Working Frequency Bandwidth Research Articles

A NOVEL DEFECTED GROUND STRUCTURE WITH BOTH ADJUSTABLE CENTER FREQUENCY AND RECONFIGURABLE BANDWIDTH

A new defected ground structure (DGS) with tunable working frequency and reconflgurable bandwidth is proposed in this paper. The prototype combines the conventional DGS with T-shaped patch featuring narrow bandwidth and two such units located symmetrically featuring wide bandwidth. The proposed structure is designed, simulated and measured. By embedding two reversely-set PIN diodes and four varactors, the proposed structure achieves a narrow bandwidth with a tuning range of 21.1% and a wide bandwidth with a tuning range of 24.6%. In comparison, the bandwidth (i10dB) is about 13.6% for the narrowband state and 49.2% for the broadband state, where an approximately 4-times extension is obtained.

Power amplifier bandwidth expansion via dual fulfillment of class E conditions

The calculation procedure and experimental investigation of class E power amplifier with broadening of the working frequency bandwidth have been considered. The specified broadening was achieved via double fulfillment of switching conditions at zero voltage (class E conditions) in the working frequency range. The dependence of amplifier characteristics on the parameters of output matching network were also analyzed.

Nonlinear H-Shaped Springs to Improve Efficiency of Vibration Energy Harvesters

Vibration energy harvesting is an emerging technology aimed at turning mechanical energy from vibrations into electricity to power the microsystems of the future. Most current vibration energy harvesters (VEH) are based on a mass-spring structure: this introduces a resonance phenomenon that enables an increase of VEH output power (compared to nonresonant systems); however, the working frequency bandwidth is limited. Therefore, these devices are not able to harvest energy when ambient vibrations’ frequencies shift. To solve this problem and to increase the frequency band where power can be harvested, one solution consists in using nonlinear springs. This paper introduces H-shaped nonlinear springs, their model, and their benefits to improve VEH output powers. Simulations on real vibration sources show that the output power can be higher in nonlinear devices (up to +48%) compared to linear systems.

A 79-GHz LTCC Patch Array Antenna Using a Laminated Waveguide-Based Vertical Parallel Feed

A microstrip patch array antenna based on a low-temperature co-fired ceramics (LTCC) technology is presented in this letter. The antenna is designed for the 77-81-GHz radar frequency band and uses a high-permittivity material (er = 7.3). A laminated waveguide (LWG) was chosen as transmission line, which minimizes coupling and enables the design of LWG-based vertical power dividers. Three stages of power dividers were combined to realize a vertical parallel feeding network. With this feeding-network, the radiation pattern of the proposed antenna is nearly constant across the whole 4-GHz bandwidth. A uniform aperture distribution was chosen. In total, 12 layers of LTCC tapes were used. The measured half-power beamwidth in the E-plane is ≤ 7° across the whole working frequency bandwidth. This compact LTCC antenna (28.3 × 1.2 mm2) is suitable for short/middle-range radar applications, especially for those with a small channel spacing requirement .

Design of a Microstrip Antenna Based on the Magnetoelectric Composite Material

Based on the transmission line mode theory, designed one kind of small and dual band microstrip antenna on the magnetoelectric composite material. Then do the simulation by HFSS11.0 which based on the finite element method. The simulation results show that, when the return loss less than -10dB, antenna working in band 2360MHz~2500MHz and 3900MHz ~4200MHz, Compared with ordinary antenna, this antenna not only realizes the multi band, but also in the working frequency bandwidth compared to common antenna slightly raised, antenna size is reduced nearly 85%. Good impedance matching. This microstrip antenna has some value on the mobile device miniaturization for the miniaturization and dual band.

