Superimposition of a strong microwave signal on the laser injection current: spectral characteristics and impact on modal noise

1993 ◽  
Vol 5 (1) ◽  
pp. 13-16 ◽  
Author(s):  
C.M. Olsen
Keyword(s):  
Spectral Characteristics ◽  
Microwave Signal ◽  
Injection Current ◽  
Modal Noise

АКУСТИЧНА ПОМІТНІСТЬ БЕЗПІЛОТНИХ ЛІТАЛЬНИХ АПАРАТІВ З СИЛОВИМИ УСТАНОВКАМИ НА БАЗІ ПОРШНЕВИХ ДВИГУНІВ

2020 ◽  
pp. 62-80
Author(s):  
В. В. Руденко ◽  
И. В. Калужинов ◽  
Н. А. Андрущенко
Keyword(s):  
Control System ◽  
Internal Combustion Engine ◽  
Power Plants ◽  
Combustion Engine ◽  
Spectral Characteristics ◽  
Experimental Studies ◽  
Internal Combustion ◽  
Detection Range ◽  
Acoustic Signature ◽  
Static Conditions

The presence in operation of many prototypes of UAVs with propeller propellers, the use of such devices at relatively low altitudes and flight speeds makes the problem of noise reduction from UAVs urgent both from the point of view of acoustic imperceptibility and ecology.The aim of the work is to determine a set of methods that help to reduce the visibility of UAVs in the acoustic range. It is shown that the main source of noise from the UAV on the ground is the power plant, which includes the engine and the propeller. The parameters of the power plants influencing the processes that determine the acoustic signature of the UAV were investigated. A comprehensive analysis of the factors affecting visibility was carried out. The power plants include two-stroke and four-stroke engines, internal combustion and two-blade propellers. The use of silencers on the exhaust of the internal combustion engine was considered. The spectral characteristics of the acoustic fields of the propeller-driven power plants for the operating sample of the UAV "Eco" were obtained. The measurements were carried out in one-third octave and 1/48 octave frequency bands under static conditions. The venue is the KhAI airfield. Note that the propellers that were part of the power plants operated at Reynolds numbers (Re0,75<2*105), which can significantly affect its aerodynamic and acoustic characteristics. It is shown that when choosing a UAV control system, one should take into account the fact that two-stroke piston engines are the dominant source in the noise of propeller-driven control systems in the absence of a hood and mufflers in the intake and exhaust tracts. The use of a four-stroke internal combustion engine significantly reduces the noise of the control system. In the general case, the position of the boundaries of the zone of acoustic visibility of a UAV at the location of the observer is determined by the ratio between the intensity of acoustic radiation perceived by the observer from the UAV and the intensity of sound corresponding to the natural acoustic background and depends on the degree of manifestation of acoustic effects accompanying the propagation of sound in a turbulent atmosphere - the refraction of sound waves. Absorption and dissipation of acoustic energy. The calculation and comparison of the UAV detection range was carried out taking into account the existing natural maskers.The results of experimental studies are presented that allow assessing the degree of acoustic signature of the UAV. A set of measures aimed at reducing the intensity of the acoustic signature of the UAV in various regions of the radiation spectrum has been determined.

Double Beam Spectrophotometer for Simultaneous Measurements of the Upwelling Sea Radiance and the Incident See Irradiance

2019 ◽  
pp. 105-110
Author(s):  
Mikhail Yongon Lee ◽  
Sergei V. Fedorov
Keyword(s):  
Spectral Characteristics ◽  
Sea Surface ◽  
Input Port ◽  
Silicon Photodiode ◽  
New Approach ◽  
Surface Irradiance ◽  
Simultaneous Measurements ◽  
Double Beam

The article describes the structure and the operation principle of the spectrophotometer developed on the basis of a compact rapid monochromator with one input port and two output ports and a radiometric unit where upwelling radiation radiance and sea surface irradiance channels are located. A new approach to measurements of spectral characteristics of upwelling radiation of sea based on combination of advantages of a double beam photometer with a photomultiplier and a directreading photometer with a highstability silicon photodiode for its absolute adjustment in energy units is implemented.

SPECTRAL CHARACTERISTICS OF RADAR PRECIPITATION CLUTTER REFLECTIONS IN THE Ka-BAND

2012 ◽  
Vol 71 (13) ◽  
pp. 1151-1158 ◽  
Author(s):  
M. G. Balan ◽  
V. A. Zuikov ◽  
V. A. Razskazovsky ◽  
N. G. Reznichenko
Keyword(s):  
Spectral Characteristics ◽  
Ka Band

Thymine and cytosine spectral characteristics in gas discharge

2015 ◽  
Vol 38 (0) ◽  
pp. 82-87
Author(s):  
Віктор Юрійович Шпеник ◽  
В. В. Звенигородський ◽  
Ю. В. Жменяк ◽  
Володимир Андрійович Кельман ◽  
М. І. Мигович ◽  
...  
Keyword(s):  
Spectral Characteristics ◽  
Gas Discharge
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