Microwave Frequency Band Research Articles

Improving microwave absorption efficiency of asphalt mixture by enriching Fe3O4 on the surface of steel slag particles

In order to improve microwave absorption which would be used for in situ repair of asphalt pavement, Fe3O4 was enriched on the surface of steel slag particles through an activated carbon-reduction method. The surface modified steel slags were then added into asphalt mixture to replace fine aggregates. The results showed that the microwave heating rate of modified steel slag was 84.3 °C/min. That was 34.1 and 65.1% higher than that of the control group of unmodified steel slag and fine basalt aggregate, respectively. Within the microwave frequency band of 2–4 GHz, the real part and imaginary part of the complex permittivity of the modified steel slag asphalt mixture (MSAM) increased by 6.4–12.5 and 4.7–13.7%, respectively, comparing those of the ordinary steel slag asphalt mixture (OSAM) and the ordinary basalt asphalt mixture (OBAM). Meanwhile, the real part and imaginary part of the complex permeability of the MSAM increased by 9.8–31.9% and over 6.2 times, respectively. Besides, the microwave heating rate of the MSAM increased by 44.2 and 82.1%, respectively, comparing those of the OSAM and the OBAM. Simulation indicated that after microwave heating for 15 min, the temperature within the OBAM ranged from 62.23 to 125.48 °C. Moreover, the temperature field distribution of numerical simulation was similar to that of the test results. Since microwave absorption was sharply enhanced in the asphalt pavement, it is expected to promote the microwave heating technology in the asphalt pavement.

Metamaterial Absorber Based Multifunctional Sensor Application

In this study metamaterial based (MA) absorber sensor, integrated with an X-band waveguide, is numerically and experimentally suggested for important application including pressure, density sensing and marble type detecting applications based on rectangular split ring resonator, sensor layer and absorber layer that measures of changing in the dielectric constant and/or the thickness of a sensor layer. Changing of physical, chemical or biological parameters in the sensor layer can be detected by measuring the resonant frequency shifting of metamaterial absorber based sensor. Suggested MA based absorber sensor can be used for medical, biological, agricultural and chemical detecting applications in microwave frequency band. We compare the simulation and experimentally obtained results from the fabricated sample which are good agreement. Simulation results show that the proposed structure can detect the changing of the refractive indexes of different materials via special resonance frequencies, thus it could be said that the MA-based sensors have high sensitivity. Additionally due to the simple and tiny structures it could be adapted to other electronic devices in different sizes.

BaM/YIG nano-composites: A microwave material for C to U band application

Hexaferrites have become important candidates for a variety of microwave and millimeter wave devices due to their large uniaxial magneto-crystalline anisotropy and high saturation magnetization. The goal of the present investigation is to synthesize Barium hexaferrite/Yttrium Iron Garnet (BaFe12O19/Y3Fe5O12): (BaM/YIG) Nano-Composites (NCs) to be used in broad band microwave frequency range applications, especially as microwave absorber. X-ray diffractometry, Vibrating Sample Magnetometer (VSM), and ferromagnetic resonance (FMR) techniques were used to characterize these NCs. Using a Cu coplanar wave guide and a Vector Network Analyzer, broadband (C to U) microwave absorption were investigated by placing the bulk sample in flip chip mode. Various mathematical models were employed to fit the experimental data to yield intrinsic and extrinsic damping parameters.

Simultaneous Generation of Pseudo-Bessel Vortex Modes with a RLSA

This letter shows that it is possible to simultaneously generate, in the microwave frequency band, several pseudo-Bessel beams having an azimuthal field variation, characteristic of vortex modes, by making use of a single flat antenna. Specifically, a radial line slot array has been designed to prove the concept. The design benefits of a Butler matrix network to provide the correct phase progression along the azimuthal coordinate, and it makes use of a holographic approach to assure the required aperture field distribution.

Technologies for Near-Field Focused Microwave Antennas

This paper provides a review spanning different technologies used to implement near-field focused antennas at the microwave frequency band up to a few tens of GHz: arrays of microstrip patches and printed dipoles, arrays of dielectric resonator antennas, reflectarrays, transmitarrays, Fresnel zone plate lenses, leaky-wave antennas, and waveguide arrays.

