Minimum Loss Research Articles

Multifunctional carbon Fiber@TiO2/C aerogels derived from MXene for pressure tunable microwave absorption

Developing microwave absorption (MA) materials with dynamically tunable performance stands as a pivotal endeavor to fulfill the escalating demands of electronic devices and military equipment in complex electromagnetic environments. This study presents advanced hierarchical CF@TiO2/C aerogels with pressure tunable MA performance, engineered through a novel in-situ oxidation process of MXene on carbon fiber (CF) substrates. This process facilitates the formation of a two-dimensional (2D) TiO2/C hybrid layer, which significantly enhances the polarization loss capabilities of the aerogels while maintaining excellent mechanical resilience. The unique architecture of these aerogels facilitates the modulation of their electrical conductivity and permittivity via pressure, thus enabling dynamically adjustable MA performance. Upon compression (50 %), the CF@TiO2/C aerogels showcase an outstanding effective absorption bandwidth (EAB) of 7.84 GHz, accompanied by a remarkable minimum reflection loss (RLmin) of −74.38 dB. Notably, the EAB of CF@TiO2/C aerogels can be precisely tuned from 4 to 18 GHz (covering the C-band, X-band, and Ku-band), with maximum changes in RLmin values (ΔRLmin) reaching as high as 59.30 dB, indicating substantial tunability under varying pressure. Moreover, the CF@TiO2/C aerogels also demonstrate outstanding thermal insulation and pressure sensing performance, highlighting their potential for multifunctional applications. This research not only sheds light on the intricate interplay between nanostructured materials and electromagnetic waves interactions but also sets a new strategy for the design of multifunctional, tunable microwave absorbers suitable for complex electromagnetic environments in modern electronic and military applications.

Integration of carbon microsheets and helical carbon nanocoils for efficient microwave absorption

The integration of multi-dimensional materials is a powerful approach for the construction of high-performance microwave absorbers. In this work, 2D-like carbon microsheets (CMSs) have been directly synthesized on the surfaces of 3D helical carbon nanocoils (CNCs) through a Cu catalyzed chemical vapor deposition process. The junctions formed between CMSs and CNCs create numerous polarization sites, which enhances interfacial polarization. The planar morphology of CMSs is beneficial to enhance the multiple scattering of microwave, while the 3D helical CNCs prevent the aggregation of 2D-like CMSs and simultaneously enhance the conductive loss and cross-polarization loss. By controlling the growth time, the morphologies of CMS are precisely tailored and their impedance matching is adjusted. Consequently, CMS/CNC demonstrates exceptional microwave absorption (MA) performance with a broad effective bandwidth of 6.5 GHz and a minimum reflection loss of −39.3 dB at a remarkably low filling ratio of 4 wt%. This study provides a novel multi-dimensional integrated structure for efficient MA.

High electromagnetic wave absorption and thermal conductivity of vertically oriented boron nitride/carbonyl iron/silicone rubber composites

The vertically oriented boron nitride/carbonyl iron/silicone rubber composites with tunable excellent electromagnetic wave absorption and thermal conductivity have been successfully prepared by a high-temperature molding method. Results show that the composites exhibit a maximum effective absorption band (EABmax) of 7.55 GHz with a thickness of 1.7 mm and a minimum reflection loss (RLmin) of −56.82 dB at 15.6 GHz (1.5 mm). Moreover, the composites have an excellent thermal conductivity with a maximum thermal conductivity of 4.023 W/(m·K), which is 8 times higher than that of the wave absorption material (80 wt% carbonyl iron/silicone rubber composites in this work). This work provides an inexpensive and simple effective strategy for designing advanced multifunctional composites with potential future applications in modern electronics.

