studied, as is supported by post irradiation examination. The results obtained through this experimental study will be utilized in the achievement of the overall goal of development of a sensor system to perform online monitoring of primary loop components.This manuscript has been authored in part by UT-Battelle, LLC, under contract DE AC05-00OR22725 with the US Department of Energy (DOE). The publisher acknowledges the US government license to provide public access under the DOE Public Access Plan (https://energy.gov/downloads/doe-public-access-plan [energy.gov]).

Low-profile shared-aperture metasurface array antenna with ultra-wideband radar cross section reduction and circularly polarization

This paper proposes a circularly-polarized (CP) metasurface antenna with ultra-wideband radar cross section (RCS) reduction. Initially, the relationship between RCS reduction and phase difference with different reflection amplitudes is analyzed theoretically. Inspired by the shared-aperture principle, a high-frequency resistive layer is introduced into the antenna element to further fulfill ultra-wideband RCS reduction and low-profile requirements. Numerical simulations demonstrate that the inserted layer has no effect on the radiation performance of the antenna array. Then, the proposed element and its orthogonal unit are arranged in a checkerboard pattern for good CP radiation. In this configuration, the proposed metasurface array antenna has a maximum gain of 16.7 dBi with 72.1% aperture efficiency. The bandwidth of 5 dB RCS reduction with x- and y-polarized incidences is 7.10–17.95 GHz and 7.34–17.85 GHz, respectively. The proposed design is verified by the fabrication of prototype antennas and measurements.

Dual-band metasurface generating multiple OAM beams independently in full polarizations.

In this paper, a dual-band metasurface (MS) generating multiple orbital angular momentum (OAM) beams independently in full polarizations is proposed. First, the design principle of controlling full polarizations independently is analyzed. Second, the frequency selective surface is introduced to the meta-atom design that ensures the meta-atom operates at Ku- and Ka-band independently, while, at each band, sixteen optimized meta-atoms realize the high reflection amplitude and enough phase coverage. Next, the optimized dual-band meta-atom controlling full polarizations independently is utilized to design the MS, which could generate eight independent OAM beams including the x-polarized, y-polarized, left hand circularly polarized, and right hand circularly polarized OAM beams at dual-band. Finally, the MS is designed, fabricated, and measured. Both simulated and measured results verify that the proposed MS could generate multiple OAM beams in full polarizations at dual-band, showing the perspective in the OAM-based area, such as the wireless communication, target detection, and security encryption.

Development of an Autonomous Measurement System for Estimation of Snow Profile on Road Surfaces

This paper presents the development of a novel prototype system to measure the profile of snow and detect ice on road surfaces. While researchers have previously developed methods to estimate the tire-road friction coefficient, methods to create a high resolution map of snow cover and ice on roads have not been developed. The prototype and data processing methods presented in this study provide a potential solution that would greatly benefit winter road maintenance teams. Having a device capable of creating a detailed map of snow and ice cover on roads would allow for more efficient plowing and salt deployment, better informing of the public about current road conditions, as well as better analysis of current plowing techniques to improve winter road maintenance operations. The measurement of the snow profile is based on the use of two types of inexpensive ranging sensors mounted on a rotationally controlled stepper motor platform. The technical challenges addressed in the development include analysis of the scan path over which the system scans the road, differentiation between asphalt, concrete, and snow surfaces using reflection amplitudes, accurate transformation of raw distance measurements to inertial coordinates, and identification of the Euler angles of the sensors using parameters associated with the scanned surface profile. Extensive experimental results and test data are presented, which show that the system is capable of measuring the snow profile on a road with an accuracy of ±1 cm when a reasonable portion of bare road is visible, and ±2 cm when only small portions of bare road are visible.

Rapid and Efficient Computation of Cell Paths During Ultrasonic Focusing.

