High Microwave Research Articles

Flexible Bonding of Polymer Substrates By Microwave Heating of Carbon Nanotubes

Recently, as research on developing electronic devices for simultaneous implementation of flexibility and conductivity has been continuously conducted, ensuring stable and high reliability of devices in preparation for various mechanical deformation is becoming important. When a physical force such as bending, twisting, or folding is applied, the bonding area between two substrates should ensure stability due to high stress generation. Epoxy resin materials used as standard adhesive agents have brittleness due to the nature of the material, and are weak in terms of flexibility due to increased bonding thickness due to high temperature hardening. In addition, it is difficult to apply as a bonding material in consideration of thermal deformation of the polymer substrate exposed to high temperatures during the process. To improve both flexibility and durability against fatigue deformation, Flexible bonding process is required without adhesive such as epoxy resin with poor brittleness. Surface activation bonding technologies by ion beams and vacuum ultraviolet rays have been developed in previous studies, bonding between plastic substrates by activating thin metal films surface of adhesive layer with ion beam or improving adhesive force by direct-UV radiation on the surface of the polymer substrate. In this study, a flexible bonding process between polymer substrates was developed by heating carbon nanotubes (CNTs) through microwave irradiation. High microwave absorption properties of CNT lead to heat dissipation behavior and light emission characteristics. Heat transfer mechanism of CNT applied to CNT-polymer composites, CNT electrodes fields and has been microwave assisted purification. By utilizing the microwave heating effect, we selected CNT materials for flexible substrates. Multi-walled carbon nanotubes (MWNTs) were coated on a bonded PET polymer substrate and then local heating was performed by microwaves to induce mechanical entanglement between the CNTs and the PET. In the bonding process, the output power of the microwave was adjusted to 600,800 and 1000 Watt, and the bonding strength was evaluated by quantifying the bonding strength was evaluated. For the analysis of the bonding mechanism in the area where mechanical entanglement took place, the CNT-PET bonding interface was analyzed through electron scanning microscope (SEM) measurement, and further analysis was performed for each process condition. In addition, a fracture mechanism analysis that occurred at the junction was performed after the overlapping shear strength test. Acknowledgments This work was supported by the Basic Science Research Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Education (2020M3H4A3106413, Development of Evaluation Method for Mechanical Deformation of Micro-joints in Micro-LED Module) Figure 1

Field-scale rice yield estimation based on UAV-based MiniSAR data with Ku band and modified water-cloud model of panicle layer at panicle stage.

Scientific and accurate estimation of rice yield is of great significance to food security protection and agricultural economic development. Due to the weak penetration of high frequency microwave band, most of the backscattering comes from the rice canopy, and the backscattering coefficient is highly correlated with panicle weight, which provides a basis for inversion of wet biomass of rice ear. To solve the problem of rice yield estimation at the field scale, based on the traditional water cloud model, a modified water-cloud model based on panicle layer and the radar data with Ku band was constructed to estimate rice yield at panicle stage. The wet weight of rice ear scattering model and grain number per rice ear scattering model were constructed at field scale for rice yield estimation. In this paper, the functional area of grain production in Xiashe Village, Xin'an Town, Deqing County, Zhejiang Province, China was taken as the study area. For the first time, the MiniSAR radar system carried by DJI M600 UAV was used in September 2019 to obtain the SAR data with Ku band under polarization HH of the study area as the data source. Then the rice yield was estimated by using the newly constructed modified water-cloud model based on panicle layer. The field investigation was carried out simultaneously for verification. The study results show: the accuracies of the inversion results of wet weight of rice ear scattering model and grain number per rice ear scattering model in parcel B were 95.03% and 94.15%; and the accuracies of wet weight of rice ear scattering model and grain number per rice ear scattering model in parcel C+D+E were over 91.8%. In addition, different growth stages had effects on yield estimation accuracy. For rice at fully mature, the yield estimation accuracies of wet weight of ear and grain number per ear were basically similar, both exceeding 94%. For rice at grouting stage, the yield estimation accuracy of wet weight of ear was 92.7%, better than that of grain number per ear. It was proved that it can effectively estimate rice yield using the modified water-cloud model based on panicle layer constructed in this paper at panicle stage at field scale.

