Analysis of the Electromagnetic Spectrum under the Extremely Low Frequency Band: Frequency Sub-Bands Classification

2017 ◽  
Author(s):  
Ante Salcedo ◽  
Elizabeth Martinez
Keyword(s):  
Frequency Band ◽  
Low Frequency ◽  
Electromagnetic Spectrum ◽  
Band Frequency ◽  
Extremely Low Frequency

Experimental Study of Jet Noise Characteristics of Series Connected Nozzles

2005 ◽  
Author(s):  
Qiang Xu
Keyword(s):  
Frequency Spectrum ◽  
Frequency Band ◽  
Low Frequency ◽  
Jet Noise ◽  
Steel Tube ◽  
The Other ◽  
Chamber Pressure ◽  
Band Frequency ◽  
Noise Characteristics ◽  
Frequency Peak

Put abstract text here. A serial of experiments were conducted to study the noise radiated from a series connected nozzle pair. The experiment results are presented in this paper. This nozzle pair consists of two nozzles, one is called source nozzle, and the other is a secondary nozzle. In these experiments, the structure of source nozzle was fixed while that of secondary nozzle was changeable. The source nozzle is mounted on a pressure chamber which is connected to an air compressor. A steel tube is fixed at the tail of source nozzle. The secondary nozzle is connected to the other end of the tube. Throat size of secondary nozzle is larger then that of source nozzle. 15 types of nozzles with different expansion ratio, length of expand segment, and throat structure were used as the secondary nozzle. Jet noise pressure of these nozzle pairs was measured by 40AF Free Field Microphone. The frequency spectrum of jet noise from source nozzle with steel tube under different chamber pressures was calculated. The pressure range is from 0.1 to 1.2 MPa. This result is compared with those spectrums of nozzle pair with different secondary nozzle under different chamber pressures. The trend of peak frequency shifts for different nozzle pair and different chamber pressure is presented in this paper. The secondary nozzles make frequency peak shift from the source nozzle, especially in low frequency band. Different structure of secondary nozzle has different influence on the frequency characteristics of jet noise. Length of expand segment has greater influence on low frequency peak than other two factors. Joint time-frequency analysis is also used in analyze the change of frequency spectrum during throat size decreased under fixed chamber pressure and various spectrograms are also presented. In low frequency band, frequency peak remains during the change of source nozzle throat size. But in higher frequency band, the frequency peak shifts from low frequency to higher ones as the throat size decreases.

scholarly journals Phenomena of electrostatic perturbations before strong earthquakes (2005–2010) observed on DEMETER

2012 ◽  
Vol 12 (1) ◽  
pp. 75-83 ◽  
Author(s):  
X. Zhang ◽  
X. Shen ◽  
M. Parrot ◽  
Z. Zeren ◽  
X. Ouyang ◽  
...  
Keyword(s):  
Frequency Band ◽  
Low Frequency ◽  
Coupling Mechanism ◽  
Operating Period ◽  
Strong Earthquakes ◽  
Extremely Low Frequency ◽  
Starting Point ◽  
The World ◽  
Median Level ◽  
Order Of Magnitude

Abstract. During the DEMETER operating period in 2004–2010, many strong earthquakes took place in the world. 69 strong earthquakes with a magnitude above 7.0 during January 2005 to February 2010 were collected and analysed. The orbits, recorded in local nighttime by satellite, were chosen by a distance of 2000 km to the epicentres during the 9 days around these earthquakes, with 7 days before and 1 day after. The anomaly is defined when the disturbances in the electric field PSD increased to at least 1 order of magnitude relative to the normal median level about 10−2μV2/m2/Hz at 19.5–250 Hz frequency band, and the starting point of perturbations not exceeding 10° relsupative to the epicentral latitude. Among the 69 earthquakes, it is shown that electrostatic perturbations were detected at ULF-ultra low frequency and ELF-extremely low frequency band before the 32 earthquakes, nearly 46%. Furthermore, we extended the searching scale of these perturbations to the globe, and it can be found that before some earthquakes, the electrostatic anomalies were distributed in a much larger area a few days before, and then they concentrated to the closest orbit when the earthquake would happen one day or a few hours later, which reflects the spatial developing feature during the seismic preparation process. The results in this paper contribute to a better description of the electromagnetic (EM) disturbances at an altitude of 660–710 km in the ionosphere that can help towards a further understanding of the lithosphere-atmosphere-ionosphere (LAI) coupling mechanism.

