Suppression Of Reflection Research Articles

A solution method for active suppression of reflections in anechoic chambers.

A solution method to improve an anechoic chamber at low frequencies with the use of active noise control is presented. The approach uses the Kirchhoff-Helmholtz integral to compute the reflected sound field resulting from the primary sources together with an algorithm to compute the filter coefficients of a controller driving secondary sources on the walls of the enclosure using reference signals as inputs, which are measured on a contour enclosing the primary sources. A causal frequency domain method with conjugate gradient iterations is derived to determine the controller. The method is sufficiently efficient to allow computation of a causal time-domain controller with hundreds of secondary sources and hundreds of reference sensors in two- (2D) or three-dimensional configurations using a fully coupled multiple-input multiple-output system. The paper shows the results of a simulation with 200 secondary sources, 200 reference sensors, and 225 performance sensors based on a 2D finite element simulation. The method is verified in real-time in an experiment with the objective to suppress the reflections from the walls in a smaller 2D setup. Measurements with verification microphones show that the reverberation time is effectively reduced in the real-time experiment.

Reconfigurable wide-angle broadband terahertz wave antireflection using a non-volatile phase-change material.

Actively wide-angle broadband terahertz (THz) antireflection (AR) coatings with a flexible reconfigurability have a great potential for the development of next-generation versatile THz components and systems with high performance. Here, we present a reconfigurable wide-angle broadband THz AR coating using a phase change material Ge2Sb2Te5 (GST) film, which is based on the impedance matching method. The performance of GST-based AR coating can be effectively achieved by a thermal excitation, exhibiting the complete suppression of unwanted THz-wave reflections for incidence angles from 0∘ to 50∘ in the broad frequency range of 0.1-3.0 THz. Simulation and experimental results show that the GST-based AR coating can efficiently eliminate Fabry-Perot interference caused by unwanted THz-wave reflections from the substrate, thereby significantly improving the performances of THz devices. Moreover, the active AR mechanism of the GST-based coating is investigated, which elucidates the essential role of the phase transition between the amorphous and crystalline phases in changing the conductivity of the film to achieve an impedance matching condition under thermal excitation. Additionally, the non-volatile properties of GST can enable the AR coating to retain a long-term stability for optimal wave-impedance matching without power holding requirements. Our work provides a new, to the best of our knowledge, and promising way for realizing high-performance integrated THz components and systems in the future.

Electrochemically-Switched Microwave Response of MXene in Organic Electrolyte.

The increasingly complex electromagnetic (EM) environment necessitates advanced electrically controllable electromagnetic interference (EMI) shielding materials that can adapt to varying EM conditions. This study develops a flexible electrochemically tunable EMI shielding device based on ultrathin Ti3C2Tx MXene films, exhibiting reversible shielding effectiveness (SE) modulation from 18.9 to 26.2dB in X band at 0.1 and -1.5V. Unlike the previously reported mechanism relying on interlayer spacing adjustments, the work leverages transformations of charging state and surface chemistry for tunability during the electrochemical process. The Ti3C2Tx flake size is also evidenced to play a crucial role, with smaller flakes offering higher absorption modulation despite lower SE modulation, enabling the device with high designability. When integrated with Salisbury screen structure, the device achieves adjustable absorption from 93.560% at 0.1V to 99.996% at -1V, showing a tunable reflection suppression ratio up to 32dB with an effective bandwidth of 4.2GHz. Additionally, incorporating resonant cavity structure enables absorption-dominated (over 90%) microwave-responsive switching at 0.1 and -1.5V. This work highlights significant potential of adaptive EMI shielding materials for applications in smart electronic protection, EM switch, and radar camouflage.

Study on the Suppression of Vitrinite Reflectance: A Thermal Simulation Experiment.

Vitrinite reflectance is the most widely used parameter for reconstructing the thermal history of sedimentary basins and evaluating the maturation of source rocks. However, suppression of vitrinite reflectance has also been reported, which could affect the accuracy of evaluating the degree of thermal evolution. In this article, the influence of hydrocarbon generation on vitrinite reflectance during thermal evolution is studied based on thermal simulation experiments in a closed system. The results show that hydrocarbon absorption and overpressure can lead to the suppression of vitrinite reflectance. For R 0 values between 0.6% and 2.1%, the suppression of vitrinite reflectance is primarily attributed to the impregnation of the telocollinite texture with hydrocarbons generated from type I kerogen. At R 0 values exceeding 2.1%, overpressure becomes the dominant cause of the anomalous reflectance. Under closed-system conditions, the retention of volatile products within the pore network of vitrinite hinders the structural reorganization, leading to reflectance suppression.

