Reflected Signal Research Articles

STAR-RIS-Empowered Cognitive Non-Terrestrial Vehicle Network With NOMA

In this paper, we investigate the outage behavior of a simultaneously transmitting and reflecting reconfigurable intelligent surface (STAR-RIS)-empowered cognitive non-terrestrial vehicle network with non-orthogonal multiple access (NOMA), in which Rician fading channels and imperfect/perfect successive interference cancellation (ipSIC/pSIC) are considered. In the network, STAR-RIS is utilized to assist the transmission and reflection of the superposed signals from a secondary unmanned aerial vehicle. Under the interference constraints of primary vehicle users, we derive the exact expressions of outage probability for all secondary vehicle users to evaluate the system parameters. Moreover, to gain deeper insights, the asymptotic expressions of outage probability along with the diversity order are obtained. Then, from numerical results, we confirm the correctness of our theoretical analysis and discuss the influences of key parameters on system performance. Compared with STAR-RIS-orthogonal multiple access (OMA)/non-STAR-RIS scheme, the superiority of our scheme is verified.

Determination of permanent corrections of ball reflectors

Today, there are many manufacturers of triple-prism, spherical reflectors with different mechanical characteristics. That is why there is a problem of matching the signal reflection center with the geometric one. The purpose of this work is to evaluate the methods of determining permanent corrections of electronic tacheometers, ball reflectors and to develop recommendations for their use. Method. To determine the instrument correction, a displacement interferometer is used. It contains a two-frequency He-Ne laser with a wavelength of l = 0.63 μm (red range). The study compared the results of length measurements by an interferometer and an electronic total station with a ball reflector. This allowed determining the instrument correction. The research defined the constant correction of reflectors and total stations on the phase section of the field base using the method of created linear observations. Results. Experimental studies of ball reflectors of various manufacturers and Leica electronic tacheometers were conducted. The determination of constant instrument corrections of the total station and reflector using the displacement interferometer can be performed with an accuracy of 0.1 mm. This significantly depends on the accuracy of measuring lines with the total station. The use of ball reflectors with a built-in triple prism allows significant increase of distance measurement accuracy by reducing centering errors, considering the constant instrument correction (up to 0.4 mm for Leica 1201 total stations). Scientific novelty. The methods of determining permanent corrections of ball reflectors and total stations were investigated. The proposed method determines the measurement interval length with the exception of systematic constant correction of the electronic total station and reflector. Practical relevance. The use of ball reflectors is recommended for quick and unambiguous installation at points, convenience of their use for monitoring observations, as well as for increasing the accuracy of linear measurements due to the reduction of centering errors. In order to achieve high-precision measurements of short lines, it is recommended, according to the performed studies, to carefully determine the constant correction of the total station and ball prisms. This makes it possible to increase the accuracy of line measurements at least three times compared to the declared accuracy of the total station manufacturer.

The Impact of Rayleigh Scattering in UWFBG Array-Based Φ-OTDR and Its Suppression Method.

Ultra-weak fiber Bragg grating (UWFBG) array-based phase-sensitive optical time-domain reflectometry (Φ-OTDR) utilizes the interference interaction between the reference light and the reflected light from the broadband gratings for sensing. It significantly improves the performance of the distributed acoustic sensing system (DAS) because the intensity of the reflected signal is much higher than that of the Rayleigh backscattering. This paper shows that Rayleigh backscattering (RBS) has become one of the primary noise sources in the UWFBG array-based Φ-OTDR system. We reveal the impact of the Rayleigh backscattering signal on the intensity of the reflective signal and the precision of the demodulated signal, and we suggest reducing the pulse duration to improve the demodulation accuracy. Experimental results demonstrate that using light with a 100 ns pulse duration can improve the measurement precision by three times compared with the use of a 300 ns pulse duration.