Spoof Plasmonic Waveguide-Fed 2-D Antenna Array With Improved Efficiency

Spoof planar plasmonic waveguides (SPPWs) are a new kind of low-loss surface-wave transmission line. In this letter, a two-dimensional (2-D) antenna array is excited by a one-dimensional (1-D) SPPW in a simple way, and the achievable array size is determined by the mode size of the SPPW. The proposed ${4} \times {4}$ patch array features an average gain of 19.6 dBi in the operating frequency band. Meanwhile, the antenna array is designed and fabricated in microwave frequency band, and the measured results validate the simulated high efficiency of the proposed array. Moreover, since the mode size of the SPPW can be flexibly designed, the proposed idea can be further extended into larger 2-D arrays with more elements.

Wideband helicity dependent spoof surface plasmon polaritons coupling metasurface based on dispersion design.

The surface plasmon polaritons (SPPs) have many potential application due to their local field enhancement and sub-wavelength characteristics. Recently, the gradient metasurface is introduced to couple the spoof SPPs in microwave frequency band. One of the most important issue which should be solved is the narrowband of spoof SPPs coupling on the gradient metasurface. Here, the metasurface is proposed to achieve the wideband helicity dependent directional spoof SPPs coupling for circular polarized light. Our research show that the coupling frequency of spoof SPPs on the gradient metasurface is determined by the dispersion of the metasurface, so the coupling frequency can be controlled by dispersion design. The careful design of each cell geometric parameters has provided many appropriate dispersion relations possessed by just one metasurface. The wave vector matching between the propagating wave and the spoof SPPs has been achieved at several frequencies for certain wave vector provided by the metasurface, which leads to wideband spoof SPPs coupling. This work has shown that wideband helicity dependent directional spoof SPPs coupling has been achieved with a high efficiency. Hence, the proposed wideband spoof SPPs coupling presents the improvement in practice applications.

Integrated Synthetic Bandstop Filters for Blocker Rejection at RF and Microwave Frequency Bands

In this paper, active synthetic band-stop filter (BSF) for interference rejection at 2–4, 4–8, and 8–16 GHz are presented. In the designs, a sharp notch, typically less than −50 dB for the entire frequency bands, is synthesized by subtracting the bandpass filter output from the all-pass (AP) output. The proposed synthetic notch filters allow optimization of filter dynamic range (DR) in the AP amplifier and frequency selectivity in the BPF independently, breaking the tradeoff between selectivity and DR ingrained in passive filters. In addition, the notch attenuation can be controlled independently of the filter bandwidth and center frequency tuning, providing more operational flexibility in suppressing blocker under a dynamic interference environment. The notch filters are fabricated in a 0.13- $\mu \text{m}$ SiGe BiCMOS technology. The measured gain is 0–1 dB for all three filters. The 2–4 GHz notch filter shows a 12–13 dB noise figure (NF) and a $- 2\sim -1.5$ dBm input 1-dB compression point (IP $_{{-1\text {dB}}}$ ) in the passband while drawing 20–30 mA from a 3.3-V supply. For the 4–8-GHz design, the measurement shows a 8–10-dB NF and a −1–1 dBm IP $_{-1\text {dB}}$ in the passband at the expense of 20–27.6 mA from a 3.3 V supply. For the 8–16 GHz filter, the measured NF is 14–17 dB and the IP $_{-1\text {dB}}$ is 0–4 dBm with a 70–90 mW dc power dissipation. The die areas are $0.68 \times 0.72$ mm2, $0.63 \times 0.63$ mm2, and $0.62\times 0.57$ mm2 for the S-band, C-band, and X-/Ku-band filters, respectively.

A Novel Broadband Band-pass Filter Based on Spoof Surface Plasmon Polaritons.