Magnetic bimetallic nanoparticles confined growth for enhancement of electromagnetic loss in void@Fe@SiO2/Co/C particles

The dispersion of diverse magnetic metallic in a single particle plays an important role in microwave absorption; however, its contribution is not clear due to the challenge of controllable synthesis of magnetic bimetallic nanoparticles in one micro/nanostructure. Herein, a series of magnetic bimetallic nanoparticles separately confined growth in a hollow multi-shell microsphere with proper impedance matching characteristic were prepared, which can be used as theoretical models to elucidate magnetic coupling effect between diverse magnetic metallic nanoparticles in a single particle on electromagnetic attenuation. The coupling effect of magnetic Co and Fe nanoparticles dispersed in different shell effectively enhance the microwave absorption performance of void@Fe@SiO2/Co/C particles with minimum reflection loss (RLmin) of −62.3 dB (RL=-20 dB, 99 % absorption) at a thickness of 2.05 mm, provoking the maximum radar cross-section (RCS) reduction value of perfect electric conductor (PEC) 37.37 dBm2. Meanwhile, broad effective bandwidth (EBW, RL≤-10 dB, ≥90 % absorption) response of 7.04 GHz at a thickness of 2.44 mm was achieved. These findings can provide guidance for the designation of novel magnetic broadband microwave absorbing materials (MAMs).

Inverse design of phononic topological pumping in continuous solids

Topological insulators have been widely studied for their unique properties, particularly their ability to propagate energy with minimal losses in a manner that is robust to structural defects. More recently, topological pumping, which provides a mechanism to transport energy from one location to another in a structure without the need for direct coupling between the locations, has emerged as a phenomena of interest. However, previous studies on topological pumping of phonons have been performed without developing an understanding of how the efficiency of the pumping, as well as control over the pumping pathway in continuous solids, can be systematically controlled. Therefore, in this work we introduce a novel framework for the inverse design of continuous structures that can exhibit topological pumping of phonons, that is based on two key steps: (I) shape design of unit cells that not only exhibit topologically non-trivial edge states, but whose edge states span a wide range of phase values and wavenumbers at the excitation frequency to achieve a robust pumping effect; (II) optimizing the functional form to enable nonlinear modulation of the phase, which enables control both over the pumping path, and also the efficiency of the energy transport along the desired pumping pathway. Using this approach, we are able to establish connections between the dynamical properties of the unit cell, and various properties that impact the pumping efficiency, including the bandgap width, wavevector range, unit cell truncation, and the path of the phase modulation. We further demonstrate the ability to perform pumping for both out-of-plane and in-plane elastic waves, as well as for quantum valley Hall-based topological insulators.

Graph theory-enhanced integrated distribution network reconfiguration and distributed generation planning: A comparative techno-economic and environmental impacts analysis

In today's world, eco-friendly solutions are crucial for efficient power delivery and assessing their corresponding economic and environmental benefits is essential. As innovators, it is also imperative to continually improve on existing techniques to solve a problem. Evaluating the existing literature in this area of study, gaps of improving the optimization techniques by reducing the amount of infeasible configurations the reconfiguration procedure encounters was established, additionally, the need to utilize distributed generations that significantly reduce carbon footprint in the environment was also ascertained. Hence, this paper presents an effective integration method for the simultaneous reconfiguration of Radial Distribution Networks (RDNs) and Photovoltaic (PV) DGs allocation, considering the tripodal issues of cost, operational efficiency, and environmental sustainability. A modification of the adaptive mountain gazelle optimizer (AMGO) enhanced with graph theory is deployed for the optimization procedures. The crucial feature of the proposed approach is the reduction of unfeasible configurations throughout the optimization procedure toward satisfying the network's radiality constraints, achieving consistent convergence and reduced computation time. The technical benefits are active power loss minimization, voltage stability, and voltage profile improvement. The economic benefits are analyzed by estimating the purchased power, the associated cost of power losses, and the cost of DGs and switches over a planning period of 20 years. The consequent environmental benefits are analyzed in detail, highlighting the significant reduction in pollutant emissions. The proposed model was tested on the IEEE 33- and 69-bus RDN, considering several scenarios, including synchronous network reconfiguration and DG installations. From the results procured, the simultaneous network reconfiguration and DG allocation provided better outcomes, yielding minimum active power loss of 35.36 kW, minimum voltage of 0.9541 p.u., voltage stability index of 1.9936 p.u., total planning cost of $3.456 million, and emission of 1.744 million lb/hr, respectively, for the 33-bus systems. The corresponding value for the 69-bus system is 32.57 kW, 0.9832 p.u., 2.3847 p.u., $ 2.524 million, and 2.53 million lb/hr, respectively. The proposed model was compared with other reported techniques for performance validation, and its efficacy and superior performance was established.

