Narrow Results

Impedance matching between transmission lines and antennas is an important and fundamental concept in electromagnetic theory. One definition of antenna impedance is the resistance and reactance seen at the antenna terminals or the ratio of electric to magnetic fields at the input. The primary intent of this paper is real-time compensation for changes in the driving point impedance of an antenna due to frequency deviations. In general, the driving point impedance of an antenna or antenna array is computed by numerical methods such as the method of moments or similar techniques. Some configurations do lend themselves to analytical solutions, which will be the primary focus of this work. This paper employs a neural control system to match antenna feed lines to two common antennas during frequency sweeps. In practice, impedance matching is performed off-line with Smith charts or relatively complex formulas but they rarely perform optimally over a large bandwidth. There have been very few attempts to compensate for matching errors while the transmission system is in operation and most techniques have been targeted to a relatively small range of frequencies. The approach proposed here employs three small neural networks to perform real-time impedance matching over a broad range of frequencies during transmitter operation. Double stub tuners are being explored in this paper but the approach can certainly be applied to other methodologies. The ultimate purpose of this work is the development of an inexpensive microcontroller-based system.

A perfect dual-band optical absorber is designed and measured. A low absorption peak (P1) and two high absorption peaks (P2 and P3) are obtained. The P1 peak is excited by the resonance of internal surface plasmon (ISP) mode. The P2 peak is resulted by the coupling of local surface plasma (LSP) modes and the resonance of ISP mode. The P3 peak is excited by the resonance of ISP mode. The damping constant of the gold film is optimization calculated in simulations. Measured results indicate that high absorption performed is obtained with different dielectric layers. The measured metamaterial absorber displays high absorption performed at TM and TE configurations. Moreover, the proposed metamaterial absorber is sensitivity on the change of the refractive index of the environmental media.

Explicit formulas for the design of a high-pass filter to match any series RC load to a resistive generator and to achieve the Butterworth or Chebyshev transducer power-gain characteristics of arbitrary order are presented. The significance is that it reduces the design to simple arithmetic. Illustrative examples are provided to demonstrate their usage.

In this paper, a new Simultaneous Bi-directional Data Bus architecture has been presented. The new architecture provides stable and consistent impedance matching to the transmission channel, which can significantly reduce reflections and ensure the signal integrity and transmission reliability. To validate the design, an in-depth comparative study has been performed.

This paper presents a novel low-voltage single stage CMOS RF Variable Gain Amplifier (RFVGA) designed in 130 nm IBM CMOS process technology using current feed-back gain-independent impedance matching. The proposed RFVGA has a nearly constant gain over the 400 MHz–1 GHz frequency band. Also, it has a 70 dB gain variation (-40 dB to 30 dB) which is decibel-linear within this frequency band for a control voltage in the range of 0.41 V–0.81 V. The RFVGA demonstrates high linearity (THD ≈ -60 dB) and noise immunity (average Noise Figure ≤ 6 dB). It has an input referred third-order intercept point (IIP3) of -1.5 dBm, and an input reflection coefficient (S11) under -8 dB within the frequency band of interest. Also, it dissipates around 5 mW using a 1.2 V power supply. Further, Monte Carlo simulations incorporating process, supply voltage and temperature variations (PVT variations) as well as mismatch between devices (based on width and length of devices) indicate that the design is quite robust. The proposed RFVGA is highly suitable for mobile digital television (DTV) tuner applications.

Wireless sensor networks (WSN) have observed an exponential amount of growth in the recent past. The energy associated with the sensor nodes is limited which is a major bottleneck for the WSN technologies. The sensor nodes in WSN need to be continuously charged and thus an efficient RF energy harvesting needs to be explored. In the proposed design, a dual-band rectifier antenna for RF energy harvesting has been developed for 900 MHz and 2.45 GHz frequencies as RF energy is mainly available in the range of 900 MHz–2.45 GHz. The antenna proposed is microstrip U slot antenna with S11 parameter below −10 dB at 2.45 GHz and 0.8 GHz with a gain of 5.1 dBi and 10.1 dBi at 900 MHz and 2.45 GHz, respectively. The circuit for the rectifier uses Schottky Diode HSMS-285C for the purpose of rectification. The rectifier circuit used is a Greinacher Voltage Multiplier. Impedance Matching of the rectifier has been processed out to improve the performance of the circuit. Simulations of rectifier have been done on Advanced Design System (ADS) Software. The conversion efficiency at 900 MHz and 2.45 GHz is found to be 78.7% and 51.768%, respectively. The proposed design can find its uses in large number of energy harvesting applications under wireless power transmission such as powering of Wireless Sensor Nodes.

