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In this article, a two-atom-thick diode based on 2-D materials is presented for microwave detection. The diode consists of a molybdenum disulfide monolayer/graphene monolayer heterojunction transferred onto a silicon/silicon dioxide substrate and patterned by means of nanolithography techniques to obtain a geometrical self-switching diode. The interaction between the two monolayers gives rise to a double-stage device, which behaves as a back-to-back diode in the [−3, +3] V voltage range, and as a tunnel diode when exceeding +10 V. The heterojunction can be reproduced at the wafer scale, thanks to its CMOS compatibility and ease of fabrication, and it can be used efficiently as a microwave detector up to 10 GHz, with the best performance around the ISM 2.45-GHz band. Starting from advanced quantum simulations to predict the dc behavior of the single heterojunction-based channel, the diode was fabricated and fully characterized experimentally. Lastly, a rigorous equivalent circuit model is provided, which relies on the measured scattering parameters at high frequencies and allows treating the diode embedded into a coplanar waveguide line as a two-port lossy device. This way, the device can be exploited in circuit-based numerical tools for the design of complex microwave front ends. [ABSTRACT FROM AUTHOR]

The electromagnetic scattering of modes propagating inside a parallel-plate waveguide by cylindrical posts of various cross sections is studied. Exact solutions are obtained for metallic posts of the circular and elliptical cross sections, and their respective numerical results are displayed and discussed. [ABSTRACT FROM AUTHOR]

The solutions of vegetation height and the mapping of terrain in forest have always been concerning and are still challenging problems. The purpose of this article is to provide a new technical approach for the digital terrain model (DTM) and forest topographic survey by aerial photogrammetry, in consideration of the forest vegetation height modeling problem. Based on an aerial digital orthophoto map and a digital surface model (DSM), the spectral features and geometric features that are related to forest vegetation height are analyzed and extracted. The nonlinear correlation maximal information coefficient, maximum asymmetry score, and Pearson linear correlation coefficient between feature factors and vegetation height are listed, and the correlations are evaluated as the basis for factors selection. Two kinds of support vector regression algorithms were adopted to establish the machine learning for forest vegetation height model (VHM). Therefore, the DSM can be corrected to DTM. The experimental results show that the accuracy of the forest VHM is better than 1 m. Thus, the proposed method is proved to be feasible and practical. It provides a low-cost and high-efficiency method for the VHM and DTM in forest areas by photogrammetry. [ABSTRACT FROM AUTHOR]

The Microwave Radiation Imager (MWRI) sensors aboard on the Chinese FengYun-3 (FY-3) series satellites have a great potential for long-term study of sea ice distribution. This study corrected the newly released FY-3D MWRI brightness temperature (TB) data with the Advanced Microwave Scanning Radiometer 2 (AMSR2) TB data and used an Arctic Radiation and Turbulence Interaction Study Sea Ice (ASI) dynamic tie points algorithm to derive the sea ice concentration (SIC) from these corrected MWRI TB data. We assessed the accuracy of our MWRI-ASI SIC product by comparing with the published SIC products at different spatial resolution and by validating with the Moderate Resolution Imaging Spectroradiometer (MODIS) and Sentinel-1 data. We find that MWRI-ASI SIC has the smallest difference with AMSR2-ASI SIC with the mean absolute difference (MAD) of 6.8%, and the differences mainly occur at the marginal ice zone regions. The MWRI-ASI displays the highest difference with Sea Ice Index and OSI-430-b at 25 km with the mean MAD of 11.8%. MADs between MWRI-ASI SIC and SIC products from other sensors are below 10% except for late June to early October, when those are higher. Compared with the MODIS SIC, MWRI-ASI SIC outperforms other SIC products at the same resolution, with the mean bias of −2.1% and mean RMSD of 13.5%. Although MWRI-ASI tends to under-estimate high SIC, it can capture details of large leads, ice edge, and fragmented ice area. Our MWRI-ASI SIC product at 12.5 km is promising to integrate into long-term sea ice records. [ABSTRACT FROM AUTHOR]

Impedance matching plays a vital role in a microwave atmospheric pressure plasma jet (MW-APPJ). However, real-time tuning of MW-APPJ impedance matching has rarely been investigated. In this study, we have found that the dissipated microwave power and length of a MW-APPJ are effected by the application of a DC-bias magnetic field. By placing a MW-APPJ in a gap between two electromagnets, the consumed microwave power varied with the insertion position of the MW-APPJ. When the MW-APPJ was fixed at the center of the electromagnets, the consumed microwave power decreased as the DC magnetic field intensities increased, from 12 to 750 mT. The variation of consumed microwave power was much higher at lower gas velocities, which indicates that the DC magnetic field has a relatively strong effect on microwave plasma with lower gas velocity. The length of the plasma jet also decreased with increasing DC magnetic field, which was mainly due to the variation of the consumed microwave power. To explain these interesting phenomena, the effective permittivity of microwave plasma and the equivalent circuit model of a generator under DC-bias magnetic field have been analyzed. The effective permittivity of the plasma is related to its cyclotron frequency, which is a function of the DC-bias magnetic field. The variation of the effective permittivity changes the load impedance of the plasma generator. Therefore, the reflection coefficient of the plasma generator is adjusted and the length of the plasma jet varies with the change in consumed microwave power. [ABSTRACT FROM AUTHOR]

Hard disk drives (HDDs) used for data servers are exposed to various vibrations. These vibrations are mainly caused by the cooling fan that controls the temperature inside the server. The vibration affects the positioning accuracy of magnetic heads that read/write digital data. This is an obstacle to obtaining high data transfer rates. To compensate for vibration, the control system for the magnetic heads must have higher frequency control bandwidth as the spectra of these vibrations have peaks up to 10 kHz. In current HDDs, the control system is a triple-stage system consisting of a voice coil motor (VCM), a milliactuator, and a microactuator. In this article, we propose a design strategy for a triple-stage control system to compensate for vibration. The design strategy addresses unstable controllers in the control system. The gain of the feedback controllers of the VCM and milliactuators is increased to expand the control bandwidth. Although these feedback loops become an unstable system due to the increase in the controller gain, the controller for the microactuator is designed to stabilize the overall feedback loop. As a result, the control system achieves high control bandwidth. The performance of the proposed control system is calculated based on the compensation of the vibration caused by the data server. The proposed design can improve positioning accuracy by approximately 48%–58% compared with the conventional controller design. [ABSTRACT FROM AUTHOR]