Boundary conditions in flutter simulations of subsonic, transonic and supersonic blade cascades

Simulations of blade flutter are highly sensitive to undesired wave reflections at inlet and outlet boundaries. A careful treatment of boundary conditions is required to prevent the generation of perturbations. This study is motivated by the need to perform flutter analysis of low-pressure steam turbine blades, for which supersonic inflow conditions may occur in the near-tip region. The exact steady non-reflecting boundary condition (NRBC), the spectral NRBC and a simple isentropic boundary condition are implemented in a time-marching flow solver and applied to turbomachinery flutter simulations covering a wide range of operating conditions. For the first time, the spectral NRBC is applied to a blade flutter simulation with a supersonic inlet and its performance is analysed and compared with other boundary condition formulations. It is shown that an effective non-reflective treatment in the design of the boundary condition is essential for an accurate aeroelastic prediction at all operating conditions, including the subsonic flow regime. The limitation of the exact steady NRBC to spatial modes causes it to perform poorly in some unsteady flow simulations, whereas the spectral NRBC achieves a satisfactory suppression of undesired wave reflections in all investigated cases.

Suppression of Lattice Doubling in Quasi-Skutterudite La3Rh4Sn13: A Comparison of Temperature and Hydrostatic Pressure Routes.

We present structural properties at different temperatures and high-pressure (HP) of La3Rh4Sn13 which is one of the interesting systems in the Remika phase RE3Rh4Sn13 (RE=Sr, Ca, La, Pr, Ce) quasi-skutterudite series using synchrotron diffraction. Data at ambient conditions revealed the presence of several weak reflections, which could be accounted only with a superlattice I* structure (I4132) with lattice parameter a~19.457 Å. However, above 350 K, a complete suppression of the weak superlattice reflections of the I* structure is observed. Data at higher temperatures is found to be well described by the I structure (Pm-3n) having half the lattice parameter compared to the I* structure. HP-XRPD at ambient temperature showed that pressures greater than 7.5 GPa result in similar suppression of the weak I* superlattice reflections. Data at higher pressures is found to be well described by the I structure (Pm-3n), similar to the high-temperature phase. HP Raman measurements demonstrated changes that seem to be consistent with a locally more ordered structure as in the case of the I*→I transition. Our findings on La3Rh4Sn13 open up new avenues to study unexplored HP phenomena, especially the superconductivity in these Remika phase quasi-skutterudites.

Absorption–diffusion integrated acoustic metasurface for scattering reduction

Absorption and diffusion are expected to reduce the energy intensity of reflected waves, while combining the advantages of both can further disperse incoming energy and improve acoustic stealth performances. In the paper, an absorption-diffusion integrated acoustic metasurface (ADM) is proposed, achieving high-performance acoustic backward scattering reduction in the operating bandwidth ranging from 6550 Hz to 6950 Hz. In order to obtain the proposed ADM, two kinds of subwavelength dual-layer unit cells with phase differences of 180° and low amplitudes (<0.4) are introduced. The highly efficient absorption of acoustic waves is achieved by extending the acoustic wave propagation path of the proposed unit cells. Meanwhile, the destructive interference between the pre-designed unit cells also contributes to diffusion-like scattering, which contributes to further suppression of specular reflection. Both simulated and experimental results demonstrate that the proposed ADM can achieve excellent acoustic backward scattering reduction. The proposed integrated mechanism can provide a method for achieving high-performance acoustic wavefront manipulation, which has potential applications in stealth technology, camouflage, noise control, and other relevant applications.