A NOVEL TECHNIQUE FOR IMPROVING THE PERFORMANCE OF SALISBURY SCREEN

The most common and simple structure to reduce the level of the reflected power from a metallic surface is the single layer structure known as Salisbury screen which is a sheet of porous material impregnated with graphite and spaced a quarter-wavelength off a metallic backing plate. The main disadvantage of this mechanism is the narrow frequency bandwidth. Many techniques have been reported to improve the working frequency bandwidth but with some degradation in the other technical properties of the overall structure. In this paper a novel technique has been introduced based on a spatial kind of material called the circuit analog screen. Theoretical analysis shows that the bandwidth of the reflected power will be improved if the graphite sheet of the Salisbury screen has been loaded by circuit analog screen with spatial geometry with spatial parameters.

Adaptive Tuned Vibration Absorber based on Magnetorheological Elastomer

This study presents an adaptive tuned vibration absorber (ATVA) which is based on magnetorheological elastomer (MRE). Traditional dynamic absorber has limited its application and vibration absorption capacity for its narrow working frequency bandwidth. MRE is a kind of smart material whose modulus can be controlled by applied magnetic field. Based on MREs, an ATVA which works on shear mode is proposed in this study. After the vibration mode shapes of the ATVA are analyzed, the mechanical structure of the ATVA is brought forward. Then the magnetic circuit of the ATVA is identified by ANSYS software. By using a modified dipole model, the shift-frequency properties of the ATVA versus magnetic field and strains are theoretically analyzed and simulated. Furthermore, by employing a beam with two ends supported, its shift-frequency property and vibration absorption capacity are experimentally justified. The experimental results demonstrate that the designed ATVA has better performance than traditional passive absorber in terms of frequency-shift property and vibration absorption capacity.

Stability analysis of the constant temperature anemometer with frequency depended amplifier gain

AbstractIn this paper we are concerned with the stability and the dynamic response of the constant temperature anemometer. The amplifier of the presented hot–wire anemometer has one pole with high time constant, which affect the presented amplifier to behave in the anemometer working frequency bandwidth with the frequency depended gain. For precise description of the anemometer dynamical response the used transfer function of the amplifier is first order of zeros and third order of poles. The hot–wire response to the sine‐wave voltage perturbation was calculated and measured. The root curves of the transfer function were presented.

Prediction of backscatter coefficient in trabecular bones using a numerical model of three-dimensional microstructure.

A model of ultrasonic backscattering for cancellous bone saturated by water is proposed. This model assumes that scattering is caused by the solid trabeculae and describes the cancellous bone as a weak scattering medium. The backscatter coefficient is related to the spatial Fourier transform of bone microarchitecture and to the density and compressibility fluctuations between the solid trabeculae and the saturating fluid. The computations of the model make use of three-dimensional numerical images of bone microarchitecture, obtained by tomographic reconstructions with a 10 microm spatial resolution. With this model, the predictions of the frequency dependence and of the magnitude of the backscatter coefficient are reasonably accurate. The theoretical predictions are compared to experimental data obtained on 19 specimens. An accuracy error of approximately 1 dB was found (difference between the averaged experimental values and theoretical predictions). One limit of the model may come from inaccurate values of trabecular bone characteristics needed for the computations (density and longitudinal velocity), which are yet to be precisely determined for human trabecular bone. However, the model is only slightly sensitive to variations of bone material properties. It was found that an accuracy error of 2.2 dB at maximum resulted from inaccurate a priori values of bone material properties. A computation of the elastic mean free path in the medium suggests that multiple scattering plays a minor role in the working frequency bandwidth (0.4-1.2 MHz). It follows from these results that a weak scattering medium model may be appropriate to describe scattering from trabecular bone.

Traveling-wave integrated optical modulator with a working-frequency bandwidth of 4 GHz

An investigation was made of a traveling-wave integrated optical modulator utilizing a microstrip electrode structure and tunnel-coupled channel waveguides formed in Ti:LiNbO3. The modulator characteristics were as follows: the half-wave voltage was 10 V (at a wavelength of 1.3 μm), the working frequency bandwidth was at least 4 GHz, the dynamic range (for a laser radiation power of 5 mW) was about 40 dB, and the level of the higher harmonics (at 1 GHz) was 35 dB.