Entire Frequency Research Articles

A Modified Slow-Wave Structure for Backward-Wave Oscillator Design in THz Band

In this paper, a novel slow-wave structure (SWS), called quasi-parallel-plate (QPP), is proposed for terahertz (THz) backward-wave oscillator BWO design. Compared with the conventional SWSs, the novel SWS has a wider “cold” bandwidth and higher interaction impedance. The Particle-in-cell (PIC) results show that the BWO can produce over 0.82 W output power in the operating frequency range from 0.82 to 1 THz by utilizing an operating voltage range from 5 to 10 kV. The interaction efficiency over the entire operating frequency band is above 2.8%. This SWS, which employing a circular electron beam of 3 mA, can be considered as a promising THz SWS for BWO design with characteristics of moderate operating voltage, wide tunable bandwidth, high efficiency, and compact structure.

21.5-to-33.4 GHz Voltage-Controlled Oscillator Using NMOS Switched Inductors in CMOS

To demonstrate the applicability of NMOS switched variable inductors in the millimeter wave frequencies, a 21.5 to 33.4 GHz wide tuning range LC voltage-controlled oscillator (LC-VCO) with frequency tunable output buffers that uses variable inductors is reported. The measured phase noise at 10 MHz offset of VCO fabricated in a 65 nm bulk CMOS process varies from -117 to -109 dBc/Hz. The oscillator core consumes 4 or 6 mA from a 1.2 V power supply. These correspond to a record 43.3% tuning range. FOMT ranges from -191.7 to -181.9 dBc/Hz. With tunable output buffers, the measured signal output power is above -15 dBm across the entire frequencies.

Characteristics of UV Irradiated Waste Biopolymer from Renewable Resources (Part 1)

Waste cooking oil has proven to be a problematic material in the developed countries since people usually pour waste cooking oil into the kitchen drainage because they unaware that this waste can be recycled. Thus, in this study, the converted waste cooking oil into polymer was fabricated by using hot compression machine and named as waste biopolymer (WB). Vibration transmissibility test was conducted to determine the WB characteristics before and after UV-irradiated. It is revealed the similar vibration transmissibility responses curves were obtained at 1mm, 0.1g and 0.15g base excitation levels for the entire testing frequency except for the displacement transmissibility from base to moveable top plate at 1.5 mm. There was only one resonance peak occurred over the testing frequency which was 15 - 23 Hz for the displacement transmissibility and 15 – 25 Hz for the acceleration transmissibility test on shaking table. No other variation used on the displacement and acceleration amplitude to control the transmissibility test of UV-irradiated WB system based on shaking table. Evidently, small changes on the frequency of the vibration transmissibility were shifted to higher value of UV-irradiated WB with overall percentages of changes are below 5% except for displacement transmissibility at 1.5 mm. This shows the photo-stability of WB after UV-irradiation is high and could be used for further study.

A Dual-Band-Notched Antenna for UWB Communication Systems Using Two Different Shaped Slots

A compact planar ultra-wideband (UWB) monopole antenna with controllable dual-band-notched characteristics is presented in this paper. U-shaped inverted slot and vertical up C-shaped slot are embedded in the feed line and in the radiating patch, for rejecting WiMAX and WLAN frequency bands, respectively. Moreover, the bandwidth of each rejected band can be independently shifted by adjusting the dimensions of the corresponding band-notched structure. The proposed antenna with two rejected bands characteristics is successfully simulated, prototyped, and measured. The measured results show that the proposed antenna operates until upper 10.6 GHz for voltage standing wave ratio (VSWR) less than 2 and exhibits bands rejection of 3.20–4.1 GHz (24.66%) and 5.20–5.96 GHz (13.62%) frequency band. Furthermore, the proposed antenna shows good radiation characteristics, stable peak gain, and provides more than 80% radiation efficiency, on the entire UWB frequency range except in the notched frequency bands, which prospects the employment in the UWB communication systems.