Groundwater Level Variation Analysis Using Hydrogeophysical Methods in an Area of Campo Sujo in Cerrado, Chapada dos Veadeiros Region, Goiás

Cerrado’s campo sujo areas have been one of the main focuses of anthropic occupation in the Chapada dos Veadeiros region, Brazil’s Central Plateau, as they are easily accessible flattened areas with less dense vegetation. They are usually associated with wetlands representing excellent water reservoirs and groundwater recharge zones. The environmental characterization and analysis of water level variation are essential to investigate the impacts of human occupation. Hydrogeophysics represents one of the main subsurface research tools due to its easy application and efficiency in identifying the water level, with emphasis on Ground-penetrating radar (GPR), and electrical resistivity tomography (ERT). An analysis of GPR sections with 200, 400, and 900 MHz frequency antennas associated with the resistivity model was carried out to identify structures, and map the groundwater level. The overlapping data compose a hydrogeophysical model with good correlation to direct measurements of water level in a monitoring well, and soil horizons mapped in a trench. The GPR proved to be efficient in mapping the water level, mainly about to the survey with a 400 MHz antenna, shown as a horizontal reflector associated with attenuation portions of the reflection signal, registering in profile the lowering of the water level from 1.68 m in May to 3.35 m in August. The resistivity model showed a good correlation with the variations between the mapped soil horizons. The analysis shows that constructing a hydrogeophysical model is an excellent alternative for identifying the water level, and characterizing the shallow subsurface by applying non-invasive techniques. The study area represents a preserved area of campo sujo, and the research data can be used for comparison with future surveys, in addition to representing a base hydrogeophysics methodology that showed promising results for the physiographic characteristics of the area, which can be replicated in regions of similar geoenvironmental aspects.

PCA-based detection of phosphorous deficiency in wheat plants using prompt fluorescence and 820 nm modulated reflection signals.

Phosphorus deficiency induces biochemical and morphological changes which affect crop yield and production. Prompt fluorescence signal characterizes the PSII activity and electron transport from PSII to PSI, while the modulated light reflection at 820 (MR 820) nm investigates the redox state of photosystem I (PSI) and plastocyanin (PC). Therefore, combining information from modulated reflection at 820 nm with chlorophyll a fluorescence can potentially provide a more complete understanding of the photosynthetic process and integrating other plant physiological measurements may help to increase the accuracy of detecting the phosphorus deficiency in wheat leaves. In our study, we combined the chlorophyll a fluorescence and MR 820 signals to study the response of wheat plants to phosphorus deficiency as indirect tools for phosphorus plant status characterization. In addition, we studied the changes in chlorophyll content index, stomatal conductance (gs), root morphology, and biomass of wheat plants. The results showed an alteration in the electron transport chain as a specific response to P deficiency in the I-P phase during the reduction of the acceptor side of PSI. Furthermore, P deficiency increased parameters related to the energy fluxes per reaction centers, namely ETo/RC, REo/RC, ABS/RC, and DIo/RC. P deficiency increased the values of MRmin and MRmax and decreased νred, which implies that the reduction of PSI and PC became slower as the phosphorus decreased. The principal component analysis of the modulated reflection and chlorophyll a fluorescence parameters, with the integration of the growth parameters as supplementary variables, accounted for over 71% of the total variance in our phosphorus data using two components and provided a reliable information on PSII and PSI photochemistry under P deficiency.

Accurate Measurement of Frozen Soil Depth Based on I-TDR

In this study, a new method for determining the depth of frozen soil, Impulse Response Time Domain Reflectometry, is discussed. This method uses the principle of impedance measurement and the law of time–frequency domain convolution to convert the frequency-domain reflection signal into a time-domain signal and accurately determines the soil freezing front by measuring the difference between the impedance of frozen soil and unfrozen soil. The advantage of this method is that it solves the problems of small bandwidth, long rising edge time, and large measurement errors in the traditional TDR method to effectively improve the measurement accuracy of the soil-freezing front. Under laboratory conditions, soils of different textures (sand, loess, black soil, and red soil) were selected for experimental determination, and the results showed that compared with the traditional TDR method, the RMSE of the I-TDR method was small, and the method was applicable under different soil texture conditions, which could provide a new method for monitoring frozen soil in cold areas. In addition, the application of this method has important guiding significance for improving the efficiency of winter irrigation water, especially for guiding agricultural production, farmland irrigation, drainage engineering construction, meteorological frozen soil monitoring, and other aspects in cold and arid areas.