Graphene-Wrapped Magnetic Multichamber Ti3C2Tx Spheres for Stable Broadband Microwave Absorption.

Two-dimensional transition metal carbides/nitrides (MXenes) have aroused widespread interest in the field of microwave absorption because of their unique layered structures. However, the inherent aggregation, poor impedance matching, and low chemical stability of MXenes inevitably obstruct their practical applications. Herein, a multichamber Fe3O4/Ti3C2Tx@reduced graphene oxide (FT@RGO) hierarchical structure was constructed through self-assembly and sacrificial template strategies where the Ti3C2Tx nanosheets were assembled into hollow microspheres that were decorated with Fe3O4 nanospheres and wrapped by RGO nanosheets. The massive heterointerfaces and interior cavities favor enhanced microwave absorption performance via interfacial polarization, multiple scattering/reflections, and dielectric-magnetic synergistic effects. Consequently, the synthesized ultralight FT@RGO foam (0.009 g/cm3) presents superior microwave absorption ability with the minimum reflection loss of -50.5 dB at the matching thickness of 2.5 mm and effective absorption bandwidth of 8.0 GHz covering the frequency range of 10.0-18.0 GHz at the thickness of 2 mm. Furthermore, the encapsulation of hollow Ti3C2Tx spheres by RGO nanosheets avoids direct contact with external air, which considerably improves the stability of Ti3C2Tx and ensures the long-term application of FT@RGO foam in a conventional environment. This work provides a reference for the structural design of MXene-based materials as broadband and durable microwave absorbers.

Lightweight carbon fiber aerogel@hollow carbon/Co3O4 microsphere for broadband electromagnetic wave absorption in X and Ku bands

The increasing proliferation of modern communications, radar systems, and military equipment operating in the X and Ku bands (8–18 GHz) has exacerbated the issue of electromagnetic wave (EMW) pollution, highlighting the urgent need for lightweight, broadband EMW-absorbing materials. In this paper, the lightweight carbon fiber aerogel@hollow carbon/Co3O4 microsphere (CFA@H–C/Co3O4) were composed by ZIF-67 derived hollow carbon/Co3O4 microsphere and bamboo cellulose fiber derived carbon fiber aerogels and constructed by in-situ chemical deposition, dopamine treatment and pyrolysis. Carbon fiber aerogels form a lightweight three-dimensional (3D) interconnected conductive network, which expands the multiple reflection and absorption paths of EMW and increases the dielectric loss. The hollow carbon/Co3O4 microsphere inhibits the collapse of the structure by forming a polydopamine shell through the self-polymerization effect of dopamine on the surface of ZIF-67 during pyrolysis, showing dipole polarization loss, interface polarization loss and magnetic loss, which plays an important role in improving EMW polarization loss and optimizing impedance matching. The minimum reflection loss (RLmin) of CFA@H–C/Co3O4 reaches −43.5 dB at frequency of 12.88 GHz with thickness of 3.0 mm and the effective absorption bandwidth (EAB) of CFA@H–C/Co3O4 reaches 7.84 GHz (10.08–17.92 GHz) with thickness of 3.0 mm, covering most of X and Ku bands at a low filling ratio of 15 wt%. The radar cross-section (RCS) value of CFA@H–C/Co3O4 is 22.68 dB m2 lower than the perfect electrical conductor (PEC). This study provides valuable insights into materials that can improve the absorption bandwidth of electromagnetic waves in the X and KU bands.

