Insensitive Characteristics Research Articles

Fluid and thermal effect on temperature-dependent power increase of electric vehicle's permanent magnet synchronous motor using compound water cooling method

Taking advantage of compound housing water jacket (HWJ) and hollow-shaft water jacket (SWJ) cooling based on the temperature-dependent power of permanent magnet synchronous motor (PMSM) is a solution for enhanced electric vehicle (EV) performance. The fluid and temperature field of a 40 kW PMSM at three typical continuous working points were studied, covering low to high speeds of EVs. The influence of different coolant flowrates on power of motor was obtained by multi-physics field coupling analysis method. The impact of current control modes was also investigated. 3D computational fluid dynamics (CFD) conjugate heat transfer calculation combined with 3D lumped parameter thermal network (LPTN) was adopted to calculate the flow and temperature. Temperature-dependent material properties were taken into consideration in electromagnetic finite element analysis (FEA). The models were modified and validated by experiments. Once compounding SWJ on the basis of a strong HWJ cooling, the PM temperature can continue to decrease over 20 degC. The insensitive characteristic of PM temperature towards SWJ flow rate was observed. Under constant current control mode, 3.8 %, 6 % and 4 % PMSM power enhancement by compound cooling were proved at three typical working points. Under current open-loop, 7 %, 16 %, and 10 % increases with compound cooling were confirmed.

Electric and magnetic resonances inducing triple-stopband terahertz metamaterial filter

A polarization insensitive triple-stopband terahertz metamaterial filter is proposed. This filter consists of a flexible polyimide substrate and periodically arranged copper structures on its top. The shape of the metal unit is a “田” inside a square ring. The simulation results show that the resonant frequencies of the filter are 0.107, 0.23, and 0.271 THz; the stopband depths are −35.56 dB, −42.7 dB, and −37.485 dB; the 3 dB bandwidths are 34, 53, and 32 GHz; and the relative bandwidths are 31.78%, 23%, and 11.8%, respectively. Effective parameter analysis demonstrates that the first resonance originates from the negative effective permittivity and positive effective permeability, but the reason for the latter two resonances is opposite to the first. The surface current distributions indicate that the first resonance is electric type, while the latter two resonances are the lower and higher orders magnetic resonances, respectively. Then, we verify the triple-stopband characteristic of the filter based on the equivalent circuit. Finally, the analysis reveals that the performance of the filter is independent of the incident polarization angle. This filter has the characteristics of multi-frequency, broadband, deep stopband, polarization insensitivity, and simple structure, which can be used in terahertz communication, detection, and other fields.

Temperature tunable ultra-wideband absorber based on ionic liquid

Abstract In this paper, a temperature tunable ultra-wideband absorber based on ionic liquid is proposed for the microwave frequency band. The absorber consists of a band-resistive frequency selective surface, a 3D resin cavity vessel, and an ionic liquid ([EMIm][N(CN)2]) layer. Numerical simulation analysis shows that the absorptivity is more than 90% and a relative bandwidth is 113.04% in the range of 7.5–27 GHz. Meanwhile, the absorber absorptivity has different tuning effects in different frequency bands with the change of temperature. Along with the temperature going up, the absorptivity decreases in the low-frequency band of 6.5–14 GHz, the absorptivity increases in the high-frequency band of 28 GHz–40 GHz. It is worth mentioning that the proposed ionic liquid-based absorber has the characteristics of wide incidence angle and polarization insensitivity. Finally, the temperature tunable absorber model based on ionic liquid is fabricated by 3D printing technology. The experimental results are consistent with the simulation results, demonstrating that the absorber is practically feasible. In summary, the absorber achieves a wide frequency tuning range, which gives it great potential application prospects in fields such as frequency-selective thermal radiators.

Synthesis and Characterization of 3,4-Bis[3(2-azidoethoxy)furazan-4-yl]furoxan (DAeTF): A Novel Low-Melting Insensitive Energetic Material.

