scholarly journals Design of a Miniaturized Rectangular Multiturn Loop Antenna for Shielding Effectiveness Measurement

Sensors ◽  
2020 ◽  
Vol 20 (11) ◽  
pp. 3178
Author(s):  
Sangwoon Youn ◽  
Tae Heung Lim ◽  
Eunjung Kang ◽  
Dae Heon Lee ◽  
Ki Baek Kim ◽  
...  
Keyword(s):  
High Frequency ◽  
Low Frequency ◽  
Loop Antenna ◽  
Shielding Effectiveness ◽  
Frequency Range ◽  
Ferrite Core ◽  
Very Low Frequency ◽  
Effectiveness Measurement ◽  
Antenna Factor ◽  
Plastic Case

This paper proposes a novel miniaturized rectangular loop antenna sensor consisting of a multiturn wire and a cuboid ferrite core. The lateral surface of the ferrite core is tightly wound by the multiturn wire. To verify its feasibility, the antenna sensor is fabricated, and the antenna factor (AF) levels are measured using the three-antenna method from the very low frequency (VLF) to the high-frequency (HF) bands. The measured AF levels are 31.8 dB (with a covering plastic case) and 33.1 dB (without a covering plastic case) at 30 kHz. In addition, the proposed antenna is employed in the shielding effectiveness measurement of a small commercial cabinet to observe its suitability for shielding effectiveness (SE) measurement of small shielding enclosures. The SE values averaged over the frequency range from 10 kHz to 3 MHz are 4.1 dB and 12 dB in the horizontal and vertical polarizations, respectively.

scholarly journals A Compact Four-Port Coplanar Antenna Based on an Excitation Switching Reconfigurable Mechanism for Cognitive Radio Applications

2019 ◽  
Vol 9 (15) ◽  
pp. 3157 ◽  
Author(s):  
O ◽  
Jin ◽  
Choi
Keyword(s):  
Cognitive Radio ◽  
High Frequency ◽  
Coplanar Waveguide ◽  
Low Frequency ◽  
Loop Antenna ◽  
Ultra Wideband ◽  
Frequency Range ◽  
Uwb Antenna ◽  
High Isolation ◽  
Loop Antennas

In this paper, we propose a compact four-port coplanar antenna for cognitive radio applications. The proposed antenna consists of a coplanar waveguide (CPW)-fed ultra-wideband (UWB) antenna and three inner rectangular loop antennas. The dimensions of the proposed antenna are 42 mm × 50 mm × 0.8 mm. The UWB antenna is used for spectrum sensing and fully covers the UWB spectrum of 3.1–10.6 GHz. The three loop antennas cover the UWB frequency band partially for communication purposes. The first loop antenna for the low frequency range operates from 2.96 GHz to 5.38 GHz. The second loop antenna is in charge of the mid band from 5.31 GHz to 8.62 GHz. The third antenna operates from 8.48 GHz to 11.02 GHz, which is the high-frequency range. A high isolation level (greater than 17.3 dB) is realized among the UWB antenna and three loop antennas without applying any additional decoupling structures. The realized gains of the UWB antenna and three loop antennas are greater than 2.7 dBi and 1.38 dBi, respectively.

scholarly journals Dynamic cerebral autoregulation during passive heat stress in humans

2009 ◽  
Vol 296 (5) ◽  
pp. R1598-R1605 ◽  
Author(s):  
David A. Low ◽  
Jonathan E. Wingo ◽  
David M. Keller ◽  
Scott L. Davis ◽  
Jian Cui ◽  
...  
Keyword(s):  
Blood Pressure ◽  
Heat Stress ◽  
Transfer Function ◽  
High Frequency ◽  
Cerebral Autoregulation ◽  
Low Frequency ◽  
Passive Heating ◽  
Frequency Range ◽  
Very Low Frequency ◽  
Dynamic Cerebral Autoregulation