Facile constructing core-shell F–CIP@O/N-SWCNHs composites for high-performance microwave absorption and anti-corrosion

The development of electromagnetic wave-absorbing materials (EWAMs) with good environmental adaptability has emerged as a focal point of research in the realm of electromagnetic protection. Herein, a core-shell structure composite EWAMs, in which flake carbonyl iron powders and O, N co-doped single-walled carbon nanohorns are respectively a core and a shell (F–CIP@O/N-SWCNHs), has been prepared by a simple electrostatic adsorption method. The high-shape anisotropy of the F–CIP core exhibits strong specific saturation magnetization (160.47 emu/g) and excellent magnetic loss capacity. The tunable O/N-SWCNHs shell effectively enhances the dielectric properties and improves impedance matching, while the oxygen and nitrogen doping strengthens the dipole polarization. The surface protection provided by O/N-SWCNHs imparts favorable corrosion resistance and anti-oxidation properties to the F-CIP@O/N-SWCNHs. Moreover, F–CIP@O/N-SWCNHs exhibit excellent wave absorption performance. When the sample thickness is 1.53 mm, the minimum reflection loss reaches −74.8 dB. This study provides a feasible approach for the preparation of efficient EWAMs with strong environmental adaptability for the practical application of composite-absorbing materials.

Regulation of PPy Growth States by Employing Porous Organic Polymers to Obtain Excellent Microwave Absorption Performance.

Regulating the different growth states of polypyrrole (PPy) is a key strategy for obtaining PPy composites with high electromagnetic wave (EMW) absorption properties. This work finds that the growth states of PPy is regulated by controlling the amount of pyrrole added during the preparation of composites, so as to regulate the development of conductive networks to obtain excellent EMW absorption performance. The POP/PPy-200 composite achieves an effective absorption bandwidth (EAB) of 6.24GHz (11.76-18.00GHz) at a thickness of only 2.34mm, covering 100% of the Ku band. The minimum reflection loss of -73.05dB can be demonstrated at a thickness of only 2.29mm, while at the same time showing an EAB of 5.96GHz to meet the requirements of "thin", "light", "wide", and "strong". Such excellent EMW absorption performance is attributed to the conductive loss caused by the regulation of the growth states of PPy and the polarization loss caused by the heterostructure. This work also addresses the key challenge that porous organic polymers (POPs) cannot be applied to EMW absorption due to poor conductivity and providing new insights into the candidates for EMW absorbing materials.

Achieving efficient electromagnetic absorption in multifunctional carbon nanotube aerogels by manipulating radialized network structure

The rapid advancements in communication technology have greatly propelled the widespread applications of artificial intelligence (AI). While AI technology facilitates society, it also brings the unavoidable electromagnetic hazards and the issue of disposal of electronic plastic wastes. So, utilizing electronic plastic wastes to constructing carbon-based electromagnetic wave (EMW) absorption materials, are highly promising. However, how to use CNTs from plastic wastes to build good EMW absorption performance aerogels is a critical challenge. In this work, highly porous and well-interconnected network aerogels constructed by radialized CNT arrays are rationally designed under the guidance of grave-to-cradle strategy, exhibiting altered impedance matching and multiple EMW attenuation methods. Theoretical calculations suggest that a well-designed heterojunction interface structure can enhance the conductivity and interface polarization of CNTAs. The CNT aerogels (CNTAs) realize broad absorption bandwidth covering 8.48 GHz with a minimum reflection loss of −59.5 dB. Moreover, the radialized arrays network of CNTAs also endows it with electromagnetic protection, thermal management, self-cleaning, and air purification functions. These inspiring achievements of multifunctional CNTA-2 provides new help for the safe and stable promotion of the AI era.

Design of a yolk-shell ternary metal sulfide with a tunable structure for high-performance electromagnetic wave absorption.

