Subjects -> MATHEMATICS (Total: 1112 journals)
    - APPLIED MATHEMATICS (90 journals)
    - GEOMETRY AND TOPOLOGY (23 journals)
    - MATHEMATICS (818 journals)
    - MATHEMATICS (GENERAL) (45 journals)
    - NUMERICAL ANALYSIS (25 journals)

MATHEMATICS (818 journals)            First | 1 2 3 4 5     

Showing 401 - 538 of 538 Journals sorted alphabetically
Journal of Computational Physics : X     Open Access   (Followers: 1)
Journal of Computer Engineering, System and Science (CESS)     Open Access  
Journal of Contemporary Mathematical Analysis     Hybrid Journal  
Journal of Cryptology     Hybrid Journal   (Followers: 5)
Journal of Difference Equations and Applications     Hybrid Journal  
Journal of Differential Equations     Full-text available via subscription   (Followers: 1)
Journal of Discrete Algorithms     Hybrid Journal   (Followers: 4)
Journal of Discrete Mathematics     Open Access   (Followers: 1)
Journal of Dynamics and Differential Equations     Hybrid Journal  
Journal of Engineering Mathematics     Hybrid Journal   (Followers: 2)
Journal of Evolution Equations     Hybrid Journal  
Journal of Experimental Algorithmics     Full-text available via subscription   (Followers: 1)
Journal of Flood Risk Management     Hybrid Journal   (Followers: 14)
Journal of Formalized Reasoning     Open Access   (Followers: 2)
Journal of Function Spaces     Open Access  
Journal of Functional Analysis     Full-text available via subscription   (Followers: 2)
Journal of Geochemical Exploration     Hybrid Journal   (Followers: 1)
Journal of Geological Research     Open Access   (Followers: 1)
Journal of Geovisualization and Spatial Analysis     Hybrid Journal  
Journal of Global Optimization     Hybrid Journal   (Followers: 7)
Journal of Global Research in Mathematical Archives     Open Access   (Followers: 1)
Journal of Group Theory     Hybrid Journal   (Followers: 2)
Journal of Homotopy and Related Structures     Hybrid Journal  
Journal of Honai Math     Open Access  
Journal of Humanistic Mathematics     Open Access   (Followers: 1)
Journal of Hyperbolic Differential Equations     Hybrid Journal  
Journal of Indian Council of Philosophical Research     Hybrid Journal  
Journal of Industrial Mathematics     Open Access   (Followers: 2)
Journal of Inequalities and Applications     Open Access  
Journal of Infrared, Millimeter and Terahertz Waves     Hybrid Journal   (Followers: 2)
Journal of Integrable Systems     Open Access   (Followers: 1)
Journal of K-Theory     Full-text available via subscription  
Journal of Knot Theory and Its Ramifications     Hybrid Journal   (Followers: 1)
Journal of Kufa for Mathematics and Computer     Open Access   (Followers: 1)
Journal of Liquid Chromatography & Related Technologies     Hybrid Journal   (Followers: 7)
Journal of Logical and Algebraic Methods in Programming     Hybrid Journal  
Journal of Manufacturing Systems     Full-text available via subscription   (Followers: 4)
Journal of Mathematical Analysis and Applications     Full-text available via subscription   (Followers: 5)
Journal of mathematical and computational science     Open Access   (Followers: 7)
Journal of Mathematical and Fundamental Sciences     Open Access  
Journal of Mathematical Behavior     Hybrid Journal   (Followers: 3)
Journal of Mathematical Chemistry     Hybrid Journal   (Followers: 3)
Journal of Mathematical Cryptology     Hybrid Journal   (Followers: 1)
Journal of Mathematical Extension     Open Access   (Followers: 3)
Journal of Mathematical Finance     Open Access   (Followers: 9)
Journal of Mathematical Imaging and Vision     Hybrid Journal   (Followers: 6)
Journal of Mathematical Logic     Hybrid Journal   (Followers: 3)
Journal of Mathematical Modelling and Algorithms     Hybrid Journal   (Followers: 1)
Journal of Mathematical Neuroscience     Open Access   (Followers: 10)
Journal of Mathematical Sciences     Hybrid Journal  
Journal of Mathematical Sciences and Applications     Open Access   (Followers: 2)
Journal of Mathematical Sociology     Hybrid Journal   (Followers: 3)
Journal of Mathematics     Open Access  
Journal of Mathematics and Statistics     Open Access   (Followers: 8)
Journal of Mathematics and Statistics Studies     Open Access   (Followers: 4)
Journal of Mathematics and the Arts     Hybrid Journal   (Followers: 2)
Journal of Mathematics Education at Teachers College     Open Access   (Followers: 2)
Journal of Mathematics in Industry     Open Access  
Journal of Mathematics Research     Open Access   (Followers: 6)
Journal of Metallurgy     Open Access   (Followers: 8)
Journal of Modern Mathematics Frontier     Open Access  