Evolution of drug-resistant microbial species is one of the major challenges to global health. Development of new antimicrobial treatments such as antimicrobial peptides needs to be accelerated to combat this threat. However, the discovery of novel antimicrobial peptides is hampered by low-throughput biochemical assays. Computational techniques can be used for rapid screening of promising antimicrobial peptide candidates prior to testing in the wet lab. The vast majority of existing antimicrobial peptide predictors are non-targeted in nature, i.e., they can predict whether a given peptide sequence is antimicrobial, but they are unable to predict whether the sequence can target a particular microbial species. In this work, we have used zero and few shot machine learning to develop a targeted antimicrobial peptide activity predictor called AMP0. The proposed predictor takes the sequence of a peptide and any N/C-termini modifications together with the genomic sequence of a microbial species to generate targeted predictions. Cross-validation results show that the proposed scheme is particularly effective for targeted antimicrobial prediction in comparison to existing approaches and can be used for screening potential antimicrobial peptides in a targeted manner with only a small number of training examples for novel species. AMP0 webserver is available at http://ampzero.pythonanywhere.com. [ABSTRACT FROM AUTHOR]

ZigBee is one of the communication protocols used in the Internet of Things (IoT) applications. In typical deployment scenarios involving low-cost and low-power IoT devices, many communication features are disabled, consequently affecting the security offered by ZigBee. The ZigBee specification assumes that deployment of frame counters is sufficient to mitigate replay attacks in secure ZigBee networks. However, we demonstrate that it is insufficient in this paper (i.e., the network is no longer secure after the coordinator restarts). As a countermeasure, we present a timestamp-based scheme to mitigate replay attacks. Our mitigation strategy does not consume power significantly, and fully powered devices will be responsible for providing power-constrained devices with the current timestamp. The proposed scheme is designed for all ZigBee topologies and different states of ZigBee End Devices (ZEDs). Findings from our evaluation show that the proposed scheme can successfully mitigate replay attacks, with no significant network performance degradation even assuming a worst-case scenario (i.e., many devices are sending data simultaneously). [ABSTRACT FROM AUTHOR]

Sea ice concentration (SIC) is an indispensable parameter for the study of polar sea ice. The existing methods can obtain accurate SICs for most situations, but they usually perform poorly in low SIC regions because of the spatial differences in the neighboring pixels induced by the discontinuity of the sea ice cover. In this letter, to cope with the difficulty of this problem, an improved SIC estimation method is proposed to retrieve SIC, focusing on low SIC regions. The proposed method introduces the spatial relationships into SIC estimation by employing a total variation (TV) regularizer. Moreover, nonnegative constrained least squares (NCLS) is used to derive the optimal solutions from the SIC estimation equation. Verification was conducted in low SIC regions (0%–50%) of the Antarctic utilizing ship-based in situ data and the Moderate Resolution Imaging Spectroradiometer (MODIS), and the results were compared with those of some of the mature methods. The results indicated that the proposed method can obtain a superior accuracy with a smaller root-mean-square error (RMSE) (6.0%–14.61%) than the other algorithms in low SIC regions. Furthermore, the proposed method can accurately estimate the SIC of both first-year ice and multiyear ice. The findings of this study confirm the need to consider the spatial relationships in the processing of SIC estimation. [ABSTRACT FROM AUTHOR]

Estimation of melt pond fraction (MPF) using the Advanced Microwave Scanning Radiometer for the Earth Observing System (EOS)/2 (AMSR-E/2) brightness temperature (TB) data is required for enhancing understanding of the role of melt ponds in the Arctic and in the earth’s climate system. An original MPF retrieval is based on gradient ratio (GR), defined as the normalized difference between the 6.9 GHz horizontal (H) channel and the 89.0 GHz vertical channel GR(6/89) of AMSR-E. However, using the coarsest spatial resolution 6.9 GHz channel includes potential land contamination in TB in regions of narrow waterways such as the Canadian Arctic Archipelago (CAA). This letter aims to provide a higher resolution MPF product, derived by using 10.7, 18.7, 23.8, 36.5, and 89.0 GHz TBs at H-polarization instead of the 6.9 GHz TB H-polarization in the GR calculation. For GR(10/89)- and GR(18/89)-based MPF retrievals, the difference standard deviations were ~3.8%. This is lower than the ~14.3% standard deviation of the GR(23/89)-, GR(36/89)-, and PR(89)-based MPF retrievals. Our results suggest that the GR(10/89) and (18/89) MPF retrievals are available at a product quality similar to the original GR(6/89)-based MPF retrieval. We recommend that the GR(18/89) MPF retrieval adopted is used in nearshore environments such as in the CAA. [ABSTRACT FROM AUTHOR]

The performance of printed RF interconnect structures for microwave applications is highly dependent on their geometric characteristics as well as manufactured pattern fabrication errors/variations, that can only be insufficiently modeled by current simulation techniques. Here, for the first time, the response of such systems is accurately investigated when random fabrication errors are introduced in the geometric-design variables. To analyze these structures in a computationally efficient way, sparse-basis-polynomial-chaos-expansions (SB-PCE) are used to approximate the quantities of interest using a limited number (sparse) of basis functions. The size of the PCE series is reduced by retaining the most important terms. These are computed using the orthogonal-matching-pursuit algorithms from compressed-sensing (CS). In CS, a relatively small number of deterministic model evaluations is needed and a sparse but reliable PCE is found. The SB-PCE method is proven accurate and much more efficient (roughly two orders of magnitude shorter execution time) compared to alternative methods such as the Monte-Carlo (MC) and least-squares-PCE (LS-PCE) enabling for the first time the accurate modeling of realistic RF structures for specific manufacturing process variations. Numerical results for a monolithic-microwave-integrated circuit (MMIC) verify the effectiveness of the method and describes the structure’s performance under uncertainty. [ABSTRACT FROM AUTHOR]