This biophysical analysis explores the first-principles physics of movement of white blood cell sized particles, suspended in an aqueous fluid and experiencing progressive or standing waves of acoustic pressure. In many current applications the cells are gradually nudged or herded toward the nodes of the standing wave, providing a degree of acoustic focusing and concentration of the cells in layers perpendicular to the direction of sound propagation. Here the underlying biomechanics of this phenomenon are analyzed specifically for the viscous regime of water and for small diameter microscopic spheroids such as living cells. The resulting mathematical model leads to a single algebraic expression for the creep or drift velocity as a function of sound frequency, amplitude, wavelength, fluid viscosity, boundary dimensions, and boundary reflectivity. This expression can be integrated numerically by a simple and fast computer algorithm to demonstrate net movement of particles as a function of time, providing a guide to optimization in a variety of emerging applications of ultrasonic cell focusing.

Structural design of a coding absorber filled with graphene/carbonyl iron powder composite microspheres

Electromagnetic stealth technology played a crucial role in national defense. Encoded metasurfaces and metamaterials had been widely applied in the fields of radar and electromagnetic stealth. In this study, a filled absorber based on scattering enhancement was investigated. Graphene/iron carbonyl composite microspheres were filled into a 3D-printed shell as the absorbing material. The scattering characteristics were controlled by adjusting the absorption gradient, reflection amplitude, and reflection phase of each basic unit. The filled absorber allowed for control of the reflection amplitude through phase modulation, achieving a combined effect of electromagnetic loss and scattering characteristics, resulting in the reduction of radar cross-section. The study also examined the effect of the area fraction of the two cells on the performance of the reduced RCS. The best performance is achieved when the area fraction of cell 0 is 0.5. Simulation results show that the filled absorber effectively reduces the radar cross section in the frequency range of 9.92 GHz to 18 GHz with a minimum value of −34.58 dB. Compared with the simulation results, the measured data show that it effectively reduces the radar cross section in the frequency range of 8.32 GHz to 16.03 GHz with a minimum value of −25.08 dB. This study provided a novel approach for designing high-performance absorbers based on scattering enhancement, which held significant potential in the fields of electromagnetic wave absorption and stealth technology.

Covert Federated Learning via Intelligent Reflecting Surfaces

Over-the-air computation (OAC) is a promising technology that can achieve rapid model aggregation by utilizing the wireless waveform superposition feature to harness the interference of multiple-access channel for wireless federated learning (FL). However, OAC-based aggregation for OAC faces critical security challenges due to unfavorable and wireless broadcast properties, such as privacy leaks and eavesdropping attacks. In this paper, we propose to utilize an intelligent reflecting surface (IRS) to support covert OAC-based FL. We first derive the optimal condition for covertness in OAC with IRS and formulate a joint optimization problem to select the maximum covert devices participating in the model aggregation while satisfying the mean squared error (MSE) requirement. We then design a covert difference-of-convex-functions program (CDC) to efficiently determine the transmission power of the device, aggregation beamforming of base station (BS), phase shifts, and reflection amplitudes at the IRS. Simulation results demonstrate that our proposed approach can achieve significant performance gain compared to the baseline algorithms by deploying IRS into covert OAC-based FL.

ASSESSMENT OF CORROSION IN A PARKING DECK USING GPR

This research focused on finding the structural condition of a precast parking deck using a GPR. A GSSI SIR 4000 Bridge Scanner GPR was deployed for corrosiveness mapping of a precast deck. Small concrete slabs were prepared in the laboratory with fresh and corroded rebars to identify their differences in GPR scanned images. The GPR response from the slab indicated that the reflection amplitude obtained from the scan of the target rebar decreases with increasing depth. GPR B-scans from the fresh and corroded rebar indicated increase in corrosion. The field experiment was performed following the standard bridge deck survey procedures. Both numerical and image-based analysis methods were followed for developing the corrosiveness maps of the precast deck section. The corrosiveness map showed a few critical sections in the precast deck. A visual inspection of the precast deck matched the fault locations in the corrosiveness map. The present condition of a precast deck section was found satisfactory except for a few areas of serious cracking that need repairs to control the further growth of corrosion. GPR results showed higher accuracy with the field inspection outcomes demonstrating that a GPR can be used as a reliable non-destructive tool for the condition assessment of concrete structures.