An Optimal Reactive Power Control Strategy for a DFIG-Based Wind Farm to Damp the Sub-Synchronous Oscillation of a Power System

This study presents the auxiliary damping control with the reactive power loop on the rotor-side converter of doubly-fed induction generator (DFIG)-based wind farms to depress the sub-synchronous resonance oscillations in nearby turbogenerators. These generators are connected to a series capacitive compensation transmission system. First, the damping effect of the reactive power control of the DFIG-based wind farms was theoretically analyzed, and a transfer function between turbogenerator speed and the output reactive power of the wind farms was introduced to derive the analytical expression of the damping coefficient. The phase range to obtain positive damping was determined. Second, the PID phase compensation parameters of the auxiliary damping controller were optimized by a genetic algorithm to obtain the optimum damping in the entire subsynchronous frequency band. Finally, the validity and effectiveness of the proposed auxiliary damping control were demonstrated on a modified version of the IEEE first benchmark model by time domain simulation analysis with the use of DigSILENT/PowerFactory. Theoretical analysis and simulation results show that this derived damping factor expression and the condition of the positive damping can effectively analyze their impact on the system sub-synchronous oscillations, the proposed wind farms reactive power additional damping control strategy can provide the optimal damping effect over the whole sub-synchronous frequency band, and the control effect is better than the active power additional damping control strategy based on the power system stabilizator.

Absorption Properties of Supercooled Liquid Water between 31 and 225 GHz: Evaluation of Absorption Models Using Ground-Based Observations

AbstractMicrowave radiometers (MWR) are commonly used to quantify the amount of supercooled liquid water (SLW) in clouds; however, the accuracy of the SLW retrievals is limited by the poor knowledge of the SLW dielectric properties at microwave frequencies. Six liquid water permittivity models were compared with ground-based MWR observations between 31 and 225 GHz from sites in Greenland, the German Alps, and a low-mountain site; average cloud temperatures of observed thin cloud layers range from 0° to −33°C. A recently published method to derive ratios of liquid water opacity from different frequencies was employed in this analysis. These ratios are independent of liquid water path and equal to the ratio of αL at those frequencies that can be directly compared with the permittivity model predictions. The observed opacity ratios from all sites show highly consistent results that are generally within the range of model predictions; however, none of the models are able to approximate the observations over the entire frequency and temperature range. Findings in earlier published studies were used to select one specific model as a reference model for αL at 90 GHz; together with the observed opacity ratios, the temperature dependence of αL at 31.4, 52.28, 150, and 225 GHz was derived. The results reveal that two models fit the opacity ratio data better than the other four models, with one of the two models fitting the data better for frequencies below 90 GHz and the other for higher frequencies. These findings are relevant for SLW retrievals and radiative transfer in the 31–225-GHz frequency region.

Dielectric Behavior and A.C Conductivity of Cd2Si1-xGexO4 Compound

The effect of additives (Ge) on a.c conductivity and dielectric properties of Cd2Si1-xGexO4 compound at ( x = 0, 0.25, 0.5) at temperature range (300 – 473) K and frequency range (100 Hz-10MHz) has been studied. Experimental results indicate that the a.c conductivity and dielectric parameters are temperature, frequency and impurity dependent. The a.c conductivity in the aforesaid frequency range is found to obey the ωs law. A strong dependence of a.c conductivity and exponent s in the entire temperature and frequency range can be interpreted in terms of the correlated barrier hopping (CBH) model due to the effect of Ge element. The variation of above mentioned properties with Ge element are also investigated and results are explained in terms of lone pair configuration of the studied compositions.

Design of a Kind of Combined Antenna with Wide Band for Passive Radar Application

The wide band antenna is a key technique for the passive radar. This paper proposed a new kind of wide band antenna combined with the Archimedean spiral and hemispherical helix for passive radar application. For the new antenna, the planar Archimedean spiral is mounted on the top of the hemispherical helix, and it is fed at the center of the Archimedean spiral. An antenna with specific structure and parameters was designed and simulated to obtain its radiation performances over the operating frequency range from 2GHz to 10GHz. For entire operating frequency range, the simulated gain is greater than 5 dBi and the voltage standing wave ratio (VSWR) is less than 2 when the characteristic impedance of transmission line at the terminal is 240Ω. Wide beam and approximately circular polarization characteristics are also observed. The simulation results demonstrate that the new kind of antenna has wide band radiation performances, which can be used in passive radars. Furthermore, the proposed antenna has simple structure and low cost, so it is suitable for mass fabrication.