By using integrated lumped elements based on through-silicon via (TSV) technology, a 3-D low-pass filter (LPF) with ultracompact size and ultrawide stopband is proposed. The 3-D magnetic coupling is enhanced between microsize spiral inductors to increase the mutual inductance and improve the high-frequency performance. A coaxial TSV with enhanced capacitance in high resistivity silicon (HRS) is utilized both as capacitor and as a vertical interconnection without any overhead in area and routing. The 3-D nature of the proposed filter yields a miniaturized size of $0.2\times0.10$ mm2. The LPF is analyzed with equivalent circuit model and validated with the well-matched $S$ -parameters obtained by finite element method simulation and measurement. With −3-dB cutoff frequency at 2.6 GHz, the LPF exhibits an insertion loss below 1 dB, a reflection loss over 17 dB in the passband, and a suppression level over 20 dB from 5.28 up to 40 GHz in the stopband. [ABSTRACT FROM AUTHOR]

Abstract A modified load‐modulation network to design a fully integrated wideband Doherty power amplifier (DPA) from 4.6 to 5.5 GHz is presented in this letter. The modified load‐modulation network uses only two π‐type high‐pass equivalent quarter wavelength transmission lines (QWTLs). Unlike the existing methods, the bandwidth of the load‐modulation network composed of two merged π‐type equivalent QWTLs is broadened. Furthermore, a drain bypass capacitor compensation method is proposed to reduce the leakage of RF power after the drain supply inductors are merged. For verification, a wideband monolithic microwave integrated circuit DPA was designed and fabricated using a 0.25‐μm gallium nitride based high‐electron‐mobility transistor process. Measurement results show that a saturated power of 41.6–42.4 dBm, a saturated drain efficiency (DE) of 65.3–72%, and a 6‐dB back‐off DE of 45–55.4% are achieved from 4.6 to 5.5 GHz. Using a 160‐MHz orthogonal frequency‐division multiplexing signal with a peak‐to‐average power ratio of 6.2 dB, the high average efficiency of 49% with an adjacent channel leakage ratio of –47.2 dBc after linearisation was obtained at an average output power of 35 dBm at 4.9 GHz.

Abstract The idea to use a lower threshold, but slightly slower transistor over the fastest transistor type for large‐signal circuits is presented with experimental verification for a compact divide‐by‐4 true single phase clock (TSPC) frequency divider. The use of the lowest threshold PMOS devices resulted in self‐resonance frequencies of 41.7, 56, and 60 GHz at supply voltages of 0.5, 0.8 and 0.9 V, respectively. Compared to a divider of the same architecture in the same technology, but with higher threshold voltage devices, this corresponds to improvements of 67%, 33% and 27%, respectively. Power consumptions of 26 and 355 μW were measured for a 20 GHz and a 70 GHz input signal for supply voltages of 0.5 and 0.9 V, respectively. The best knowledge of the authors, these results are the best reported to date for TSPC divider architecture, and they compete with state of the art for inductorless current‐mode logic dividers.

Abstract This letter presents an analytical framework to study the distortion effect of power amplifiers (PA) in a single‐stream millimetre wave (mmWave) system with a radio‐frequency beamforming architecture. A third‐order nonlinearity PA model is used. The impact of PA nonlinearity on the transmitter performance is evaluated by means of its normalised mean square error. Also, the effect of PA compression on the system capacity in a line‐of‐sight channel is analysed. All analytical results are supported with Monte‐Carlo simulations.

Abstract This paper presents a millimeter‐wave (mm‐wave) V‐band mixer. The source‐driven transformer‐coupled up‐converter topology can alleviate the local oscillator (LO) leakage problem. The proposed V‐band up‐converter has been implemented on 65 nm CMOS technology. The experimental results show that the LO leakage level can be reduced to –43.1 dB. The up‐converter occupies 0.11 mm2 in area excluding signal pads.

Heating concentrations widely exist in microwave heating, which may destroy heated samples. In this article, we report that with spheres being surrounded in dielectrics, the heating concentration of spheres can be reduced in microwave applicators with moving elements. First, electric field properties in electrically large cavities with moving elements are analyzed by the statistical approach. It reveals that the heating concentration can be studied under exposure to plane waves. Second, based on the Mie theory and the quasi-physical optics, the method for controlling the concentration locations of spheres is discussed. Then, the theoretical model utilizing dielectrics is presented to reduce the concentration of spheres in microwave applicators with moving elements. The results show that when the concentration location is far from the sphere center, the concentration can be reduced in the motion of moving elements. Finally, the heating process of a potato sphere with a radius of 3.0 cm is studied in a practical microwave applicator with the alumina ceramics (AC). Experiments show that both the heating efficiency and heating uniformity can be improved significantly by the proposed method. [ABSTRACT FROM AUTHOR]

This article introduces the design and analysis of a small-size coaxial resonant applicator for high-speed microwave heating-assisted additive manufacturing of multiple materials, such as continuous carbon fiber reinforced polymer composites, thermoplastic, and metal parts. The elaborated coaxial resonant applicator reduces the size and has a resonant frequency between 2.4 and 2.5 GHz. A TEM wave is stimulated in the applicator where the electrical field is polarized perpendicular to the filaments and, therefore, allows a maximum penetration depth. The electrical conductive filament is designed as a part of the inner conductor to enhance coupling efficiency. To prevent microwave leakage induced by the conductive material, a compact quarter wavelength filter was developed. The equivalent circuit of the filter was used to analyze the influence of structural parameters on the resonance frequency. The filter has been tested and good agreement between measured and simulated results is obtained. The heating behavior with varying input power has been investigated for polyamide, polylactic acid, and continuous carbon fiber reinforced polyamide filaments. [ABSTRACT FROM AUTHOR]

