DE1806909A1 - Delay line for ultrasonic vibrations - Google Patents

Description

Patent attorney

Stuttgart-Feuerbach '

Short street 8

F.PoB.Telle-A.J. Judeinstein 2-13

INTERNATIONAL STANDARD ELECTRIC CORPORAi ¹ ION, NiSW YORK Delay line for ultrasonic vibrations

The priority of the application in France of November 15, 1967 No. PV1Z8Z7 ¹ + has been claimed.

The invention relates to a metallic delay line in the form of a square with a long propagation path through ™

successive internal reflections takes place, and concerns in particular means for suppressing the ultrasonic vibrations which are off the beam axis.

Such devices are used to delay signals from one to 10,000 microseconds whose frequency spectrum is in the Frequency band from a few megahertz to a few hundred megahertz. These delay lines are generally made of molten material Quartz or glass and the transmission material is a quartz crystal. The quartz delay lines are in the shape of a cut out polygonal plate, the thickness of which is between ten and twenty wavelengths. The vibration mode is for example -

show a shear oscillation, the direction of which is parallel to the main '

surfaces of the plate runs. This mechanical disturbance spreads in the material at different speeds. One of these types of shear has a velocity that depends on the frequency depends and called "non-scattering" type or also "zero order type" will. The other species, on the other hand, have speeds that are in Regarding frequency vary and called "scattering" or "dispersion" are designated. Because a sufficiently defined and constant delay time is necessary, the scatter must either be suppressed or greatly weakened. The suppression must be

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1.11.1968 909825/1106

Reduction of the plate thickness to half a wavelength can be carried out. In this case the only type of propagation is that "Non-Scattering". A glass plate of such a small thickness is very fragile, which is why a metal foil is used. The material for this foil is generally an alloy of predominantly Iron, winding and chrome.

Such metal delay lines are described, for example, in the article "A survey of ultrasonic delay lines operating below 100 Mc / s ", published in" Proceedings of the Institution of Electrical and Electronic Engineers ", October 19651 pages 4θ6 to 1 ^ 28. These lines are usually of the shape of a rectangle, the two corners of which are cut off on the same side, at which the transducers are arranged. As a result of Width of the beam of ultrasonic vibrations that are guided in the transmitter, the paths of the vibrations are not the same and am A phase shift occurs at the output of the delay line.

The object of the invention is to provide a metallic delay line specify a device for suppressing the ultrasonic vibrations is provided, which are removed from the beam axis.

According to the invention, the ultrasonic delay line consists of a plate of a material suitable for propagating ultrasonic vibrations, the upper and lower surfaces of which with a Absorbent is coated in such a way that a given, uncoated path remains free for this vibration.

These and other features and objects of the invention will be described with the aid of the drawing, in which a single figure is a view of one of the surfaces of a delay line according to the invention ^{; !} finding shows. ■ · ^ίί! "■■ '■'■" - '. ■.' ■ · '■' ■■

The delay line shown consists of a piece of one Foil 1 made from an alloy of predominantly iron, nickel and chromium. The thickness of the film is half a wavelength of the ultrasonic

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signal to be delayed. It has, for example, the shape of a rectangle in which two corners lying on one side are cut off, at which the input transformer 2 and the output transformer are arranged on it. These transducers, which can be quartz crystals or piezoelectric ceramic materials, are edge-welded. The signal to be delayed is generated by a device k and the delayed signal is applied to a device 5 which practically consists of an amplifier. The link between the transducers 2 and 3 are ^{un (n} * cle devices k and 5 is formed by a wire, a metallic spring or a flexible sheet, which is applied to the transducers are formed. These springs or blades are not shown. · Λ

The transducer is arranged in such a way that the mode of vibration in the film 1 is a pair of scissors, the direction of which is parallel to the plane of the film and the direction of propagation of which is at an oblique angle to the side 6. The alignment of this side 6 in relation to the sides of the rectangle must be such that the angle of incidence of the ultrasonic oscillation of the rectangle is greater than a certain angle, the so-called critical angle. At this critical angle, the reflection begins to vibrate in shear and longitudinal. The critical angle is generally close to 30 ° ^and the side 6 is oriented so that the angle of incidence is equal to k5 ° . The path of the ultrasonic vibration, which is represented by the angularly extending gap 7, at least relates to the conditions i vibration propagating along the axis of the beam. The vibrations on both sides of the axle are also reflected on the sides of the film and picked up by the transducer 3. Their path is different and thus corresponds to a delay different from that which follows the ultrasonic vibration propagating along the axis. This is a broadening of the output signal with respect to the input signal. In order to suppress this parasitic effect, it is absorbed by a material on the main surfaces of the film 1, which are shown in dotted lines in the drawing. This material is chosen so that it has a high absorption factor for the ultrasonic vibrations and on

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the film adheres well. This material can be an organic glue with high adhesive strength. Good results have been achieved with an epoxy resin achieved. In general, a material can be used for bonding metals. There is also low temperature welding possible. The width of the path thus obtained can be equal to or slightly greater than the width of the transducers. The knockdown of the Absorbent material on the areas shown in dotted lines is known, for example masks can be used.

Investments;

6 claims
1 sheet of drawing

909825/1 106

Claims (6)

Claims 1. 'Ultrasonic delay line, characterized by a plate made of a material suitable for the propagation of ultrasonic vibrations and an absorbent with which the upper and lower surface of the plate is coated so that a given uncoated path remains free for the vibrations. 2. delay line according to claim 1, characterized in that the plate is thinner than half a wavelength. 3 «delay line according to claim 2, characterized in that M input and output for the ultrasonic vibrations are arranged on the plate at points at a distance from one another, which establish the beginning and the end of the path. k. Delay line according to Claim 3> characterized in that the plate is a rectangle in which two adjacent corners are cut off at an angle of more than 30 and the input and output lie at these corners. 5 · delay line according to claim ^ f, characterized in that the path is angled and crosses itself at least once. 6. delay line according to claim 1, characterized in that the absorbent is an epoxy resin. ^ F.P.E.Teile e.a. 2-13 909825/1106 Blank page