On the Equivalent-Circuit-Based Design of Double-Lossy-Layer Wide Transmissive Rasorbers With Ultrawide Reflection Suppression Band

On the Equivalent-Circuit-Based Design of Double-Lossy-Layer Wide Transmissive Rasorbers With Ultrawide Reflection Suppression Band

Polarization-Based Reflection Suppression Method and Its Application to Target Detection

Active illumination light becomes strongly reflective interference light after specular reflection. It causes saturation in some areas of the image during target detection, resulting in the inability to recognize detailed target feature information. This greatly limits the application of active illumination detection. Based on the Mueller matrix analysis of the difference in polarization characteristics between the background specular reflected light and the target reflected light, we propose a reflection suppression method based on orthogonal polarization imaging. The method employs a polarization modulation strategy in a bidirectional manner between the light source and the detector. First, the polarization information difference is amplified by active polarized illumination between the background specular reflected light and the target reflected light. Then, the target recovery is achieved by suppressing the background specular reflected light through the polarized orthogonal imaging method. Meanwhile, this method can also be used for moving target detection. The experimental results show that the reflection suppression method of orthogonal polarization imaging can effectively suppress the interference of specular reflection on the target image. Additionally, it can reduce the problems of missed and false detection that occurs in moving target detection and improve the active illumination detection effect.

Vitrinite Reflectance Suppression Revisited

Vitrinite Reflectance Suppression Revisited

Improved accuracy and robustness of electron density profiles from JET's X-mode frequency-modulated continuous-wave reflectometers.

JET's frequency-modulated continuous wave (FMCW) reflectometers have been operating well with the current design since 2005, and density profiles have been automatically calculated intershot since then. However, the calculated profiles had long suffered from several shortcomings: poor agreement with other diagnostics, sometimes inappropriately moving radially by several centimeters, elevated levels of radial jitter, and persistent wriggles (strong unphysical oscillations). In this research, several techniques are applied to the reflectometry data analysis, and the shortcomings are significantly improved. Starting with improving the equilibrium reconstruction that estimates the background magnetic field, adding a ripple correction in the reconstructed magnetic field profile, and adding new inner-wall reflection positions estimated through ray-tracing, these changes not only improve the agreement of reconstructed profiles to other diagnostics but also solve density profile wriggles that were present during band transitions. Other smaller but also persistent wriggles were also suppressed by applying a localized correction to the measured beat frequency where persistent oscillations are present. Finally, the burst analysis method, as introduced by Varela etal. [Nucl. Fusion 46 S693 (2006)], has been implemented to extract the beat frequency from stacked spectrograms. Due to the strong suppression of spurious reflections, the radial jitter that sometimes would span several centimeters has been strongly reduced. The stacking of spectrograms has also been shown to be very useful for stacking recurring events, like small gas puff modulations, and extracting transport coefficients that would otherwise be below the noise level.

Independently controlled multifrequency rejection bands in a broadband filter design using shorted T-shaped stub loaded resonator with central square ring

This article discusses the development and analysis of a broadband filter capable of suppressing specific frequencies of wireless applications at 4.7 GHz for WLAN, 8.3 GHz, and 11.5 GHz (for satellite communication) by combining a T-shaped stub loaded resonator with a central square ring to achieves high performance and compact size within the bandwidth of interest. The filter achieves low signal loss of 0.4 dB across the entire passband of 14.9 GHz bandwidth, good reflection suppression exceeding 10 dB, and independently adjustable multi stopbands. It utilizes a simple planar topology for a small footprint of 0.52 λg × 0.32 λg, where λg represents the wavelength at 4.7 GHz. The proposed filter evaluated using classical method an even-odd-mode analysis, and a 3D software tool HFSS-15 is used for simulations. The physical prototype is built on a Rogers RO-4350 substrate using LPKF S63 ProtoLaser machine. To confirm the accuracy and performance of the prototype, measurements were conducted using a ZNB20 vector network analyser. The simulations and measurement results confirm its effectiveness, paving the way for applications in various fields such as radar systems, medical imaging, and wireless communication.

Tuning and total resonant suppression of reflection in the photonic bandgap range of Bragg reflector by two-dimensional nanoparticle array

The influence of a dielectric layer with an embedded 2D array of metal nanoparticles on the spectral characteristics of a distributed Bragg reflector is theoretically studied and numerically validated. A significant dependence of the reflectivity of the hybrid structure on the location of the nanoparticle array relative to the maxima and minima of the optical field in the surface dielectric layer is demonstrated. It is found that the application of a dilute ensemble of nanoparticles (the interparticle distance is from 2 to 5 times larger than the nanoparticle size) in the region of high optical field localization makes it possible to obtain a total suppression of reflection in the photonic bandgap range of distributed Bragg reflector. Contrariwise, if the optical field is almost zero at the nanoparticle array location, its impact on the scattered light is negligible, that is, the resonant nanoparticles are masked by a highly reflective photonic structure. The target wavelength can be tuned inside the photonic bandgap range by adjusting the shape of nanoparticles and interparticle distance in the array.