Journal of Multidisciplinary Modeling and Optimization     Open Access  
Journal of Multivariate Analysis     Hybrid Journal   (Followers: 13)
Journal of Natural Sciences and Mathematics Research     Open Access  
Journal of Nonlinear Analysis and Optimization : Theory & Applications     Open Access   (Followers: 4)
Journal of Nonlinear Mathematical Physics     Hybrid Journal   (Followers: 1)
Journal of Nonlinear Science     Hybrid Journal   (Followers: 1)
Journal of Numerical Cognition     Open Access   (Followers: 1)
Journal of Numerical Mathematics     Hybrid Journal   (Followers: 2)
Journal of Optimization     Open Access   (Followers: 5)
Journal of Peridynamics and Nonlocal Modeling     Hybrid Journal  
Journal of Problem Solving     Open Access   (Followers: 2)
Journal of Progressive Research in Mathematics     Open Access   (Followers: 5)
Journal of Pseudo-Differential Operators and Applications     Hybrid Journal  
Journal of Pure and Applied Algebra     Full-text available via subscription   (Followers: 4)
Journal of Quantitative Analysis in Sports     Hybrid Journal   (Followers: 9)
Journal of Quantitative Linguistics     Hybrid Journal   (Followers: 6)
Journal of Scientific Computing     Hybrid Journal   (Followers: 18)
Journal of Scientific Research     Open Access  
Journal of Symbolic Computation     Hybrid Journal   (Followers: 1)
Journal of the Australian Mathematical Society     Full-text available via subscription  
Journal of the Egyptian Mathematical Society     Open Access  
Journal of the European Mathematical Society     Full-text available via subscription   (Followers: 1)
Journal of the Indian Mathematical Society     Hybrid Journal   (Followers: 1)
Journal of the Institute of Mathematics of Jussieu     Hybrid Journal  
Journal of the London Mathematical Society     Hybrid Journal   (Followers: 2)
Journal of the Nigerian Mathematical Society     Open Access   (Followers: 1)
Journal of Theoretical and Applied Physics     Open Access   (Followers: 8)
Journal of Topology and Analysis     Hybrid Journal  
Journal of Transport and Supply Chain Management     Open Access   (Followers: 16)
Journal of Turbulence     Hybrid Journal   (Followers: 9)
Journal of Uncertainty Analysis and Applications     Open Access   (Followers: 1)
Journal of Universal Mathematics     Open Access  
Journal of Urban Regeneration & Renewal     Full-text available via subscription   (Followers: 11)
JRAMathEdu : Journal of Research and Advances in Mathematics Education     Open Access   (Followers: 5)
JUMLAHKU : Jurnal Matematika Ilmiah STKIP Muhammadiyah Kuningan     Open Access   (Followers: 3)
JURING (Journal for Research in Mathematics Learning)     Open Access   (Followers: 1)
Jurnal Ilmiah AdMathEdu     Open Access  
Jurnal Matematika     Open Access   (Followers: 1)
Jurnal Matematika Integratif     Open Access  
Jurnal Matematika, Sains, Dan Teknologi     Open Access  
Jurnal Natural     Open Access  
Jurnal Pendidikan Matematika Raflesia     Open Access  
Jurnal Penelitian Pembelajaran Matematika Sekolah     Open Access  
Jurnal Penelitian Sains (JPS)     Open Access  
Jurnal Riset Pendidikan Matematika     Open Access  
Jurnal Sains Matematika dan Statistika     Open Access  
Jurnal Tadris Matematika     Open Access  
Jurnal Teknologi dan Sistem Komputer     Open Access  
Kontinu : Jurnal Penelitian Didaktik Matematika     Open Access   (Followers: 3)
Kreano, Jurnal Matematika Kreatif-Inovatif     Open Access   (Followers: 6)
Le Matematiche     Open Access  
Learning and Teaching Mathematics     Full-text available via subscription   (Followers: 7)
Lettera Matematica     Hybrid Journal  
Lietuvos Matematikos Rinkinys     Open Access   (Followers: 3)
Limits : Journal of Mathematics and Its Applications     Open Access   (Followers: 1)
Linear Algebra and its Applications     Full-text available via subscription   (Followers: 23)
Linear and Multilinear Algebra     Hybrid Journal   (Followers: 8)
Lithuanian Mathematical Journal     Hybrid Journal  
LMS Journal of Computation and Mathematics     Free  
Lobachevskii Journal of Mathematics     Open Access  
Logic and Analysis     Hybrid Journal   (Followers: 1)
Logic Journal of the IGPL     Hybrid Journal   (Followers: 1)
Logica Universalis     Hybrid Journal  
manuscripta mathematica     Hybrid Journal  
MaPan : Jurnal Matematika dan Pembelajaran     Open Access  
Marine Genomics     Hybrid Journal   (Followers: 2)
Matemáticas, Educación y Sociedad     Open Access  
Matematicheskie Zametki     Full-text available via subscription  
Matematika     Open Access  
Matematychni Studii     Open Access  