Microwave imaging based on the inverse scattering problem has attracted many interests in microwave community. To obtain a satisfactory imaging quality, in most cases, a scattering-free environment is desired. In this work, to provide such an environment, we experimentally demonstrate a compact microwave imager integrated with a board-integrated, multiport vector network analyzer and a miniaturized, cylindrical anechoic chamber dedicatedly designed for inverse scattering-based microwave imaging. Based on the principle of electrically induced transparency and the effective medium equivalence, an inhomogeneous, ultrathin, dual-angle absorbing surface was designed, simulated, and implemented, to simultaneously absorb incident and scattered fields. Experimental imaging verified its effectiveness. The proposed imager would help the promotion of practical imaging, showing the potential in on-side imaging. [ABSTRACT FROM AUTHOR]

This study investigated various types of Micro-Electro- mechanical Systems (MEMS)-based detectors, which enabled the derivation of a general formula via microwave network analysis. Multiple microwave parameters were measured and converted into a problem involving N-port network structural design with the derived formula. Furthermore, a compact integrated detector was proposed by removing a redundant power divider. Additionally, one processing circuit was designed to compensate for the output voltages from the detector and calculate the microwave parameters. The detector fabrication process is compatible with GaAs monolithic microwave integrated circuit (MMIC) process. Experimental results indicate that the revised detector is at least 35% smaller than that obtained using existing methods. This approach can detect multiple parameters, including frequency, power, and phase detection on a monolithic chip. [ABSTRACT FROM AUTHOR]

Microwave cloud polarized observations have shown the potential to improve precipitation retrievals since they are linked to the orientation and shape of ice habits. Stratiform clouds show larger brightness temperature (TB) polarization differences (PDs), defined as the vertically polarized TB (TBV) minus the horizontally polarized TB (TBH), with ~10 K PD values at 89 GHz due to the presence of horizontally aligned snowflakes, while convective regions show smaller PD signals, as graupel and/or hail in the updraft tend to become randomly oriented. The launch of the global precipitation measurement (GPM) microwave imager (GMI) has extended the availability of microwave polarized observations to higher frequencies (166 GHz) in the tropics and midlatitudes, previously only available up to 89 GHz. This study analyzes one year of GMI observations to explore further the previously reported stable relationship between the PD and the observed TBs at 89 and 166 GHz, respectively. The latitudinal and seasonal variability is analyzed to propose a cloud scattering polarization parameterization of the PD-TB relationship, capable of reconstructing the PD signal from simulated TBs. Given that operational radiative transfer (RT) models do not currently simulate the cloud polarized signals, this is an alternative and simple solution to exploit the large number of cloud polarized observations available. The atmospheric radiative transfer simulator (ARTS) is coupled with the weather research and forecasting (WRF) model, in order to apply the proposed parameterization to the RT simulated TBs and hence infer the corresponding PD values, which show to reproduce the observed GMI PDs well. [ABSTRACT FROM AUTHOR]

Particle-in-cell (PIC) simulations of a microwave oven free-running 2.45 GHz “cooker” ten-vane magnetron operating with a “cold” explosive-emission cathode in a uniform axial magnetic field are performed with two computer codes, improved concurrent electromagnetic PIC (ICEPIC), and CST Particle Studio (CST-PS). PIC simulations are done to compare results obtained by these two codes to each other and, in such a way, identify all possible advantages and disadvantages of each code performance as a reliable tool allowing to predict all important characteristics of the magnetron operation. Results of the PIC simulations show that the range of applied voltages within which the magnetron is able to operate in the $\pi $ -mode at an external uniform axial magnetic field 0.19 T is much broader as it is predicted by the CST-PS code, from 4.00 to 4.70 kV, than as it predicted by the ICEPIC code, from 3.90 to 4.10 kV. It is also shown that while the magnetron startup time gradually decreases, as it is predicted by the ICEPIC code, from about 700 ns (3.90 kV) to about 100 ns (4.20 kV) with the applied voltage increase, it initially chaotically varies, as it is predicted by the CST-PS code, between about 1000 ns (4.03 kV) and about 300 ns (4.01 kV) and only then gradually decreases down to 10–20 ns (4.40–4.60 kV) with the applied voltage increase. Additional PIC simulation with MAGIC or VORPAL codes would be interesting to perform as well to compare the obtained with these codes simulation results with results described in this article. [ABSTRACT FROM AUTHOR]

A key objective in multiview learning is to model the information common to multiple parallel views of a class of objects/events to improve downstream tasks such as classification and clustering. In this context, two open research challenges remain; achieving scalability: how can we incorporate information from hundreds of views per event into a model? and being view-agnostic: how to learn robust multiview representations without knowledge of how these views are acquired? In this work, we study a neural method based on multiview correlation to capture the information shared across a large number of views by subsampling them in a view-agnostic manner during training. We analyze the error of this bootstrapped multiview correlation objective using matrix concentration theory to provide an upper bound on the number of views to subsample for a given embedding dimension. Our experiments on a diverse set of audio and visual tasks—multi-channel acoustic activity classification, spoken word recognition, 3D object classification, and pose-invariant face recognition—demonstrate the robustness of view bootstrapping to model a large number of views. Results and analysis underscore the applicability of our method for a view-agnostic learning setting. [ABSTRACT FROM AUTHOR]

This letter presents a four-way power-combined $D$ -band silicon–germanium (SiGe) power amplifier (PA), which simultaneously achieves high output power and high efficiency. A 4-to-1 planar coupled-line Wilkinson combiner is used, which has low loss and provides broadband impedance transformation. The PA is designed in a 90-nm SiGe BiCMOS technology platform and operates over a bandwidth of 110–145 GHz, with 18.2 dB of gain. The design achieves a peak output power of 21.9 dBm at 130 GHz, with a power-added efficiency (PAE) of 12.5%. The PA maintains greater than 20-dBm output power with greater than 8.7% PAE, from 115 to 140 GHz. This work demonstrates the first silicon-based $D$ -band PA, which simultaneously achieves greater than 20-dBm output power and 10% PAE. [ABSTRACT FROM AUTHOR]