This study tested the hypothesis that passive heating impairs cerebral autoregulation. Transfer function analyses of resting arterial blood pressure and middle cerebral artery blood velocity (MCA Vmean), as well as MCA Vmean and blood pressure responses to rapid deflation of previously inflated thigh cuffs, were examined in nine healthy subjects under normothermic and passive heat stress (increase core temperature 1.1 ± 0.2°C, P < 0.001) conditions. Passive heating reduced MCA Vmean [change (Δ) of 8 ± 8 cm/s, P = 0.01], while blood pressure was maintained (Δ −1 ± 4 mmHg, P = 0.36). Coherence was decreased in the very-low-frequency range during heat stress (0.57 ± 0.13 to 0.26 ± 0.10, P = 0.001), but was >0.5 and similar between normothermia and heat stress in the low- (0.07–0.20 Hz, P = 0.40) and high-frequency (0.20–0.35 Hz, P = 0.12) ranges. Transfer gain was reduced during heat stress in the very-low-frequency (0.88 ± 0.38 to 0.59 ± 0.19 cm·s−1·mmHg−1, P = 0.02) range, but was unaffected in the low- and high-frequency ranges. The magnitude of the decrease in blood pressure (normothermia: 20 ± 4 mmHg, heat stress: 19 ± 6 mmHg, P = 0.88) and MCA Vmean (13 ± 4 to 12 ± 6 cm/s, P = 0.59) in response to cuff deflation was not affected by the thermal condition. Similarly, the rate of regulation of cerebrovascular conductance (CBVC) after cuff release (0.44 ± 0.22 to 0.38 ± 0.13 ΔCBVC units/s, P = 0.16) and the time for MCA Vmean to recover to precuff deflation baseline (10.0 ± 7.9 to 8.7 ± 4.9 s, P = 0.77) were not affected by heat stress. Counter to the proposed hypothesis, similar rate of regulation responses suggests that heat stress does not impair the ability to control cerebral perfusion after a rapid reduction in perfusion pressure, while reduced transfer function gain and coherence in the very-low-frequency range during heat stress suggest that dynamic cerebral autoregulation is improved during spontaneous oscillations in blood pressure within this frequency range.

Autonomic cardiovascular control in conscious mice

2000 ◽  
Vol 279 (6) ◽  
pp. R2214-R2221 ◽  
Author(s):  
Armin Just ◽  
Jörg Faulhaber ◽  
Heimo Ehmke
Keyword(s):  
High Frequency ◽  
Low Frequency ◽  
Cardiovascular Control ◽  
Adrenergic Blockade ◽  
Frequency Range ◽  
Autonomic Tone ◽  
Very Low Frequency ◽  
Autonomic Blockade ◽  
Autonomic Cardiovascular Control ◽  
The Impact

Autonomic cardiovascular control was characterized in conscious, chronically catheterized mice by spectral analysis of arterial pressure (AP) and heart rate (HR) during autonomic blockade or baroreflex modulation of autonomic tone. Both spectra were similar to those obtained in humans, but at ∼10× higher frequencies. The 1/ f relation of the AP spectrum changed to a more shallow slope below 0.1–0.2 Hz. Coherence between AP and HR reached 0.5 or higher below 0.3–0.4 Hz and also above 2.5 Hz. Muscarinic blockade (atropine) or β-adrenergic blockade (atenolol) did not significantly affect the AP spectrum. Atropine reduced HR variability at all frequencies, but this effect waned above 1 Hz. β-Adrenergic blockade (atenolol) slightly enhanced the HR variability only above 1 Hz. α-Adrenergic blockade (prazosin) reduced AP variability between 0.05 and 3 Hz, most prominently at 0.15–0.7 Hz. A shift of the autonomic nervous tone by a hypertensive stimulus (phenylephrine) enhanced, whereas a hypotensive stimulus (nitroprusside) depressed AP variability at 1–3 Hz; other frequency ranges of the AP spectrum were not affected except for a reduction below 0.4 Hz after nitroprusside. Variability of HR was enhanced after phenylephrine at all frequencies and reduced after nitroprusside. As with atropine, the reduction with nitroprusside waned above 1 Hz. In conclusion, in mice HR variability is dominated by parasympathetic tone at all frequencies, during both blockade and physiological modulation of autonomic tone. There is a limitation for further reduction but not for augmentation of HR variability from the resting state above 1 Hz. The impact of HR on AP variability in mice is confined to frequencies higher than 1 Hz. Limits between frequency ranges are proposed as 0.15 Hz between VLF (very low frequency range) and LF (low frequency range) and 1.5 Hz between LF and HF (high frequency range).