In this paper, we present a novel broadband bandpass filter based on spoof surface plasmon polaritons (SSPPs) in the microwave frequency band. The proposed bandpass filter includes three parts: (1) coplanar waveguide (CPW); (2) matching transition; and (3) coupled structure that is an asymmetric coupled filter constructed by five grooved strips. The proposed bandpass filter realizes excellent low loss performance from 7 to 10 GHz, in which its insertion loss is around 1.5 dB in the same frequency band. Meanwhile, this filter has a good band stop characteristic from 3 to 7 GHz. A simple but accurate transmission line model was proposed to evaluate the proposed broadband SSPPs filter. The measured data, simulated results and the results obtained from the transmission line model have shown a very good agreement. The proposed planar broadband filter plays an important role for filtering surface plasmon polaritons (SPPs) waves in plasmonic circuits and systems.

Nonequilibrium laser plasma of noble gases: Prospects for amplification and guiding of the microwave radiation

We developed the analytical model of relaxation of a low-density plasma channel produced in noble gases (Xe, Ar) by a femtosecond KrF laser pulse and investigated the temporal evolution of its dielectric permittivity. It was demonstrated that the strong nonequilibrium of the photoelectron energy spectrum and the presence of Ramsauer minimum in transport scattering cross section make such a plasma channel an optically denser medium in comparison with non-ionized gas in the microwave frequency band and consequently such a channel appears to be a waveguide. In xenon this nonequilibrium state of a plasma leads to both transportation and amplification of the microwave signal during the relaxation of the photoelectron energy spectrum. It was also shown that a circular metal waveguide partially filled with such a nonequilibrium Xe plasma provides efficient amplification of the sub-THz microwave signal.

Broadband transition between microstrip line and spoof SP waveguide

A broadband transition from microstrip line to spoof surface plasmon (SP) waveguide is proposed. The transition transforms the guided wave into a spoof SP polariton in a broad microwave frequency band. A back-to-back transition sample is fabricated using the proposed method. Good agreement between the measurement and simulation is obtained. The measured results show an insertion loss <2 dB and a return loss below −11 dB from 2.2 to 10 GHz. The proposed broadband transition may pave a way for advanced conventional plasmonic integrated microwave devices and circuits.

Investigation of mechanism: spoof SPPs on periodically textured metal surface with pyramidal grooves.

In microwave and terahertz frequency band, a textured metal surface can support spoof surface plasmon polaritons (SSPPs). In this paper, we explore a SSPPs waveguide composed of a metal block with pyramidal grooves. Under the deep subwavelength condition, theoretical formulas for calculation of dispersion relations are derived based on the modal expansion method (MEM). Using the obtained formulas, a general analysis is given about the properties of the SSPPs in the waveguides with upright and downward pyramidal grooves. It is demonstrated that the SSPPs waveguides with upright pyramidal grooves give better field-confinement. Numerical simulations are used to check the theoretical analysis and show good agreement with the analytical results. In addition, the group velocity of the SSPPs propagating along the waveguide is explored and two structures are designed to show how to trap the SSPPs on the metal surface. The calculation methodology provided in this paper can also be used to deal with the SSPPs waveguides with irregular grooves.

Multi-frequency and polarimetric quantitative analysis of the Gulf of Mexico oil spill event comparing different SAR systems

Synthetic aperture radar (SAR) images were acquired over the Deepwater Horizon spill's main slick with a number of different instruments during response to the catastrophic accident in 2010. These included instruments operating in different microwave frequency bands (L-C-X band), and, for TerraSAR-X and COSMO-SkyMed, more than one acquisition system operating in the X-band. In this work, for the first time the diverse SAR data acquired over the Deepwater Horizon spill have been compared and quantitatively analyzed with the goal of determining the different capabilities of the last generation SAR systems in the analysis of this important test case. Using the nearest acquisitions in time over the same areas, backscattering coefficients and polarimetric features, when available, have been evaluated. The derived information and comparison of sensors is discussed, in particular taking into consideration the Noise Equivalent Sigma Zero (NESZ) value characterizing each instrument. Although, as expected, an increase of the damping ratio values is noted at higher frequencies, the best slick discrimination capability has been obtained with the L-band UAVSAR sensor, characterized by a more effective NESZ value, while the satellite SAR sensors are shown to have in some cases significant noise contamination to polarimetric parameters. Anomalous behavior at X-band measurements has been also registered and discussed. Through the analysis of all the available data an evaluation of the impact of low noise SAR for oil characterization in the considered context is provided.