The synthesis and characterization of low-melting-point insensitive energetic materials are crucial due to their increasing applications in melt-cast explosives. In this work, a furazan-derived energetic compound, 3,4-bis[3(2-azidoethoxy)furazan-4-yl]furoxan (DAeTF), exhibiting insensitive and high-energy characteristics, is rationally designed and synthesized. The structure of DAeTF is characterized by nuclear magnetic resonance spectroscopy, Fourier transform infrared spectroscopy, elemental analysis, mass spectrometry, and single-crystal X-ray diffraction. The thermal properties of DAeTF are investigated using differential scanning calorimetry, in situ FTIR spectroscopy and thermogravimetric-differential scanning calorimetry-Fourier transform infrared-mass spectrometry and thermal decomposition mechanism was elucidated in combination with bond energy calculations. The detonation performance of DAeTF is predicted by the EXPLO5 program. The results indicate that DAeTF has thermal stability (Td = 251.7 °C), high energy level (D = 7270 m/s) and significant insensitivity (IS = 60 J). Additionally, its relatively low melting point (Tm = 60.5 °C) facilitates processing and loading. These characteristics indicate that DAeTF is a promising candidate as an insensitive melt-cast explosive in future applications.

INS/UWB fusion localization algorithm in indoor environment based on variational Bayesian and error compensation

Localization technology is crucial for indoor robot navigation. However, because of the intricacies inherent in the indoor setting, the signal transmission is vulnerable to the interference of obstacles, which leads to the decline of positioning accuracy. Ultra-Wideband (UWB) has the characteristics of channel insensitivity and high localization accuracy. Inertial navigation system (INS) functions independently as a navigation system, and its positioning results will not be affected due to non-line-of-sight (NLOS) interference. When using UWB to locate the mobile node, the Variational Bayesian Gaussian Mixture Model (VBGMM) clustering algorithm based on Gaussian Mixture Model (GMM) is applied to lessen the influence of NLOS propagation. This paper proposed a loose coupling of the INS and UWB, which combines the advantages of the two subsystems and improves the performance of the positioning system. On the basis of INS autonomous positioning, the maximum entropy fuzzy generalized probability data association filter (MEF-GPDAF) is used to modify the INS positioning results, and then the virtual inertia points are further built to compensate the error of the corrected coordinates. Finally, Unscented Kalman Filter is applied to the compensated coordinates for enhanced positioning. Simulation indicates that the proposed approach in this paper exhibits superior location accuracy. The real experimental results show that the proposed algorithm achieves an average improvement of 61.12% in positioning accuracy.

High-performance ultra-simple solar absorber with extremely high tolerance for fabrication errors

Broadband metamaterial perfect absorbers have drawn considerable attention from researchers for a broad range of applications in electromagnetic stealth, solar energy harvesting and other fields. However, it is extremely challenging to integrate the excellent characteristics of ultra-broadband, perfect absorption, polarization independent, and insensitivity to wide incidence angles into a structurally simple absorber. Herein, we present an ultra-wideband solar perfect absorber with an ultra-simple structure, which consists of a Si3N4-Ti-Si3N4-Ti four-layer structure. The optimized structure offers more than 92 % absorption in the bandwidth range of 450–2750 nm, and the average absorption is up to 97.3 %. Moreover, we elaborate the physical mechanism to achieve the broadband perfect absorption. For solar thermal systems, the absorber is capable of absorbing 95.7 % of the sunlight, its blackbody radiation absorption is as high as 98.0 % at 1900 K and it has a photothermal conversion efficiency of 90.2 % at 1000 K. Furthermore, the absorber displays the characteristics of being independent of polarization and insensitive to wide incidence angles. Additionally, the absorber possesses a very high tolerance for manufacturing errors. It is shown that the designed absorber is ultra-simple in structure and excellent in performance, and has excellent application prospects in fields including solar thermal conversion.

Thermally-stable solar energy absorber structure with machine learning optimization

Major problems that the world is currently confronting include global warming and the energy crisis, and the optimal absorption of solar spectrum radiation is a pivotal stage for a green future for the effective usage of solar thermal energy. The available solar absorbers are temperature sensitive and do not provide perfect absorption for a wide operation range. The major objectives of the proposed paper are to overcome these limitations and present an ultrawideband thermally stable solar absorber. The developed absorber utilizes a high melting point material comprising a Ti reflector element, a Si3N4 dielectric layer, and a pi-shaped top TiN metal layer. Within the spectral range spanning from 200 to 2500 nm, a notable average absorption rate of 97.69 % is attained. This structure has also demonstrated exceptionally under the AM1.5 conditions with a spectral absorption efficiency of 96 %. This work presents a novel optimization approach for solar absorbers, employing K-nearest neighbor (KNN) regression models to enhance design optimization by simulation time reduction with an R2 score of 0.999. The novelty resides in the absorber surface shape, utilization of cost efficient, sustainable, and thermally stable materials, as well as the KNN regression model for optimization of proposed solar absorber structure. Due to the angle and polarization insensitive characteristics, this structure can be potentially utilized for solar energy harvesting and shielding.