Mathematica Eterna     Open Access  
Mathematica Scandinavica     Full-text available via subscription   (Followers: 1)
Mathematica Slovaca     Hybrid Journal   (Followers: 1)
Mathematical and Computational Forestry & Natural-Resource Sciences     Free  
Mathematical Communications     Open Access  
Mathematical Computation     Open Access   (Followers: 1)
Mathematical Geosciences     Hybrid Journal   (Followers: 3)
Mathematical Journal of Interdisciplinary Sciences     Open Access   (Followers: 1)
Mathematical Medicine and Biology: A Journal of the IMA     Hybrid Journal   (Followers: 1)
Mathematical Methods in the Applied Sciences     Hybrid Journal   (Followers: 4)
Mathematical Methods of Statistics     Hybrid Journal   (Followers: 4)
Mathematical Modelling and Analysis     Open Access   (Followers: 1)
Mathematical Modelling in Civil Engineering     Open Access   (Followers: 5)
Mathematical Modelling of Natural Phenomena     Full-text available via subscription   (Followers: 1)
Mathematical Models and Methods in Applied Sciences     Hybrid Journal   (Followers: 2)
Mathematical Models in Engineering     Open Access   (Followers: 3)
Mathematical Notes     Hybrid Journal  
Mathematical Proceedings of the Cambridge Philosophical Society     Full-text available via subscription   (Followers: 2)
Mathematical Programming Computation     Hybrid Journal   (Followers: 3)
Mathematical Sciences     Open Access  
Mathematical Social Sciences     Hybrid Journal   (Followers: 1)
Mathematical Theory and Modeling     Open Access   (Followers: 13)
Mathematical Thinking and Learning     Hybrid Journal   (Followers: 3)
Mathematics and Statistics     Open Access   (Followers: 5)
Mathematics Education Forum Chitwan     Open Access   (Followers: 1)
Mathematics Education Journal     Open Access   (Followers: 2)
Mathematics Education Research Journal     Partially Free   (Followers: 18)
Mathematics in Science and Engineering     Full-text available via subscription  
Mathematics of Control, Signals, and Systems (MCSS)     Hybrid Journal   (Followers: 5)
Mathematics of Quantum and Nano Technologies     Open Access  
Mathématiques et sciences humaines     Open Access   (Followers: 6)
Mathematische Annalen     Hybrid Journal   (Followers: 1)
Mathematische Nachrichten     Hybrid Journal   (Followers: 1)
Mathematische Semesterberichte     Hybrid Journal  
Mathematische Zeitschrift     Hybrid Journal   (Followers: 1)
MathLAB Journal     Open Access   (Followers: 5)
MATI : Mathematical Aspects of Topological Indeces     Open Access  
MATICS     Open Access   (Followers: 2)
Matrix Science Mathematic     Open Access   (Followers: 1)
Measurement Science Review     Open Access   (Followers: 3)
Mediterranean Journal of Mathematics     Hybrid Journal  
Memetic Computing     Hybrid Journal  
Mendel : Soft Computing Journal     Open Access  
Metaheuristics     Hybrid Journal  
Metals and Materials International     Hybrid Journal  
Metascience     Hybrid Journal   (Followers: 1)
Metrology and Instruments / Метрологія та прилади     Open Access   (Followers: 1)
Milan Journal of Mathematics     Hybrid Journal  
Mitteilungen der DMV     Hybrid Journal  
MLQ- Mathematical Logic Quarterly     Hybrid Journal   (Followers: 1)
MONA : Matematik- og Naturfagsdidaktik     Hybrid Journal   (Followers: 5)
Monatshefte fur Mathematik     Hybrid Journal  
Moroccan Journal of Pure and Applied Analysis     Open Access   (Followers: 4)
Moscow University Mathematics Bulletin     Hybrid Journal  
MSOR Connections     Open Access   (Followers: 1)
Multiscale Modeling and Simulation     Hybrid Journal   (Followers: 3)
MUST : Journal of Mathematics Education, Science and Technology     Open Access   (Followers: 1)
Nagoya Mathematical Journal     Hybrid Journal  
Nano Research     Hybrid Journal   (Followers: 4)
Nanotechnologies in Russia     Hybrid Journal   (Followers: 1)
Natural Resource Modeling     Hybrid Journal   (Followers: 1)
New Mathematics and Natural Computation     Hybrid Journal  
Nonlinear Analysis : Modelling and Control     Open Access   (Followers: 1)
Nonlinear Analysis : Theory, Methods & Applications     Hybrid Journal   (Followers: 1)
Nonlinear Analysis: Hybrid Systems     Hybrid Journal  
Nonlinear Analysis: Real World Applications     Hybrid Journal   (Followers: 2)
Nonlinear Differential Equations and Applications NoDEA     Hybrid Journal  
Nonlinear Engineering     Open Access  
Nonlinear Oscillations     Hybrid Journal   (Followers: 1)

  First | 1 2 3 4 5     

Similar Journals
Journal Cover
Journal of Infrared, Millimeter and Terahertz Waves
Journal Prestige (SJR): 0.803
Citation Impact (citeScore): 2