The Ultra-Wideband Software Defined Microwave Radiometer (UWBRAD) is a wideband radiometer operating from 0.5 to 2 GHz for remote sensing of polar ice sheet temperature profiles. Small-scale (cm to m) fluctuations in firn density in the upper portion of the ice sheet significantly impact observed brightness temperatures. Previously, a fully coherent model based on solving Maxwell’s equations for thousands of layers throughout the entire ice sheet was developed. Density profiles in the model are described as the sum of a smooth average density profile with a spatially correlated random process that represents density fluctuations. In this article, we develop a “partially coherent” implementation of the coherent model that captures the impact of variations in ice density on predicted brightness temperatures while improving computational efficiency. The partially coherent model divides the ice sheet into blocks. Within each block, the coherent model is applied to take into account coherence among the contributions of closely spaced layers. A Monte Carlo procedure is used to calculate the average block reflection and transmission parameters. Between adjacent blocks, interactions are assumed to be incoherent, and the radiative transfer theory is used to incoherently cascade block parameters. Results of the partially coherent model are in good agreement with the fully coherent model and also with Soil Moisture Ocean Salinity (SMOS) and UWBRAD brightness temperature observations. [ABSTRACT FROM AUTHOR]

An active–passive microwave retrieval algorithm for simultaneous determination of soil surface roughness parameters [vertical root-mean-square (RMS) height (${s}$) and horizontal correlation length (${l}$)] is presented for bare soils. The algorithm is based on active–passive microwave covariation, including the improved Integral Equation Method (I2EM), and is tested with global soil moisture active passive (SMAP) observations. The estimated retrieval results for ${s}$ and ${l}$ are overall consistent with values in the literature, indicating the validity of the proposed algorithm. Sensitivity analyses showed that the developed roughness retrieval algorithm is independent of permittivity for ${\varepsilon }_{s} > 10$ [-]. Furthermore, the physical model basis of this approach (I2EM) allows the application of different autocorrelation functions (ACF), such as Gaussian and exponential ACFs. Global roughness retrieval results confirm bare areas in deserts such as Sahara or Gobi. However, the type of ACF used within roughness parameter estimation is important. Retrieval results for the Gaussian ACF describe a rougher surface than retrieval results for the exponential ACF. No correlations were found between roughness results and the amount of precipitation or the soil texture, which could be due to the coarse spatial resolution of the SMAP data. The extension of this approach to vegetated soils is planned as an add-on study. [ABSTRACT FROM AUTHOR]

We present a new approach of the passive microwave pulse compression for gigawatt power generation. Two stages of resonant-cavity-based pulse compressors are cascaded and the peak power gain is multiplied to 12. Candidate passive pulse compressors and cascaded schemes are studied theoretically from the perspective of a linear time-invariant (LTI) system. The compact $S$ -band (2.856 GHz) prototype system consists of six correction cavities and two storage cavities, with the ability to flatten the first-stage pulses and generate the two-stage compressed pulses with exponentially decaying waveforms. It compresses power pulses of 100 MW and $3.6~\mu \text{s}$ generated by commercial klystrons to the peak power of 1.2 GW and full-width at half-maximum (FWHM) pulse durations of 100 ns. The pulse phase is controllable and the power can be combined for either input sources or outputs. This would be attractive to various applications, such as high gradient accelerator and hot dense plasma generation. [ABSTRACT FROM AUTHOR]

This article introduces a new dual-input nonisolated zero-voltage switching (ZVS) dc–dc boost converter. The proposed converter hybridizes two bidirectional and unidirectional boost converters to harvest energy from a rechargeable energy storage element and a clean energy dc generator, respectively. Hence, the proposed circuit utilizes three power switches, one power diode, two inductors, and an output filtering capacitor. The ZVS of all the power switches and zero-current switching (ZCS) for the power diode are realized without any auxiliary circuit. The soft-switching performance is designed to be valid for the whole power ranges of the converter input sources and the output load. The converter power switches are switched in pulsewidth modulation manner with two individual duty ratios, allowing to regulate the converter output voltage and control the extracted power from the input unidirectional port through a simple and useful control system. Depending on the converter duty ratios, its basic operation principle is analyzed in two different operation cases. The proposed converter benefits from a simple and compact structure, minimum numbers of power switches and magnetic elements, and high efficiency. The behavior of the proposed converter is analytically investigated, and a low-power laboratory prototype is designed and fabricated to evaluate the converter performance in different operating conditions. [ABSTRACT FROM AUTHOR]

Substrate Integrated (SI) technologies, either completely or partially filled with dielectric, as well as completely empty (i.e. without any dielectric material), have been object of intense research in the last years. Their performance in terms of losses, cost and size are mid-way between those of classical planar lines and rectangular waveguides. Many communication devices have already been successfully designed, manufactured and measured in all these SI technologies. But these measurements are mostly done at room temperature under atmospheric pressure conditions. However, the good results (in terms of low loss, profile and cost) of these novel technologies, especially the completely empty versions, close to the performance of the rectangular waveguide, make them a very good alternative for being used in small satellite payloads. Up to now, few attention has been given to the thermal analysis of these SI technologies, still missing a complete comparative study of these effects under both, atmospheric pressure and vacuum conditions. In this work the same filter is implemented on four different SI technologies (including completely and partially filled with dielectric, as well as empty -no dielectric- versions). The four filters are designed, manufactured, and measured at different temperatures according to the thermal testing standards for space applications. The thermal study is performed under atmospheric pressure conditions and, for the first time, under high vacuum conditions. Finally, a comparison with all previous available thermal studies (all of them performed at atmospheric pressure levels) is included.