Multi-band tunable electromagnetically induced transparencies based on active metasurface with polarization-independent property

The analogue of an electromagnetically induced transparency (EIT) spectrum is achieved using a metasurface that consists of an array of cross and L-shaped resonators. The mechanism of the EIT-like phenomenon are analyzed, and the influence of geometrical parameters on the effect is discussed. We achieve a multi-band EIT-like through structure configuration. In particular, polarization-independent EIT is realized. A potential application in sensing is suggested and the sensitivity of 65 GHz RIU−1 is obtained. We also investigate the impact of analyte and substrate on the transmission spectrum. We find that when the analyte thickness is higher than 40 μm, the EIT spectral shift is less affected by the analyte thickness. The thickness insensitive characteristics are beneficial for reducing errors caused by analyte dose, thereby improving the accuracy of sensing. By introducing a phase change material, vanadium dioxide, we obtain active control of the EIT effect. Our results provide valuable insights into the development of multi-band tunable compact devices based on metasurfaces.

Improving Performance Insensitivity of Large-Scale Multiobjective Optimization via Monte Carlo Tree Search.

The large-scale multiobjective optimization problem (LSMOP) is characterized by simultaneously optimizing multiple conflicting objectives and involving hundreds of decision variables. Many real-world applications in engineering can be modeled as LSMOPs; simultaneously, engineering applications require insensitivity in performance. This requirement typically means that the algorithm should not only produce good results in terms of performance for every run but also the performance of multiple runs should not fluctuate too much. However, existing large-scale multiobjective optimization algorithms often focus on improving algorithm performance, but pay little attention to improving the insensitivity characteristic of algorithms. This directly leads to substantial limitations when solving practical problems. In this work, we propose an evolutionary algorithm called large-scale multiobjective optimization algorithm via Monte Carlo tree search, which is based on the Monte Carlo tree search and aims to improve the performance and insensitivity of solving LSMOPs. The proposed method samples decision variables to construct new nodes on the Monte Carlo tree for optimization and evaluation, and it selects nodes with good evaluations for further searches in order to reduce the performance sensitivity caused by large-scale decision variables. We propose two metrics to measure the sensitivity of the algorithm and compare the proposed algorithm with several state-of-the-art designs on different benchmark functions and metrics. The experimental results confirm the effectiveness and performance insensitivity of the proposed design for solving LSMOPs.

A low-frequency ultrathin metamaterial absorber using magnetic material

In this paper, an ultra-thin metamaterial absorber (UMA) in the S-band is designed. The overall structure adopts a three-layer design. The top layer is a magnetic material, and the middle layer of the UMA is composed of a centrally symmetrical open square ring (four edges are opened) and a circular pattern placed at the center, which is etched on the FR4 dielectric substrate by printed circuit board technology. The absorptivity of the absorber is more than 90% in 1.73–4.04 GHz under normal incidence, and the fractional bandwidth is 80.1%. The total thickness of the absorber is about 3.4 mm, corresponding to 0.02 λL at the lowest operating frequency. Moreover, it also has good polarization insensitivity and wide-angle incident characteristics. The absorption mechanism of the UMA is analyzed from the aspects of power loss density and surface current. Finally, a sample was fabricated and measured. The measured results are in good agreement with the simulation results, which verifies the effectiveness of the design method.

A high-quality broadband tunable terahertz metamaterial absorber based on graphene

We design a graphene-based broadband tunable terahertz metamaterial absorber (MMA). Its structure consists of a surface graphene pattern layer, a medium layer and an underlying metal film. CST simulation results show that the absorption bandwidth for more than 90% absorption rate reaches 2.12 THz, and the range is 3.2–5.32 THz. The absorption bandwidth for more than 99% absorption rate reaches 1.38 THz, and the range is 3.45–4.83 THz, which was not achieved by most of the previous MMA. Multiple reflection interference theory is used to confirm the simulation results. In order to explore the physical mechanism of wideband absorption, we study the surface electric field distribution of the structure. We also find that the absorber has polarization insensitivity and wide-angle incidence characteristics. The absorption frequency of the absorber can be adjusted by changing the chemical potential of graphene. Therefore, the absorber has potential applications in terahertz absorption, filtering and sensing.