Number of Followers: 2  
  Hybrid Journal Hybrid journal (It can contain Open Access articles)
ISSN (Print) 1866-6892 - ISSN (Online) 1866-6906
Published by Springer-Verlag Homepage  [2643 journals]
  • Electromagnetic-Induced Transparency Resonance with Ultrahigh Figure of
           Merit Using Terahertz Metasurfaces
    • Abstract: Abstract In this paper, a terahertz metasurface supercell consists of two ring resonators with slightly different radii is proposed. Electromagnetic-induced transparency (EIT)–like resonance is excited with an ultrahigh figure of merit. Furthermore, the impact of the coupling between the two rings is investigated on the transmission amplitude response, the quality factor, and the EIT peak amplitude by varying the radius of the top resonator. The achieved figure of merit of the EIT peak reaches 88.65 and almost 20,000 when gold and a perfect electric conductor are used for the metallic layer, respectively. The simplicity and unique properties of the proposed design could render it to be a desirable candidate for filtering, slow light applications, and sensing.
      PubDate: 2021-02-26
  • Sensitive Near-Field Slit Probe with High  Spatial Resolution for Passive
           Millimeter-Wave Microscopy
    • Abstract: Abstract A novel type of near-field slit probe with high sensitivity and high spatial resolution is proposed. We tested the implementation of this in passive millimeter-wave microscopy at frequencies around 50 GHz. The slit probe comprises a standard rectangular waveguide incorporating a triple-screw tuner penetrating into the waveguide, followed by a four-section quarter-wave transformer, and a metal-coated silicon chip with a micro-slit aperture fabricated at the probe tip using a bulk micromachining technique. The probe allows the transmission of the thermal radiation collected at the probe aperture to the radiometric receiver used in passive millimeter-wave microscopy to be maximized, resulting in highly sensitive measurements. The system noise temperature of the radiometric receiver including the slit probe used in the passive measurements was found to be 1800 K, meaning that a temperature resolution of 0.18 K with the integration time set to 1 s was achieved. This system noise temperature is four times better than that when a tapered slit probe with no tuning circuit was used. Image acquisition with a spatial resolution of better than 100 μm was demonstrated over the temperature range from 210 to 310 K.
      PubDate: 2021-02-26
  • Enhanced Magneto-Optical Kerr Effect of GaAs-Based P-N Junctions in the
           Terahertz Range
    • Abstract: Abstract We demonstrate that the magneto-optical Kerr effect at normal incidence in the terahertz (THz) frequency range is useful for evaluating carrier transport properties of particular layers of a p-n junction. Since a single p-type thin film only exhibits a small magneto-optical Kerr effect, magneto-optical Kerr spectroscopy cannot be used to determine the carrier densities of such a film with high sensitivity. However, because the electric field is enhanced at the p-layer in a p-n junction due to the interference between the THz waves that are reflected at the highly doped substrate and the p-layer at the surface, it is possible to conduct magneto-optical Kerr spectroscopy with a higher sensitivity. We numerically calculate and experimentally determine the spectra of the ellipticity and polarization rotation angles for single n- and p-GaAs epitaxial layers and GaAs-based photovoltaic devices with a p-i-n structure and evaluate the carrier densities of the n- and p-layers. At normal incidence, this method has a high spatial resolution, which is beneficial for imaging of large-area devices.
      PubDate: 2021-02-23
  • Contribution of Microwave to the Formation of Octacalcium Phosphate
           Intercalating Succinate Ions
    • Abstract: Abstract We applied microwave light with frequencies 10, 212, and 419 GHz to form octacalcium phosphate (OCP) intercalated with succinate ions (SCI). The composition of starting reagents (i.e., α-type tricalcium phosphate (TCP), calcium hydrogenphosphate dihydrate (DCPD), and SCI in pure water) did not enable us to form OCP intercalated with SCI in a thermostatic water bath. Although microwave irradiation typically acts as a heat source in water, it has brought a valuable contribution to OPC formation. This paper reports the following interesting result; microwave irradiation of power less than 0.1 W enabled us to synthesize OCP intercalated with SCI which was not possible to form with power values exceeding 0.1 W.