Herein, we report a strategy for preparing a novel ternary metal sulfide (TMS) with a yolk-shell structure based on a "penetration-solidification-annealing" method. A series of FeCoNiSxGy with tunable structure, different morphology and composition was synthesized by adjusting the degree of sulfuration. Due to the synergistical manipulation of rich interface, defects, vacancies and electrical conductivity, as well as the unique yolk-shell structure, the appropriate sulfuration strategy achieved excellent impedance-matching and strong dielectric loss. The as-synthesized FeCoNiSxGy sulfides were blended with paraffin wax (under a filler loading of 30 wt%), which had the minimum reflection loss of -49.44 dB (2.20 mm) and the effective absorption bandwidth of 4.76 GHz (1.6 mm). In conclusion, this work could aid the design and regulation of a new type of ternary metal sulfides with high-performance electromagnetic wave absorption.

C/Co3O4/Diatomite Composite for Microwave Absorption.

Transition metal oxides have been widely used in microwave-absorbing materials, but how to improve impedance matching is still an urgent problem. Therefore, we introduced urea as a polymer carbon source into a three-dimensional porous structure modified by Co3O4 nanoparticles and explored the influence of different heat treatment temperatures on the wave absorption properties of the composite. The nanomaterials, when calcined at a temperature of 450 °C, exhibited excellent microwave absorption capabilities. Specifically, at an optimized thickness of 9 mm, they achieved a minimum reflection loss (RLmin) of -97.3 dB, accompanied by an effective absorption bandwidth (EAB) of 9.83 GHz that comprehensively covered both the S and Ku frequency bands. On the other hand, with a thickness of 3 mm, the RLmin was recorded as -17.9 dB, with an EAB of 5.53 GHz. This excellent performance is attributed to the multi-facial polarization and multiple reflections induced by the magnetic loss capability of Co3O4 nanoparticles, the electrical conductivity of C, and the unique three-dimensional structure of diatomite. For the future development of bio-based microwave absorption, this work provides a methodology and strategy.

Chelation approach to long-lived and reversible chromium anolytes for aqueous flow batteries

Iron chromium flow battery (ICFB) has the advances of low cost, safety, and independent design of power and capacity, but is restricted by the deactivation of chromium anolytes. Here, a complex of diethylenetriaminepentaacetic acid with chromium ion (CrDTPA) is designed with minimum capacity loss rate and best cycling stability. DTPA is an octadentate ligand and chelates with chromium ions in a seven-coordinated manner. The coordination structure was studied by Nuclear Magnetic Resonance, Fourier transform infrared and UV–vis absorption spectra, and identified as a robust structure. CrDTPA has good electrochemical activity and reversibility with a redox potential of −1.145 V versus saturated calomel electrode. A novel iron chromium flow battery (NICFB) is designed by coupling CrDTPA anolytes and Fe(CN)6 catholytes. NICFB displays high energy conversion efficiency with coulombic efficiency of 99.0 % and energy efficiency of 82.2 % at 40 mA cm−2. Importantly, NICFB shows superior cycling stability without performance decay for 160 cycles, ranking the best among recently reported ICFBs. This chelation approach provides a simple and practical method to solve chromium anolytes deactivation and improve cycling stability.

Multi-heterogeneous interfaces boost dielectric polarization in PBA-derived Co/MnO@NC ternary composites for electromagnetic wave absorption