Evaluation of Microwave Absorption Performance of Annealed Cr2AlC at Different Temperatures

Cr2AlC (CAC) has attracted increasing attention due to high conductivity and excellent oxidation resistance, which is useful for high-temperature microwave absorption. However, systematic research on microwave absorption performance of CAC at high temperatures is still lacking. In this work, CAC was synthesized by salt bath method followed by annealing at 500 °C–950 °C. Effects of various annealing temperatures on compositions and electromagnetic properties were studied. Results revealed slight oxidation of CAC at annealing temperature of 500 °C, with formation of small amounts of Al2O3 and Cr2O3 on the surface. Increase in annealing temperature to 950 °C generated Al2O3 and Cr2O3 components in CAC. CAC annealed at 500 °C showed better microwave absorption properties than annealed at 950 °C and pure CAC. Effective absorption bandwidth (Reflection loss, RL < −10 dB) of CAC annealed at 500 °C was estimated to 2.3 GHz (9.7–12.0 GHz), and RLmin was −28.1 dB with thickness of 2.0 mm. The reason for this had to do with appropriate micro-oxidation, which could increase the permittivity of CAC and enhance dielectric loss capability for electromagnetic waves. In sum, these findings look promising to have referential significance for the application and promotion of CAC in the field of high temperature microwave absorption.

Performance and mechanism evaluation of dopamine-hexamethylene diamine-iron tetraoxide composite rubber powder incorporated styrene-butadiene-styrene modified asphalt

• The microwave absorber PDA-HDA-Fe 3 O 4 was synthesized by a one-pot facile method. • PDA-HDA-Fe 3 O 4 /SBS-RP-MA realized improved viscoelasticity and rutting resistance. • PDA-HDA-Fe 3 O 4 /SBS-RP-MA had high microwave absorption. • Some functional groups of PDA-HDA dispersed agglomeration of Fe 3 O 4 in asphalt. In order to improve the mechanical properties, high temperature rheological properties, and self-healing of modified asphalt, the microwave absorber iron tetraoxide (Fe 3 O 4 ) was modified and polydopamine-hexamethylene diamine-Fe 3 O 4 (PDA-HDA-Fe 3 O 4 ) was prepared, which was compounded with rubber powder/styrene butadiene styrene modified asphalt (RP-SBS-MA). Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy analyses confirmed that chemical composition and crystal morphology of PDA-HDA-Fe 3 O 4 remained unchanged. Scanning electron microscopy and atomic force microscopy revealed that the surface morphology of the modified Fe 3 O 4 was altered which could increase the mechanical interlocking interaction with the base asphalt. Dynamic shear rheometer test showed that at 46 °C, the storage modulus and loss modulus of 1 %PDA-HDA-Fe 3 O 4 /RP-SBS-MA were respectively 61.96 % and 69.65 % higher compared to that of RP-SBS-MA. The results of the multi-stress creep recovery test showed that at 3.2 kPa, the strain of 1 %PDA-HDA-Fe 3 O 4 /RP-SBS-MA was reduced by 54.16 % compared to that of RP-SBS-MA. Microwave heating tests analysis showed that the temperature of 1 %PDA-HDA-Fe 3 O 4 /RP-SBS-MA was 20.48 % and 2.41 % higher than those of RP-SBS-MA and 1 %Fe 3 O 4 /RP-SBS-MA, respectively. This was attributed to the improved microwave absorption capacity of the modified asphalt upon the addition of PDA-HDA-Fe 3 O 4 . These convincing results of the newly prepared PDA-HDA-Fe 3 O 4 /RP-SBS-MA could be envisioned of great promise for designing advanced functional asphalts for targeted applications.

