Maximum Frequency Shift Research Articles

An empirical model relating U.S. monthly hail occurrence to large‐scale meteorological environment

AbstractAn empirical model relating monthly hail occurrence to the large‐scale environment has been developed and tested for the United States (U.S.). Monthly hail occurrence for each grid box is defined as the number of hail events that occur there during a month; a hail event consists of a 3 h period with at least one report of hail larger than 1 in. The model is derived using climatological annual cycle data only. Environmental variables are taken from the North American Regional Reanalysis (NARR; 1979–2012). The model includes four environmental variables convective precipitation, convective available potential energy, storm relative helicity, and mean surface to 90 hPa specific humidity. The model differs in its choice of variables and their relative weighting from existing severe weather indices. The model realistically matches the annual cycle of hail occurrence both regionally and for the contiguous U.S. (CONUS). The modeled spatial distribution is also consistent with the observed hail climatology. However, the westward shift of maximum hail frequency during the summer months is delayed in the model relative to observations, and the model has a lower frequency of hail just east of the Rocky Mountains compared to observations. Year‐to‐year variability provides an independent test of the model. On monthly and annual time scales, the model reproduces observed hail frequencies. Overall model trends are small compared to observed changes, suggesting that further analysis is necessary to differentiate between physical and nonphysical trends. The empirical hail model provides a new tool for exploration of connections between large‐scale climate and severe weather.

Residual stress and electromagnetic characteristics in loop type frequency selective surface embedded hybrid structures

Residual stresses occur in frequency-selective surface (FSS)-embedded composite structures after co-curing due to differences between the coefficients of thermal expansion between composite skins and FSSs. Furthermore, the electromagnetic characteristics may be affected by the deformation of the FSS pattern by residual stresses. Therefore, we studied the changes in electromagnetic characteristics due to the deformation of FSS, using residual stresses to deform loop-type FSS-embedded hybrid composites. We considered the effects of loop-type FSS patterns of equal dimension as well as the stacking sequences of composite laminates on the electromagnetic characteristics of FSSs: Square loop, triangular loop and circular loop. The stacking sequences of composite laminates considered in this study were [0]8, [0/90]4, [±45]4 and [0/±45/90]2. The FSS was located between composite laminates in the middle plane. To determine the residual stresses and deformations in the FSS embedded laminate structures, the thermal loading condition in the finite element analysis was induced by cooling the hybrid structures from 125°C to 20°C based on the cure cycle of the composite. Also, the electromagnetic reflection characteristics of the hybrid structures were predicted using deformed models by residual stresses, considering the effects of stacking sequence of composite laminates. The results showed that the maximum residual stresses and deformations were produced in the [0]8 composites with all three loop-types of FSS pattern. However, the maximum resonance frequency shifts occurred in the square and triangle loop-types with stacking sequence of [0]8, while the maximum resonance frequency shift occurred in the circular loop-type with stacking sequence of [0/±45/90]2.

Tuning the resonant frequency of resonators using molecular surface self-assembly approach.

In this work, a new method to tune the resonant frequency of microfabricated resonator using molecular layer-by-layer (LbL) self-assembly approach is demonstrated. By simply controlling the polymer concentration and the number of layers deposited, precisely tuning the frequency of microfabricated resonators is realized. Due to its selective deposition through specific molecular recognitions, such technique avoids the high-cost and complex steps of conventional semiconductor fabrications and is able to tune individual diced device. Briefly, film bulk acoustic resonator (FBAR) is used to demonstrate the tuning process and two types of LbL deposition methods are compared. The film thickness and morphology have been characterized by UV-vis reflection spectra, ellipsometer and AFM. As a result, the maximum resonant frequency shift of FBAR reaches more than 20 MHz, meaning 1.4% tunability at least. The minimum frequency shift is nearly 10 kHZ per bilayer, indicating 7 ppm tuning resolution. Pressure cooker test (PCT) is performed to evaluate the reliability of LbL coated FBAR. Furthermore, applications for wireless broadband communication and chemical sensors of LbL coated FBAR have been demonstrated.

Broadband linear high-voltage amplifier for radio frequency ion traps.

