scholarly journals Analysis and Design of Absorbers for Electromagnetic Compatibility Applications

2021 ◽  
Author(s):  
Shiva Hayati Raad
Keyword(s):  
Electromagnetic Compatibility ◽  
Wave Spectrum ◽  
Low Frequency ◽  
Microwave Frequency ◽  
Frequency Range ◽  
Analysis And Design ◽  
Matching Layer ◽  
Pyramidal Absorbers ◽  
Graphene Material ◽  
Carbon Loading

Absorbers are one of the key components in the realm of electromagnetic compatibility. Depending on the frequency range of interest, different types of absorbers can be utilized for this purpose. This chapter introduces the analysis and modeling of ferrite-based absorbers for low-frequency applications (below 1 GHz) and discusses the issues encountered in their installation, resulting in air gaps. Later, different kinds of pyramidal absorbers, commonly used in the broadband microwave frequency range (above 1 GHz), are presented, and analytical and numerical approaches for predicting their performance are reviewed. The combination of the ferrite tile and pyramidal dielectric absorbers is also provided. Then, some practical aspects of designing hybrid absorbers, including the influence of carbon loading and matching layer on their performance, are mentioned. Finally, the absorber operating frequency extension to the millimeter-wave spectrum using metamaterial structures or graphene material is presented.

Dielectric Studies of Binary Mixtures of 1-Propanol and Fluorobenzene

2013 ◽  
Vol 209 ◽  
pp. 203-206 ◽  
Author(s):  
Ashvin N. Prajapati ◽  
Vipinchandra A. Rana ◽  
A.D. Vyas ◽  
S.P. Bhatanagar ◽  
D.H. Gadani
Keyword(s):  
Dielectric Constant ◽  
Binary Mixtures ◽  
Complex Permittivity ◽  
High Frequency ◽  
Low Frequency ◽  
Microwave Frequency ◽  
Static Dielectric Constant ◽  
Frequency Range ◽  
Optical Dielectric Constant ◽  
Optical Dielectric

Complex permittivity spectra of 1-Propanol (1-PrOH), Fluorobenzene (FB) and their binary mixtures are obtained in radio and microwave frequency range using Vector network analyzer (VNA) operating in the frequency range 0.3 MHz to 3.0 GHz and standard microwave benches operated at 9.1 GHz and 19.61 GHz. Static dielectric constant (ε0) and high frequency limiting dielectric constant (ε∞1) for binary mixtures of 1-PrOH and FB are obtained by extrapolating the complex permittivity data towards low frequency side and high frequency side on complex plane plots. Optical dielectric constant (ε∞ = n2) for binary mixtures are measured using Abbe's refractometer. Excess static dielectric constant (ε0)E, Kirkwood correlation parameters (g, geff and gf) and Bruggeman factor (fB) are determined from the values of static dielectric constant (ε0) and optical dielectric constant (ε∞). These parameters have been discussed to explore the molecular interaction between the molecular species.

scholarly journals Optimized 3-D electromagnetic models of composite materials in microwave frequency range: application to EMC characterization of complex media by statistical means

2017 ◽  
Vol 6 (2) ◽  
pp. 46
Author(s):  
S. Lalléchère
Keyword(s):  
Composite Materials ◽  
Electromagnetic Compatibility ◽  
Microwave Frequency ◽  
Electromagnetic Modeling ◽  
Shielding Effectiveness ◽  
Frequency Range ◽  
Homogenization Model ◽  
Electromagnetic Models ◽  
Electromagnetic Mixing

The aim of this proposal is to demonstrate the ability of tridimensional (3-D) electromagnetic modeling tool for the characterization of composite materials in microwave frequency band range. Indeed, an automated procedure is proposed to generate random materials, proceed to 3-D simulations, and compute shielding effectiveness (SE) statistics with finite integration technique. In this context, 3-D electromagnetic models rely on random locations of conductive inclusions; results are compared with classical electromagnetic mixing theory (EMT) approaches (e.g. Maxwell-Garnett formalism), and dynamic homogenization model (DHM). The article aims to demonstrate the interest of the proposed approach in various domains such as propagation and electromagnetic compatibility (EMC).