Seismic ahead-prospecting based on deep learning of retrieving seismic wavefield

Unknown geology ahead of the tunnel boring machine (TBM) brings a large safety risk for tunnel construction. Seismic ahead-prospecting using TBM drilling noise as a source can achieve near-real-time detection, meeting the requirements of TBM rapid drilling. Seismic wavefield retrieval is the key data processing step for the efficient utilization of TBM drilling noise. The traditional solution is based on cross-correlation to extract reflected waves, but the reference waves remain in the result, disturbing the imaging and interpretation of the adverse geology. To solve this problem, the deep learning method was introduced in wavefield retrieval to improve the accuracy of geological prospecting. We trained a deep neural network (DNN) with its strong nonlinear mapping capability to transform seismic data from TBM drilling noise to data from the active source. The issue lies in its features for this specific tunnel task, including the decay of the seismic signal with time and the incomplete spatial correspondence. Thus, we improved a classical DNN with the time constraint as an additional input, and an additional pre-decoder to enlarge the receptive field. Additionally, a loss function weighted by the ground truth and time constraint is improved to achieve an accurate retrieval of the effective signal, considering the little effective information in tunnel data. Finally, the workflow of the proposed method was given, and a dataset designed with reference to the field case was employed to train the network. The proposed method accurately retrieved the reflection signal with higher dominant frequencies, which helped improve the accuracy of imaging. Numerical simulations and imaging on typical geological models show that the proposed method can suppress reference waves and get more accurate results with fewer artifacts. The proposed method has been applied in the Gaoligongshan Tunnel and imaged two abnormal zones, providing meaningful geological information for TBM drilling and tunnel construction.

Aging Analysis of Cable Insulation Material by Terahertz Time-domain Spectroscopy

Insulation materials with high sealing, high insulation, high elasticity, and other characteristics are widely used in the power industry. In this paper, the terahertz time-domain reflection spectrum of cable insulation materials is studied, the optical parameters of cable insulation materials are extracted to characterize the aging state of cable insulation materials, the terahertz time-domain reflection signal of insulation materials with different degrees of aging is tested, and the terahertz reflection spectrum of insulation sheaths is analyzed. The relationship between the aging degree and absorption coefficient in terahertz time-domain spectral reflection mode is obtained. There are obvious differences in the absorption characteristics of cable insulation materials with different degrees of aging in the terahertz band. The longer the aging time is, the greater the absorption coefficient is and the lower the refractive index is. Terahertz time-domain reflectometry plays a role in cable protection with high detection accuracy in the characterization of cable insulation materials.

Design of a simple side-incident TE11 mode microwave probe for nondestructive pipe inspection

This study proposed a simple side-incident TE11 mode microwave probe for the rapid and long-range inspection of cracks in metallic pipes. The probe feeds the microwaves to a metallic pipe, which works as a waveguide; the reflection signal provoked by a defect is measured for detection and localization. The probe enables the detection of both circumferentially and axially oriented cracks, unlike those reported in earlier studies. To achieve better performance, numerical simulations were conducted to evaluate the conversion efficiency and optimize the insertion length of the coaxial cable and the exposed length of the cable core wire. The simulation results suggest that the optimized probe configuration is feasible for pipes with various diameters by proportionally changing the current probe configuration. Although injected microwaves propagated in two directions, the ratio of microwaves to one direction could be controlled by adjusting the inclination angle and the exposed length of the cable core wire. Subsequently, three TE11 probes fabricated according to the simulation results were used to detect circumferential and axial slits in a brass pipe. The results showed that circumferential slits in the vertical positions (parallel to the nontilted coaxial cable) and axial slits in the horizontal positions (perpendicular to the nontilted coaxial cable) caused large reflections, consistent with the electromagnetic field distribution of the TE11 mode microwaves in a circular waveguide. Further experiments verified the feasibility of the designed probe for pipes with different diameters and for directional pipe inspection.

