High frequency component of terahertz-radiation spectrum enhanced by using an excitation source with short pulse duration on an n-type InAs immersed in magnetic field

In August–September, 2018 in the Pechora Sea during the 38th flight of NIS “Academician Nikolay Strakhov” complex geologic-geophysical researches were conducted. Magnetic survey was carried out along with seismic profiling where as the radiator of elastic fluctuations the electrospark Sparker radiator was used. The group of a sea magnetometry was faced by a problem of mapping of the top layer of a sedimentary cover, including allocation of zones of development of thin deposits, buried paleochannels, zones of jointing and geological explosive violations. Hydromagnetic survey and interpretation of the received materials was as a result executed that allowed to estimate spectral structure of the abnormal magnetic field (AMF) and to allocate three frequency components to which there corresponds the deep range of sources of the field. Leaning on the received estimates of depths, and comparing them to the description of wells, also temporary bindings for the allocated deep ranges of sources of magnetic field were defined. High-frequency component, there corresponds the arrangement of sources of AMF in the topmost part of a section. The top edges of sources lie in the range of depths from 35 to 70 m that possibly correspond to deposits of pleystotsenovy age. It is possible that the thin deposits created during the last Valdai freezing can be sources of these high-frequency anomalies. The second deep range is created by sources of AMF the top edges of which are located in the range of depths of 260–510 m that possibly corresponds to stratigrafichesky range from top Yura to the lower chalk. The third, the deep range of bedding of the top edges of sources of AMF allocated by authors is determined by the most low-frequency part of a range and according to authors reflects the late Devonian stage of activization of magmatism.

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A Topological Model of the Solar Magnetic Field Reversals

International Astronomical Union Colloquium ◽

10.1017/s0252921100079677 ◽

1991 ◽

Vol 130 ◽

pp. 234-236

Author(s):

E.E. Benevolenskaya

Keyword(s):

Magnetic Field ◽

Magnetic Fields ◽

High Frequency ◽

Low Frequency ◽

Frequency Component ◽

High Frequency Component ◽

Time Interval ◽

Solar Cycles ◽

Polarity Reversals ◽

Odd Cycles

The phenomenon of a three-fold reversal of the solar polar magnetic field in both hemispheres has not been observed during the last 115 years. Such three-fold reversals took place in the southern hemisphere alone in the even cycles Nos 12 (1885.8), 14 (1908.4) and in the northern hemisphere alone in solar cycles Nos 16 (1928.5), 18 (1949.0), 20 (1970.6). The single reversal took place in the odd cycles, the only exception is the solar cycle No 19 (Fig. 1).There are periods of 1.7-2.5 years in the variation of background magnetic fields (Makarov et al., 1985). It determines the quasi-period of the high-frequency component and corresponds to a time interval between the zones of alternating polarity of the magnetic field. This enables us to show topologically that single and three-fold polarity reversals of the solar magnetic fields can result from interaction of two types of magnetic fields: a low-frequency component with period of the order of 20 years and a high frequency component with period of order of 1.7-2.5 years (Benevolenskaya and Makarov, 1990).

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Laser-Generated Ultrasonic Technique for Inspecting Delamination in CFRP

Key Engineering Materials ◽

10.4028/www.scientific.net/kem.321-323.968 ◽

2006 ◽

Vol 321-323 ◽

pp. 968-971

Author(s):

Won Su Park ◽

Sang Woo Choi ◽

Joon Hyun Lee ◽

Kyeong Cheol Seo ◽

Joon Hyung Byun

Keyword(s):

High Frequency ◽

Ultrasonic Method ◽

Piezoelectric Sensor ◽

Frequency Component ◽

Guided Wave ◽

Center Frequency ◽

High Frequency Component ◽

Ultrasonic Technique ◽

Non Destructive Evaluation ◽

Non Destructive

For improving quality of a carbon fiber reinforced composite material (CFRP) by preventing defects such as delamination and void, it should be inspected in fabrication process. Novel non-contacting evaluation technique is required because the transducer should be contacted on the CFRP in conventional ultrasonic technique during the non-destructive evaluation and these conventional contact techniques can not be applied in a novel fiber placement system. For the non-destructive evaluation of delamination in CFRP, various methods for the generation and reception of laser-generated ultrasound are applied using piezoelectric transducer, air-coupled transducer, wavelet transform technique etc. The high frequency component of laser-generated guided wave received with piezoelectric sensor disappeared after propagating through delamination region. Air-coupled transducer was tried to be adopted in reception of laser-generated guided wave generated by using linear slit array in order to generate high frequency guided wave with a frequency of 1.1 MHz. Nevertheless, it was failed to receive high frequency guided wave in using air-coupled transducer and linear slit array. Transmitted laser-generated ultrasonic wave was received on back-wall and its frequency was analyzed to establish inspecting technique to detect delamination by non-contact ultrasonic method. In a frequency spectrum analysis, intensity ratio of low frequency and center frequency was approvable parameter to detect delamination.

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