A radiometer of the reflection coefficient magnitude

A simple meter of integral values of the reflection coefficient magnitude in the microwave frequency band and a wide frequency band using a low-intensity noise signal is described. Its principle of operation is based on one of the modifications of the null measurement methods. On the one hand, the application of this principle increased the measurement accuracy and, on the other hand, significantly simplified the design of the meter and implemented it as a portable device. The integral error of the nonlinearity of the transfer characteristic in absolute values of the reflection coefficient magnitude did not exceed 0.003 with a measurement resolution of 0.001.

DOUBLE SPLITTING OF MULTIPLICATION LAYER IN AVALANCHE GENERATOR DIODES AND GENERATION OF TWO-FREQUENCY SELF-EXCITED OSCILLATIONS

Development of high-power sources of electromagnetic oscillations in microwave and THz frequency bands is a challenge for radio-electronic engineers. Design of avalanche-generator diodes that generate two phase locked oscillations in microwave and THz ranges is considered in the paper. Summation of two generating oscillations with either close or different frequencies allows managing power and spectral characteristics of the output signal. The physical processes occurring in the avalanche-generator diodes on the basis of abrupt Si and GaAs p–n-junctions at the constant reverse biased voltage are investigated. The effect of double splitting of the multiplication layer has been revealed. In the suggested avalanche-generator diodes, regular and chaotic self-oscillations of electron and hole components of the output power are excited in p- and n-regions of the p–n-junction, respectively.

Metamaterial Absorber Based Multifunctional Sensors

In this paper, several important applications of a metamaterial absorber (MA) based sensors such as temperature, pressure, moisture, and density are presented. Since the sensing ability mostly considers the resonance frequency, the frequency range where the resonance shifts occur linearly or non-linearly depending on the temperature, pressure, moisture, and density changes is selected carefully. The model is composed of X shaped resonators (XSR), dielectric substrate, the sensing layer, dielectric substrate again, and metallic plate, in order. Sensing layer changes its dielectric behavior depending on the temperature, pressure, moisture, and density variations and letting us to determine the unknown values of the mentioned parameters. According to the results, the proposed model can be used in myriad sensing applications for the studied microwave frequency band.

Resource Allocation for Cognitive Satellite Communications With Incumbent Terrestrial Networks

The lack of available unlicensed spectrum together with the increasing spectrum demand by multimedia applications has resulted in a spectrum scarcity problem, which affects satellite communications (SatCom) as well as terrestrial systems. The goal of this paper is to propose resource allocation (RA) techniques, i.e., carrier, power, and bandwidth allocation, for a cognitive spectrum utilization scenario where the satellite system aims at exploiting the spectrum allocated to terrestrial networks as the incumbent users without imposing harmful interference to them. In particular, we focus on the microwave frequency bands 17.7–19.7 GHz for the cognitive satellite downlink and 27.5–29.5 GHz for the cognitive satellite uplink, although the proposed techniques can be easily extended to other bands. In the first case, assuming that the satellite terminals are equipped with multiple low block noise converters (LNB), we propose a joint beamforming and carrier allocation scheme to enable cognitive space-to-Earth communications in the shared spectrum where fixed service (FS) microwave links have priority of operation. In the second case, however, the cognitive satellite uplink should not cause harmful interference to the incumbent FS system. For the latter, we propose a joint power and carrier allocation (JPCA) strategy followed by a bandwidth allocation scheme, which guarantees protection of the terrestrial FS system while maximizing the satellite total throughput. The proposed cognitive satellite exploitation techniques are validated with numerical simulations considering realistic system parameters. It is shown that the proposed cognitive exploitation framework represents a promising approach for enhancing the throughput of conventional satellite systems.