Outage and DMT Analysis of Partition-Based Schemes for RIS-Aided MIMO Fading Channels

In this paper, we investigate the performance of multiple-input multiple-output (MIMO) fading channels assisted by a reconfigurable intelligent surface (RIS), through the employment of partition-based RIS schemes. The proposed schemes are implemented without requiring any channel state information knowledge at the transmitter side; this characteristic makes them attractive for practical applications. In particular, the RIS elements are partitioned into sub-surfaces, which are periodically modified in an efficient way to assist the communication. Under this framework, we propose two low-complexity partition-based schemes, where each sub-surface is adjusted by following an amplitude-based or a phase-based approach. Specifically, the <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">activate-reflect</i> (AR) scheme activates each sub-surface consecutively, by changing the reflection amplitude of the corresponding elements. On the other hand, the <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">flip-reflect</i> (FR) scheme adjusts periodically the phase shift of the elements at each sub-surface. Through the sequential reconfiguration of each sub-surface, an equivalent parallel channel in the time domain is produced. We analyze the performance of each scheme in terms of outage probability and provide expressions for the achieved diversity-multiplexing tradeoff. Our results show that the asymptotic performance of the considered network under the partition-based schemes can be significantly enhanced in terms of diversity gain compared to the conventional case, where a single partition is considered. Moreover, the FR scheme always achieves the maximum multiplexing gain, while for the AR scheme this maximum gain can be achieved only under certain conditions with respect to the number of elements in each sub-surface.

Tunable strong plasmon–exciton coupling based modulator employing borophene and deep subwavelength perovskite grating

Two-dimensional materials support deeply confined and tunable plasmonic modes, which have great potential for achieving device miniaturization and flexible manipulation. In this paper, we propose a diffraction-unlimited system (period ≈ λ/20) composed of borophene layer and perovskite grating to investigate the strong coupling between the borophene guiding plasmon (BGP) and perovskite exciton (PE) modes. The resonant energy of the BGP mode could be electrically tuned to match the energy of the PE mode, and a remarkable Rabi splitting is attained under zero-detuning conditions. The splitting energy could reach 230 meV due to the strong field enhancement provided by the BGP mode. Taking advantage of the proposed electrically tunable hybrid system, not only is the reflective amplitude modulation depth up to 99.9%, but the 1.76π phase range modulation is achieved. Furthermore, by increasing the distance between the borophene layer and perovskite grating, a passive parity-time symmetry breaking could be observed with the vanished energy splitting. Our results deepen our understanding of light–matter interactions at the sub-wavelength scale and provide a guideline for designing active plasmonic devices.

Identification of interbedded gas hydrate and free gas using amplitude versus offset forward modelling

AbstractThe complex contacts between gas hydrate and free gas have been confirmed by gas hydrate pilot production in the Pearl River Mouth Basin, South China Sea. The laminated clay silt reservoirs have high amplitude reflections which may be filled with different saturations of gas hydrates, free gas and the coexistence between gas hydrate and free gas. To distinguish the variations of amplitude reflections caused by different reservoirs properties below the bottom simulating reflection, we combine the forward modelling, pre‐stack gathers with different incident angles and well log analysis to conduct the seismic responses. A number of geological models are established with variable saturations and different interfaces between gas hydrate and free gas. First, we analyse the seismic and well log responses at Sites W11, W01 and W17 near the production test area. Then, we perform the forward modelling to quantify the differences among seismic reflections with different saturations, thickness, incident angles and strata dips in free gas‐ or gas hydrate‐bearing geological models. We extract the seismic amplitudes along the bottom simulating reflection and other layers to compare with the amplitudes generated from forward modelling. The results indicate that the inclined intervals below the bottom simulating reflection have high amplitude, continuous reflection and polarity reversal which may be caused by thin gas reservoir and the interlayered gas hydrate and free gas with different saturations. The top interfaces of the gas hydrate‐ and free gas‐bearing layers show typical Class III amplitude versus offset and exhibit high amplitude reflections at seismic data with near, mid and far‐incident angles, which are easy to distinguish. Seismic response of far‐incident angle can be used to identify the coexistence of gas hydrate and free gas.