      PubDate: 2021-02-17
  • Starting currents of modes in cylindrical cavities with mode-converting
           corrugations for second-harmonic gyrotrons
    • Abstract: Abstract A self-consistent system of equations (known as single-mode gyrotron equations) is extended to describe the beam-wave interaction in a cylindrical gyrotron cavity with mode-converting longitudinal corrugations, which produce coupling of azimuthal basis modes. The system of equations is applied to investigate the effect of corrugations on starting currents of the cavity modes. For these modes, eigenvalues, ohmic losses, field structure, and beam-wave coupling coefficients are investigated with respect to the corrugation parameters. It is shown that properly sized mode-converting corrugations are capable of improving the selectivity properties of cylindrical cavities for second-harmonic gyrotrons.
      PubDate: 2021-02-15
  • A Compact 28/38 GHz MIMO Circularly Polarized Antenna for 5 G Applications
    • Abstract: Abstract A novel design is introduced for dual-band operation at 28/38 GHz for improving microstrip antennas. Also, the design support circularly polarized antenna that works in millimetre band applications. This proposed antenna is attached to a circular hole in the centre of the patch with four slits embedded in the corners. Also, small holes are etched at sides of the patch to achieve the resonant frequencies and improve the return loss value with achieving very wide band at 38 GHz. A single-feed circularly polarized antenna at 28 GHz and 38 GHz with return loss − 30 dB and − 42 dB, respectively, which makes it suitable for operation at 5 G wireless communication designs. A single element design can cover the frequency ranges of 27.6–28.3 GHz at 28 GHz with bandwidth 2.5% and 35.2–47.2 GHz at 38 GHz with very wide bandwidth 32.4%. Simulated results show that the proposed antenna has good circular polarization in both frequencies of left-hand circular polarization (LHCP). On the other hand, MIMO antenna with four ports is constructed. The four ports are arranged at the corner and middle of substrate with dimension 100 × 75 × 0.508 mm3. Meanwhile, resonant implementation frequencies in a millimetre wave of the MIMO achieved more mutual coupling minimization that effectively accomplished <− 36 dB. In addition, the numerical and experimental results are achieved to evaluate the performance of both single- and four-port MIMO antennas. The diversity gain (DG), envelop correlation coefficient (ECC), total active radiation coefficient (TARC) and channel capacity loss (CCL) also are calculated, and the results are suitable for 5 G applications.
      PubDate: 2021-02-13
  • Study of the Effect of Reflections on High-Power, 110-GHz Pulsed Gyrotron
    • Abstract: Abstract The effect of reflection is studied experimentally and theoretically on a high-power 110-GHz gyrotron operating in the TE22,6 mode in 3μs pulses at 96kV, 40A. The experimental setup allows variation of the reflected power from 0 to 33% over a range of gyrotron operating conditions. The phase of the reflection is varied by translating the reflector along the axis. Operating at a higher efficiency point, at 4.40T with 940kW of output power, reflected power exceeding 11% causes a switch from operation in the TE22,6 to simultaneous operation in the TE22,6 and TE21,6 modes with a large decrease of the total gyrotron output power. This switching effect is in good agreement with simulations using the MAGY code. Operating at a more stable point, 4.44T with 580kW of output power, when the reflection is increased, the output power remains in the TE22,6 mode but it decreases monotonically with increasing reflection, dropping to 200kW at 33% reflection. Furthermore, at a reflection above 22%, a power modulation at 25 to 30MHz is observed, independent of the phase of the reflected wave. Such a modulated signal may be useful in spectroscopic and other applications.
      PubDate: 2021-02-05
  • Theoretical Analysis of Frequency Stabilization and Pulling Effects in a
           Gyrotron with Delayed Reflection
    • Abstract: Abstract The effect of delayed reflection on frequency stabilization and pulling in a gyrotron oscillator is studied. Simple theoretical formulas for start-oscillation current, oscillation frequency, and frequency stabilization rate are derived in the framework of the linear (or small-signal) theory and verified by numerical simulation for the gyrotron with fixed axial profile of the RF field. Capabilities of increasing frequency stability are analyzed. A possibility of expanding frequency tunability range owing to excitation of high-order axial modes is demonstrated.