Ultra-broadband shielding of cellulose nanofiber commingled biocarbon functional constructs: A paradigm shift towards sustainable terahertz absorbers

Terahertz (THz) spectrum and technology are envisioned to be a highly promising solution for enabling 6G and beyond wireless networks. This demand coincides with an urgent need to develop efficient electromagnetic interference shields to alleviate electromagnetic pollution in the THz range. Fully bioderived THz shields could be a sustainable solution to transcend towards a biocarbon economy. Herein, we report an environmentally benign and facile approach to fabricating 3D porous ultra-light aerogels and flexible nanopapers from cellulose nanofibers and highly conductive biocarbon fully derived from biomass. These functional constructs showcased excellent broadband THz shielding performance in both sub THz (W band) and THz region (0.4–2.0 THz). The THz shielding effectiveness of a 600 µm thick nanopaper and 3.00 mm aerogel was found to be 46 dB and 70 dB, with superior THz absorption behaviour and minimal reflection of THz signals. The electronic structure and charge transfer properties were examined under an external electric field based on density-functional theory. The results show that the effect of the external electric field induces intramolecular charge transfer from the lower-graphitic sheet to the upper-graphitic sheet of the nanocomposite suitable for THz excitation. Moreover, these sustainable absorbers could deliver similar THz shielding performance compared to graphene foam (74 dB), exemplifying their humungous potential as advanced functional materials for futuristic THz devices.

Performance analysis of frequency selective reflectors based on rectangular loop pair for wideband applications

This paper presents performance analysis of single layered bandstop frequency selective surfaces (FSSs) for C-band and ultra-wideband (UWB) frequency ranges respectively. These FSSs are based on polarization dependent (PD) single rectangular loop pair (RLP). RLP arrays in square and rectangular grids are developed and simulated to evaluate signal rejection and reflection for incident transverse electric (TE) and transverse magnetic (TM) waves. Further, orthogonal patterns are printed back-to-back (BTB) on dielectric substrate to study wave propagation and effect on wave polarization. Non-linearities in the reflection phase of BTB arrays are then mitigated by printing orthogonal FSS arrays on the same side of the dielectric substrate. The equivalent circuit models (ECMs) of these FSSs are also presented to predict their transmission characteristics. Later, two FSSs with wideband and ultra-wideband rejection capability are developed and experiments are carried out. The array of merged RLP arranged in square grid exhibits stopband from 4.5 GHz to 8.4 GHz with polarization independence (PI) and it is angularly stable while merged array of RLP arranged in rectangular grid exhibit ultra-wide stopband from 2.3 GHz to 11.5 GHz but it is not angularly stable. The measured transmission responses of all FSSs proposed here are close to simulated results.

Towards Deep Learning Augmented Robust D-Band Millimeter-Wave Picocell Deployment

D-band millimeter-wave, a key wireless technology for beyond 5G networks, promises extremely high data rate, ultra-low latency, and enables new Internet of Things applications. However, massive signal attenuation, complex response to building structures, and frequent non-availability of the Line-Of-Sight path make D-band picocell deployment challenging. To address this challenge, we propose a deep learning-based tool, that allows a network deployer to quickly scan the environment from a few random locations and predict Signal Reflection Profiles everywhere, which is essential to determine the optimal locations for picocell deployment.

Time‐lapse PS‐wave time‐shifts and quantitative pressure‐saturation discrimination applications

AbstractWe show that time‐lapse (4D) time‐shifts from PS‐wave data are valuable as they are very sensitive to pressure changes, whereas 4D time‐shifts from PP‐wave data are sensitive to both pressure and saturation changes. This gives another opportunity from using 4D amplitudes alone to understand and discriminate areas of pressure changes from areas of saturation changes in field data. 4D PS time‐shifts sense transmission related changes taking into consideration propagation through the altered medium, whereas amplitude changes are reflection or backscattered signals from the boundary. Therefore, these two attributes will be complimentary in 4D interpretation. Rock‐physics‐based time‐shift cross‐plots are generated to analyse how pressure and saturation changes in a reservoir impact PP‐ and PS‐wave time‐shifts. The developments of 4D time‐shifts are shown fixing the reservoir properties and varying reservoir layer thickness. Synthetic seismic data from a wedge is modelled to understand differences between 4D amplitude and time‐shift changes and the value of PS time‐shifts. Cases with pressure changes only and saturation changes only are also analysed with the wedge model. The method is next applied to two 4D field data sets. One is in the North Sea and the other offshore Brazil. In these field data sets, with different levels of noise in the 4D data, we see interpretable results from PS‐wave time‐shifts that can help in 4D signal understanding and improve reservoir characterization and monitoring practices. We believe that with modern acquisition and processing, this technology is realizable and provides quantitative and accurate 4D interpretations. It is shown that the use of PS‐wave data can lead to a larger chance of success in placing development wells.

