DE1219602B - Process for the production of a delay medium for ultrasonic delay lines - Google Patents

Description

FEDERAL REPUBLIC OF GERMANY

GERMAN

PATENT OFFICE

EDITORIAL

Int. Cl .:

H03h

German class: 21g-34

Number: 1219 602

File number: W 35413IX d / 21 g

Filing date: October 12, 1963

Opening day: June 23, 1966

The invention relates to a method of manufacturing a delay medium for ultrasonic delay lines with attached electroacoustic transducers for the introduction and removal of acoustic waves in the form of shear vibrations.

Ultrasonic delay lines of conventional design generally have an acoustic medium on appropriately selected surfaces attached to piezoelectric transducers. The medium becomes usually formed by a solid, e.g. B. by quartz, glass, ceramic, or by certain acoustically isotropic metals and metal salt crystals. The simplest form of a delay line is made in the use of a rod as an acoustic medium with a transducer at each end is attached. An electrical signal fed to one transducer, the input transducer, generates a acoustic wave progressing along the rod, which after arriving at the other transducer, the output transducer, in turn creates an electrical signal. The transit time of the acoustic wave through the rod determines the time delay of the signal.

Improved, known embodiments generally have a body as the delay medium that is more acoustic for multiple passes Waves is designed taking advantage of multiple reflections on facet-like surfaces.

Most of the known measures look good the formation of a delay line and its manufacture have primarily the geometric Form of the delay medium on the subject, but not measures with regard to nature of the delay medium itself.

Virtually all solid state delay lines can use any of the known delay media, often glass or Quartz is preferred.

A disadvantage of the known delay media is that the time delay caused in them changes undesirably high with temperature for many applications. Complex compensation measures are therefore required. Thus, for example, the mean temperature coefficient of the time delay between -20 and +100 ^o CfürArsensulfidbei200-10- ⁶ / ° C, for calcium aluminate at 40 x 10 ~ y ^o C, and for quartz at -76 · 10- "V ⁰ C. This Materials are all known to be pertinent delay media.

. The object of the invention is to make a delay medium available for a composition Method of manufacturing a delay medium for ultrasonic delay lines

Applicant:

Western Electric Company Incorporated,

New York, N.Y. (V. St. A.)

Representative:

Dipl.-Ing. H. Fecht, patent attorney,

Wiesbaden, Hohenlohestr. 21

Named as inventor:

Lawson Egerton, Basking Ridge, N. J .;

Joseph Raymond Hensler, Rochester, N. Y .;

John Thorvald Krause, Murray Hill, N. J .;

Norbert Joachim Kreidl,

Rochester, N. Y. (V. St. A.)

Claimed priority:
V. St. v. America November 30, 1962
(241440)

make, in particular by a very small temperature coefficient of the time delay excels.

Since the invention is aimed at the chemical composition of the delay medium, come the advantages resulting from the unexpected properties of the material according to the invention, when used in all known or future ultrasonic delay line forms in same dimensions to wear.

To solve the above problem, the method described at the beginning is assumed; according to the invention it is provided that the delay medium consists of the following components in the specified The following is composed of proportions:

Table 1

SiO ₂ 73.50 to 76.00 mole percent

PbO 14.70 to 16.70 mole percent

K ₂ O 8.00 to 9.50 mole percent

BaO 0.5 to 1.50 mole percent

Sb ₂ O ₃ 0.05 to 0.20 mole percent

The delay medium of the invention is a glass of specific and highly critical composition. It is an effective acoustic medium with a high time delay per length

609 580/323

unit. A decisive advantage, however, is to be seen in the fact that the time delay is practical is independent of temperature and is only subject to small changes over time, the material possesses therefore no signs of aging.

In the following the invention is based on the drawing described; it shows

Fig. 1 is an oblique view of a simple ultrasonic delay line, in which the according to the invention Delay medium can be used,

FIG. 2 shows the dependence of the temperature coefficient of the delay on the composition of the medium, specifically on the change in the SiO ₂ and PbO proportions, and FIG

3 shows the dependence of the time delay per unit length of the delay _{medium on the change in the SiO 2} and Pboe components.

The delay line of Fig. 1 comprises a delay medium 10 as well as piezoelectric ones Converter 11 and 12. Electrical lines 13 and

14 feed an input signal to the input transducer 11, causing it to vibrate elastic is excited, which then proceed along the medium 10 at the speed of sound. Reach the sound waves generate the output transducer 12 in the piezoelectric crystal of the same elastic deformations, which in turn result in a changing tension between: electrical lines

15 and 16 generate, whereby the electrical signal is restored with a corresponding delay.