      PubDate: 2021-01-30
  • Micromachining and Characterisation of Folded Waveguide Structure at
    • Abstract: Abstract The demand of high-speed wireless communication has increased, which need the data rate to be in the order of Terabyte per second (Tbps) in the near future. Terahertz (THz) band communication is a key wireless communication technology to satisfy this future demand. This would also reduce the spectrum scarcity and capacity limitation of current wireless systems. Microfabricated Folded Waveguide TWTs are the potential compact sources of wide band and high-power terahertz radiation. This study primarily focuses on machining technology for THz waveguide components requiring ultra-high precision micromachining. Rectangular waveguides, especially Folded Waveguides (FW), are even more difficult to manufacture using conventional machining techniques due to their small size and very tight tolerances. The criticalities in micromachining of FW for 0.22 THz have been addressed in this article. Half hard free cutting Brass IS 319-H2 was used as a work material due to its electrical and mechanical properties. Waveguide size of 0.852 × 0.12 mm was machined within ± 3–5 μm linear tolerances, surface roughness in the order of 45 nm Ra, and flatness less than half of wavelength (< λ/2). The split top and bottom blocks of the folded waveguide were aligned by dowel pins which matched within a tolerance of ± 5 μm. The perpendicularity and parallelism were maintained within 5 μm tolerance. This work explored and established the application of micromilling as reasonably suitable for the THz waveguides followed by ultrasonic cleaning as deburring. It also investigated the measured folded waveguide losses which were close to simulated values.
      PubDate: 2021-01-25
  • A 61.2-dBΩ, 100 Gb/s Ultra-Low Noise Graphene TIA over D-Band Performance
           for 5G Optical Front-End Receiver
    • Abstract: Abstract This work reports in first time a 100-Gb/s, ultra-low noise, variable gain multi-stagger tuned transimpedance amplifier (VGMST-TIA) over the D-band performance. The whole work is binding into two phases. The first phase involves the modeling and characterization of graphene field-effect transistor (GFET) with an optimized transition frequency of operation. While in the second phase, a TIA design employs a T-shaped symmetrical L-R network at the input, which mitigates the effect of photo diode capacitance and achieves a D-band of operation. The proposed work uses a VGMST to establish TIA, which realizes optimum noise performance. The high gain 3-stage VGMST-TIA effectively minimizes the white noise and illustrates a sharp out-of-band roll-off to achieve considerable noise reduction at high frequencies. The active feedback mechanism controls the transimpedance gain by tuning the control voltage which results better group delay. Besides, an L-C circuit is employed at the output to enhance bandwidth. The full TIA is implemented and fabricated using a commercial nano-manufacturing 9-nm graphene film FET on a silicon wafer using 0.065-μm process. The TIA achieves a flat transimpedance gain of 61.2 dBΩ with ± 9 ps group delay variation over the entire bandwidth. The proposed TIA measured an impedance bandwidth of 0.2 THz with ultra-low input-referred noise current density of 2.03 pA/√Hz. The TIA supports a 100-Gb/s data transmission due to large bandwidth; therefore, a bit-error-rate (BER) less than 10−12 is achieved. The chip occupies an area of 0.92 * 1.34 mm2 while consuming power of 21 mW under supply of 1.8 V.
      PubDate: 2021-01-14
  • Mechanical Tuning of the Terahertz Photonic Bandgap of 3D-Printed
           One-Dimensional Photonic Crystals
    • Abstract: Abstract Mechanical tuning of a 3D-printed, polymer-based one-dimensional photonic crystal was demonstrated in the terahertz spectral range. The investigated photonic crystal consists of 13 alternating compact and low-density layers and was fabricated through single-step stereolithography. While the compact layers are entirely polymethacrylate without any intentional internal structures, the low-density layers contain sub-wavelength sized slanted columnar inclusions to allow the mechanical compression in a direction normal to the layer interfaces of the photonic crystal. Terahertz transmission spectroscopy of the photonic crystal was performed in a spectral range from 83 to 124 GHz as a function of the compressive strain. The as-fabricated photonic crystal showed a distinct photonic bandgap centered at 109 GHz, which blue shifted under compressive stress. A maximum shift of 12 GHz in the bandgap center frequency was experimentally demonstrated. Stratified optical models incorporating simple homogeneous and inhomogeneous compression approximations were used to analyze the transmission data. A good agreement between the experimental and model-calculated transmission spectra was found.
      PubDate: 2021-01-08
  • Selective Laser Melting Process of Al–Based Pyramidal Horns for the
           W-Band: Fabrication and Testing
    • Abstract: Abstract In the context of exploring the possibility of using Al-powder Selective Laser Melting to fabricate horn antennas for astronomical applications at millimeter wavelengths, we describe the design, the fabrication, the mechanical characterization, and the electromagnetic performance of additive manufactured horn antennas for the W-band. Our aim, in particular, is to evaluate the performance impact of two basic kinds of surface post-processing (manual grinding and sand-blasting) to deal with the well-known issue of high surface roughness in 3D printed devices. We performed comparative tests of co-polar and cross-polar angular response across the whole W-band, assuming a commercially available rectangular horn antenna as a reference. Based on gain and directivity measurements of the manufactured samples, we find decibel-level detectable deviations from the behavior of the reference horn antenna, and marginal evidence of performance degradation at the top edge of the W-band. We conclude that both kinds of post-processing allow achieving good performance for the W-band, but the higher reliability and uniformity of the sand-blasting post-process encourage exploring similar techniques for further development of aluminum devices at these frequencies.
