DE1243797B - Electromechanical shear wave converter - Google Patents

Description

FEDERAL REPUBLIC OF GERMANY

GERMAN

PATENT OFFICE

EDITORIAL

Int. α .:

H03h

H04r
German class: 21g-34

Number: 1243 797

File number: T 30000IX d / 21 g

Filing date: December 11, 1965

Opened on: July 6, 1967

The invention relates to an electromechanical shear wave converter with a disk-shaped Converter body made of ferrite material. The largest areas of the transducer body are made up of the windings an excitation coil surrounding the transducer body and are one of the transducer body pre-magnetizing permanent magnets opposite. The preferred application is the one according to the invention Converter as part of an electromechanical delay device, which in turn is preferably is used in color television receivers.

In the case of electromechanical converters of this type, there is often a desire to change their radiation characteristics for the power emitted on one side in the half-space. One way to do this is by different excitation of the individual elements of the radiant surface. To achieve this The aim has already been proposed that the pre-polarization of the transducer generating magnetic Field that penetrates the transducer body approximately perpendicular to the radiating surface, from the center to let the surface become weaker towards its edges. The field strength in the center of the transducer surface is chosen so that it has the optimum value there for generating the largest having electromechanical coupling factor. The desired field weakening is achieved by a Shaping the polarizing permanent magnet by making the air gap between its surface and allows the transducer body to increase from the inside out. This method is quite true effective, but creates difficulties in the manufacture of the permanent magnets.

The invention is based on the object of setting the radiation characteristics of the transducer without changing the pre-polarizing magnet. According to the invention this The object is achieved in that the distance between the turns of the excitation coil from one another from the center of the transducer body varies towards the outside.

The principle of the invention consists in not changing the pre-polarizing magnetic field, but rather to deform the alternating field of the excitation coil.

The figure shows a particularly clear exemplary embodiment for a converter according to the invention shown, in which the conditions are particularly simple.

The transducer consists of a flat, cuboid ferrite body 1, which is surrounded by the turns 3 of the excitation coil. The largest area of the transducer body 1 is at the same time the radiating upper electromechanical shear wave transducer

Applicant:
Telefunken

Patentverwertungsgesellschaft mb H.,
Ulm / Danube, Elisabethenstr. 3

Named as inventor:

Dipl.-Phys. Dr. rer. nat. Manfred Börner,

Ulm / Danube

area and consists of a rectangle with the edge lengths α undo. The turns 3 of the excitation coil run essentially on this rectangle, and in the selected example parallel to the edge b.

As a material for the coil you can choose one that has a glass or enamel melt Can be firmly connected to the ferrite material of the transducer body 1. It is important to ensure that that the temperature expansion coefficient of the coil material is matched to that of the ferrite material. If the demands on the thermal shock resistance are not too great, however, this is usually already suitable very thin copper tape. It is also useful here to use the turns made from this material to gold or silver to reduce electrical losses. Another possibility to apply the coil turns to the ferrite material of the transducer consists in making them to produce burned-in metal coatings, preferably silver coatings.

A permanent magnet 2 faces a largest area of the transducer body 1, with the south pole of the magnet 2 facing the transducer body 1 and the north pole of the magnet facing away from the transducer body in the example shown. The bias field thus penetrates the ferrite body perpendicular to its largest surface. Under the influence of this field and the interaction of the alternating coil field, the transducer body then executes shear vibrations, the wavelength of which at higher frequencies of the alternating exciter field is small compared to the dimensions α undo of the transducer surface. For example, at an excitation frequency of 4 MHz, the edge lengths α and b are approximately 10 mm and the shear wavelength X _s is 0.8 mm.

709 609/35 ^K

Claims (1)

The turns. 3 of the excitation coil have a mutual spacing which, in the example shown, increases along the edge α of the transducer body 1 from the center towards both edges. In this way, the emitted shear waves are bundled in a horizontal direction. If the turns 3 run parallel to the edge α and if their spacing along the edge b increases in the same way, the radiated energy is bundled in the vertical direction. Claim: Electromechanical shear wave converter with a disk-shaped converter body made of fer- rit material, the largest areas of which are surrounded by the windings of the transducer body Excitation coil are coated and a permanent magnet that magnetizes the transducer body opposite, in particular for use in a delay device, thereby characterized in that the distance between the turns (3) of the excitation coil from one another from the center of the transducer body (1) to the outside varies. Considered publications:
U.S. Patent No. 2,696,590. 1 sheet of drawings 709 609/395 6.67 © Bundesdruckelei Berlin