Abstract This letter presents a rotary travelling‐wave oscillator (RTWO) with reliable direction control in a standard 130 nm complementary metal–oxide–semiconductor (CMOS) technology. To achieve low phase noise (PN), and low power consumption, 16‐stages customised transmission line segments are designed and simulated on electromagnetic tools. The PN is investigated through modelling the RTWO as multiple standing‐wave oscillators. The proposed oscillator achieves 11.2% tuning range, 190.3 dBc/Hz figure‐of‐merit (FoM) at 1 MHz offset and 192.3 dBc/Hz FoM at 10 MHz offset with 5.8‐mW power consumption from 16‐GHz carrier.

Abstract A high‐temperature 2.1 GHz oscillator based on a AlGaN/GaN high electron mobility transistor (HEMT) is successfully designed, implemented, and characterised for the first time. The system is explicitly designed such that the final circuit consists of a single transistor bonded to a printed circuit board (PCB), and no further passive components besides the transmission lines to attach the connectors are used. Extensive characterisation of the high electron mobility transistor has been carried out up to 300∘C in order to extract large‐ and small‐signal models. Since the system does not rely on passive tolerances and a specific model of the used transistor has been extracted, a sustainable oscillation of the design at high temperature is assured. The capabilities of the designed circuit are verified by measurements up to 230∘C, showing a promising performance with around 0 dBm output power and a phase noise of −74 dBc/Hz at 1 MHz offset at the highest characterised temperature.

Abstract This paper presents a high conversion gain and highly linearised up‐conversion mixer designed in 65 nm CMOS process, which translates intermediate frequency of 2.4 GHz and local oscillator frequency of 21.6–24 GHz in radio frequency. In the proposed mixer, the tranconductance stage consists of a common source route with neutralisation technique and dual capacitive cross coupled‐common gate route to achieve high linearity and stability. In addition, it also includes dual negative resistance switches with improved inter‐stage matching network to enhance the conversion gain and to decrease the noise figure. The mixer achieves the conversion gain of 4.7 dB, the measured output 1‐dB compression point of 0.41 dBm and noise figure of 3.8 dB at 24 GHz. In an automotive radar application, the proposed mixer showed a high conversion gain, an excellent output 1‐dB and a low noise figure with power consumption of approximately 5.2 mW at a 1.2 V supply.

The lack of fault samples is a challenging issue for fault diagnosis in the industrial process. It is difficult for conventional fault diagnosis methods to achieve satisfactory results under small samples. This article proposes a general transfer framework with evolutionary capability to address the above issue. First, a general transfer framework is proposed, in which the transfer learning strategy is applied to guarantee the number and diversity of expanded samples and achieve accurate modeling. Second, the adaptive mixup (Admixup) method is presented, which can adaptively expand the fault samples and make the shared distribution smoother to guarantee the stability and accuracy of the fault diagnosis results. Finally, an optimized evolution strategy is designed, in which the transformation matrix is used as an evolutionary channel to reduce the fault diagnosis errors without retraining the framework as fault samples increase. The presented framework can utilize the generalization of small samples and the knowledge of various working condition samples to achieve accurate modeling. The proposed framework is applied to simulated and real industrial processes. Experiment results illustrate that the fault diagnosis model can be effectively established by the proposed framework under small samples, and the proposed framework is evolutionary capable. [ABSTRACT FROM AUTHOR]

Modal network theory has proven to be a useful tool in analyzing waveguide discontinuities. Ports of a modal network correspond to waveguide eigenmodes on either side of the discontinuity. In this work, modal network theory is extended beyond conventional/geometrical waveguide discontinuities. We use the modal network formulation to analyze discontinuities resulting from metasurfaces. Specifically, we analyze azimuthally invariant cascaded sheet metasurfaces placed in a cylindrical waveguide excited by TM0n modes. The metasurface comprises multiple radially varying electric admittance sheets separated by dielectric spacers. We derive the modal representation of a single inhomogeneous, electric sheet admittance using two approaches: a conventional numerical integration approach and a discrete Hankel transform (DHT) approach. We show that the DHT approach is more efficient. Subsequently, the modal matrices of cascaded sheet metasurfaces are derived using the DHT. Finally, we propose an optimization-based procedure to synthesize transparent metasurface-based mode converters. The mode converters transform a set of incident modes on one side to another set of desired modes on the opposite side of the metasurface. Two designs are synthesized at 10 GHz: a single-mode converter, and a mode splitter. The designs are verified using the commercial finite element electromagnetic solvers. [ABSTRACT FROM AUTHOR]

This work proposed a programmable pulsed radio-frequency (PRF) stimulator for trigeminal neuralgia (TN) relief on demand. The implantable stimulator is a miniaturized micro-system which integrates a wireless interface circuit, a sensor interface circuit, a PRF pattern generation circuit and a logic controller. The multifunctional stimulator capable of delivering current/voltage stimulation provides the choice of the biphasic sinusoidal, square and patterned waveform for PRF treatment researches. The external handheld device can wirelessly transmit the parameters of frequency, amplitude, pulse duration and repetition rate of the pulse train to the implanted stimulator. While stimulating, the temperature sensor can monitor the operating temperature. The feedback signal is transmitted in medical implanted communication system (MICS). The micro-system is fabricated in a 0.35 μm CMOS process with a chip size of 3.1 × 2.7 mm2. The fabricated chip was mounted on a 2.6 × 2.1 cm2 test board for studying the in vivo efficacy of pain relief by PRF. Animal studies of PRF stimulation and commonly-used medication for trigeminal neuralgia are also demonstrated and the presented results prove that PRF stimulation has greater effectiveness on trigeminal neuralgia relief comparing to the medication. The effectiveness period lasts at least 14 days. The results of neural recording show that the PRF stimulation of trigeminal ganglion (TG) attenuated neuron activities without being severely damaged. Pathology also revealed no lesion found on the stimulated area. [ABSTRACT FROM AUTHOR]