      PubDate: 2021-01-08
  • Study on a Depressed Collector for a 75 GHz Low-Voltage Compact Gyrotron
           for Industrial Application
    • Abstract: Abstract The low-voltage compact gyrotron is suitable for industrial applications. However, the beam-wave interaction efficiency is low in conventional low-voltage gyrotron. To improve the whole tube efficiency, a compact depressed collector is introduced in developing a 75 GHz low-voltage compact gyrotron. The compact depressed collector is directly connected to the output waveguide. It is grounded and isolated with the cavity by a ceramic ring which is easy to be connected with the application system. The design of the original tube electron beam voltage and electron beam current are 10 kV and 1.2 A. In the particle-in-cell (PIC) simulation, the operating mode is TE0,1 and the generated power is 1.2 kW operated at the frequency of 75.5 GHz, which corresponds to an electron efficiency of 10%. When the depressed collector is performed and the electron reflux is under 5%, the efficiency of the whole tube can reach 30%, and when the reflux rate is controlled at about 15%, the efficiency of the whole tube can reach 50%. The dissipation power would be sufficiently reduced.
      PubDate: 2021-01-07
  • Compact Highly Directive MIMO Vivaldi Antenna for 5G Millimeter-Wave Base
    • Abstract: Abstract In this paper, a novel design for a 5G base station (BS) antenna is proposed. The proposed antenna consists of two orthogonally polarized antennas. The two antennas are modified compact Vivaldi antennas operating in the two recommended 5G operating bands; 28 and 38 GHz with measured impedance bandwidth of 26.5–40 GHz. The orthogonality of the two antennas allows the use of two antennas on the same substrate within one enclosure to serve two sectors separately. So, instead of using two enclosures to serve two sectors, only one enclosure is required. The two elements may be part of two separate MIMO distributions. To minimize the isolation between the MIMO antennas elements with low complexity and low cost, the antenna elements have been distributed along the z-direction with half-wavelength spacing between elements including Electromagnetic band-gap (EBG) structure in between them. The simulation results have been shown that the measured mutual coupling between the array elements is improved from − 32 to − 45 dB at 28 GHz and from − 22 to − 59 at 38 GHz. The envelope correlation coefficient (ECC) is enhanced and the diversity gain (DG) is improved simultaneously. The suggested structure has been designed on CST Microwave Studio 2019. The two orthogonal antennas’ overall size approaches 34 mm × 55.8 mm × 0.203 mm3. The measured gain of the suggested design is enhanced from 10.4 to 12.8 dB at 28 GHz whereas a minor change is noticed at 38 GHz. The maximum simulated radiation efficiency approaches 96%. The antenna is fabricated and tested where good experimental results are noticed compared to the simulation results.
      PubDate: 2021-01-07
  • Broadband Rotary Joint Concept for High-Power Radar Applications
    • Abstract: Abstract To allow antenna movements in azimuth and elevation in high-power radar applications, rotary joints are essential. They allow the rotation of a transmission line and therefore are important transmission line components. In the present paper, a broadband rotary joint concept for high-power W-band radar applications is proposed. To avoid a twist of the polarization plane of a linearly polarized mode, like HE11, a combination of two broadband polarizer is used. A cross polarization of Xpol ≤ − 20 dB can be achieved within the considered frequency range from 90 GHz to 100 GHz. This corresponds to a suitable value for radar applications.
      PubDate: 2021-01-05
  • Developments in Terahertz Ellipsometry: Portable Spectroscopic
           Quasi-Optical Ellipsometer-Reflectometer and Its Applications
    • Abstract: Abstract The paper presents a new instrument—a portable spectroscopic quasi-optical (QO) THz ellipsometer-reflectometer (SQOTER). It combines two independent experimental techniques: THz ellipsometry and reflectometry. SQOTER is based on the hollow dielectric beamguide and beamguide components as a QO transmission line. This ultra-broadband line provides operation of the setup within 0.1…1 THz frequency range. The setup provides measurements of the ellipsometric parameters (at variable incidence angle) and the reflection coefficient (at normal incidence) in the wide spectral range. A detailed analysis of the spectral characteristics of QO transmission line and components was carried out. The principles and details of SQOTER measurements were described and its accuracy was estimated. A special system based on a silicon wafer was created for SQOTER testing. Reflection coefficients of this system measured independently by ellipsometry and reflectometry were compared and showed good agreement. The portable SQOTER capabilities connected with research and industrial applications have been demonstrated.