Electrical and shielding properties of epoxy composites with Ni–C and Co–C core-shell nanoparticles

The electrical and microwave shielding properties of epoxy-based composites (CMs) filled with metal-nanocarbon Ni–C and Co–C core-shell particles have been studied for the broad frequency range (16–67) GHz. The decrease of electrical resistivity of CMs with the increase of Ni content in core-shell particles and temperature in the range of 77–293 K was found. The observed sufficient increase of microwave shielding efficiency (32–40 dB at sample thickness of 2.2 mm) in K a - and V-band for CMs with high Ni content correlates with increased electrical conductivity . A high microwave absorption index (0.999 at f = 65 GHz) of (Me–C)/epoxy CMs can be attributed to the enhanced dielectric and magnetic losses. The modeling of microwave absorption capability of 60 wt% (Ni x -C)/epoxy CMs showed that the microwave absorption peaks can be observed only for the narrow frequency range, (18–25) GHz at a sample thickness of 0.6–1.0 mm with the effective bandwidth (2.3–4.8) GHz. • Epoxy composites filled with 60 wt% of (Ni–C) and (Co–C) core-shell particles. • Decrease of electrical resistivity with increase of Ni content and temperature. • Increase of EMI shielding due to enhanced electric loss for higher Ni content. • Reflection loss in (Ni–C)/epoxy composites versus Ni content and sample thickness. • High microwave absorption index (∼0.999 at f = 65 GHz) for (Ni–C)/epoxy composites.

CoNi-MoS2 composites with high microwave absorption performance

• The use of CoNi alloy to improve the microwave absorption properties of MoS2. • The CoNi-MoS2 has a reflection loss of −60.93 dB with the thickness of 4.93 mm. • This work provides a strategy for the synthesis of efficient microwave absorbers. Composites consisting of magnetic CoNi particles and flower MoS 2 (CoNi-MoS 2 ) have been prepared, by using a hydrothermal reaction method, for microwave absorption. When the CoNi-MoS 2 molar ratio is 1:1, optimal absorption performance is achieved, with reflection loss of −60.93 dB at 5.68 GHz, while the thickness is 4.93 mm. The outstanding microwave absorption performance is attributed to the synergy of the magnetic and dielectric losses, which greatly improves the impedance matching and increases the decay constants of the materials.

(Invited) Towards the Physical Reliability of 3D-Integrated Systems: Broadband Dielectric Spectroscopic (BDS) Studies of Material Evolution and Reliability in Integrated Systems

In this paper, we present an overview of our current research focus in developing non-destructive metrology for monitoring reliability issues in 3D- integrated electronic systems. We introduce a suite of non-destructive metrologies that can serve as early warning monitors for reliability issues. These Broadband Dielectric Spectroscopic (BDS) techniques are based on the application of high frequency microwaves (up to 40 GHz) to devices under various external stress, to probe impedance changes due to material and structural changes in integrated circuits. We illustrate the capabilities of the techniques with four case studies of potential reliability issues in 3D-IC interconnects.

Ultra-fast green microwave assisted synthesis of NaFePO4-C nanocomposites for sodium ion batteries and supercapacitors

Sodium ion batteries are favored in stationary and large scale power storage due to their low cost and nontoxicity. As the lithium is replaced with sodium due to the cost motive, a cheap processing method is needed to maintain the cell price as low as possible. We report an ultra-fast synthesis method that utilizes the high microwave absorbance of silicon carbide content in rice straw ash. Amorphous/maricite mixtures of sodium iron phosphates-carbon composites (NaFePO4-C) are synthesized, crystallized, and carbon coated using one-step microwave heating. The sodium ion electroactive composites are prepared using different microwave heating durations ranging from 30 to 100 s. High purity inert gases are not needed during synthesis, processing, and even at cell assembly. The materials are characterized by elemental analysis techniques, X-ray diffraction (XRD), scanning/transmission electron microscope (SEM/TEM), and Raman spectroscopy. The electrochemical performance of the synthesized nanocomposites is examined as sodium ion battery cathode and as symmetric supercapacitors. The optimum synthesis time is 60 s for the application as sodium ion batteries and as a supercapacitor. The maximum specific capacity is 108.4 mA h g−1 at 0.2 C in the case of using it as a battery cathode. While the capacitance is 86 F g−1 at 0.5 A g−1 as a supercapacitor. The capacity retention is 92.85% after 40 cycles at 0.2 C as sodium ion battery electrode. For supercapacitor, the capacity retention is 81.7% after 1000 cycles.