Ultra-wideband and wide-angle metamaterial absorber for solar energy harvesting from ultraviolet to near infrared

In this paper, an ultra-wideband solar absorber consisting of a four-layer structure of Al2O3-TiN-Al2O3-Ti is proposed. The proposed absorber achieves an average absorption of 97.85% in the wavelength range of 250–2000 nm (49.96% improvement over the reference planar structure), and its bandwidth of absorption over 90% is even as high as 1742 nm. As a result of the symmetrical design of the structure, the absorber has polarization insensitivity and wide-angle absorption characteristics. In particular, the absorber has a large process tolerance in the structural parameters and a high degree of universality for other metals and dielectric materials, which is highly advantageous in manufacturing. In addition, we explored the reasons for the high absorption of the structure in detail, discussed the influence of different structures on the absorption, and analyzed the absorption characteristics and thermal conversion efficiency of the structure under the solar spectrum. The proposed structure provides a broader bandwidth and higher light absorption than the recently reported work and further reduces the structure’s thickness. Therefore, the absorber will have broad application prospects in photothermal conversion, solar cells, imaging, and stealth.

Terahertz metamaterials for broadband, high modulation depth modulator, and tunable dual-band absorber based on metal-vanadium dioxide hybrid structure

Terahertz metamaterials for broadband, high modulation depth modulating, and tunable dual-band absorbing are designed based on the similar composite structure of metal and vanadium dioxide film arrays. By using external excitation to induce the insulator-metal phase transition of the vanadium dioxide layer, the transmission characteristics of the metamaterial can be manipulated. High modulation depths of more than 80% are achieved in the range of 0.2–0.8 THz, and the bandwidth width with modulation depths exceeding 60% is up to 140%. By increasing the dielectric thickness and adding a metal ground, the initial broadband modulator can be switched to a dual-band absorber when the vanadium dioxide is in the metal phase. Furthermore, the modulation effect and the absorption performance exhibit insensitive characteristics to the polarization angle of incident waves. This work provides potential applications in broadband modulation of terahertz communication as well as dual-band absorption for terahertz detection.

Tri-band metasurface absorber based on square rotational symmetry

In this paper, a multi-band metasurface absorber is designed, measured and investigated. There are four centrosymmetric two-tangent copper trapezoids that make up its unit cell. The parameters of the unit cell have great influence on the frequency of absorption peaks, with optimized parameters leading to absorptivity of 99.4%, 93.9% and 99.7% at 4.80GHz, 8.68GHz and 10.92GHz, respectively. The physical mechanism of absorption is further analyzed based on the distributions of surface current, electric and magnetic field, as well as the impedance matching. Furthermore, the absorber exhibits characteristics of polarization insensitivity and incident sensitivity, which are demonstrated through experiment. In addition, the proposed absorber is able to monitor different environments that the sensitivities are 0.15 GHz/PIU, 0.50 GHz/PIU and 1.53 GHz/PIU at three absorption peaks. In addition, the FOM of the proposed sensors at corresponding resonant frequencies are 0.68, 1.61 and 4.78, respectively. The result reflects that the proposed metasurface shows effective sensing abilities. The designed metasurface absorber has potential applications in both military and civil fields.

Highly sensitive and polarization-insensitive terahertz microfluidic biosensor based on gap plasmon model

The gap plasmon resonance can generate a local enhanced electric field and make the electromagnetic field energy mostly confined in the microfluidic, thereby increasing the interaction between the detection sample and terahertz wave. In this paper, a five-layer microfluidic terahertz biosensor based on gap plasmon resonance is presented. The simulation results show that the designed biosensor can realize a resonant absorption peak with near-perfect absorption at the frequency of 0.655 THz and high refractive index sensitivity of 191.3 GHz/RIU. In addition, the biosensor possesses the characteristics of polarization insensitivity and 50° incidence angle insensitivity due to the symmetry of the metal metasurface, which make the biosensor can be widely used in the biological label-free detection, medical trace element detection.