Two-color unidirectional reflections by modulating the spatial susceptibility in a homogeneous atomic medium.

Non-reciprocal reflections of optical signals are unusual yet fascinating to achieve the imminent applications of non-reciprocal photonic devices and circuits. The complete non-reciprocal reflection (unidirectional reflection) was recently found to be achievable in a homogeneous medium, if the real and imaginary parts of the probe susceptibility satisfy the spatial Kramers-Kronig (KK) relation. We propose a coherent four-level tripod model for realizing dynamically tunable two-color non-reciprocal reflections by applying two control fields with linearly modulated intensities. We found that, the unidirectional reflection can be obtained if the non-reciprocal frequency regions are located in the electromagnetically induced transparency (EIT) windows. This mechanism is to break the spatial symmetry by the spatial modulation of susceptibility to induce unidirectional reflections, the real and imaginary parts of the probe susceptibility are no longer required to satisfy the spatial KK relation.

Research on Underground Pipeline Detection Method Based on Background Matrix Subtraction and Three-Dimensional Velocity Spectrum

Ground-penetrating radar (GPR) can detect urban underground pipelines and image their spatial distribution. However, due to the interference of direct wave and ground reflected wave in radar profile, the detection accuracy of underground pipeline depth is low. In order to improve the reliability and accuracy of the interpretation of ground penetrating radar data, it is necessary to suppress the noise, and then to detect underground pipelines. Firstly, on the basis of data collection, a background matrix subtraction (BMS) method is proposed to suppress noise signals, and the Noise reduction effect is compared and analyzed by two groups of simulation data and two groups of measured data examples with the method of reducing average channel and singular decomposition. Then, a three-dimensional velocity spectrum (3DVS) method is proposed to estimate the buried depth of underground pipeline in radar profile, and the propagation velocity of electromagnetic wave in underground media is calculated by automatically scanning the hyperbolic reflection signal. The estimated velocity is used to carry out back-propagation migration (BPM) processing on the ground penetrating radar profile, and the underground pipeline is accurately detected. Finally, the underground pipeline detection method based on BMS and 3DVS is applied to a residential area in Nanjing, Jiangsu, China. The detection results show that the effect of BMS is obviously better than that of mean-reducing method and singular decomposition method, which can suppress the noise well on the basis of ensuring that the effective signal is not lost. It is helpful to identify the characteristics of target signal in ground penetrating radar profile, and improve the accuracy and reliability of data interpretation. The error between the velocity value estimated by the 3DVS method and the real value is less than 3.8%, and the buried depth error of pipeline target in the obtained data is 1.4%, which indicates that the algorithm has practical application value and can realize the accurate positioning of underground pipelines.

Superconductivity and fermionic dissipation in quantum Hall edges

Proximity-induced superconductivity in fractional quantum Hall edges is a prerequisite to proposed realizations of parafermion zero modes. A recent experimental work [G\"ul et al., Phys. Rev. X 12, 021057 (2022)] provided evidence for such coupling, in the form of a crossed Andreev reflection signal, in which electrons enter a superconductor from one chiral mode and are reflected as holes to another, counterpropagating chiral mode. Remarkably, while the probability for crossed Andreev reflection was small, it was stronger for $\ensuremath{\nu}=1/3$ fractional quantum Hall edges than for integer ones. We theoretically explain these findings, including the relative strengths of the signals in the two cases and their qualitatively different temperature dependencies. An essential part of our model is the coupling of the edge modes to normal states in the cores of Abrikosov vortices induced by the magnetic field, which provide a fermionic bath. We find that the stronger crossed Andreev reflection in the fractional case originates from the suppression of electronic tunneling between the fermionic bath and the fractional quantum Hall edges. Our theory shows that the mere observation of crossed Andreev reflection signal does not necessarily imply the presence of localized parafermion zero modes, and suggests ways to identify their presence from the behavior of this signal in the low-temperature regime.

Quantification of the Phenomena Affecting Reflective Arterial Photoplethysmography.

