Single Parabolic Reflector Research Articles

A high-power ultrasonic transducer operated in MHz range by circular plate bending mode using a single parabolic reflector

This research developed a HF, high-power ultrasonic transducer. Operating at 1.54 MHz, the transducer generated plane waves through the excitation of the thickness mode of a piezoelectric ring. These waves are subsequently focused by a parabolic reflector, exciting the bending mode of a circular plate and yielding substantial mechanical output at the center. Under a driving voltage of 48 Vpp, the transducer achieved a saturation velocity of 11.7 mpp/s. The mechanical quality factor ( Qm ) of the resonant mode is calculated using the half-power bandwidth method, resulting in a value of approximately 1250. The proposed transducer exhibits outstanding performance and holds promising applications in the fields of biology, medicine, and sonochemistry.

A K / Ka ‐band dielectric and metallic 3D printed aperture shared multibeam parabolic reflector antenna for satellite communication

A K/Ka-band (22-33 GHz) high-gain aperture shared multibeam parabolic reflector antenna is proposed. It performs a two-dimensional beam scanning from a shared single parabolic reflector by introducing off-focal feeds. The feed array is placed on and off the focal of the parabolic reflector. Traditionally, the feed blockage has a great impact on the performance of the antenna, which reduces the gain and increases the sidelobe level. The purpose of this paper is to suppress the negative effects of feed blockage by using hybrid material processing method. Both dielectric and metallic 3D printing technologies are used for antenna fabrication. The parabolic reflector antenna is printed by selective laser melting using aluminum alloy. The feed array and the supporting structures are printed by stereolithography apparatus in resin to control the blockage. The method helps to suppress the sidelobe level from −10 to −15 dB and to enhance gain by up to 2.3 dBi. The reflection coefficient is less than −10 dB, while the coupling coefficient between the ports is less than −20 dB over the entire designed band. At 31.5 GHz, the simulated maximum gain of the antenna are 30.7, 29.1, and 29.7 dBi, when different port separately excites. Multiple beams at ±15° and 0° are observed on both E- and H-planes. Besides, it also verifies the possibility to use dielectric and metallic 3D printing technologies in hybrid for microwave device fabrication.

Design and Performance of a 1.5 axis Sun tracking Concentrated Photovoltaic System

This paper reports the design and testing of a concentrated solar photovoltaic thermal (CSPVT) system. The system consists of the PV panel, its cooling system, the parabolic concentrator, and the sun tracking mechanism. Photo Voltaic Thermal (PVT) systems are already a promising technique for improving energy yields and efficiencies of PV panels. The current work adds a concentration effect to make further improvements, especially on yields. Unlike the case of other research which uses plane mirrors along the sides of PV panels, this work employs a single parabolic reflector of concentration ratio 1.3, integrated with the panel mounting. A cooling system is also integrated with the mounting, so that the specially designed sun tracking mechanism turns the entire assembly, keeping both panel and reflector facing the sun without affecting the coolant flow in the adjoining pipes. This is one of the novelties of this work. We use vertical axis tracking but with seasonal adjustment of tilt. Hence the 1.5 axis in the title of this paper. Southern hemisphere spring tests in Cape Town showed a 60.2% electric power gain when compared with yields from an identical fixed panel. We also develop and test a MATLAB program using actual weather data for the experimentation period, and do a TRNSYS simulation using the software’s embedded TMY (typical meteorological year) weather data for the period. We find MATLAB results to be closer to experimental ones, while TRNSYS ones are not far out on totals. We conclude that CSPVT has much potential to increase both yields and efficiencies. In addition, we suggest that TRNSYS simulation would probably be most useful in cases where actual weather data is not available.

Along‐track SAR interferometry using a single reflector antenna

A method to generate several phase centres on a single parabolic reflector antenna fed by a digital beamforming array is presented. Among other applications, along-track SAR interferometry at higher frequencies, as for example, in the Ka-band, is considered. Flexibility in size, position and amount of phase centres is similar as for a setup using a direct radiating array.

On the use of antenna weight functions in field strength prediction and interference reduction

In this paper two methods for calculating the received electromagnetic field by a single-parabolic reflector antenna in the shadow region behind a finite-width screen are proposed and analysed. The first one is referred to as the far-field approach and treats the obstacle and reflector antenna diffraction separately. The antenna simply is replaced by a point source having the receiving properties of the reflector antenna considered. The second method is called the near-field approach and considers the combined effect of obstacle and antenna diffraction. It is shown that considerable differences between the results of both methods may exist, even for an obstacle-antenna separation large compared to the Rayleigh distance of the antenna, and both for a CW and broadband analysis of the communications channel. It is concluded that the near-field method gives the best results and can be applied to many practical problems such as interference reduction and searching the optimal position of VSATs in urban environments.

Acoustic daylight: Imaging the ocean with ambient noise.

For many years the principal means of probing the ocean using sound has been through the use of either ‘‘active’’ or ‘‘passive’’ techniques. With an active system, an object is illuminated by a pulse of sound and its presence inferred from the echo it produces, whereas the passive approach involves simply listening for the sound that the object itself emits. Here a new method of employing sound in the ocean is reported, which is neither passive nor active. It relies on the naturally occurring, incoherent ambient noise field in the ocean as the sole source of acoustic illumination. By analogy with daylight in the atmosphere, ambient noise scattered from an object in the ocean can be focused onto an image plane, and from this acoustic image, with appropriate signal processing, a visual image can be produced on a television-type monitor of the object space in the ocean. To test this concept, several simple experiments have been conducted in the ocean off Scripps pier, with a single parabolic reflector acting as an acoustic lens, which confirm that objects illuminated only by ambient noise can indeed be ‘‘seen’’ over a frequency band between 5 and 50 kHz. [Work supported by ONR.]

Quasi-optical antennas for plasma scattering

Two types or quasi-optical antennas are examined for their suitability as a means of directing the radiation from a tunable gyrotron millimetre-wave source into a plasma for scattering. The first type of antenna has a single parabolic reflector. The second has two reflectors; the first elliptical, the second parabolic. This combination has the advantage of focusing the beam into a spot at the centre of the plasma.