On the possibility of quasi-vertical radio sounding of the ionosphere in the extremely low frequency band

JETP Letters ◽  
2007 ◽  
Vol 85 (8) ◽  
pp. 386-388 ◽  
Author(s):  
E. D. Tereshchenko ◽  
V. F. Grigor’ev ◽  
A. E. Sidorenko ◽  
A. N. Milichenko ◽  
A. V. Mol’kov ◽  
...  
Keyword(s):  
Frequency Band ◽  
Low Frequency ◽  
Extremely Low Frequency ◽  
Radio Sounding

scholarly journals A Literature Review of Bimodal Fitting

2020 ◽  
Vol 16 (4) ◽  
pp. 265-275
Author(s):  
Junghwa Bahng ◽  
Soo Hee Oh
Keyword(s):  
Cochlear Implant ◽  
Frequency Band ◽  
Hearing Aid ◽  
Low Frequency ◽  
Balance Test ◽  
Band Frequency ◽  
Hearing Aid Fitting ◽  
Fitting Procedures ◽  
Band Adjustment ◽  
Bimodal Hearing

Although there are quite a few bimodal cochlear implant users, bimodal fitting guidelines were not fully developed. Bimodal fitting optimization is one of the factors that contribute to successful bimodal outcomes. The purpose of this study is to investigate recent literatures related to bimodal fitting to establish evidence based bimodal fitting guidelines. Three databases including Google Scholar, PubMed publisher, and PLOS One were searched to review bimodal fitting literatures. A total of 599,604 articles were identified by using ten bimodal relevant keywords at the initial stage. Then, we included 192 articles with abstract review, inclusion and exclusion criteria and removals of duplicates. Lastly, two authors reviewed full texts and identified a total of 19 bimodal fitting articles. Results were categorized into type of bimodal intervention, procedures, and outcomes. Bimodal fitting procedures, test materials, and questionnaires were also summarized. A total of 18 articles consist of bimodal hearing aid fitting covering hearing aid fitting formula, gain adjustment, loudness balance, frequency band, frequency lowering technology, and overall bimodal fitting guidelines. Only one article includes bimodal cochlear implant fitting with low frequency band adjustment. Several factors including real-ear measurement, loudness balance test, frequency band selection considering cochlear dead region, and subjective questionnaires are considered to optimize bimodal hearing aid fitting. Bimodal fitting guidelines considering several relevant factors will optimize bimodal fitting and improve bimodal benefits.

Extremely low frequency band gaps of beam-like inertial amplification metamaterials

2017 ◽  
Vol 31 (27) ◽  
pp. 1750251 ◽  
Author(s):  
Mingming Hou ◽  
Jiu Hui Wu ◽  
Songhua Cao ◽  
Dong Guan ◽  
Yanwei Zhu
Keyword(s):  
Frequency Band ◽  
Low Frequency ◽  
Band Gaps ◽  
Vibration Modes ◽  
Resonance Theory ◽  
Local Resonance ◽  
Extremely Low Frequency ◽  
Low Frequency Vibration ◽  
Potential Applications ◽  
Amplification Mechanism

In this paper, extremely low frequency band gaps of beam-like inertial amplification metamaterials are investigated based on local resonance theory. Inertial amplification mechanism is proposed to obtain extremely low frequency band gaps by altering geometry parameters of the beam-like structures rather than modulating material properties, which allow first lower band gap (BG) to be attained easily compared to traditional local resonance structures. Band structures, frequency response functions (FRFs) plots and vibration modes of the beam-like structures are calculated and analyzed by employing finite element method. Numerical results show that first BG of the structure ranges from 23 Hz to 21 Hz. FRFs are in accordance with the dispersion relationship. It is found that interaction between inertial amplification and traveling wave modes in the proposed structure are responsible for formation of the first BG. This type of beam-like inertial amplification metamaterials has many potential applications in the field of low frequency vibration and noise reduction.

Radiation and public health

2021 ◽  
pp. 437-456
Author(s):  
Leeka Kheifets ◽  
Adele Green ◽  
Richard Wakeford
Keyword(s):  
Ionizing Radiation ◽  
Human Exposure ◽  
Low Frequency ◽  
Electromagnetic Spectrum ◽  
X Rays ◽  
Radio Waves ◽  
Extremely Low Frequency ◽  
Subatomic Particles ◽  
Electric And Magnetic Fields ◽  
Ionizing Radiation Exposure

The electromagnetic spectrum encompasses frequencies that range from above approximately 1020 hertz (Hz) for ionizing radiation at the high end of the spectrum to static fields and power frequencies of 50–60 Hz at the low end. In order of decreasing frequency, the spectrum comprises gamma-rays, X-rays, ultraviolet radiation, visible light, infrared radiation, microwaves, radio waves and extremely low frequency electric and magnetic fields (ELF EMF). This chapter reviews sources and health effects of human exposure to radiation within the electromagnetic spectrum, and for ionizing radiation exposure to subatomic particles, as well as reviewing policies for limiting human exposure where appropriate.

Extremely low frequency band station for natural electromagnetic noise measurement

Radio Science ◽  
2015 ◽  
Vol 50 (3) ◽  
pp. 191-201 ◽  
Author(s):  
J. Fornieles-Callejón ◽  
A. Salinas ◽  
S. Toledo-Redondo ◽  
J. Portí ◽  
A. Méndez ◽  
...  
Keyword(s):  
Frequency Band ◽  
Low Frequency ◽  
Noise Measurement ◽  
Electromagnetic Noise ◽  
Extremely Low Frequency
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