Wyniki wyszukiwania - Biblioteka Nauki

Nowa wersja platformy, zawierająca wyłącznie zasoby pełnotekstowe, jest już dostępna.
Przejdź na https://bibliotekanauki.pl

Ograniczanie wyników

Znaleziono wyników: 2

Liczba wyników na stronie

Wyniki wyszukiwania

Wyszukiwano:
w słowach kluczowych: near-field

Sortuj według:

Ogranicz wyniki do:

The influence of the frequency‑dependent spherical‑wave effect on the near‑surface attenuation estimation

100%

Ji Y. , Wang S. , Yuan S. , Yan B.

tom Vol. 67, no. 2

577--587

The knowledge of Q is desirable for improving seismic resolution, facilitating amplitude analysis and seismic interpretation. The most commonly used methods for Q estimation are the frequency-spectrum-based methods. Generally, these methods are based on the plane wave theory assuming that the transmission/reflection loss is frequency independent. This assumption is reasonable in the far-field situation and makes the transmission/reflection coefficient irrelevant with the Q estimation result. However, in the near-surface context, this assumption is invalid because the seismic wave propagates in the form of spherical wave in the real seismic surveys and the spherical-wave transmission/reflection coefficient is frequency dependent. As a result, deviation will exist. In this paper, the influence of the spherical-wave effect on the Q estimation in the near-surface context was proved in both synthetic data and field data for the first time, and it was found that the deviation due to the sphericalwave effect is of order comparable to the intrinsic attenuation. The compensation method based on the forward modeling is then proposed to correct this deviation, and the effectiveness of the proposed method is proved by the reasonable estimated results of both synthetic data and field data example. These results raise caution for the interpretation of the extracted Q in the near-surface context if they do not account for the spherical-wave effect and point to the necessity of incorporating a frequency-dependent term in the frequency-spectrum-based method when applied to the Q estimation in the near surface.

Pomiary charakterystyk anten w strefie bliskiej

84%

Pyszak S. , Wnuk M.

tom Vol. 48, nr 12

80-85

Przedstawiono podstawy teoretyczne pomiarów anten w strefie bliskiej. Omówiono zaprojektowane, zestawione i uruchomione stanowisko do pomiaru anten w polu bliskim metodą planarną, kartezjańską z wykorzystaniem komory bezodbiciowej. Uzyskane dane pomiarowe przeliczono w specjalnie opracowanym w środowisku Matlab programie matematycznym. Obliczone wartości pola w strefie dalekiej zostały przekształcone do postaci umożliwiającej prezentację w formie przekroju przestrzennej charakterystyki promieniowania anteny. Wyliczone charakterystyki promieniowania zostały porównane do wyników pomiarów przeprowadzonych w polu dalekim. Uzyskano dużą zgodność wyników.

The paper presents the theory basis of antenna radiation pattern measurements in the near-field. The designed and implemented in ane-choic chamber laboratory stand for antenna pattern measurements in the near field is described. For antenna pattern calculation the "planar" and cartesian method is used. The obtained measurements results are recalculated using Matlab specialized software. The calculated field values in the far field are converted into sectional view of three-dimensional antenna pattern form. The calculated antenna patterns basing on measurements in near-field are compared with the result of antenna pattern measurements in far-field. The big correlation of results is obtained.