Highly Thermally Stable Energetic Compounds Based on 6-Amino-5-nitropyrimidine

Two energetic materials (2 and 4) were designed and synthesized from 3,5-diamino-1,2,4-triazole (DAT) and 3,5-diamino-4-nitropyrazole (DANP) as starting materials. Both of them were fully characterized by NMR spectroscopy, IR spectroscopy, and single-crystal X-ray diffraction analysis. Compounds 2 (Td = 295 °C) and 4 (Td = 300 °C) exhibit good thermal stabilities by differential scanning calorimetry. The detonation performances (2: D = 7281 m s–1, P = 18.6 GPa; 4: D = 7436 m s–1, P = 20.5 GPa) were calculated by EXPLO5 software. Their mechanical sensitivities (2: IS > 20 J, FS = 360 N; 4: IS > 20 J, FS = 360 N) were measured by BAM standard tests. Both 2 and 4 exhibited high thermal stabilities, insensitive characteristics, and fair detonation performances, which give them good potential as heat-resistant explosives.

Triple broadband polarization-insensitive tunable terahertz metamaterial absorber on a hybrid graphene-gold pattern

In this paper, we propose a triple broadband metamaterial absorber with a composite hybrid structure of graphene and gold patch embedded in silica. Based on the analogy of a transmission line, this technique may yield polarization-insensitive triple-broadband terahertz absorption with adjustable active control by combining the benefits of gold and graphene. Simulation results indicate that when graphene’s electrochemical potential (Fermi energy) is adjusted to 0.9 eV, the absorber exhibits three broadband absorptions of more than 90% in the frequency ranges of (1.1-2.72) THz, (5.39-6.47) THz, and (9.25-10.97) THz, with a total bandwidth of 4.42 THz for the TE waves. The bandwidth for the TM waves is around 4.29 THz with absorbance greater than 90% in the frequency ranges of (1.14–2.64) THz, (5.51–5.5) THz, and (9.18–10.98) THz. Moreover, the proposed metamaterial absorber is polarization insensitive for both the TE and TM waves and maintains a strong absorption efficacy for both the TE and TM waves at incident angles of less than 40°. Therefore, a single layer of hybrid graphene-gold patch makes the proposed structure extremely simpler and provides triple broadband absorption with a much higher bandwidth with polarization insensitive characteristics, hence, could be used in soaking electromagnetic waves, modulators, detecting signals, tunable filtering, and other broadband devices.

An Additively Manufactured Wide Angle and Broadband Electromagnetic Camouflage Metasurface

An arched dual-wavelength cloaking-illusion-integrated metasurface with polarization insensitive and wide angle characteristics consisting of two-layer meta-atoms is realized by thermal programming curved conformal method. Its different units on each layer perfectly create the illusion in the excellent frequency band respectively. The work will greatly promote the innovative design and practical application of multi-layer metasurface. Further details can be found in the article number 2201728 by Qingxuan Liang and co-workers.

Enhanced ultrathin ultraviolet detector based on a diamond metasurface and aluminum reflector.

Metasurface is a kind of sub-wavelength artificial electromagnetic structure, which can resonate with the electric field and magnetic field of the incident light, promote the interaction between light and matter, and has great application value and potential in the fields of sensing, imaging, and photoelectric detection. Most of the metasurface-enhanced ultraviolet detectors reported so far are metal metasurfaces, which have serious ohmic losses, and studies on the use of all-dielectric metasurface-enhanced ultraviolet detectors are rare. The multilayer structure of the diamond metasurface-gallium oxide active layer-silica insulating layer-aluminum reflective layer was theoretically designed and numerically simulated. In the case of gallium oxide thickness of 20 nm, the absorption rate of more than 95% at the working wavelength of 200-220 nm is realized, and the working wavelength can be adjusted by changing the structural parameters. The proposed structure has the characteristics of polarization insensitivity and incidence angle insensitivity. This work has great potential in the fields of ultraviolet detection, imaging, and communications.

3D printed terahertz metamaterial absorber with visual light transparent

Design, fabrication and testing of a 3D printed terahertz (THz) all-dielectric metamaterial broadband absorber is reported. It consists of periodic resonant cells array on a substrate made of transparent polylactic acid. The thickness of the substrate is only 0.1 mm, which makes it flexible and transparent to visible light. The absorber has the characteristics of polarization insensitivity and wide incident angle. Through analysis and simulation, we propose a theory of grating modes and waveguide resonance modes superposition to explain the broadband absorption mechanism of this type of absorber. Next, a transmission–reflection integrated terahertz time domain spectroscopy system is built to test the absorber. The experimental results show that it can achieve broadband absorption with an absorption rate of more than 80% at 0.31 THz∼1.5 THz, and the absorptivity can reach 99.8% at 0.48 THz. Furthermore, based on the flexibility of 3D printing, the characteristics of the absorber can be easily changed by modifying the size and shape of the unit cell.