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Electromagnetic Diffraction from a Metallic Spherical Cavity.
Published in S. S. Vinogradov, P. D. Smith, E. D. Vinogradova, Canonical Problems in Scattering and Potential theory Part II, 2002
S. S. Vinogradov, P. D. Smith, E. D. Vinogradova
A study of the focal region is essential for the proper design of any focusing system. Theoretically, the best shape of a reflector is parabolic. From a geometric optics perspective, any bundle of parallel rays reflected from the concave surface of a parabolic mirror, collects at the same point of the optical axis, the focus. However, in practice, instead of focusing to a single point, the rays concentrate in a region known as the focal spot. In better designs, the extent of this spot is about a wavelength. However the centre of the spot is usually shifted some distance from the focal point predicted by GO, even for the supposedly ideal parabolic dish (albeit of finite extent).
Antennas
Published in Mike Tooley, David Wyatt, Aircraft Communications and Navigation Systems, 2017
The principle of the parabolic reflector antenna is shown in Figure 2.27. Signals arriving from a distant transmitter will be reflected so that they pass through the focal point of the parabolic surface (as shown). With a conventional parabolic surface, the focal point lies directly on the axis directly in front of the reflecting surface. Placing a radiating element (together with its supporting structure) at the focal point may thus have the undesirable effect of partially obscuring the parabolic surface! In order to overcome this problem the surface may be modified so that the focus is offset from the central axis.
Luminaires
Published in J. R. Coaton, A. M. Marsden, Lamps and Lighting, 2012
The parabola is the most commonly used reflector contour: it is defined by the equation y2 = 4ax (Figure 18.8), where a is the shortest distance of the focal point to the reflector, i.e. the focal length of the parabola. The most important property of the parabolic reflector is that if a point source is placed at its focus a parallel beam of light is obtained.
Atmospheric water generation from desiccants using solar passive thermal collectors: a review
Published in International Journal of Ambient Energy, 2023
Rahul Srivastava, Avadhesh Yadav
Another experiment on water generation through solar concentrators was done by Elashmawy and Alshammari (2020). Elashmawy (2019) already used a tubular solar still (TSS) system to produce water from composite desiccant of black cotton cloth filled with CaCl2 solution. He modified his tubular solar still system and added a parabolic concentrator to increase the temperature of the absorber to produce more water from the composite desiccant. This system is shown in Figure 11. The tubular solar still was kept at the line of focus of the parabolic concentrator. This system produced 0.51 L/kg of CaCl2. Due to the addition of a parabolic concentrator, the efficacy and productivity of TSS were increased by 82.3% and 292.4% respectively. Water was generated from the air in extremely low humidity (16%) region. This is a remarkable advantage of this system and can be a good option for arid regions. The water generation cost of this system is also low, i.e. $0.15/L.
High resolution FTIR and diode laser spectroscopy of trifluoromethylacetylene and tetrafluoromethane in a supersonic jet expansion
Published in Molecular Physics, 2022
M. Caviezel, V. Horká-Zelenková, G. Seyfang, M. Quack
Figure 2 shows a block diagram of the diode laser spectrometer. As a light source we use different lead-salt tunable diode lasers (TDL, Laser Analytics) emitting in the infrared spectral range from 600 to 3300 cm. The laser diode is mounted in a laser head connected with a helium cryostat. The laser frequency is controlled by the diode temperature and the laser current. The minimum temperature which can be reached with the cryostat is T = 10 K. Due to the short cavity and diffraction effects the laser beam of the TDL usually shows a quite strong divergence. To obtain a parallel beam the laser diode is placed in the focus of a parabolic mirror (OAP1) [89]. Removing the folding mirror M1 the laser beam is made parallel through the two apertures A1 and A2 and which is then focussed by the parabolic mirror OAP2 to the detector D1. The beam will stay close to parallel when the diode laser is in the focus of the parabolic mirror OAP1. The divergence of the beam depends on the type of the laser and the laser parameters (temperature, laser current).
Thermal performance of the steam boiler based on Scheffler solar concentrator for domestic application: Experimental investigation
Published in Australian Journal of Mechanical Engineering, 2021
Vikrant Kamboj, Himanshu Agrawal, Anish Malan, Avadhesh Yadav
Solar energy is one of the substantial, reliable renewable power resources which can perform an essential role in matching the increasing energy demand and protect the depleting fossil fuel resources. Solar concentrators are mainly used to concentrate solar energy for high and medium temperature for thermal applications or power generation. Based on the type of focus, solar concentrators can be classified as line-focus concentrators like a parabolic trough, linear Fresnel lens or point-focus concentrators like the solar dish, Scheffler solar concentrator. A Scheffler solar concentrator is a lateral section of the paraboloid which includes reflecting surface, a receiver, manual tracking system, thermal energy utilisation system and the working fluid which transfer the heat. The entire radiations incident on the reflecting surface is reflected towards the focus. The working fluid in the receiver placed at the focus of the reflecting surface receives concentrated solar energy.