Very low frequency

About: Very low frequency is a research topic. Over the lifetime, 1540 publications have been published within this topic receiving 24233 citations. The topic is also known as: VLF.

Practical experience using VLF Tan Delta and partial discharge measurement in medium voltage cable

Abstract: Condition assessment of power cables is one of the most important tasks in maintenance and management of power networks. Significant investment has been made to ensure the reliability of cable systems. Very Low Frequency (VLF) test is an alternative method for 50 Hz AC voltage test. Using VLF voltage source, Tan Delta (TD) and Partial Discharge (PD) measurement can be carried out simultaneously. TD measurement is a nondestructive integral test to assess the overall cable condition, while PD measurement can be used to localize defects that generate electric discharge activities. This paper focuses on the practical experience using combined VLF testing with TD and PD to assess health condition and localize defects in medium voltage cables. Field experience with VLF TD and PD will be shared. Detailed testing and evaluation technique will be described.

Discovery and insights from DSX mission’s high-power VLF wave transmission experiments in the radiation belts

Abstract: Space weather phenomena can threaten space technologies. A hazard among these is the population of relativistic electrons in the Van Allen radiation belts. To reduce the threat, artificial processes can be introduced by transmitting very-low-frequency (VLF) waves into the belts. The resulting wave-particle interactions may deplete these harmful electrons. However, when transmitting VLF waves in space plasma, the antenna, plasma, and waves interact in a manner that is not well-understood. We conducted a series of VLF transmission experiments in the radiation belts and measured the power and radiation impedance under various frequencies and conditions. The results demonstrate the critical role played by the plasma-antenna-wave interaction around high-voltage space antennae and open the possibility to transmit high power in space. The physical insight obtained in this study can provide guidance to future high-power space-borne VLF transmitter developments, laboratory whistler-mode wave injection experiments, and the interpretation of various astrophysical and optical phenomena.

Exit Areas of VLF Waves Inferred from the Multistation Measurements at Roberval, Canada

Abstract: The characteristics of the wave exit area on the lower boundary of the ionosphere is inferred from the distribution of the magnetic intensities of the VLF waves simultaneously received at six observation stations near the Siple conjugate point at Roberval in Canada on July 23, 1979. In order to estimate the characteristics of the wave exit area, we have to make some assumptions about the conditions of the input wave injected to it and the propagation mechanism in free space. Applying the principle of Huygence for electromagnetic wave in free space to the wave radiated from the exit area, we compute the distributions of the wave magnetic intensity on the ground. By a least square technique, we infer the location and shape of the exit area making the wave intensity distribution observed on the ground. The obtained results are as follows. It was found that three wave exit areas at least existed over the observation station network. It was confirmed that the signals radiated from the Siple transmitter (Siple waves) were propagated along the ducts in the magnetosphere. The wave exit areas were generally elongated in the east-west direction, suggesting that the shapes of the ducts are also elongated in the east-west direction.

Navigation using VLF environmental features

Abstract: This paper examines the use of Very Low Frequency (VLF) electromagnetic signals to perform location estimation with-out any knowledge of the source of the VLF signal or their interaction with the environment. Signals were collected from different locations in a variety of indoor environments. The signals are divided into equal time length segments and processed into feature sets. A logistic regression and an Ar-tificial Neural Network are then both trained on the sample statistics to give a set of parameters to return likelihood of each locations with the correct location being determined as the position with the highest likelihood. This approach using either method achieved an error of less than 1% for 17 locations recorded for 10 minutes each.

Observations on GEOS-1 of whistler mode turbulence generated by a ground-based VLF transmitter

Abstract: Signals launched by the NLK Jim Creek transmitter in Alaska on 18.60 and 18.65 kHz have been observed on GEOS-1. Data for one pass over Alaska on June 11, 1977, are presented here. The peak amplitude of the signals is ∼5 pT (0.6 mV/m), which is received when the satellite is close to exact conjugacy at 7500 km altitude. While the weaker signals received at some distance from conjugacy behave as expected from linear theory, the stronger signals received closer to conjugacy have features which indicate that some non-linear process is active. These features are: 1) a turbulent electric frequency spectrum 2) an increased electrostatic character of the waves. The threshold field amplitude of the supposed (but unidentified) non-linear interaction is ∼1 pT.