Three-dimensional porous manganese oxide/nickel/carbon microspheres as high-performance electromagnetic wave absorbers with superb photothermal property

Regulating electromagnetic parameters and thus improving impedance matching characteristics by multi-component design is regarded as a prospective approach to obtain highly efficient electromagnetic wave absorption materials. Whereas, it is still challenging to fabricate microwave absorbers with strong absorption capacity and durability in harsh conditions. Based on the above considerations, three-dimensional porous multi-functional manganese oxide/nickel/carbon microspheres had been designed and prepared through a combined approach of facile solvothermal reactions and subsequent carbonization processes. The textural characteristic examinations demonstrated that, numerous manganese oxide and Ni nanoparticles of 15–20 nm in diameter were well dispersed in the carbon-based microspheres of approximately 0.8–1 μm in size. Microwave absorption property evaluation indicated that the minimum reflection loss reached up to −53.6 dB at 9.5 GHz, and effective absorption bandwidth of 3.7 GHz was achieved at matching thickness of merely 2.0 mm. The electromagnetic wave attenuation mechanisms analysis displayed that excellent impedance matching and various dissipation pathways, including magnetic loss, interfacial and dipole polarization relaxation synergistically contributed to the high microwave absorption performances of the porous composites. Radar cross-sectional simulation and photothermal measurements verified that the materials were supposed to have promising foregrounds in complicated circumstances.

Magneto-electric adjustable Co/C porous layer coated flaky carbonyl iron composites with bifunctions of anti-corrosion and microwave absorption

Coating carbon materials on the surface of magnetic metal is an effective strategy to obtain lightweight high performance anticorrosive absorbers. Herein, the structure of the dense anticorrosive shell (Co/C porous layer) coated on the surface of the magnetic core (Flaky carbonyl iron, FCI) was successfully constructed. And the electromagnetic parameters of the composites can be precisely adjusted by controlling the mass reaction ratio of polydopamine/sodium dodecyl benzene sulfonate modified Co/C composites (Co/C@PDA-SDBS) and polydopamine/polyethyleneimine modified FCI (FCI@PDA-PEI). When the reaction ratio was 4:6 (FCI@Co/C-4/6), the sample exhibited excellent microwave absorption performance with suitable impedance matching and strong attenuation ability. The minimum reflection loss (RLmin) value reached − 72.6 dB at 14.8 GHz and the maximum effective absorption bandwidth (EAB) covered the Ku band (11.8–18 GHz) with a thickness of only 1.5 mm. Besides, the dense Co/C layer with effective isolation of FCI@Co/C-4/6 also represented the excellent corrosion resistance for its higher Ecorr (−0.193 V) and lower Icorr (0.33 μA/cm2). Therefore, our research provides a novel approach for reducing the application thickness of FCI and paves the way for commercial application of lightweight high performance anticorrosive microwave absorbents.

Thermal Response and Mechanical Behaviors of Compact Basalts Induced by Microwave Irradiation

Microwave pretreatment could be an invaluable method to improve the efficiency of the rock breakage in the excavation and comminution operations. To investigate the influence of microwave irradiation on the thermal response and mechanical behavior of compact rocks, a series of physical and mechanical experiments were conducted on the nontreated and treated basalts. The mineral compositions of the basalts were obtained by X-ray diffraction (XRD) test. Scanning electron microscope (SEM) images and geological sketch were utilized to analyze the propagation pattern of the microcracks and macrofractures caused by the microwave irradiation. High power density microwave can induce the complication of the microcracks and exchange the pattern of the macrofracture network. Based on the uniaxial compression strength (UCS) test, the mechanical performance of the basalts was evidently reduced with the increase of the microwave power and exposure time. The experimental results prove that microwave-assisted method has significant potential application to preweakening rocks in civil and mining engineering.

Fe3O4@C 3D foam for strong low-frequency microwave absorption

Low-frequency microwave absorbing materials have been challenging for many years. Three-dimensional dielectric/magnetic porous materials are beneficial for improving the low-frequency microwave absorbing performance because of natural resonance and improved impedance matching. In this study, Fe3O4@C 3D foam was prepared by carbothermal reduction method and the microwave attenuation performances and mechanisms were studied. By adjusting the content of Fe3O4@C 3D foam in paraffin composites, the low-frequency microwave attenuation capacity could be effectively optimized. The minimum reflection loss (RLmin) of paraffin composite with 40% (in mass fraction) loading exhibits −54.7 dB at 4.1 GHz for a thickness of 4.0 mm. Surprisingly, the paraffin composite with 50% (in mass fraction) loading could almost cover 2–4 GHz (S-band) in the thickness range of 3.5–5.5 mm. The strong low-frequency microwave attenuation property of Fe3O4@C 3D foam is mainly attributed to excellent low-frequency impedance matching, natural resonance, interfacial/dipole polarization, multiple reflection and scattering. This method provides a new perspective for preparing lightweight and high performance low-frequency microwave absorbing materials.