We developed a linear high-voltage amplifier for small capacitive loads consisting of a high-voltage power supply and a transistor amplifier. With this cost-effective circuit including only standard parts sinusoidal signals with a few volts can be amplified to 1.7 kVpp over a usable frequency range at large-signal response spanning four orders of magnitude from 20 Hz to 100 kHz under a load of 10 pF. For smaller output voltages the maximum frequency shifts up to megahertz. We test different capacitive loads to probe the influence on the performance. The presented amplifier is sustained short-circuit proof on the output side, which is a significant advantage over other amplifier concepts. The amplifier can be used to drive radio frequency ion traps for single charged nano- and microparticles, which will be presented in brief.

Estimation of the velocity of underwater objects in the passive mode using frequency-shift data

A method for estimating the velocity of a broadband noise source at intermediate distances, based on the data for frequency shifts of interference maxima, is described. The effect of interference on the error in determining the object velocity using a horizontal extended receiving antenna is discussed.

Spatial interference of normal waves in oceanic waveguides

Expressions are derived for the frequency shifts of interference maxima that occur at separate observation points because of a two-dimensional anisotropic random perturbation of the oceanic medium. A relation between the frequency shifts of the field maxima at the observation points and the variations in the phase differences between interfering normal waves is revealed. The use of the frequency shifts in solving direct problems of wave propagation is discussed.

Frequency shifts initiated by surface roughness

The problem of correlation between the temporal spectra of the frequency shifts of interference maxima of a sound field and oceanic perturbation has been solved in the adiabatic approximation. The case of wind-induced roughness is considered on the basis of the relationship established. The questions of surface roughness monitoring efficiency are discussed.

A novel tunable optoelectronic oscillator based on a photonic RF phase shifter

A novel tunable optoelectronic oscillator (OEO) based on a photonic radio frequency (RF) phase shifter is proposed and analyzed, which consists of a dual-drive Mach-Zehnder modulator (DMZM), a 90° hybrid coupler and a tunable microwave amplifier (TMA). This tunable OEO has a simple configuration, and the frequency of the oscillating signal can be tuned by adjusting the amplification factor of the tunable amplifier. The simulation results show that the maximum frequency shift from the center oscillation frequency is 1.48 MHz when the amplification factor of the TMA is set at 10.

Integrated system modeling analysis of a cryogenic multi-cell deflecting-mode cavity resonator

A deflecting mode cavity is the integral element for six-dimensional phase-space beam control in bunch compressors and emittance transformers at high energy beam test facilities. RF performance of a high-Q device is, however, highly sensitive to operational conditions, in particular in a cryo-cooling environment. Using analytic calculations and RF simulations, we examined cavity parameters and deflecting characteristics of TM110,π mode of a 5 cell resonator in a liquid nitrogen cryostat, which has long been used at the Fermilab A0 Photoinjector (A0PI). The sensitivity analysis indicated that the cavity could lose 30%–40% of deflecting force due to defective input power coupling accompanying non-uniform field distribution across the cells with 40 ∼ 50 MeV electron beam and 70–80 kW klystron power. Vacuum-cryomodules of the 5 cell cavity are planned to be installed at the Fermilab Advanced Superconducting Test Accelerator facility. Comprehensive modeling analysis integrated with multi-physics simulation tools showed that RF loading of 1 ms can cause a ∼5 K maximum temperature increase, corresponding to a ∼4.3 μm/ms deformation and a 1.32 MHz/K maximum frequency shift. The integrated system modeling analysis will improve design process of a high-Q cavity with more accurate prediction of cryogenic RF performance under a high power pulse operation.

Frequency shifts of sound field maxima in few-mode propagation, which are initiated by internal wave solitons

The problem of frequency shifts of sound field interference maxima, which are due to the motion of internal wave solitons in the ocean medium and cause intermodal transformation effects, has been solved for few-mode propagation regime. Simulation results are presented and the conditions of applicability of the adiabatic approximation, in which normal waves can be considered as independent, are discussed. The numerical experiment data are used to analyze the possibility of reconstructing the soliton parameters by measuring the frequency shifts of wave field maxima.