Vernier Ellipsometry Sensing with Ultralow Limit‐of‐Detection and Large Dynamic Range by Tuning of Zero‐Reflection Points

AbstractOptical sensors using zero‐reflection points (ZRPs) enable excellent sensitivity due to the accompanying phase singularities and the steepest slope of the reflectivity curve. Here, the collaborative manipulation of three ZRPs in a simple platform formed by a lithography‐free, metal‐dielectric‐metal structure with unsurpassed, experimentally demonstrated, limit of detection ≈2 × 10−8 refractive index unit is reported. The sensor relies on: i) strong coupling between p‐polarized surface plasmon polariton and photonic waveguide, leading to reflection suppression, Rabi splitting and phase singularities; ii) simultaneous implementation of two orthogonally polarized ZRPs, enabling spectral overlap of s‐polarized photonic modes (Rs) with the coupled p‐polarized resonances (Rp); and iii) ellipsometry‐based sensing where the s‐polarized ZRPs provide a stable reference to boost the sensor performance in terms of the amplitude ratio and phase difference of Rp and Rs thereby naturally forming a refinement measuring scale akin to a Vernier scale. Remarkably, the precise manipulation of ZRPs enables resetting the sensor to its optimal sensing point. The capability has been demonstrated for a biosensor of SARS‐CoV‐2 spike (S2) protein that can track the full functionalization process then reset to perform dose‐dependent detection of the S2 protein. This work provides a new strategy for the development of optical sensors and perfect light absorbers.

Far‐red, high‐resolution, reflection‐free images of the anterior segment in retroillumination

Aims/Purpose: Retroillumination observation of the anterior segment is a routine examination method as old as the slit lamp, but capturing good quality images is difficult because of patient glare, the presence of corneal and or lens reflections, and limited resolution. We have modified a slit lamp to overcome these limitations and present the first series of images obtained.Methods: On a Topcon SL‐D7 slit lamp, we replaced the light source with a far‐red LED (Thorlabs, M780L3, 200 mW, 800 mA at 780 nm) and added a monochrome camera with sufficient resolution (Baumer, VCXU‐123 M). Reflection suppression was achieved by modifying the optical path (patent pending). In a clinical trial validated by an ethics committee (IDRCB: 2021‐A01496‐35), we acquired images of 5 different diseases after pupillary dilation: cataract, posterior capsule opacification, hereditary stromal dystrophy, Fuchs' corneal endothelial dystrophy (FECD), Bowman's membrane dystrophy.Results: Our innovative prototype device made it possible to obtain images of 3000 × 4096 pixels for 13.3 × 9.7 mm (×40 magnification). In 100% of the cases, one or more clear images on the area of interest were obtained without glare, and without disturbing reflections in 90% of the cases. Some pseudophakic patients showed minimal to moderate light reflection. The images were sufficiently resolved to allow precise analysis of disease areas, such as each guttae of the FECD.Conclusions: Our retroilluminator prototype provides, for the first time to our knowledge, high‐resolution images of the different structures of the anterior segment, easy to acquire and likely to facilitate the diagnosis and follow‐up of patients. Improvements to the prototype are underway to remove some persistent reflections. One of the first applications will be the classification of the severity of endothelial damage in FECD.

Separation and Suppression of Strong Reflections via a Multiscale Attention Deep Learning Model

Separation and Suppression of Strong Reflections via a Multiscale Attention Deep Learning Model

Ultrasonic pitch-catch measurement wavefield analysis and casing reflection suppression

Ultrasonic pitch-catch measurements are increasingly recognized in cement bond evaluations for their unique ability to discern between light cement and mud within the annulus. They also effectively capture reflections from the annulus-formation interface, also known as the third-interface echo (TIE), in a single-cased hole. The TIE offers valuable insights into the condition of the annulus behind the casing and can be leveraged to calculate casing eccentering, annulus thickness, and image annulus-formation interface. However, the TIE may be obscured by reflections from the casing's inner surface, as well as multiple reflections from the casing and the tool housing. This overlap can lead to complications in data interpretation. Furthermore, the use of only two wave trains at near and far receivers in ultrasonic pitch-catch measurement adds to the difficulty of suppressing casing reflections. To tackle these challenges, we first analyze the wavefield in various models and then develop a phase-shift interpolation (PSI)-based technique to suppress casing reflections. This method initially converts the two waveforms into array waveforms using the PSI approach, then employs a median filter to suppress casing reflections. Finally, we can pick TIE arrival time from the refined data to further estimate the casing eccentering. The effectiveness of proposed technique in suppressing casing reflections and their multiples is verified by numerical simulations and a field example. These breakthroughs are poised to greatly enhance the precision and reliability of cement bond evaluations.

