Tested Frequency Range Research Articles

RF MEMS Extended Tuning Range Varactor and Varactor Based True Time Delay Line Design

MEMS varactors are one of the important passive MEMS devices. Their applica- tions include use in VCOs, tunable impedance matching networks, tunable fllters, phase shifters, and true time delay lines. The shunt capacitive structure has been employed in most of the conventional MEMS varactor designs because of its simplicity. However, the capacitance ratio of this conventional shunt capacitive MEMS varactor is limited to 1.5 because of the MEMS Pull- In efiect, which happens when the de∞ection between the MEMS top and bottom metal plates increase beyond 1/3 of the airgap between the two metal plates. At that time, the top metal plate will quickly snap down. This efiect is the major limitation in MEMS varactor designs and can cause nonlinearity and mechanically instability. In order to eliminate this Pull-In efiect, the author employed the so-called MEMS extended tuning range structure. This structure utilizes a variable height top metal beam with separate actuation parts. The airgap between the center part of the top beam and the bottom plate has been designed to be less than 1/3 of the airgap between the top beam and the bottom actuation pads. When DC bias is applied to the actuation parts, the entire top beam will move down together. Consequently, before the Pull-In efiect happens at the actuation parts, the center part has already traveled through its entire tuning range, which means that the capacitive ratio of this kind of MEMS varactor can go to inflnity. A fabrication process employing a GaAs substrate has been designed based on surface micro- machining technology. The maximum capacitance ratio of the designed MEMS extended tuning range varactor is 5.39 with a Cmax value of 167fF. Based on this MEMS varactor design, a Ka-band MEMS varactor based distributed true time delay line has been designed. This dis- tributed true time delay line includes a high impedance CPW transmission line with 70› un- loaded impedance at 28GHz and eight MEMS extended tuning range varactors based on the varactor design periodically loaded on the CPW line. The testing results show that a 56 - phase delay variation has been achieved at 28GHz. The measured insertion loss at 28GHz is i1:07dB at the up-state and i2:36dB at the down-state. The measured return losses, S11 and S22, are both below i15dB at 28GHz and below i10dB over the entire tested frequency range of 5GHz to 40GHz.

Dielectric properties of salmon fillets as a function of temperature and composition

Dielectric properties for anterior, middle, tail, and belly portions of Alaska pink salmon ( Oncornynchus gorbuscha) fillets were measured at frequencies between 27 and 1800 MHz from 20 to 120 °C to provide insights for improving the modeling of microwave (MW) and radio frequency (RF) commercial sterilization processes of salmon products. Compositional differences contributed to the observed slight differences in the dielectric properties for different parts of salmon fillet. For all portions of the fillet, similar trends in dielectric constant and loss factor measurements were observed as a function of temperature (20–120 °C). At RF frequencies of 27 and 40 MHz, the dielectric constant decreased with increasing temperature. But at microwave frequencies (e.g., 915, 1800 MHz), an opposite trend was observed. The dielectric loss factor increased with increasing temperature over the tested frequency range. Calculations from electrical conductivity of minced salmon fillets measured at different temperatures suggest that ionic conductivity was the major contributor to temperature dependent behaviors of dielectric properties at RF frequencies.

Electrical impedance spectroscopy analysis of eggplant pulp and effects of drying and freezing–thawing treatments on its impedance characteristics

The electrical impedance characteristics of eggplant pulp were investigated; the effects of drying and freezing–thawing treatments on the pulp samples were discussed by means of electrical impedance spectroscopy analysis. Fresh eggplant pulp was subjected to vacuum drying, hot-air drying and freezing–thawing treatments respectively, the electrical impedance of the non-treated, partially dried and frozen–thawed pulp tissue was measured using a LCR tester over a frequency range of 42 Hz to 5 MHz; the impedance spectra were analyzed with two lumped element models and a distributed element model based on the Cole–Cole impedance equation; the circuit model parameters representing physiological properties of the tissue were calculated using non-linear regression analysis. Results showed that the impedance loci of the fresh as well as partially dried samples could be described by the models, and the distributed model fitted the experimental data significantly better than the two lumped models did. After drying, the impedance of the samples increased dramatically across the test frequency range due to the loss of moisture; the increase in the impedance of hot-air dried sample was statistically higher than that of vacuum dried sample under the present experimental conditions. After freezing–thawing treatment, the impedance spectrum of the sample lost its original character and became almost independent of the test frequencies, which verified that the membranes of the cells were severely damaged during the freezing process.