Simulation models for MIMO wireless channels

In recent years, with the excellence performance in the system spectrum efficiency, MIMO technology has become the concerned topic in the mobile communication technology development process. In order to make better use of MIMO technology, the characteristics of MIMO channel had to be studied, and it is inevitable to accurately model and simulate MIMO wireless channels in different conditions. Wireless communication environment is very complex, so it is difficult to modeling of MIMO channel. In this paper, carrier wave frequency, the maximum Doppler frequency shift, AOA (Angle of Arrival) distribution, power azimuth spectrum and adjacent antenna spacing were token into account integrating. Expressions of the spatial correlation coefficient for different power azimuth spectrum (PAS) distributions were studied. A MIMO channel model was brought forward which has spatial selectivity, frequency selectivity, and time correlation. Simulation shows this related channel capacity is consistent with theoretical channel capacity. Thereby the rationality of this modeling was validated. This model provides powerful implement for simulation of MIMO capability, analysis of system capacity and evaluation of performance. DOI: http://dx.doi.org/10.11591/telkomnika.v11i1.1883

TERAHERTZ SENSING APPLICATION BY USING FRACTAL GEOMETRIES OF SPLIT-RING RESONATORS

In this study, we report the simulation, fabrication and characterization of a dual-band fractal metamaterial used for terahertz sensing application. By applying the fractal structures of square Sierpinski (SS) curve to the split-ring resonators (SRRs), more compact size and higher sensitivity can be achieved as privileges over conventional SRRs. The in∞uence of difierent geometrical parameters and the order of the fractal curve on the performances are investigated. Then overlayers are added to the fractal SRRs in order to explore the performance of the entire system in terms of sensing phenomenon. The changes in the transmission resonances are monitored upon variation of the overlayer thickness and permittivity. Measured results show good agreement with simulated data. At the second resonance of the second-order SS-SRRs, maximum frequency shifts of 19.8GHz, 26.3GHz and 37.8GHz were observed for a 2m, 4m and 10m thickness of photoresist. The results show good sensitivity of the sensors suggesting they can be used for a myriad of terahertz sensing applications in biology and chemistry.

Fabrication and Characterization of MEMS-Based Resonant Organic Gas Sensors

Polymer coated thermal-piezoresistive micromechanical resonant silicon nanobalances have been utilized for detection and concentration measurement of volatile organic compounds in gas phase. Polyglycolic acid, which is the main polymer ingredient of the shipley-1813 photoresist, was used as the absorbent coating layer. Experiments have shown that polymer thickness determines the achievable sensitivity towards the gas molecules. The main challenge is to coat the devices with a thick layer of polymer while still maintaining their high-Q resonance. Multiple polymer coating approaches have been demonstrated. Following polymer deposition, in order to find the sensitivity of the devices, they were tested by exposure to regular gasoline and toluene vapor. The best measurement results were obtained by utilizing the photoresist already present on the resonant structures from the fabrication process. A maximum frequency shift of 3600 ppm (55 kHz) was obtained from a 15.5 MHz resonator with a ~ 1.5 μm thick coating upon exposure to nitrogen saturated with toluene vapor at room temperature. Based on the measurement results, minimum detectable concentration of toluene in the gas phase for such devices is in the range of a few ppm.

Frequency shifts of sound field maxima under the effect of intense internal waves

Numerical simulation is carried out to study frequency shifts of a low-frequency sound field maxima under the effect of solitary internal waves (solitons) propagating along an acoustic track in the presence of mode coupling. The frequency shifts are measured by the correlation method. Simulation data obtained with allowance for mode coupling and data obtained in the adiabatic approximation are compared and analyzed.

DETUNING STUDY OF IMPLANTABLE ANTENNAS INSIDE THE HUMAN BODY

This study quantifles the detuning and impedance mismatch of antennas implanted inside the human body. Maximum frequency shifts caused by variations in the electrical properties of body tissues and difierent anatomical distributions were derived. The results are relevant to the design of implantable antennas. They indicate the bandwidth enhancement and initial tuning necessary for correct functioning. The study was carried out using electromagnetic modeling based on the flnite-difierence time-domain method and high- resolution anatomical models. Four anatomical computer models of two adults and two children were used. The implanted antennas operated in the Medical Implant Communication Service band. The most important detuning and impedance mismatch was found for subcutaneous locations and in areas where a layer of fat tissue was present. The maximum frequency shift towards higher frequencies was 70MHz. The frequency shift did not occur symmetrically around 403MHz, but was shifted towards higher frequencies.