      PubDate: 2021-01-05
  • A 183-GHz FMCW Transceiver Module for Wireless Fuse Applications
    • Abstract: Abstract This paper presents the design, construction, and testing of a 183-GHz FMCW transceiver module for wireless fuse applications. The transmitter consists of a square-triangle wave converter, a Ku-band VCO, a 91.5-GHz × 2 × 3 multiplying and amplifying chain, a 10-dB multi-hole directional coupler, and a 183-GHz frequency doubler. For the multiplying chain, the generated 91.5-GHz signal power is partly coupled out by the 10-dB coupler. The coupled output power is used as local oscillator (LO) signal to pump the 183-GHz subharmonic mixer (SHM). The receiver is cascaded by a 183-GHz SHM and a low-noise immediate frequency (IF) amplifier. The measured typical output power of the 183-GHz transceiver is 48 mW and the minimum noise temperature of the receiver is 620 K at 181 GHz. At 5-mm and 10-mm detection distance, the measured signal noise ratio (SNR) of transceiver IF signal is higher than 30 dB and 17 dB at 10 KHz bandwidth, respectively. The SNR is high enough for the following signal processing.
      PubDate: 2021-01-04
  • Influence of an External Signal with Harmonic or Stepwise-Modulated
           Parameters on the High-Power Gyrotron Operation
    • Abstract: Abstract Nonlinear dynamics of a gyrotron with high-order operating mode, driven by an external signal with harmonic or stepwise modulation of its parameters or by two monochromatic signals, was studied theoretically. Conditions for locking and control of the radiation frequency were found. Exit from the locking regime is accompanied by the beats of the operating mode or excitation of spurious modes. Simulations were performed using a megawatt-power TE28.12 mode gyrotron as the example (Chirkov et al., Appl Phys Lett 106(26), 2015).
      PubDate: 2021-01-04
  • Excitation of Electromagnetically Induced Transparency Effect in
           Asymmetrical Planar Terahertz Toroidal Dipole Metasurfaces
    • Abstract: Abstract We proposed and fabricated J-shaped planar structure metasurfaces to achieve excitation of dual-frequency toroidal dipole resonances simultaneously, which results in electromagnetically induced transparency effect in the terahertz band. The mutual coupling of two asymmetric J-shaped metal rings in the metasurface units excites low-frequency and high-frequency toroidal dipole resonances, and a transparent window was formed. The fitted curves based on the Fano resonance model have a good consistency with the simulated transmission spectrum of the metasurfaces, which explains this coupling effect deeply. The resonant mode and radiant mechanism were revealed by the analysis of the electromagnetic field distribution and the numerical calculation of the multipole moment. Furthermore, the toroidal dipole resonant response can be adjusted by the structural parameter, indicating the sensing characteristics of the metasurfaces. The simple and flexible planar toroidal dipole metasurfaces with electromagnetically induced transparency effect provide more possibilities for the development and application of terahertz functional devices.
      PubDate: 2021-01-01
  • Wideband Circularly Polarized Magnetoelectric Dipole Array Using T E 340
           -Mode Cavity and Sequential Rotation Feed-Network at 60 GHz
    • Abstract: Abstract In this paper, a 4 × 4 60-GHz circularly polarized (CP) magnetoelectric (ME) dipole array based on TE340-mode substrate integrated cavity (SIC) and sequential rotation feed-network (SRFN) is proposed. The ME dipole array is constructed by 3 printed circuit board (PCB) layers with its assembled size of 21 × 23 × 2.4 mm3. The top layer is the radiation layer with 2 × 2 subarrays. The second layer includes 2 × 2 TE340-mode SICs. The bottom layer is the substrate integrated waveguide (SIW)-SRFN. By combining ME dipole, SRFN and high-order-mode SIC techniques, a compact 4 × 4 array with wide axial-ratio (AR) and impedance bandwidths is obtained. The measured results show that the − 10-dB impedance bandwidth is 24% (54–68.7 GHz), the 3-dB AR bandwidth is 25.9% (52–67.5 GHz), the 3-dB gain bandwidth is 22.5% (54–67.5 GHz) and the peak gain is 19.4 dBic at 62 GHz. The proposed array is a good candidate for 60 GHz wireless communications with its advantages of compact size, wide impedance bandwidth, wide AR bandwidth and high gain.
      PubDate: 2021-01-01
School of Mathematical and Computer Sciences
Heriot-Watt University
Edinburgh, EH14 4AS, UK
Tel: +00 44 (0)131 4513762

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