Electric-Controlled Metasurface Antenna Array with Ultra-Wideband Frequency Reconfigurable Reflection Suppression

The electric-controlled metasurface antenna array (ECMSAA) with ultra-wideband frequency reconfigurable reflection suppression is proposed and realized. Firstly, an electric-controlled metasurface with ultra-wideband frequency reconfigurable in-phase reflection characteristics is designed. The element of the ECMSAA is constructed by loading the single electric-controlled metasurface unit on the conventional patch antenna element. The radiation properties of the conventional patch antenna and the reflection performance of electric-controlled metasurface are maintained when the antenna and the metasurface are integrated. Thus, the ECMSAA elements have excellent radiation properties and ultra-wideband frequency reconfigurable in-phase reflection characteristics simultaneously. To take a further step, a 6×10 ECMSAA is realized based on the designed metasurface antenna element. Simulated and measured results prove that the reflection of the ECMSAA is dynamically suppressed in the P and L bands. Meanwhile, high-gain and multi-polarization radiation properties of the ECMSAA are achieved. This design method not only realizes the frequency reconfigurable reflection suppression of the antenna array in the ultra-wide frequency band but also provides a way to develop an intelligent low-scattering antenna.

A novel approach to interface high-Q Fabry–Pérot resonators with photonic circuits

The unique benefits of Fabry–Pérot resonators as frequency-stable reference cavities and as an efficient interface between atoms and photons make them an indispensable resource for emerging photonic technologies. To bring these performance benefits to next-generation communications, computation, and time-keeping systems, it will be necessary to develop strategies to integrate compact Fabry–Pérot resonators with photonic integrated circuits. In this paper, we demonstrate a novel reflection cancellation circuit that utilizes a numerically optimized multi-port polarization-splitting grating coupler to efficiently interface high-finesse Fabry–Pérot resonators with a silicon photonic circuit. This circuit interface produces a spatial separation of the incident and reflected waves, as required for on-chip Pound–Drever–Hall frequency locking, while also suppressing unwanted back reflections from the Fabry–Pérot resonator. Using inverse design principles, we design and fabricate a polarization-splitting grating coupler that achieves 55% coupling efficiency. This design realizes an insertion loss of 5.8 dB for the circuit interface and more than 9 dB of back reflection suppression, and we demonstrate the versatility of this system by using it to interface several reflective off-chip devices.

Cost-Effective Full-Color 3D Dental Imaging Based on Close-Range Photogrammetry.

Dental imaging plays a crucial role in clinical dental practice. Conventional 2D dental imaging serves general-purpose tasks, such as patient documentation, while high-precision 3D dental scanning is tailored for specialized procedures, such as orthodontics and implant surgeries. In this study, we aimed to develop a cost-effective 3D imaging technique that could bridge the gap between conventional dental photography and high-precision 3D dental scanning, with the goal of improving patient dental care. We developed a 3D imaging technique based on close-range photogrammetry and termed it close-range photogrammetry-based dental imaging (CPDI). We evaluated this technique on both in vitro dental models and in vivo teeth. For dental models, we conducted a parametric study to examine the effects of the depth of field and specular reflection on reconstruction quality. We showed that the optimal results were achieved with an f/5.6 lens and without a circular polarizer for reflection suppression. This configuration generated 3D scans with 57.7 ± 3.2% and 82.4 ± 2.7% of reconstructed points falling within ±0.1 mm and ±0.2 mm error margins, respectively. With such accuracy, these 3D dental models can faithfully represent dental morphology and features. During in vivo imaging, we were able to reconstruct high-quality 3D models of the anterior arch, further demonstrating its clinical relevance. The reconstructed models carry both 3D shapes and detail full-color surface textures, which positions CPDI as a versatile imaging tool in different areas of clinical dental care.