Photoplethysmography (PPG) is a widely emerging method to assess vascular health in humans. The origins of the signal of reflective PPG on peripheral arteries have not been thoroughly investigated. We aimed to identify and quantify the optical and biomechanical processes that influence the reflective PPG signal. We developed a theoretical model to describe the dependence of reflected light on the pressure, flow rate, and the hemorheological properties of erythrocytes. To verify the theory, we designed a silicone model of a human radial artery, inserted it in a mock circulatory circuit filled with porcine blood, and imposed static and pulsatile flow conditions. We found a positive, linear relationship between the pressure and the PPG and a negative, non-linear relationship, of comparable magnitude, between the flow and the PPG. Additionally, we quantified the effects of the erythrocyte disorientation and aggregation. The theoretical model based on pressure and flow rate yielded more accurate predictions, compared to the model using pressure alone. Our results indicate that the PPG waveform is not a suitable surrogate for intraluminal pressure and that flow rate significantly affects PPG. Further validation of the proposed methodology in vivo could enable the non-invasive estimation of arterial pressure from PPG and increase the accuracy of health-monitoring devices.

Quantifying amplitude-variation-with-offset uncertainties related to calcite-cemented beds using a Monte Carlo simulation

Calcite cement often occurs locally, forming thin layers of calcite-cemented sandstone characterized by high seismic velocities and densities. Because of their strong impedance contrast with the surrounding rock, calcite-cemented intervals produce detectable seismic reflection signals that may interfere with target reflections at the top of a reservoir. In this case, the amplitude-variation-with-offset (AVO) of the effective seismic signature will be altered and may even create a false hydrocarbon indication. From the Monte Carlo simulation, we find that the presence of thin calcite-cemented beds increases the uncertainty of the Bayesian pore-fluid classification based on the AVO attributes intercept and gradient. In the case example of a North Sea turbiditic oil and gas field, the probability of a false-positive hydrocarbon indication increases from 3%–5% to 18%–21% assuming an equal probability of the occurrence of brine, oil, and gas. The results confirm that calcite-cemented beds can create a pitfall in AVO analysis. Realistic estimates of the AVO uncertainty are crucial for the risk assessment of well placement decisions.

Study on the effect of different angles on the propagation characteristics of acoustic emission signals in wood.

To explore the propagation characteristics of acoustic emission (AE) signals in wood at different angles. The AE signals at different angles were obtained by changing the angle of incidence by sawing the inclined surfaces at different angles. The Zelkova schneideriana specimen was sawn 5 times with an increment of 15°, and 5 different incidence angles were obtained. AE signals were collected by 5 sensors arranged equally on the surface of the specimen, AE energy and energy attenuation rate were calculated. The reflection signals corresponding to different angles were collected on the uncut specimen by changing the position of the sensors, and the propagation speed of the AE signals at different angles was calculated. The results showed that the kinetic energy provided by the external excitation is small, and the AE energy is mainly provided by the displacement potential energy. With the change of the incidence angle, the AE kinetic energy changes significantly. With the increase of the reflection angle, the speed of the reflected wave also continued to increase, and finally stabilized at 4600 m/s.

Meta-Material Sensor-Based Internet of Things for Environmental Monitoring by Deep Learning: Design, Deployment, and Implementation

Using widely deployed Internet of Things (IoT) sensors to perceive the environmental distribution is crucial in many IoT applications, such as intelligent healthcare and smart home. As using traditional sensors will lead to high costs and maintenance, it is important to design the next-generation IoT sensor to reduce the cost of ubiquitous deployment. For this purpose, we propose a novel IoT system based on low-cost and fully passive meta-material sensors. Specifically, the meta-material sensors can sense multiple environmental conditions such as temperature and humidity levels, and transmit back the information by signal reflection, simultaneously. With the information contained in the received signals, a wireless receiver can obtain detailed environmental distributions. However, it is not trivial to achieve high sensing accuracy in the meta-material sensor based IoT system because the structure of the meta-materials, the deployment positions of sensors, and the reconstruction function for environmental distributions need to be jointly optimized. To handle this challenge, we propose an algorithm to design the meta-material based IoT system with the help of a deep learning approach. Simulation results verify that the proposed algorithm effectively maximizes the sensing accuracy. Experimental evaluations also show that the proposed scheme can obtain humidity distribution with an accuracy of over 93%.