Frequency response mismatches among microphones inevitably result in performance deterioration of signal processing algorithms for microphone arrays. A frequency response calibration method based on the consensus strategy is proposed in this article. Adaptive calibration filters concatenated with microphone channels are first introduced to compensate for the frequency response mismatches among microphones. Then, the frequency response mismatch problem is formulated as the minimization of a cost function measuring the spectrum mismatches among neighboring microphone channel outputs. Finally, the consensus strategy is used to design the calibration filter in each microphone channel. By using the consensus strategy, the proposed frequency response calibration method is robust to the room impulse response and noise differences among microphones. The proposed method outperforms gain calibration methods and the centralized frequency response calibration method. Experimental results reveal the validity of the proposed method. [ABSTRACT FROM AUTHOR]

Retrievals of sea ice thickness from passive microwave measurements have been limited to thin ice because microwaves penetrate at most the upper 50 cm of sea ice. To overcome such a limitation, a method of retrieving Arctic basin-scale ice thickness is developed. The physical background of this method is that the scattering optical thickness at microwave frequencies within the freeboard layer is linearly proportional to the physical thickness of the ice freeboard. In this study, we relate the optical thickness estimated from the Advanced Microwave Scanning Radiometer 2 (AMSR2) with ice freeboard estimated from the CryoSat-2 (CS2) by employing a piecewise linear fit. The results show a strong linear relationship between the AMSR2-estimated and CS2-measured ice freeboards with a correlation coefficient of 0.85 and bias and RMSE of 0.0001 and 0.04 m, respectively; this evidence suggests that the method can provide Arctic basin-scale ice freeboard with a comparable accuracy level of CS2. The method is also applied to estimate ice freeboard for the periods of the Scanning Multichannel Microwave Radiometer (SMMR) (1978–1987) and AMSR-E (2002–2011). It is shown that the area-averaged ice freeboard has decreased significantly with the linear trends of 1.5 cm/decade. In addition, there seems to be a change of ice freeboard distributions over the Arctic. Furthermore, the algorithm is extended to the ice thickness retrieval by using the hydrostatic balance equation, showing that operational basin-scale ice thickness retrieval will be possible from satellite passive microwave measurements if a realistic snow depth on sea ice is employed. [ABSTRACT FROM AUTHOR]

An algorithm for ice/water detection of ice less than 30 cm in thickness (thin ice) using dual-polarized synthetic aperture radar (SAR) and passive microwave data has been developed based on insights from previous work. The frequency chosen from those available was in the C-band. For the radiometer layer ice concentrations, land contaminated pixels were removed. For the SAR layers, a novel approach to their use in ice detection was developed using the coefficient of variation (COV), defined as the ratio of the standard deviation of the normalized radar cross section, σ0, to the mean σ0. The COV reduced the complicated signatures of breaking waves and thin ice to bright ice pixels on a dark water background. The co-pol and cross-pol COV layers and the radiometer layer were merged according to physics-based rules, except in regions adjacent to land or the ice edge where only the SAR layers were valid. The detection algorithm was applied to 233 Sentinel 1a and 1b dual-polarization images of the freeze-up from 2015, 2016, 2018, and 2019 in the Beaufort and Chukchi Seas. The synergistic ice retrievals showed improved agreement with manual operational analyses in the marginal ice zone over other automated operational products. [ABSTRACT FROM AUTHOR]

This article presents a dual-mode resonant flyback single power-conversion inverter with reduced number of power components. Unlike conventional flyback converters, it transfers power in a resonant manner during the first half of the switching period and in a linear way during the remaining half of the switching period. It operates in above resonance mode below the computed instantaneous power level, and in below resonance mode above this instantaneous power level. The secondary diodes of the resonant flyback converter are merged into two of the secondary-side switches in the proposed inverter configuration, which reduces the number of active-power components. The operation principle of the inverter is presented and analyzed. By using the dual-mode control strategy, the proposed converter achieves maximum efficiency of 94.3% with total harmonic distortion of 3.8%. Experimental results with a prototype 240-W inverter verify the performance. [ABSTRACT FROM AUTHOR]

Radio frequency (RF) and microwave is a very specialized research area that deals with the design and development of devices operating in the RF spectrum. The development cycle of microwave devices requires dedicated software packages and sophisticated equipment, which are typically very costly, especially for developing countries where only a very few universities have the facilities to pursue RF and microwave activities. [ABSTRACT FROM AUTHOR]

In this work, a novel 3-D equivalent circuit model of thermoelectric microelectro-mechanical system (MEMS) microwave power sensor is proposed. According to the model, the 3-D temperature distribution and the response time of the thermoelectric MEMS microwave power sensor are obtained. The thermoelectric MEMS microwave power sensor is designed and fabricated based on GaAs monolithic microwave integrated circuit (MMIC) technology. The measured results show that the sensitivity of the sensor is 0.06 mV/mW at 10 GHz and the time constant is 85 μs. The theoretical results of the model show that the sensitivity is 0.076 mV/mW at 10 GHz and the time constant is 56.24 μs. The measured results are relatively consistent with the theoretical results. Furthermore, the heat dissipation in the substrate can be obtained accurately, and the transient response of the sensor can be further studied according to the 3-D equivalent circuit model. Therefore, this work has a certain reference value and guiding significance for the research of thermoelectric MEMS microwave power sensors. [ABSTRACT FROM AUTHOR]

A method to extend categorical triple collocation (CTC) to five data sets, three of which must have conditionally independent errors, is presented. The method is shown to enable comparison of three passive microwave sea ice concentration data sets, and can easily be extended to for use with more data sets. The method is evaluated in the Gulf of Saint Lawrence, on the east coast of Canada, during the freeze-up period. It is found that the ice concentration data set from the European space agency sea ice climate change initiative (ESA-SICCI) and the NASA Team 2 (NT2) algorithms have higher balanced accuracy than that from the Artist sea ice (ASI) algorithm. [ABSTRACT FROM AUTHOR]