The elaborate construction of multi-component composites has been deemed as a promising strategy to enhance dielectric polarization response capability in the preparation of highly efficient microwave absorbers. However, the rational design and integration of homogeneous composites with diverse components continues to pose a great challenge. Herein, we propose a straightforward self-assembly-carbonization strategy for fabricating Co/MnO@NC ternary composites derived from CoMn-Prussian Blue Analogous precursors, featuring enriched heterogeneous interfaces and balanced magneto-electric coupling synergy. The ternary composites effectively introduce diverse dissipation mechanisms, including interfacial polarization behavior originated from the constructed heterogeneous interfaces, dipole polarization relaxation triggered by atomic defects, and optimized magnetic loss ability from well-dispersed metallic Co species. Benefiting from these advantages, the Co/MnO@NC composites demonstrate superior electromagnetic wave absorption performances, with a minimum reflection loss value of −61.37 dB at the thickness of 3.5 mm and effective frequency absorption bandwidth of 6.32 GHz, covering the full Ku-band. Furthermore, power loss density and radar cross-section simulations validate that the Co/MnO@NC ternary composites possess exceptional microwave signal attenuation abilities, with a maximum radar cross-section reduction value of up to 27.98 dBm2 at 0°. Such outstanding absorption properties exceed those of most currently reported ternary composites and exhibit significant potential to replace conventional ferromagnetic-based absorbers. This work offers a straightforward strategy to fabricate ternary composites with excellent electromagnetic wave attenuation properties and sheds novel insights into the dissipation mechanisms.

Fabrication of MXene-encapsulated Co@C nanoparticles for efficient microwave absorption in the X-band

Two-dimensional MXene has structural advantages in electromagnetic wave scattering due to its layered structure, but MXene materials can lead to impedance mismatch problems due to their high dielectric constants, so it is still a challenge to design highly efficient wave-absorbing materials based on MXene with low reflection loss, thin thickness, and wide absorption frequency. In this study, composite wave-absorbing materials were fabricated from Co–Co PBA precursors and MXene using liquid nitrogen flash freezing and freeze-drying techniques. By treating MXene and the PBA precursor at a high temperature of 750 °C, a rich heterogeneous interface was formed between Co@C and MXene (CCM7), and the impedance matching was optimized to improve the reflection loss capability. The optimized sample has an effective absorption bandwidth of 4.1 GHz at 2.5 mm covering the entire X-band with a minimum reflection loss of −61.42 dB. It is also demonstrated that CCM7 is satisfactory for Radar Cross-Section of flat panels and unmanned aerial vehicles by CST calculations, and this work provides a fresh perspective on the use of effective MXene composites for microwave absorption.

Growth behavior of anisotropic monometallic MOFs derivatives with the high absorbing and thermal properties

The growth behavior and morphological characteristics of metal-organic frameworks (MOFs) should be considered as important factors in understanding their structure. Therefore, MOFs with atypical shapes, heterogeneous structures or abnormal properties that grow anisotropic can serve as components and templates for further directed assembly or conversion into MOF derivatives with excellent performance in electromagnetic wave absorption. Cobalt (Co) and nickel (Ni) metals have good magnetic properties and are common materials for the preparation of monometallic MOF-derived. In this study, various MOF materials with anisotropic properties, such as rod-like, flower-like, and braided, were prepared by adjusting the molar ratio of Co and Ni solvent to the organic ligand. Due to the rich inter-facial polarization and strong magnetic coupling network of the magnetic composites, Ni-MOF-b (Ni-MOF with braided shape) was prepared for the first time when the molar ratio of nickel nitrate to linker was 1:1.2. The Ni-C-b was obtained after pyrolysis of Ni-MOF-b, the minimum reflection loss of Ni-C-b was –50.7 dB at 4.0 mm. In addition, the thermal conductivity of the film prepared with Ni-C-b as filler is 2.2 W/mK. The film with integrated good heat dissipation and wave absorbing properties provides a research idea for the design of multifunctional integrated film.