In power line communication (PLC), coupling transformers are usually required for coupling, band-pass filtering and impedance matching. However, coupling transformer design involves so many parameters that it is typically an imprecise and experimental procedure. In addition, the cost and size of transformers prevent them from being an economic and compact solution for PLC couplers. This paper first analyzes a simplified, distributed parameter model of the power line, which can be used to calculate power line impedance easily and accurately. Next, a low-cost, band-pass matching coupler with compact architecture is designed to replace the coupling transformer for direct current PLC (DC-PLC), which ensures impedance matching on the basis of an accurate power line impedance instead of using an average value. Finally, simulations as well as laboratory tests are conducted under 95–125kHz (CENELEC B-band), which confirm the new coupler’s excellent band-pass filtering and impedance matching performance.

In this work, reduced graphene oxide (RGO)/ferroferric oxide (RGO/Fe₃O₄) hybrid composite was successfully fabricated by a facile one-step solvothermal method. The structure, chemical composition, morphology and magnetic properties of the samples were investigated in detail. Fe₃O₄ microspheres with an average diameter of 250nm were uniformly anchored on the surface of the RGO sheets without large aggregation. Moreover, the results demonstrated that the hybrid composite exhibited obviously enhanced microwave absorption properties compared with the pure Fe₃O₄ microspheres. The minimum reflection loss (RL) of the hybrid composite reached $-$36.8dB at 17.2GHz with a thickness of 5.0mm and its effective absorption bandwidth (lower than $-$10dB) was 3.9GHz with a thickness of 2.5mm. Significantly, the hybrid composite exhibited a dual-waveband absorption characteristic covering the C and Ku bands. Besides, the relationship between the matching thickness and peak frequency was reasonably explained according to the quarter-wavelength matching theory. Therefore, the obtained composite was a promising candidate for application in microwave absorption.

Development of microwave absorbing materials with tunable thickness and bandwidth is particularly important for practical applications, but its realization remains a great challenge. Here, we report carbon coated core-shell FeSiCr/Fe₃C embedded in two-dimensional carbon nanosheets network (FeSiCr/Fe₃C@C/C) nanocomposites fabricated by plasma arc-discharging method. FeSiCr/Fe₃C@C/C has the best microwave absorption properties in which the minimum calculated reflection loss (RL) can reach $-42.3$dB at 11.5GHz with a coating thickness of 2.4mm and the efficient absorption bandwidth (RL$<-10$dB) almost covers 4.5–18GHz range by adjusting the coating thicknesses from 1.3 to 5.0mm. The improved microwave absorption properties could be ascribed to the optimized impedance matching and enhanced polarization loss, conduction loss and internal reflections of the propagated microwave.

In this study, we have successfully synthesized porous CoO–Co@RGO composites using GO and Co-based metal-organic frameworks (MOFs) as precursors. Due to particular structures and advantageous characteristics, the synthesized porous CoO–Co@RGO composites exhibit outstanding electromagnetic (EM) wave absorbing properties with a filler loading of 10wt.% in wax matrix. The maximum reflection loss (RL) of the prepared porous CoO–Co@RGO was $-34.22$dB with 2.1mm thickness, and the effective absorption bandwidth as wide as 6.24GHz (11.76–18GHz), which covers the full Ku-band. Remarkably, the achieved all values ofRL were under $-10$dB with 1.0–5.0mm thickness, the corresponding to bandwidth range can be tuned to 13.84GHz (4.16–18GHz). The superior absorbing performance is attributed to suitable magnetic loss, high dielectric loss and large attenuation mainly caused by conduction loss and polarization relaxation.

The structure of plasma antenna is more complex than metal antenna to reach ideal gain, efficiency, matching, etc. Therefore, earlier plasma antenna prototypes were always featured with larger size and weight. The NSSC research team has developed new prototypes with equivalent performance as metal antenna. In recent research, we also optimized the antenna structure to reduce size and weight. The new plasma antenna prototype is much smaller than the former ones, and its power consumption is also reduced from more than 100 watts to about 30 watts.