Usefulness of Colored 3D Imaging of Respiratory Impedance in Asthma

PurposeRecently, the clinical application of the forced oscillation technique (FOT) has progressed with the spread of commercially available FOT devices, including the impulse oscillation system and MostGraph. We investigated the usefulness of color 3D imaging of respiratory impedance in asthma using MostGraph.MethodsWhole-breath and within-breath respiratory system resistance (Rrs) and reactance (Xrs) were measured in 78 patients with asthma. Color 3D images were classified into three patterns: the chronic obstructive pulmonary disease (COPD)-like pattern (high values of Rrs and Xrs with a marked respiratory cycle and frequency dependence), the asthma pattern (moderately high Rrs over the entire frequency and a respiratory cycle with slight Xrs changes), and a normal-like pattern (low Rrs and Xrs with few within-breath changes). The classification was performed by three researchers, who were unaware of the clinical information, and the clinical characteristics were compared among the three groups.ResultsColor 3D imaging provided a COPD-like pattern in 25 patients, an asthma pattern in 39 patients, and a normal-like pattern in 14 patients. Patients with the COPD-like pattern were predominantly female with a higher body mass index, lower forced expiratory volume in 1 second (FEV1) and forced vital capacity (FVC), and higher Rrs and Xrs values (whole-breath and within-breath variation). Those with the normal pattern had higher FEV1 and FVC, and a lower single-breath nitrogen washout slope. There were no differences in asthma control or exhaled nitric oxide levels among the three groups.ConclusionsThese results suggest that color 3D imaging of respiratory impedance may show asthma phenotypes.

RFID Tag Antenna Design Based on an Improved Coupling Source Shape

An improved coupling source structure for radio frequency identification (RFID) tag antenna is proposed, which can not only achieve broadband operation, but can also easily carry out a complex conjugate impedance match between antenna and RFID chip. The impedance bandwidth of the proposed antenna is approximately 15% (842–985 MHz) with respect to the center frequency of 925 MHz and covers the entire UHF RFID frequency band. It is confirmed that this kind of antenna is suitable for all the different tag antennas' applications.

DC-50 GHz RF-MEMS SPDT switch for high-reliability applications

A large band SPDT (single-pole double-throw) switch based on a very advanced RF-MEMS switch technology for redundancy schemes are presented. This device allowed to reach state-of-the-art working bandwidth (DC-50 GHz) and RF performances (IL (Insection loss) 25 dB, and RL > 20 dB). The 200 mm MEMS technology process has demonstrated a very good stability with very low dispersion (deviations < 0.05 dB for the IL and < 0.6 dB for the isolation over the entire wafer and frequency range). An accurate electrical equivalent circuit, modeling the SPDT in the DC-65 GHz frequency band, has allowed to extract a contact resistance which is as low as 1.4 Ω. © 2012 Wiley Periodicals, Inc. Microwave Opt Technol Lett 55:333–335, 2012; View this article online at wileyonlinelibrary.com. DOI 10.1002/mop.27330

Reduction of Secondary Lobes in Aperture Synthesis Radiometry

In a synthetic aperture radiometer, the sidelobe level is determined by the shape of the synthetic pattern, which, in turn, depends on the window used to weight the visibility samples. Reduced sidelobes are obtained when the weighted visibility is smooth with no abrupt changes in the entire spatial frequency domain. Since standard 2-D windows have circular symmetry, the sidelobes are reduced if visibility samples are chosen only within a circle. This technique has been successfully tested with Soil Moisture and Ocean Salinity data, demonstrating an important reduction of sidelobes with some degradation of spatial resolution.