Effects of microstructure on permeability and power loss characteristics of the NiZn ferrites

Polycrystalline Ni 0.35Zn 0.55Cu 0.1Fe 2O 4 ferrites with different microstructures were investigated. It was found that although the two samples had greatly different microstructures, their initial permeability values were almost the same. This fact was attributed to the advantage of big grain size on permeability could be counteracted by the disadvantage of closed pores on permeability. The sample with large grain size had worse frequency stability due to the low-frequency resonance induced by big grain size. When samples excited under large flux density, the sample with large grain size and closed pores could obtain lower power loss (Pcv). However, for the low induction condition, the sample with small grain size had better performance on Pcv in our testing frequency range. These results were explained in terms of the influences of grain boundaries and closed pores to the domain wall movement.

Modulation rate transfer functions in bottlenose dolphins (Tursiops truncatus) with normal hearing and high-frequency hearing loss

Envelope following responses were measured in two bottlenose dolphins in response to sinusoidal amplitude modulated tones with carrier frequencies from 20 to 60 kHz and modulation rates from 100 to 5,000 Hz. One subject had elevated hearing thresholds at higher frequencies, with threshold differences between subjects varying from +/-4 dB at 20 and 30 kHz to +40 dB at 50 and 60 kHz. At each carrier frequency, evoked response amplitudes and phase angles were plotted with respect to modulation frequency to construct modulation rate transfer functions. Results showed that both subjects could follow the stimulus envelope components up to at least 2,000 Hz, regardless of carrier frequency. There were no substantial differences in modulation rate transfer functions for the two subjects suggesting that reductions in hearing sensitivity did not result in reduced temporal processing ability. In contrast to earlier studies, phase data showed group delays of approximately 3.5 ms across the tested frequency range, implying generation site(s) within the brainstem rather than the periphery at modulation rates from 100 to 1,600 Hz. This discrepancy is believed to be the result of undersampling of the modulation rate during previous phase measurements.

Modal decomposition method for acoustic impedance testing in square ducts

Accurate duct acoustic propagation models are required to predict and reduce aircraft engine noise. These models ultimately rely on measurements of the acoustic impedance to characterize candidate engine nacelle liners. This research effort increases the frequency range of normal-incidence acoustic impedance testing in square ducts by extending the standard two-microphone method (TMM), which is limited to plane wave propagation, to include higher-order modes. The modal decomposition method (MDM) presented includes four normal modes in the model of the sound field, thus increasing the bandwidth from 6.7 to 13.5 kHz for a 25.4 mm square waveguide. The MDM characterizes the test specimen for normal- and oblique-incident acoustic impedance and mode scattering coefficients. The MDM is first formulated and then applied to the measurement of the reflection coefficient matrix for a ceramic tubular specimen. The experimental results are consistent with results from the TMM for the same specimen to within the 95% confidence intervals for the TMM. The MDM results show a series of resonances for the ceramic tubular material exhibiting a monotonic decrease in the resonant peaks of the acoustic resistance with increasing frequency, resembling a rigidly-terminated viscous tube, and also evidence of mode scattering is visible at the higher frequencies.