Evaluation of Special Hearing Aids for Deaf Children

1971 ◽  
Vol 36 (4) ◽  
pp. 527-537 ◽  
Author(s):  
Norman P. Erber
Keyword(s):  
Hearing Aids ◽  
High Frequency ◽  
Hearing Aid ◽  
Low Frequency ◽  
Acoustic Stimulation ◽  
Deaf Children ◽  
Frequency Range ◽  
Frequency Limit ◽  
Unpublished Studies ◽  
Published Research

Two types of special hearing aid have been developed recently to improve the reception of speech by profoundly deaf children. In a different way, each special system provides greater low-frequency acoustic stimulation to deaf ears than does a conventional hearing aid. One of the devices extends the low-frequency limit of amplification; the other shifts high-frequency energy to a lower frequency range. In general, previous evaluations of these special hearing aids have obtained inconsistent or inconclusive results. This paper reviews most of the published research on the use of special hearing aids by deaf children, summarizes several unpublished studies, and suggests a set of guidelines for future evaluations of special and conventional amplification systems.

scholarly journals An Improved Time Integration Method Based on Galerkin Weak Form with Controllable Numerical Dissipation

2021 ◽  
Vol 11 (4) ◽  
pp. 1932
Author(s):  
Weixuan Wang ◽  
Qinyan Xing ◽  
Qinghao Yang
Keyword(s):  
High Frequency ◽  
Integration Method ◽  
Time Integration ◽  
Low Frequency ◽  
Weak Form ◽  
High Accuracy ◽  
Numerical Dissipation ◽  
Frequency Range ◽  
Time Integration Method ◽  
Numerical Damping

Based on the newly proposed generalized Galerkin weak form (GGW) method, a two-step time integration method with controllable numerical dissipation is presented. In the first sub-step, the GGW method is used, and in the second sub-step, a new parameter is introduced by using the idea of a trapezoidal integral. According to the numerical analysis, it can be concluded that this method is unconditionally stable and its numerical damping is controllable with the change in introduced parameters. Compared with the GGW method, this two-step scheme avoids the fast numerical dissipation in a low-frequency range. To highlight the performance of the proposed method, some numerical problems are presented and illustrated which show that this method possesses superior accuracy, stability and efficiency compared with conventional trapezoidal rule, the Wilson method, and the Bathe method. High accuracy in a low-frequency range and controllable numerical dissipation in a high-frequency range are both the merits of the method.

Electromagnetic Property of La0.7Sr0.3MnO3/Ag Composite at High Frequency

2015 ◽  
Vol 655 ◽  
pp. 182-185
Author(s):  
Ke Lan Yan ◽  
Run Hua Fan ◽  
Min Chen ◽  
Kai Sun ◽  
Xu Ai Wang ◽  
...  
Keyword(s):  
High Frequency ◽  
Single Phase ◽  
Low Frequency ◽  
Electromagnetic Property ◽  
High Frequency Range ◽  
Frequency Range ◽  
Free Electron Concentration ◽  
Theoretical Simulation ◽  
Electrical And Magnetic Properties ◽  
Three Phase

The phase structure, and electrical and magnetic properties of La0.7Sr0.3MnO3(LSMO)-xAg (xis the mole ratio,x=0, 0.3, 0.5) composite were investigated. It is found that the sample withx=0 is single phase; the samples withx=0.3 and 0.5 present three phase composite structure of the manganese oxide and Ag. With the increasing of Ag content, the grain size of the samples increases and the grain boundaries transition from fully faceted to partially faceted. The permittivity of spectrum (10 MHz - 1 GHz) and the theoretical simulation reveal that the plasma frequencyfpincrease with Ag content, due to the increasing of free electron concentration, which is further supported by the enhancement of conductivity. While for the permeability (μr'), theμr'decrease with the increasing of Ag content at low frequency range (f< 20 MHz), while at the relative high frequency range (f> 300 MHz), theμr'increased with Ag content. Therefore, the introduction of elemental Ag resulted in a higherμr'at the relative high frequency range.