Acoustic absorption evaluation of high-modulus puncture resistance composites made by recycled selvages

Glass fabric and Kevlar fabric reinforced recycled nonwovens were produced to form G-Ply and K-Ply high-modulus composites. Three types of composites — non-hot-pressed (N-), hot-pressed (H-) and laminated (L-) composites, were respectively combined by various plies, including non-treated G-Ply or K-Ply, hot-pressed G-Ply or K-Ply, and laminated-together G-Ply or K-Ply. Their acoustic absorption and puncture resistance were respectively discussed in terms of plies number, fabric interlayer, ply sequence and backed air thickness. It is found that the maximum acoustic absorption coefficient occurs at lower frequencies as increase of layers. The K-Ply N-composite shows higher porous acoustic absorption coefficient but lower puncture resistance as compared to G-Ply at more than three layers. The backed air improves acoustic absorption of N-composite almost at entire frequency and H-, L-composites at certain vibrating frequency. For combinations of one K-Ply and four G-Ply, the K-Ply sequence has a significant effect on acoustic absorption of N-composite and L-composite.

A UWB Bidirectional Rectangular Ring Antenna Fed by CDM with a Rod and Ridges for Constant Beam Direction

This paper presents an ultra-wideband (UWB) rectangular ring antenna excited by a circular disc monopole (CDM) with a conducting rod and two double ridges to radiate bidirectional pattern with constant beam direction along the entire UWB frequency range of 3.1–10.6 GHz. The conducting rod and double ridges at the upper wall of the ring are added to solve the tilted beam problem at the higher edge frequency whereas the double ridges at the lower wall are used to enhance the impedance bandwidth. The dimensions of the rectangular ring and the CDM are initially considered to achieve the bidirectional pattern with the suitable resonant frequencies and bandwidth. Then, the parameters of copper rod and two double ridges are determined by parametric study using CST Microwave Studio simulation software. The prototype antenna was fabricated, and the measured results show good agreement with the simulated ones. The obtained bandwidth of |S11|&lt;-10 dB can cover the UWB frequency range as well as the bidirectional beam radiation with constant beam direction (θ=0°,180° and ϕ=90°). The minimum and maximum measured gains are 3.1 dBi to 5.3 dBi, respectively. The proposed antenna possesses compact size with good radiation performance that can be a promising candidate for UWB applications.

A 16-$\Omega$ Audio Amplifier With 93.8-mW Peak Load Power and 1.43-mW Quiescent Power Consumption

A low-distortion three-stage class-AB audio amplifier is designed to drive a 16-Ω headphone speaker load. High power efficiency is achieved using fully differential internal stages with local common-mode feedback and replica biasing of the output stage. The threshold voltage of nMOS transistors was made comparable to that of pMOS transistors by negatively biasing the p-substrate in order to achieve high linearity. Multiple compensation networks guarantee the stability of the audio amplifier when driving a wide range of capacitive loads from 10 pF to 5 nF. Peak power delivered to the load is measured as 93.8 mW (corresponding to 46.9 mW RMS) with -77.9-dB total harmonic distortion; quiescent power is only 1.43 mW. The power-supply rejection ratio from both ±1.5-V supplies exceeds 63 dB over the entire audio frequency range. The design is implemented in a 0.5-μm CMOS process and occupies 0.34 mm2 of area.

Frequency and Time Domain Characterization of a Novel Hexagonal-shaped Microstrip Antenna for Ultra Wideband Applications

This paper presents frequency- and time-domain characterization of a new hexagonal-shaped monopole antenna with small slots for ultra-wideband (UWB) applications. The antenna was simulated using commercial software tools (CST) microwave studio and Agilent ADS. Neltec make a soft substrate having a dielectric constant of 2.2 and a board thickness of 0.254 mm (10 mil) was used to fabricate the proposed antenna. Frequency-domain characterization using an automatic network analyzer showed return loss less than -10 dB over the entire UWB frequency band. To study the effect of various parameters on the antenna performance, the detailed parametric study was carried out. The radiation patterns and group delay characteristics were measured in an anechoic chamber. Using an Agilent DSO9000A oscilloscope, time-domain characterization of the antenna was carried out. The simulated and measured results in the time domain showed good agreement. It was observed that the proposed antenna shows reasonably good frequency characteristics and time-domain pulse distortion is small indicating usefulness of the antenna for UWB communication applications.

Statistical significance testing and clinical effectiveness studies.