scholarly journals Electromagnetic Properties of Carbon Gels

Materials ◽  
2019 ◽  
Vol 12 (24) ◽  
pp. 4143 ◽  
Author(s):  
Jimena Castro-Gutiérrez ◽  
Edita Palaimiene ◽  
Jan Macutkevic ◽  
Juras Banys ◽  
Polina Kuzhir ◽  
...  
Keyword(s):  
Electrical Conductivity ◽  
Dielectric Permittivity ◽  
Low Frequency ◽  
Microwave Frequency ◽  
Power Laws ◽  
Wide Frequency Range ◽  
Electromagnetic Properties ◽  
Frequency Range ◽  
Carbon Gels ◽  
Electrical Conductivities

The electromagnetic properties of various carbon gels, produced with different bulk densities, were investigated in a wide frequency range (20 Hz–36 GHz). The values of dielectric permittivity and electrical conductivity at 129 Hz were found to be very high, i.e., more than 105 and close to 100 S/m, respectively. Both strongly decreased with frequency but remained high in the microwave frequency range (close to 10 and about 0.1 S/m, respectively, at 30 GHz). Moreover, the dielectric permittivity and the electrical conductivity strongly increased with the bulk density of the materials, according to power laws at low frequency. However, the maximum of microwave absorption was observed at lower densities. The DC conductivity slightly decreased on cooling, according to the Arrhenius law. The lower activation energies are typical of carbon gels presenting lower DC electrical conductivities, due to a higher number of defects. High and thermally stable electromagnetic properties of carbon gels, together with other unique properties of these materials, such as lightness and chemical inertness, open possibilities for producing new electromagnetic coatings.

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.

Dynamic Damping and Stiffness Characteristics of the Rolling Tire

2001 ◽  
Vol 29 (4) ◽  
pp. 258-268 ◽  
Author(s):  
G. Jianmin ◽  
R. Gall ◽  
W. Zuomin
Keyword(s):  
Dynamic Behavior ◽  
Variable Parameter ◽  
Low Frequency ◽  
Vertical Load ◽  
Frequency Range ◽  
Inflation Pressure ◽  
Vehicle Simulation ◽  
Dynamic Damping ◽  
Speed Range ◽  
Stiffness Characteristics

Abstract A variable parameter model to study dynamic tire responses is presented. A modified device to measure terrain roughness is used to measure dynamic damping and stiffness characteristics of rolling tires. The device was used to examine the dynamic behavior of a tire in the speed range from 0 to 10 km/h. The inflation pressure during the tests was adjusted to 160, 240, and 320 kPa. The vertical load was 5.2 kN. The results indicate that the damping and stiffness decrease with velocity. Regression formulas for the non-linear experimental damping and stiffness are obtained. These results can be used as input parameters for vehicle simulation to evaluate the vehicle's driving and comfort performance in the medium-low frequency range (0–100 Hz). This way it can be important for tire design and the forecasting of the dynamic behavior of tires.

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.

A waveform inversion technique for measuring elastic wave attenuation in cylindrical bars

Geophysics ◽  
1992 ◽  
Vol 57 (6) ◽  
pp. 854-859 ◽  
Author(s):  
Xiao Ming Tang
Keyword(s):  
Elastic Wave ◽  
Wave Attenuation ◽  
Waveform Inversion ◽  
Finite Size ◽  
Low Frequency ◽  
Frequency Range ◽  
Multiple Reflections ◽  
Low Frequencies ◽  
The Time Domain ◽  
Attenuation Values

A new technique for measuring elastic wave attenuation in the frequency range of 10–150 kHz consists of measuring low‐frequency waveforms using two cylindrical bars of the same material but of different lengths. The attenuation is obtained through two steps. In the first, the waveform measured within the shorter bar is propagated to the length of the longer bar, and the distortion of the waveform due to the dispersion effect of the cylindrical waveguide is compensated. The second step is the inversion for the attenuation or Q of the bar material by minimizing the difference between the waveform propagated from the shorter bar and the waveform measured within the longer bar. The waveform inversion is performed in the time domain, and the waveforms can be appropriately truncated to avoid multiple reflections due to the finite size of the (shorter) sample, allowing attenuation to be measured at long wavelengths or low frequencies. The frequency range in which this technique operates fills the gap between the resonant bar measurement (∼10 kHz) and ultrasonic measurement (∼100–1000 kHz). By using the technique, attenuation values in a PVC (a highly attenuative) material and in Sierra White granite were measured in the frequency range of 40–140 kHz. The obtained attenuation values for the two materials are found to be reliable and consistent.

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