Nanoliter Droplet Characterization using Vibrating Crystal Sensor with Surface-attached Polymer Hydrogel Coating

This paper presents a novel method for nanoliter droplet characterization using a polymer coated sensor of a low-cost quartz crystal microbalance (QCM). The gold electrode of the crystal sensor was coated by a surface-attached polymer hydrogel film of about 2µm thickness using simple spin casting and photocrosslinking procedure [1,2]. The resonance frequency of the coated crystal sensor was continuously recorded at the sample rate of 2 Hz over 90 seconds before and after loading a micro droplet of filtered double-distilled water. Good repeatability (max. CV = 3.8%) and good linearity (r(x,y)= 0.995) of the maximum resonance frequency shift have been observed during 144 dispenses for 6 different droplet volumes in the range from 3 nl to 13 nl. A calibration line for the measured domain of the maximum frequency shift in relation to droplet mass was established according to the gravimetric calibration of the used dispenser with an ultra-microbalance. © 2012 Published by Elsevier Ltd.

Highly Sensitive UV Sensors Based on SMR Oscillators

The interest in ultraviolet (UV) light sensors have been stimulated in the fields of ozone layer and ultraviolet radiation monitoring, satellite communications and UV astronomy. Zinc oxide (ZnO) thin film is an attractive candidate for acoustic wave devices and ultraviolet optoelectronics, due to its high coupling coefficient and the direct energy band gap of approximately 3.2eV at room temperature. In general, thin film bulk acoustic wave (TFBAW) devices, which are solidly mounted resonator (SMR) devices in this study, possess a higher operating frequency and better frequency response than those of surface acoustic wave (SAW) devices. Therefore, ZnO thin films in the SMR devices acting as both the piezoelectric layer and UV sensing layer were adopted to investigate the acoustic and UV properties in this study. The SMR-based oscillator is composed of a high frequency amplifier, the matching networks, and an SMR device. The resonance frequency of the SAW oscillator is 619.31MHz with output power of -18.75 dBm, and the phase noise is -60.63 dBc at 100kHz. The frequency shifts of SMR oscillators show a trend as a function of the illumination intensities of UV light. Finally, the maximum frequency shift of 552kHz could be obtained when the illumination intensity of UV light was 212μW/cm2.

Thin-film superconducting resonator tunable to the ground-state hyperfine splitting of 87Rb

We describe a thin-film superconducting Nb microwave resonator, tunable to within 0.3 ppm of the hyperfine splitting of 87Rb at fRb = 6.834683 GHz. We coarsely tuned the resonator using electron-beam lithography, decreasing the resonance frequency from 6.8637 GHz to 6.8278 GHz. For in situ fine tuning at 15 mK, the resonator inductance was varied using a piezoelectric stage to move a superconducting pin above the resonator. We found a maximum frequency shift of about 8.7 kHz per 60-nm piezoelectric step and a tuning range of 18 MHz.

Design of Tunable Bandpass Filters With Ferrite Sandwich Materials by Using a Piezoelectric Transducer

With their high relative permeability and high permittivity, magneto-dielectric materials show great potential in tunable bandpass filter designs. This paper presents a novel tunable bandpass filter with magneto-dielectric perturbation by using a piezoelectric transducer (PET) on a microstrip hairpin. Compared to traditional dielectric perturbation, the frequency tunability of the bandpass filter with magneto-dielectric is much larger while the insertion loss is not much affected. NiCo-ferrite films were adopted to laminate magneto-dielectric sandwich structure on a commercially available Rogers substrate. Novel bandpass filter designs with self-biased NiCo-ferrite films on one layer to five layers of the sandwich structure were compared and investigated. A maximum frequency shift of 240 MHz with respect to the unperturbed condition has been achieved.

Frequency shifts of sound field maxima in oceanic waveguides

The frequency shifts of sound field maxima that are caused by the variability of the medium in an oceanic waveguide are described. The condition under which the time spectrum of the frequency shifts of interference maxima is proportional to the time spectrum of fluctuations in the dispersion characteristic of the waveguide is determined.