Effectiveness studies, by definition, must reflect patient and treatment variables that exist in the real world of practice. This includes identifying the covariates that contribute to both positive and negative outcomes. The use of clinically significant change and reliable change indices is reviewed to demonstrate that patient changes can be made on the basis of normative comparisons, using outcome relevant variables that reflect the diversity of problems that are of concern to our clients. Therefore, neither agreement on a single outcome index nor plotting the entire outcome frequency distributions of the comparison group, as called for by Krause (see record 2011-19228-002), is required. Various methods currently exist and are used to address the limitations Krause cites with respect to randomized trials, outcome relevant covariates, file-drawer effects, and so forth. The identification and prediction of an individual's treatment response can be done in treatment as usual studies, where outcome relevant covariates have not been controlled, by studying change at the individual level. By studying such individuals and their combined continuums of treatment response, we can then identify clinically relevant outcome variables and alter the course of treatment accordingly.

Rheological Evaluation of Petroleum Jelly as a Base Material in Ointment and Cream Formulations : Linear Viscoelastic Behavior

ABSTRACT − The objective of the present study is to systematically characterize a linear viscoelastic behavior of petro-leum jelly in small amplitude oscillatory shear flow fields correspondent to the rheological ground state. With this aim, usinga strain-controlled rheometer, the dynamic viscoelastic properties of commercially available petroleum jelly have been mea-sured at 37 o C (body temperature) over a wide range of angular frequencies at an extremely small strain amplitude of 0.1%. In this article, the linear viscoelastic behavior was reported in detail and then explained from a structural view-point ofpetroleum jelly and discussed in depth with respect to the consumer’s requirements. Main findings obtained from this studycan be summarized as follows : (1) The storage modulus is always greater than the loss modulus over an entire range ofangular frequencies studied, meaning that the linear viscoelastic behavior of petroleum jelly is dominated by an elastic naturerather than a viscous nature. (2) Petroleum jelly shows a desirable linear viscoelastic behavior with respect to the consumer’srequirements because it is undesirable for the product to flow down from the skin at an initial stage upon contact with thehuman skin. (3) A fractional derivative model shows an excellent applicability to describe a linear viscoelastic behavior ofpetroleum jelly. However, this model should be used with a special caution because there exists no physical meaning forthe model parameters. (4) A modified form of the Cox-Merz rule gives a good ability to predict the relationship betweensteady shear flow properties (nonlinear behavior) and dynamic viscoelastic properties (linear behavior) for petroleum jelly.Key words

Q kink of the nonlinear O(3) σ model involving an explicitly broken symmetry

The (1 + 1)-dimensional nonlinear O(3) σ model involving an explicitly broken symmetry is considered. Sphalerons are known to exist in this model. These sphalerons are of a topological origin and are embedded kinks of the sine-Gordon model. In the case of a compact spatial manifold S1, sine-Gordon multikinks exist in the model. It is shown that the model admits a nonstatic generalization of the sine-Gordon kink/multikink, Q kink/multikink. Explicit expressions are obtained for the dependence of the Q kink energy and charge on the phase frequency of rotation. The Q kink is studied for stability, and expressions are obtained for the eigenfunctions and eigenfrequencies of the operator of quadratic fluctuations. It is shown that the Q kink is unstable over the entire admissible frequency range ω ∈ [−1, 1]. The one-loop quantum correction to the static-kink mass is calculated, and the Q-kink zero mode is quantized. It is shown that, in a general static case, the field equations of the model are integrable in quadratures.

Uniform asymptotic conversion of Helmholtz data from 3D to 2D

Abstract The conversion of a three-dimensional acoustic data set into an equivalent two-dimensional acoustic data set is essential for seismic interpretation where the amplitude is a key issue. The transfer function for such a transformation should be estimated and we propose the construction of such a transfer function via the computation of the pressure field when considering the Helmholtz equation. Ray theory is used in order to improve the homogeneous transfer function that is typically applied to three-dimensional data to obtain the input two-dimensional data set used in many inversion algorithms. The improved transfer function uses a uniform expansion that directly includes the source singularity. The entire useful frequency bandwidth is more accurately preserved by using the uniform expansion. A synthetic example is presented for the Helmholtz equation for the bore-hole geometry encountered in cross-well radar experiments.