Case-embedded cooling for high heat flux microwave multi-chip array

• A case-embedded cooling is developed for microwave multi-chip module. • An analytical model is proposed to calculate thermal resistance. • The application range of the embedded cooling is determined. • A thermal test vehicle composed of 4 × 4 chip array is manufactured. • The accuracy of the model is verified by 3D simulation and experiment. This work proposes a case-embedded cooling (CECool) for microwave multi-chip module and theoretically studies its cooling capacity based on an improved analytical model. In this solution, the microfluidic cooling is integrated inside the case of the module to shorten the path of heat transfer. The model is used to calculate the thermal resistance from the chip to the coolant. The accuracy of the model is improved by setting the thermal diffusion angle to vary with the difference in thermal conductivities between the materials, which is validated by 3D finite-element-method simulation. Thermal performance of the remote cooling approach is studied first to help determine the application range of the CECool. By optimizing the materials and the microchannel, the thermal resistance of the CECool can be reduced to 5.7 °Cmm 2 /W. It is possible to increase the maximum tolerant heat flux to 1300 W/cm 2 by enhancing the microfluidic cooling and choosing the chip type, meanwhile keeping the rise of junction temperature below 60 °C. A thermal test vehicle composed of 4 × 4 chip array is manufactured for demonstration. The accuracy of the model is verified by the experiment at 471 W/cm 2 . The maximum error is only 5.4%.

Holy cross-moon shaped dual band perfect metamaterial absorber for C-band application

In this paper, a dual band electromagnetic perfect metamaterial absorber (PMA) is presented for C-band application. This new design comprises of a moon shape and a holy cross shape metal bar which are surrounded by a circular ring resonator (CRR) and an octagonal close ring resonator (OCRR). Flame retardant 4 dielectric material of thickness 1.6 mm is used as a substrate. Commercially available high frequency electromagnetic simulator CST microwave studio used to simulate the proposed unit cell within the frequency range 2–6 GHz. The numerical simulation shows two resonance peaks at 4.10 GHz and 4.96 GHz with excellent absorption rate. The projected PMA exhibits maximum absorption of 99.99 % (4.10 GHz) and 99.57 % (4.96 GHz) in transverse electric (TE) mode at normal incidence angle. The structure of the unit cell was optimized through some recognized parametric studies like design optimization, resonators widths, gaps among resonators etc. The numerical results for 2 × 2 and 4 × 4 arrays are also investigated. The simulated result of 2 × 2 array shows resonance at 4.14 GHz and 4.98 GHz with absorptivity of 99.06 % and 99.58 %, respectively whereas 4.12 GHz and 4.69 GHz with absorptivity of 92.35 % and 97.62 %, respectively for 4 × 4 array. These two results are quite resembled with the unit cell result. The extracted numerical results are tested and authenticated by some validation processes as equivalent circuit modeling through ADS software, and different electromagnetic simulator such as high-frequency structure simulator (HFSS) which is revealed an unimportant disparity. The offered perfect metamaterial absorber is fit for satellite communication, stealth-coating technology, defense and security uses.

Catalyst-Free Accelerated Three-Component Synthesis of Betti Bases in Microdroplets.

Due to their important roles in medicine and asymmetric metal catalysis, the formation of Betti bases has attracted wide interest in organic chemical community. Traditional multicomponent reaction methods for synthesizing Betti bases normally require long reaction times under harsh conditions (high temperature, microwave or ultrasonic irradiation, etc.) in the presence of various catalysts. In this study, we developed a mild, highly efficient and environmentally friendly method to synthesize Betti bases without the use of any catalysts in microdroplets. The Betti reaction was accelerated by 6.53×103 in microdroplets by comparing the measured rate constant in bulk. Fifteen Betti bases were synthesized by the microdroplet method using a variety of aldehydes, naphthols and amines with 68-98 % yields at a scaled-up amount of 1.9 g h-1 . Overall it is an attractive alternative to classic organic synthesis for the construction of Betti bases and derivatives.