Anderson-Stuart Model to Analyze AC and DC Conductivity of Lithium Zinc-Silicate Glass / Glass-Ceramics

2007 ◽  
Vol 280-283 ◽  
pp. 919-924
Author(s):  
M.S. Jogad ◽  
V.K. Shrikhande ◽  
A.H. Dyama ◽  
L.A. Udachan ◽  
Govind P. Kothiyal
Keyword(s):  
High Frequency ◽  
Glass Ceramics ◽  
Low Frequency ◽  
Frequency Region ◽  
Dc Conductivity ◽  
Frequency Range ◽  
High Frequency Region ◽  
Dc Conductivities ◽  
Conductivity Variation ◽  
Different Temperatures

AC and DC conductivities have been measured by using the real (e¢) and imaginary (e¢¢) parts of the dielectric constant data of glass and glass-ceramics (GC) at different temperatures in the rage 297-642K and in the frequency range 100 Hz to 10 MHz. Using Anderson –Stuart model, we have calculated the activation energy, which is observed to be lower than that of the DC conductivity. The analysis for glass/glass-ceramics indicates that the conductivity variation with frequency exhibits an initial linear region followed by nonlinear region with a maximum in the high-frequency region. The observed frequency dependence of ionic conductivity has been analyzed within the extended Anderson–Stuart model considering both the electrostatic and elastic strain terms. In glass/glassceramic the calculations based on the Anderson-Stuart model agree with the experimental observations in the low frequency region but at higher frequencies there is departure from measured data.

Generation of extra and very low-frequency (ELF/VLF) radiation by ionospheric electrojet modulation using high-frequency (HF) heating waves

2002 ◽  
Vol 68 (4) ◽  
pp. 267-284 ◽  
Author(s):  
S. P. KUO
Keyword(s):  
High Frequency ◽  
Thermal Instability ◽  
Loss Rate ◽  
Inelastic Collision ◽  
Modulation Frequency ◽  
Low Frequency ◽  
Heating Power ◽  
Very Low Frequency ◽  
Hf Heating ◽  
Heating Wave

Extra and very low-frequency (ELF/VLF) wave generation by modulated polar electrojet currents is studied numerically. Through Ohmic heating by the amplitude-modulated high-frequency heating wave, the conductivity and thus the current of the electrojet are modulated accordingly to set up the ionospheric antenna current. Stimulated thermal instability, which can further enhance the electrojet current modulation, is studied. It is first analysed analytically to determine the threshold heating power for its excitation. The nonlinear evolutions of the generated ELF/VLF waves enhanced by the instability are then studied numerically. Their spectra are also evaluated. The field intensity of the emission at the fundamental modulation frequency is found to increase with the modulation frequency in agreement with the Tromso observations. The efficiency enhancement by the stimulated thermal instability is hampered by inelastic collisions of electrons with neutral particles (mainly due to vibration excitation of N2), which cause this instability to saturate at low levels. However, the electron inelastic collision loss rate drops rapidly to a low value in the energy regime from 3.5 to 6 eV. As the heating power exceeds a threshold level, significant electron heating enhanced by the instability is shown, which indeed causes a steep drop in the electron inelastic collision loss rate. Consequently, this instability saturates at a much higher level, resulting to a near step increase (of about 10–13 dB depending on the modulation wave form) in the spectral intensity of ELF radiation. The dependence of the threshold power of the HF heating wave on the modulation frequency is determined.

scholarly journals Investigation of Native Speaker and Second Language Learner Intuition of Collocation Frequency

2021 ◽  
Author(s):  
Anna Siyanova ◽  
S Spina
Keyword(s):  
Language Learning ◽  
High Frequency ◽  
Native Speakers ◽  
Native Speaker ◽  
Low Frequency ◽  
Language Learner ◽  
Very Low Frequency ◽  
Second Language Learner ◽  
L2 Learners ◽  
L1 And L2

© 2015 Language Learning Research Club, University of Michigan. Research into frequency intuition has focused primarily on native (L1) and, to a lesser degree, nonnative (L2) speaker intuitions about single word frequency. What remains a largely unexplored area is L1 and L2 intuitions about collocation (i.e., phrasal) frequency. To bridge this gap, the present study aimed to answer the following question: How do L2 learners and native speakers compare against each other and corpora in their subjective judgments of collocation frequency? Native speakers and learners of Italian were asked to judge 80 noun-adjective pairings as one of the following: high frequency, medium frequency, low frequency, very low frequency. Both L1 and L2 intuitions of high frequency collocations correlated strongly with corpus frequency. Neither of the two groups of participants exhibited accurate intuitions of medium and low frequency collocations. With regard to very low frequency pairings, L1 but not L2 intuitions were found to correlate with corpora for the majority of the items. Further, mixed-effects modeling revealed that L2 learners were comparable to native speakers in their judgments of the four frequency bands, although some differences did emerge. Taken together, the study provides new insights into the nature of L1 and L2 intuitions about phrasal frequency.

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