Heavy and light impact sources to rate impact sound transmission and changes due to applied floor toppings

The magnitude and spectrum of the power injected by an impact source depends on the impedance of the source and floor. If standardized impact tests are meant to give ratings that correlate well with subjective impressions of footstep noise, it follows that the impact source used should have the same impedance as an average human foot at least over the range of test frequencies. The ISO tapping machine, the Japanese tire machine, and an 18‐cm‐diam rubber ball do not satisfy this criterion. Consequently, their impact spectra differ from those from a live walker. Floor toppings, in particular, are ranked differently. Examples of discrepancies will be presented for direct transmission between vertically separated rooms. For horizontally and diagonally separated rooms, flanking transmission controls the impact sound pressure level. The sound pressure level depends not only on the power injected by the source, but also source location relative to the flanking junction because of propagation attenuation across the floor. Sensitivity to source location is similar for different sources (ISO tapping machine and Japanese ball), suggesting that the same source could be used for direct and flanking transmission measurements if the source adequately simulates the impedance of a human foot.

Diabetes Management in Patients Receiving Palliative Care

A literature review revealed no evidence-based guidelines specific to managing diabetes in the context of palliative care. The purpose of the current project was to describe the management practices of doctors and nurses caring for people with diabetes and advanced disease. Palliative care doctors, palliative care nurses, endocrinologists, and diabetes nurse educators participated in this study. A two-phase project was undertaken: 1) two focus groups, and 2) a cross-sectional survey using a self-completed questionnaire. The focus group and questionnaire data identified that doctors and nurses used a range of practices and blood glucose testing frequencies to control blood glucose based on experience and not according to a robust evidence base. Implications for practice include the importance of collaboration between diabetes and palliative care specialists, and the need to develop clinical management guidelines.

Viscoelastic characterization of selected foods over an extended frequency range

Three disparate food systems (gummy candy, Mozzarella cheese, and cooked ham) were characterized for their viscoelastic behavior under isothermal conditions over an extended frequency range of 10−3 to 104 Hz using broadband viscoelastic spectroscopy (BVS). The materials were tested for any stress-induced fluid flow. However, no evidence of fluid flow was found under the tested frequency range. Validity of time–temperature superposition for the selected materials was also tested and compared with data from BVS.

Study of transport properties of Ge50−xSbyTe100+x−y thin film alloy

The transport properties of Ge50−xSbyTe100+x−y Alloys where 0 ≤ x ≤ 15 and 0 ≤ y ≤ 30 in the thin films state were studied. The temperature dependence of the d.c. electrical conductivity measurements for all prepared composition with different thickness, shows that, all samples behaves as a semiconductor up to a specific temperature at which an abrupt transition appears. That transition is due to the change of the semiconductor from non-degenerate to degenerate state. The temperature dependence of a.c. electrical conductivity measurements shows that, the a.c. conductivity for all films are frequency independent in the tested frequency range from 0.12 to 10 kHz. Thermoelectric power was found to have positive sign indicating that these alloys are p-type semiconductors. The value of temperature coefficient γ was found to be in the order of 10−4 (eV/K). The calculation of the free-charge carrier concentration and charge mobility shows that, the abrupt transition appears in thermoelectric power and conductivity are due to an abrupt increase in the mobility.

Effect of Moisture on Hydrothermal Modification of Yam Dioscorea hispida Dennst Starch

AbstractStarch from Thai yam Dioscorea hispida Dennst; locally known as kloy kao niaw (KKN), was hydrothermally modified (HM) at moisture contents (MC) between 13 and 30 g water/100 g starch (wb) at 90°C for 10 h. All treatments caused a decrease in swelling power and amylose leaching, and an increase in gelatinization temperature of the starch indicating a strengthened network within the starch granule. However, when setting 7 g starch/100 g (wb) gelatinized starch dispersion to gel and subjecting the samples to dynamic rheological tests, only HM KKN starch modified at 13 g water/100 g starch (wb) gave starch gel with higher complex modulus (G*) when compared to native KKN starch gel over the test frequency range (0.001 to 30 Hz). The X‐ray diffraction pattern revealed that KKN starch granule's crystalline structure changed from B to C‐type when modified at 13 g water/100 g starch (wb) and stayed unchanged when modified at 18 to 30 g water/100 g starch (wb).