Investigation of circularly polarized MIMO antenna with enhanced isolation for sub-6 GHz application

This article demonstrates the design process for a unique, two-port, circularly polarized (CP) multiple input multiple outputs (MIMO) antenna for fifth-generation (5G) applications operating at sub-6 GHz. The proposed 2-port CP MIMO antenna comprises a patch antenna with a distinctive slot and a circular split ring resonator (SRR) at the ground plane. The circular patch antenna’s resonant frequency is moved to a lower frequency by the addition of a circular SRR at the ground plane. Investigating a special slot at the patch antenna can help in the enhancement of circular polarization and bandwidth. A sequence of parasitic elements in the shape of ‘h’ is placed in the space between the two antenna elements for decoupling. The minimum 20 dB inter isolation among the antenna elements in the proposed 2-port CP MIMO antenna’s operating band is made possible by these h-shaped parasitic elements. In addition, to ensure the proposed antenna is more reliable for 5G applications at sub-6 GHz, other diversity parameters including Envelop Correlation Co-efficient (ECC), Mean Effective Gain (MEG), Diversity Gain (DG), TARC (Total Active Reflection Co-efficient) and CCL (channel capacity loss) are also calculated . In comparison to existing MIMO systems of the same order, the proposed 2-port CP MIMO antenna appears to have the minimum channel capacity loss and excellent diversity performance. The proposed 2-port CP MIMO antenna achieves an impedance bandwidth of 3.3 to 3.6 GHz with impedance matching better than 10 dB and has an axial ratio bandwidth of 3.35 to 3.51 GHz with a steady radiation pattern in both planes over the operating frequency bands.

Sulfidation and reassembly strategy enables yolk-shell metal sulfide/alloy nanoparticles @carbon with efficient electromagnetic wave absorption

Constructing hybrid metal-organic frameworks (MOFs) demonstrates significant potential to improve electromagnetic wave (EMW) absorption performance by leveraging synergistic effects between composition and structure, addressing challenges in tuning electromagnetic parameters of single-composition MOFs. This study proposes a sophisticated strategy involving sulfidation-interface growth-reassembly: sulfide nanoparticles form by sulfidating the core (CoFe-MIL-88A), and then ZIF-67 guests grow and reassemble on the sulfided host MOF, resulting in a layered EMW absorption material. The composite material integrates synergistic effects, which include high conductive loss and defect/interface/dipole polarization induced by N and S atom doping. The CFSNC composite material outperforms previously published values, achieving a minimum reflection loss (RLmin) of −65.96 dB and an effective absorption bandwidth (EAB) of 6.15 GHz with a thickness of merely 2 mm. Simulation calculations of the real far-field radar cross-section (RCS) further validate its practical application potential. This work introduces novel ideas and methods for designing and preparing high-performance EMW absorption materials, offering both theoretical insights and practical applications.

Long-term reprojection loss for self-supervised monocular depth estimation in endoscopic surgery

Aim: Depth information plays a key role in enhanced perception and interaction in image-guided surgery. However, it is difficult to obtain depth information with monocular endoscopic surgery due to a lack of reliable cues for perceiving depth. Although there are reprojection loss-based self-supervised learning techniques to estimate depth and pose, the temporal information from the adjacent frames is not efficiently utilized to handle occlusion in surgery. Methods: We design long-term reprojection loss (LT-RL) self-supervised monocular depth estimation techniques by integrating longer temporal sequences into reprojection to learn better perception and to address occlusion artifacts in image-guided laparoscopic and robotic surgery. For this purpose, we exploit four temporally adjacent source frames before and after the target frame, where conventional reprojection loss uses two adjacent frames. The pixels that are visible in the target frame but occluded in the immediate two adjacent frames will produce the inaccurate depth but a higher chance to appear in the four adjacent frames during the calculation of minimum reprojection loss. Results: We validate LT-RL on the benchmark surgical datasets of Stereo correspondence and reconstruction of endoscopic data (SCARED) and Hamlyn to compare the performance with other state-of-the-art depth estimation methods. The experimental results show that our proposed technique yields 2%-4% better root-mean-squared error (RMSE) over the baselines of vanilla reprojection loss. Conclusion: Our LT-RL self-supervised depth and pose estimation technique is a simple yet effective method to tackle occlusion artifacts in monocular surgical video. It does not add any training parameters, making it flexible for integration with any network architecture and improving the performance significantly.