Soft sensor plays an increasingly important role in modern industrial processes for estimating key quality variables which are hard to measure. With the development of deep learning technologies, soft sensors based on the deep learning methods have drawn great attention. Aiming to predict key quality variables, a supervised weighted nonlinear dynamic system (WNDS) model aided by the maximal information coefficient (MIC) is proposed in this article. The variational autoencoder is employed into the system for extracting nonlinear dynamic features. The supervised WNDS model can simultaneously analyze the correlations between variables and the relationships between historical samples and present samples. Furthermore, the proposed method is extended to a semisupervised form, in order to handle the imbalanced numbers between routinely recorded process data and limited labeled quality data. The prediction performance is validated by an industrial case. [ABSTRACT FROM AUTHOR]

A recently developed concept for designing passive microwave components using functional vertical interconnect accesses (vias) for vertical integration in printed circuit boards (PCBs) is extended and transferred to the low temperature cofired ceramic (LTCC) technology. Given the changed material properties and new technology constraints, it is shown how and to what extent the controlled vertical interconnect accesses (via) structures can behave as quasi-transmission lines, thus allowing for another degree of freedom in component design. To demonstrate the validity and utility of functional vias, several novel microwave components are proposed and subsequently analyzed including vertically integrated 2- and 3-way Wilkinson power dividers, as well as vertically integrated 90° and 180° hybrid couplers. Prototypes for the 2-way and 3-way power dividers were manufactured on an LTCC multilayer substrate. Both measurement and full-wave simulation results are in excellent agreement and thus provide a proof of the concept. [ABSTRACT FROM AUTHOR]

In this letter, we established the feasibility of producing localized ablation zones using microsecond pulsed microwave ablation (MWA) as an alternative to conventional continuous wave (CW) MWA. We verified that a thin floating-sleeve dipole ablation probe can withstand pulsed power delivery with peak powers as high as 25 kW, with pulsewidth on the order of 1 μs. We conducted MWA experiments in egg white using CW and pulsed modes of operation and found that ablation zones achieved via pulsed MWA are comparable in dimension to those created via CW MWA when the average power and procedure duration are equivalent. Finally, we performed pulsed MWA experiments in bovine liver and confirmed that pulsed MWA consistently produces large, localized ablation zones and temperatures that exceed 100 °C. Establishing the feasibility of pulsed MWA opens the opportunity for developing a coupled MWA treatment and imaging system using pulsed MWA and microwave-induced thermoacoustic signals for real-time monitoring of MWA. [ABSTRACT FROM AUTHOR]

In this paper, we present a novel transmission line architecture in thin-film lithium niobate (TFLN) platforms to improve the velocity match between the microwave and the optical wave. Compared to conventional coplanar waveguide (CPW), the microwave index (nm) of the proposed slotted electrodes can be optimized from 2.1 to 3 while maintaining the high modulation efficiency and 50- Ω impedance match. Equivalent-circuit model analysis and finite-element simulation are performed. The simulated half-wave voltage (Vπ) of 1.2 V and E-O modulation bandwidth greater than 80 GHz is obtained for a 2-cm-long modulator. By utilizing the slotted slow-wave electrode, TFLN Mach-Zehnder modulators with CMOS-compatible operating voltage and 3-dB modulation bandwidth greater than 100 GHz are potentialized. [ABSTRACT FROM AUTHOR]

In this paper, we describe a novel method for the five-degrees-of-freedom (5-DoF) pose estimation of a smartphone using the acoustic signal from only one external speaker. To obtain the smartphone’s 5-DoF pose using this speaker, we apply the concept of “mirror-image” speakers to effectively obtain a multiplicity of signals. Here, the primary reflected signals from the wall or floor are captured as signals transmitted from “virtual speakers” located at (wall or floor) mirror-image positions with respect to the real speaker’s location. By using the smartphone built-in stereo microphones, we can obtain not only its three-dimensional (3-D) position but also its yaw and pitch angles, giving a 5-DoF pose estimation. Holding the smartphone sideways, we can calculate arrival angles for each speaker using the two microphones, and identify which (real or mirror-image) speaker is the signal source. We can then robustly identify the 5-DoF pose by utilizing the information obtained from arrival angles and an acceleration-based pitch angle. For our experiments, we located the speaker and estimated the smartphone’s 5-DoF pose at several places along a 2-m wide corridor. Its measurement range was $2.0\times 2.0\times 1.9\,\,\text{m}^{3}$. The results within the effective operating range gave 90th-percentile errors of less than 114.35 mm for the 3-D position, less than 7.96° for the yaw angle, and 7.09° for the pitch angle. We also clarified the effectiveness of the proposed method which can extend speakers’ baselines beyond the physical limit of the corridor via dilution-of-precision measures. Moreover, we identified limitations of the proposed method using simulations. [ABSTRACT FROM AUTHOR]

Generally, ground stress accumulates in the process of earthquake (EQ) preparation. The change trend of microwave brightness temperature ($T_{B}$) of rock with stress change is an important factor for the understanding of the microwave anomalies associated with EQs. However, it is not yet clear whether the downtrend of rocks’ $T_{B}$ is associated with increased stress. To confirm this, in this article, the instantaneous field of view of the microwave radiometer was identified first. Then, the microwave observation experiments were conducted on granite samples at 6.6 GHz under cyclic loading and outdoor conditions with weak background radiation. It was found that besides uptrend and fluctuation, the downtrend of granite samples’ $T_{B}$ also correlates with stress, with an occurrence probability of 47.62% and a maximum rate of −0.038 K/MPa. The variation trends of $T_{B}$ with stress are not uniform across different areas of the same sample. To reveal the cause of this phenomenon, the permittivity of single-crystal quartz, one of the main mineral compositions of granite, was measured when it was under compassion loading at the direction perpendicular or parallel to the optical axis. For quartz, the real part of the permittivity rises (falls) when the two directions are perpendicular (parallel), causing the $T_{B}$ to fall (rise). The optic axes of minerals are randomly distributed in granite samples, which make the variation in the permittivity of minerals also random, thereby resulting in the nonuniformity of stress-induced $T_{B}$ variation in granite samples. Finally, the implications of these results were discussed. [ABSTRACT FROM AUTHOR]