As is known, acoustic waves can propagate in a continuum either as longitudinal waves or as shear waves. In the case of delay lines, shear waves are generally preferred because they have a lower propagation speed than longitudinal waves and thus provide a higher time delay. As mentioned, it is intended, in particular, to achieve a negligible temperature dependence of the time delay. The temperature dependence of the time delay is not the same for shear and longitudinal waves. It has been found that the delay medium according to the invention, when used in delay lines excited to shear vibrations, has an unexpectedly small temperature dependence of the delay. Measurements have shown that in a still to be described composition of the medium, the temperature coefficient of the time delay at all vanishes, while remaining less than about ± 10- ⁶ / ° C in the above Zusammeüsetzüngsbereich.

Whether a delay line is excited to shear vibrations or longitudinal vibrations depends on the selected crystal cut surfaces of the piezoelectric transducers. Shear wave generating Converters are well known.

To determine specific operating characteristics glass samples of the following composition were prepared in Molpfözent.

Table 2

SiO ₂ .-. 72.00 to 76.00

PbO .... 14.31 to 18.31

E ₂ O ..-. 8.85

BaO 0.73

Sb ₉ O ₃ 0.10

The conditions for performing the melting, afterglow and cooling processes and their control can be changed within a wide range. So was z. B. in some cases a fire raw ingredients melted in a refractory crucible or a platinum crucible, and in other cases a continuous melt process can be used. Similarly change Temperatures, times and the other conditions

ίο according to the amount of glass to be produced. Therefore the values given below for temperatures and melting conditions are only examples to be understood, but not as a limitation to this.

The glasses according to the invention were in some cases melted in a clay crucible about 61 cm high and about 86 cm in diameter. The crucible was preheated to around 1430 ° C. Then part of the mixed fire was added to the crucible and, after it had melted, further parts of the fire ₅ until the batch was complete. Entering the fire in the manner described above took about 7 hours. A refractory stirrer was used to stir the melt. The melt was kept at about 1430 ° C. while stirring. Stirring was continued at this temperature for about 8 hours.

The glass was then cooled to about 1250 ° C., the stirrer removed and the glass poured. It took cooling from 1430 to 1050 ° C, removing the stirrer and pouring about 3 hours. After casting, the glass was embedded in a cooling furnace, the first part of which was kept at about 520 ° C, and post-annealed for about 6 hours.

It has been found that the relative SiO ₂ : PbO ratios have the greatest influence on the temperature coefficient of retardation. The other constituents were kept constant at the stated percentages. The last two ingredients BaO and Sb ₂ O ₃ were added because of their glass-forming properties.

The average temperature coefficient of the delay (in 10 ~ ⁶ / ° C) depending on the

. Change in the ratio of SiO ₂ : PbO within the selected range is shown in FIG. 2 shown. The values show that practically zero temperature coefficient is obtained for the specific composition set out below.

Table 3

SiO ₂ .
Pbö.
K ₂ O.
BaO.

Sb ₂ O ₃

74.4
15.9
8.85
0.73
0.10

If ± 6 ■ 1Ö ~ ^{6 is selected} as the permitted change, the limits for SiO _{2 are} 74.4 to 76.0 and for PbO 14.8 to 16.3. It has been found that minor deviations in the remaining components can be tolerated without any appreciable changes in the desired low temperature coefficient occurring as a result. Therefore, the limit values given in the table for the individual components are to be regarded as lying within the scope of the invention.

Other, for example, properties which are of interest for the composition according to the invention were determined within the same range of the compositions shown in Table 2. In Fig. 3, the delay time per unit length in microseconds per centimeter is at an operating frequency of 15 MHz plotted as the ordinate. The abscissa is the same as that of the Fig. 2. The delay time per unit length for the glass according to Table 3 is 3.89 microseconds per centimeter.

The attenuation of these materials was determined at 20MHz and the losses were approximate Found 0.55 decibels per centimeter.

Another and important factor determined for these compositions was the dependence of the delay time per unit length on time. The delay time per unit length of known delay media often changed considerably over time. A sample of the glasses according to the invention was subjected to an accelerated aging process. Since aging progresses fastest immediately after a heat treatment and then continues approximately with the logarithm of time, the test sample was subjected to quenching in an air stream from 500 to 150 ° C instead of slow cooling with the intention of introducing a maximum aging rate. Under these accelerated test conditions, the sample showed an aging rate of 6 x 10 -4 ^s per decade. This can be considered an extremely excellent value.

Claims (2)

Patent claims: 1. A method of making a delay medium for ultrasonic delay lines with attached electroacoustic transducers for the introduction and acceptance of acoustic waves in shear mode, characterized in that the delay medium composed of the following components in the specified proportions will: SiO ₂ 73.5 to 76.0 mole percent PbO 14.7 to 16.7 mole percent K ₂ O 8.0 to 9.5 mole percent BaO 0.5 to 1.5 mole percent Sb ₂ O ₃ .... 0.05 to 0.20 mole percent 2. The method according to claim 1, characterized in that the following composition is used: SiO ₂ 74.4 mole percent PbO 15.9 mole percent K ₂ O 8.85 mole percent BaO 0.73 mole percent Sb ₂ O ₃ 0.10 mole percent 1 sheet of drawings 609 580/323 6.66 © Bundesdruckerei Berlin