A Tunable Electrically Small Antenna for Ground Wave Transmission

A tunable, electrically small, wire antenna is developed for HF/VHF ground wave transmission. A variable capacitor is serially connected to tune the resonant frequency of the antenna. The optimal position for the placement of the capacitor is evaluated by numerical simulation. The tuning range and sensitivity are also investigated. A prototype antenna is built and tested, and the measured tuning performance is compared to the simulation results. Transmission loss tests are carried out in several nonline-of-sight environments. The measured transmission loss of the tunable small antenna is found to be within 1 to 2 dB of that of a commercial whip across the tested frequency range.

Modal decomposition method for high‐frequency acoustic impedance testing

Accurate duct acoustic propagation models are required to characterize and reduce aircraft engine noise. These models ultimately rely on measurements of acoustic impedance for candidate materials used in engine nacelle liners. This paper seeks to increase the frequency range of acoustic impedance testing by extending the standard two‐microphone method (TMM), which is limited in bandwidth to ranges where only plane waves propagate, to include higher‐order modes. The modal decomposition method (MDM) presented includes the first four normal modes in the model of the sound field and thus increases the frequency range from 6.7 to 13.5 kHz for a 2.54‐ by 2.54‐cm waveguide. To resolve both the incident and reflected amplitudes of the first four modes, eight microphone measurements are required. This paper formulates and simulates the MDM and applies it to measurement of the reflection coefficient for various specimens over the tested frequency range of 0.2 to 13 kHz. Mode scattering, predominately from the plane‐wave mode into other modes, is revealed. The experimental uncertainty of the method is discussed.

Bottlenose dolphins audiogram dependence on azimuth: Evoked potential study

ABR thresholds to tonal pips were measured in two bottlenose dolphins at different azimuthal positions of the sound source. The tested frequency range was from 8 to 128 kHz. Azimuth varied within a limit of 90 degree relative to the animals’ longitudinal axis. This experimental paradigm allowed us to obtain ABR audiograms at different locations of the sound source. The zero-azimuth audiogram, at the sound source position in front of the animal, was of a standard appearance (minimum thresholds at frequencies of 38 90 kHz, steep threshold increase at higher frequencies, and shallower increase at lower frequencies). The audiograms at lateralized sound-source positions looked in a different manner. With the azimuth increase, high-frequency thresholds rose much higher than low-frequency ones, so at azimuths of 6090, the threshold versus frequency function was almost monotonous: the lowest threshold was observed at the lowest frequency (8 kHz) and the highest threshold at the highest frequency (128 kHz). With monaural ABR recording, audiograms contralateral to the sound source featured higher thresholds and steeper threshold increase with frequency as compared to the ipsilateral ones. [Work supported by the Russian Foundation for Basic Research.]

The Characteristics of Parallel-connected Transmission Lines

The characteristics of two uncoupled parallel-connected trans mission lines in are investigated by transmission line method analysis and circuit layout experiments. By adequate setting the characteristic impedances values and the electrical length of two transmission lines, the band pass or band rejection phenomenon will achieve at the designed frequency point. The validity of the derived results from transmission line method is verified by the experimental results. The numerical and the experimental results show a good agreement in the testing frequency range.

Nanocrystalline W-Doped SrBi<sub>2</sub>Ta<sub>2</sub>O<sub>9</sub> of Layered Perovskite Structure Derived from Mechanical Activation

To study the effects of doping the layered perovskite SrBi2Ta2O9 with an appropriate amount of tungsten, both undoped and W-doped SrBi2Ta2O9 (SBT) of nanocrystallinity were synthesized by mechanical activation of constituent oxides of strontium oxide, bismuth oxide, tantalum oxide and tungsten oxide at room temperature. A nanocrystalline single perovskite phase was observed in SrBi2(Ta1-xWx)2O9 with up to x=0.1. SrBi2(Ta0.9W0.1)2O9 shows a higher Curie temperature than that of undoped SBT, although it exhibits a very similar layered perovskite structure. The ferroelectric and impedance behaviors of SrBi2 (Ta0.9W0.1)2O9 were studied over a range of test temperatures and frequencies, in order to understand the effects of W-doping in SBT, given that W exhibits a similar ionic size to Ta but with a variable valence.