Comparison of Alkali–Silica Reaction Gel Behavior in Mortar at Microwave Frequencies

Alkali–silica reaction (ASR) is one common cause of concrete deterioration and has been a growing concern for decades. Water, in the presence of reactive aggregates used to make concrete, plays a major role in the formation, sustainment, and promotion of this reaction. In this process, free water becomes bound within ASR gel, resulting in expansion and deterioration of concrete. Devising a test approach that is sensitive to the state of water (free or bound) has the potential to become a method-of-choice for ASR detection and evaluation, since such measures can be used to detect ASR and potentially quantify reaction progression. Microwave signals are sensitive to the presence of water, since the water relaxation frequency occurs in this frequency range. Recently, microwave nondestructive evaluation techniques have shown great potential to evaluate and distinguish between ASR-affected mortar samples and those without ASR gel. Given the complex chemistry of ASR products, their behavior is expected to differ at different microwave frequency bands. To evaluate the sensitivity of different frequencies to the presence of ASR, dielectric constant measurements were conducted at $R$ -band (1.7–2.6 GHz), $S$ -band (2.6–3.95 GHz), and $X$ -band (8.2–12.4 GHz). This paper presents the measured results for mortar samples made with reactive and nonreactive aggregates. The measurement results and subsequent analyses aid in a better understanding of the microwave signals interaction with ASR-affected cement-based materials. Moreover, the results indicate that $S$ -band appears to be the most appropriate frequency band for ASR evaluation in the microwave regime.

Synthesis and microwave absorption properties of graphene-oxide(GO)/polyaniline nanocomposite with gold nanoparticles**Project supported by the National Basic Research Program of China (Grant Nos. 2011CB932700 and 2011CB932703), the National Natural Science Foundation of China (Grant Nos. 61335006, 61378073, and 61077044), and the Beijing Natural Science Fund (Grant No. 4132031).

A composite of graphene/PANI/GAunano is synthesized using the co-blend method. The morphologies and microstructures of samples are examined by transition electron microscopy (TEM) and Fourier transform infrared spectroscopy (FTIR). Moreover, the microwave absorption properties of both graphene/PANI and GO/PANI/ GAunano composites are investigated in a microwave frequency band from 1 GHz to 18 GHz. The maximum reflection loss (RL) of GO/PANI/GAunano with a thickness of 2 mm is up to −24.61 dB at 15.45 GHz, and the bandwidth corresponding to RL at −10 dB can reach 4.08 GHz (from 13.92 GHz to 18.00 GHz) for a 2-mm-thick layer. The electromagnetic data demonstrate that GO/PANI/GAunano can be used as an attractive candidate for microwave absorbers.

Room-Temperature Electron Spin Relaxation of Triarylmethyl Radicals at the X- and Q-Bands.

Triarylmethyl radicals (trityls, TAMs) represent a relatively new class of spin labels. The long relaxation of trityls at room temperature in liquid solutions makes them a promising alternative for traditional nitroxides. In this work we have synthesized a series of TAMs including perdeuterated Finland trityl (D36 form), mono-, di-, and triester derivatives of Finland-D36 trityl, the deuterated form of OX63, the dodeca-n-butyl homologue of Finland trityl, and triamide derivatives of Finland trityl with primary and secondary amines attached. We have studied room-temperature relaxation properties of these TAMs in liquids using pulsed electron paramagnetic resonance (EPR) at two microwave frequency bands. We have found the clear dependence of phase memory time (Tm ∼ T2) on the magnetic field: room-temperature Tm values are ∼1.5-2.5 times smaller at the Q-band (34 GHz, 1.2 T) than at the X-band (9 GHz, 0.3 T). This trend is ascribed to the contribution from g-anisotropy that is negligible at lower magnetic fields but comes into play at the Q-band. In agreement with this, the difference between T1 and Tm becomes more pronounced at the Q-band than at the X-band due to increased contributions from incomplete motional averaging of g-anisotropy. Linear dependence of (1/Tm - 1/T1) on viscosity implies that g-anisotropy is modulated by rotational motion of the trityl radical. On the basis of the analysis of previous data and results of the present work, we conclude that, in the general situation where the spin label is at least partly mobile, the X-band is most suitable for application of trityls for room-temperature pulsed EPR distance measurements.