Determination of the Source Bearing in a Waveguide by Using the Sound Field Interference Pattern

2001 ◽  
Vol 47 (3) ◽  
pp. 286-290
Author(s):  
V. A. Eliseevnin
Keyword(s):  
Interference Pattern ◽  
Sound Field

scholarly journals Orthogonal ray interferometer: modification for testing convex and concave mirror surfaces

2021 ◽  
Vol 2127 (1) ◽  
pp. 012067
Author(s):  
M V Askerko ◽  
A E Gavlina ◽  
V I Batshev ◽  
D A Novikov
Keyword(s):  
Point Source ◽  
Interference Pattern ◽  
Optical Method ◽  
Present Method ◽  
Rotational Symmetry ◽  
Geometrical Parameters ◽  
Concave Mirror ◽  
Entire Surface ◽  
Optical Components

Abstract A non-contact optical method for testing of large concave and convex mirrors both spherical and aspheric is presented. It is based on the orthogonal ray interferometer modification. The point source is placed near the testing mirror and the chief ray propagates normally to its axis. The information about a tangential profile of testing mirror is contained in an interference pattern that is a result of superposition between two wavefronts, the first is reflected from the mirror, the second bypasses the mirror. Testing of the entire surface is carried out by rotating the mirror. Interferogram decoding method and algorithm for determination of an error of the testing surface are presented. The proposed method does not require bulky additional optical components what differs it from existing methods and makes promising primary for testing large astronomical mirrors. Furthermore, the method is universal and suited for surfaces with various geometrical parameters. The scheme with some modification of the present method is applied for surfaces without axis of rotational symmetry or freeform surfaces.

scholarly journals The Spec-Radiation Method as a Fast Alternative to the Re-Radiation Method for the Detection of Flaws in Wooden Particleboards

2020 ◽  
Vol 10 (19) ◽  
pp. 6663 ◽  
Author(s):  
Andreas Sebastian Schmelt ◽  
Jens Twiefel
Keyword(s):  
Real Time ◽  
Ultrasonic Testing ◽  
Sound Field ◽  
Calculation Methods ◽  
Radiation Method ◽  
Non Destructive ◽  
Time Evaluation ◽  
Sub Wavelength

For real-time evaluation of non-destructive air-coupled ultrasonic testing of wood-based materials, efficient and reliable calculation methods from ultrasonic holography are essential. Presented here is the spec-radiation method as a fast alternative to the re-radiation method. The spec-radiation method offers a more accurate and up to 88% faster evaluation than the re-radiation method for the determination of flaws in particleboards. Flaws of sub-wavelength sizes can be identified and their shape and location can be determined with this method. The spec-radiation method produces a better reproduction of the sound field than the re-radiation method, especially in the area of the measuring plane.

scholarly journals Further investigations of very long waves reflected from the ionosphere

1939 ◽  
Vol 171 (945) ◽  
pp. 188-214 ◽  
Keyword(s):  
Interference Pattern ◽  
Horizontal Surface ◽  
Long Waves ◽  
Post Office ◽  
Propagation Characteristics ◽  
The Waves ◽  
Ground Wave

In a previous paper Best, Ratcliffe and Wilkes (1936) described two kinds of measurement made on waves of length 18.8 km. (frequency 16 kc./sec.) emitted from the British Post Office sender GBR situated at Rugby. In the first kind of measurement the interference pattern produced at the ground by the superposition of the ground wave and the downcoming wave was investigated over a range of distances from 65 to 145 km. from the sender in a fine running east from Rugby. From the observed positions of the maxima and minima of this ground interference pattern it was concluded that the waves were probably reflected from a height of about 74 km. on a September day, although, because of uncertainties in assigning the order of interference to the different maxima, the possible reflexion heights of approximately 62 and 85 km. could not be definitely excluded. The results were interpreted on the assumption that reflexion took place at a horizontal surface without change of phase. In § 2 of the present paper we describe an extension of these measurements to greater distances. At first the measurements were extended to the sea along the line running east from Rugby, and later were continued to greater distances on a line running north from Rugby. These measurements enabled us to take a further step in resolving the ambiguity in the determination of the reflexion height, and to compare the propagation characteristics in a northerly and an easterly direction.

scholarly journals Experimental investigations of very long waves reflected from the ionosphere

1936 ◽  
Vol 156 (889) ◽  
pp. 614-633 ◽  
Keyword(s):  
Interference Pattern ◽  
Accurate Determination ◽  
Long Waves ◽  
Experimental Investigations ◽  
Great Length ◽  
Interference System ◽  
Phase Variations ◽  
Characteristic Features ◽  
The Waves

This paper is an account of experiments which have been carried out to determine the characteristic features (amplitude, height of reflexion, and polarization) of waves of very great length (18·8 km) reflected from the ionosphere at fairly small angles of incidence. The transmission characteristics of long waves have previously been studied by Holling-worth, Naismith, and Namba. In Hollingworth's pioneer experiment measurement were made on the space characteristics of the interference pattern produced at the ground by the superposition of the direct and the downcoming wave. the observations were made within the range 300-1000 bin from the sender, during the daytime, and one minimum and one maximum of the interference pattern were located. With the large distances to be covered the measurements extended over three months, and it was necessary to assume constancy of the conditions from day to day. The result demonstrate the presence of the interference system in a very beautiful manner, but cannot be used for an accurate determination of the height of reflexion at any one time. In §2 of the present paper we describe experiments, of the same type as Holling-worth's, carried out at shorter distances (70-140 km). The advantage of using shorter transmission distances are twofold. Firstly, it is possible to make sufficient measurements in the course of a single day (or night) to determine the reflexion height and the reflexion coefficient for a single day (or night), and, secondly, the information derived applies to the conditions of nearly vertical incidence, and so is more directly comparable with the detailed information which is now available concerning short waves. In the papers mentioned above muck attention has been given to the observation and explanation of the effects observed near sunset. It is pointed out that if the resultant signal strength on a single aerial system is alone observed, it is impossible to decide whether the changes are due to changes of amplitude, phase, or polarization of the downcoming wave. Assuming that the sunset variations are due entirely to phase variations, Hollingworth first deduced a change of reflexion height from 75 km to 90 km during sunset, but later believed that the variations were almost entirely explained by a rotation of the plane of polarization of the wave, and that the change of reflexion height was only about 2 km. Naismith states that no sunset variations are observable at short distances (100 km) from the sender, and suggests that at vertical incidence the waves are reflected from a higher level which does not exhibit changes at sunset.

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