Sound absorption property of wood for five eucalypt species

The sound absorption coefficients of wood and wood boards for five eucalypt species (Eucalyptus urophylla, Eucalyptus urophylla x E. grandis, Eucalyptus urophylla x E. tereticornis, Eucalyptus urophylla x E. camaldulensis and Eucalyptus cloeziana) that were collected from plantation in Dongmen Forestry Center of Guangxi Province, China were tested with standing wave method and their sound absorption properties were also compared. The results showed that the sound absorption coefficients of the five eucalypt wood species did not change evidently below 1000 Hz, but above 1000 Hz their sound absorption coefficients increased with the increasing frequency. The difference in sound absorption coefficient among five species of eucalypt wood is not evident at the tested frequency range (200–2000 Hz), but the sound absorption property ofEucalyptus urophylla at low frequency is better than that of other four species. The sound absorption coefficient of the tangential-sawn board is higher than that of the radial-sawn board. The sound absorption property of eucalypt wood of 0.5 cm in thickness is much better than that of 1.0 cm in thickness. It is concluded that wood sound absorption properties of eucalypts are affected by their board thickness and the type of sawn timber within the testing frequency, but the variance of wood sound absorption property among the five tested species is not significant.

Noise-induced changes of neuronal spontaneous activity in mice inferior colliculus brain slices

The inferior colliculus (IC) in vivo is reportedly subject to a noise-induced decrease of GABA-related inhibitory synaptic transmission accompanied by an amplitude increase of auditory evoked responses, a widening of tuning curves and a higher neuronal discharge rate at suprathreshold levels. However, other in vivo experiments which demonstrated constant neuronal auditory thresholds or unchanged spontaneous activity in the IC after noise exposure did not confirm those findings. Perhaps this can be the result of complex noise-induced interactions between different central auditory structures. It was, therefore, the aim of the present study to investigate the effects of noise exposure on the spontaneous electrical activity of single neurons in a slice preparation of the isolated mouse IC. Normal hearing mice were exposed to noise (10 kHz center frequency at 115 dB SPL for 3 h) at the age of 21 days under anesthesia (Ketamin/Rompun 10:1). After one week, auditory brainstem response (ABR) recordings and extracellular single-unit recordings from spontaneously active neurons within the IC slice were performed in noise-exposed and in normal hearing control mice. Noise-exposed animals showed a significant ABR threshold shift in the whole tested frequency range and a significant lower neuronal spontaneous activity in all investigated isofrequency laminae compared to controls. In both groups, the firing rate of 80% of IC neurons (approximately) increased significantly during the application of the GABA A receptor antagonist Bicucullin (10 μM). The present findings demonstrate a noise-related modulation of spontaneous activity in the IC, which possibly contribute to the generation of noise-induced tinnitus and hearing loss.

Low cycle fatigue study of lead free 99.3Sn–0.7Cu solder alloy

In this paper, low cycle fatigue studies on 99.3Sn–0.7Cu lead free solder was evaluated over a range of test temperatures (298, 348 and 398 K) and frequencies (10 −3–1 Hz), tested at four values of total strain range (2, 3.5, 5 and 7.5%). The fatigue performance of lead free 99.3Sn–0.7Cu solder was compared to 63Sn–37Pb solder. The effects of temperature and frequency on the low cycle fatigue life were discussed and were presented in Coffin–Manson and Morrow model relationships. Frequency modified Coffin–Manson and Morrow models were proposed for predicting the effect of frequency on low cycle fatigue life of 99.3Sn–0.7Cu solder alloy.

White light sources filtered with fiber Bragg gratings for RF-photonics applications

In this paper we demonstrate that broadband light emitters filtered with fiber Bragg gratings are a suitable light source for RF-photonics applications. A 0.075 nm bandwidth fiber grating illuminated by a light emitter of 40 nm bandwidth has been used as light source to feed a microwave phase shifter based on a chirped fiber Bragg grating. The device operates successfully in the tested frequency range (0.5–6) GHz and has been optically tuned in a range of 4 nm.