| 651. |
- Larsson, Christer, et al.
(författare)
-
Measuring the extinction cross section
- 2009
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Ingår i: [Host publication title missing]. - 9781424447534 ; , s. 3510-3513
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Konferensbidrag (refereegranskat)abstract
- This paper describes a method to determine the extinction cross section for a very large bandwidth in the microwave region. The method is based on measurements of the radar cross section in the forward direction to calculate the extinction cross section. The method is applicable to samples of arbitrary shape and composition. Coherent background subtraction and time domain gating is used for the frequency range [2.5, 38] GHz to increase the sensitivity. The efficiency of the background subtraction and the accuracy of the measurements are estimated.
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| 652. |
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| 653. |
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| 654. |
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| 655. |
- Larsson, Christer, et al.
(författare)
-
Wideband Measurements of the Forward RCS and the Extinction Cross Section
- 2013
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Ingår i: Applied Computational Electromagnetics Society Journal. - 1054-4887. ; 28:12, s. 1145-1152
-
Tidskriftsartikel (refereegranskat)abstract
- This paper describes the development of a method based on measurements of the radar cross section (RCS) amplitude and phase in the forward direction to determine the extinction cross section for the 2.5 GHz - 38 GHz frequency range using the optical theorem. Forward RCS measurements are technically complicated due to that the direct signal has to be subtracted from the total signal at the receiving antenna in order to extract the forward RCS. The efficiency of this subtraction as a function of time is evaluated. A traditional calibration method using a calibration target and a second method that does not require a calibration target are investigated and compared. The accuracy of the forward RCS measurements is determined using small spheres of different sizes. The spheres have a forward RCS that is straight forward to calculate with good accuracy. The method is also extended to polarimetric measurements on a small helix that are compared with method-of-moments calculations to validate the method.
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| 656. |
- Larsson, Christer, et al.
(författare)
-
Wideband Measurements of the Forward RCS and the Extinction Cross Section
- 2012
-
Ingår i: [Host publication title missing]. ; , s. 1-6
-
Konferensbidrag (refereegranskat)abstract
- This paper describes the development of a method based on measurements of the radar cross section (RCS) in the forward direction to determine the extinction cross section for the 2.5 – 38 GHz frequency range. A conventional anechoic chamber designed for monostatic measurements is used for forward RCS measurements. The extinction cross section is then calculated from the measured forward RCS using the optical theorem. The motivation for this study is to develop an experimental method that can be used to verify recent theoretical work which shows that the extinction cross section integrated over all frequencies is related to the static properties of the scatterer. Forward RCS measurements are technically complicated due to the large direct contribution from the transmitting antenna to the received signal. The direct signal has to be subtracted from the total signal at the receiving antenna in order to extract the forward RCS. The efficiency of this subtraction is evaluated in this study by performing long time measurements leading to an estimation of subtraction accuracy as a function of the time between the two measurements. Two calibration methods are investigated. The first method is the traditional calibration method used in most RCS measurements. It uses a target with known RCS as a calibration target to calibrate the target measurement. The second method that is described here does not require a calibration target. It uses a direct path measurement of the signal to calibrate the target measurement. To the best of our knowledge, the latter method is not in frequent use in the RCS community. The accuracy of the method is determined using small spheres of different sizes which have a forward RCS that is straightforward to calculate using the Mie series. The method described here is also extended to polarimetric measurements of the forward RCS and hence the possibility to determine the extinction cross section for arbitrarily polarized incident radiation. This is tested using measurements on a small helix coil and comparing with method of moments calculations.
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| 657. |
- Larsson, Christer, et al.
(författare)
-
Wideband microwave measurements of the extinction cross section---Experimental techniques
- 2009
-
Rapport (övrigt vetenskapligt/konstnärligt)abstract
- This paper describes the development of a method to determine the extinction cross section for a very large bandwidth in the microwave region. The method is based on measurements of the radar cross section in the forward direction to calculate the extinction cross section for the frequency range [2.5,38] GHz. The method is applicable to samples of arbitrary shape and composition and can also be used for polarimetric measurements. Coherent background subtraction is used to remove the contribution from antenna to antenna coupling. Time domain gating is employed to increase the sensitivity. Different calibration methods are discussed. The efficiency of the background subtraction and the accuracy of the measurements are estimated.
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| 658. |
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| 659. |
- Leijon, Mats, et al.
(författare)
-
Wave Energy from the North Sea : Experiences from the Lysekil Research Site
- 2008
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Ingår i: Surveys in geophysics. - : Springer Science and Business Media LLC. - 0169-3298 .- 1573-0956. ; 29:3, s. 221-240
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Forskningsöversikt (refereegranskat)abstract
- This paper provides a status update on the development of the Swedish wave energy research area located close to Lysekil on the Swedish West coast. The Lysekil project is run by the Centre for Renewable Electric Energy Conversion at Uppsala University. The project was started in 2004 and currently has permission to run until the end of 2013. During this time period 10 grid-connected wave energy converters, 30 buoys for studies on environmental impact, and a surveillance tower for monitoring the interaction between waves and converters will be installed and studied. To date the research area holds one complete wave energy converter connected to a measuring station on shore via a sea cable, a Wave Rider™ buoy for wave measurements, 25 buoys for studies on environmental impact, and a surveillance tower. The wave energy converter is based on a linear synchronous generator which is placed on the sea bed and driven by a heaving point absorber at the ocean surface. The converter is directly driven, i.e. it has no gearbox or other mechanical or hydraulic conversion system. This results in a simple and robust mechanical system, but also in a somewhat more complicated electrical system.
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| 660. |
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