Construction of optical system for an atomic clock-beyond atomic fountain

We demonstrate the construction of the optical system in the atomic clock-beyond atomic fountain based on 87Rb atom. The optical system includes a high-stability laser system and an optical lattice. The high-stability laser system with the new scheme of frequency locking and shift is introduced in detail, which is an important laser source for laser cooling. The optimized frequency and intensity stability are achieved to 4 × 10–14τ−1/2 (τ is the averaging time) and 4 × 10–5τ−1/2, respectively, which are highly stable. On the basis of the conventional atomic fountain clock, the optical lattice is specially investigated along the direction of gravity and its characteristics are studied systematically. For the optimized and novel exploration, we predict the achievable stability of 3.6×10−14τ−1/2 and it has the potential to be improved to 3.6×10−15τ−1/2. The realizability of the construction due to the stabilized laser and optical lattice makes the beyond fountain promising candidate for the next-generation high performance microwave atomic clock.

In-situ construction of nitrogen-doped reduced graphene oxide@carbon nanofibers towards the synergetic enhancement of their microwave absorption properties via integrating point defects and structure engineering

The aim of this work is to develop materials that can absorb microwave to meet the requirements of stealth technology and solve the problem of electromagnetic pollution. However, the challenge is having materials with high-efficient absorption properties at an ultralow filling rate and visualizing the microwave response. The strategy used in this work was to integrate point defect and microstructure in preparing materials, nitrogen-doped reduced graphene oxide@ carbon nanofibers with high-efficient microwave absorption and double-layered structure. Ethylenediamine (nitrogen source), was doped into the materials, resulting in the generation of the defects. The microwave absorption performance of the materials was affected by the degree of defects due to the dipole polarization loss and conductive loss. The optimal samples gained the maximum reflection loss of −54.7 dB and effective absorption bandwidth of 4.74 GHz at a filling rate of only 8 wt%. More significantly, the microwave absorbing mechanism was analyzed visually in the response field. Furthermore, the actual stealth effects were evaluated by the radar cross section reduction, and the value was 29.2 dBm2. The experimental results illustrated that nitrogen-doped reduced graphene oxide@ carbon nanofibers may be alternative materials with high microwave absorption performance at a low filling rate.

Transmitter and Receiver for High Speed Polymer Microwave Fiber Communication at D-Band

Transmitter and Receiver for High Speed Polymer Microwave Fiber Communication at D-Band

Nickel/porous carbon derived from rice husk with high microwave absorption performance

BHPC (biomass hierarchical porous carbon) is a new microwave absorption material with extraordinarily low density, excellent dielectric loss, and a low environmental impact. In this paper, a Ni/BHPC composite is introduced, which were fabricated using a simple electroless plating method. When the NiSO4 concentration is changed, the electromagnetic characteristics and absorption performance are optimized. The Ni/BHPC composite material exhibits excellent absorption characteristics at a NiSO4 concentration of 0.2 mol/L. With a thickness of 2.7 mm, the RLmin is −58.504 dB at 10.741 GHz. In the frequency range 8.221–12.4 GHz, with a thickness of 2.9 mm, this reflection loss (RL) is less than −10 dB. These results indicate that incorporating Ni particles into the BHPC enhances its wave absorption efficiency. The research contributes to develop high-performance porous carbon microwave absorption materials from biomass.

Microwave enhanced precision in 2D and 3D atom localization at nonzero temperatures

Two- and three-dimensional (2D and 3D) atom localization is analyzed by monitoring the probe absorption spectrum in a microwave driven X-type scheme. It is found that for both stationary and moving atom cases, the precision and certainty in atomic position can be significantly improved by proper adjustment of the system parameters. Our results also reveal that the high microwave field strength curbs the Doppler broadening effect to a large extent and enhances detection probability to 100% in 2D and 3D subspace at nonzero temperatures. Our proposed scheme may be helpful for experimental realization of high precision position measurement and atom nanolithography at room temperature.