US2777997A

US2777997A - Ultrasonic delay lines

Info

Publication number: US2777997A
Application number: US255128A
Authority: US
Inventors: David L Arenberg; Robert M Ashby
Original assignee: Individual
Current assignee: Individual
Priority date: 1951-11-06
Filing date: 1951-11-06
Publication date: 1957-01-15
Anticipated expiration: 1974-01-15

Description

Jan. 15, 1957 D QI ,ARIENBERG ETAL 2,777,997

ULTRASCNICYDELAY'LINES- Filed Nov 6, 1951" FIG. 2

l NTORS DAVID L. NBERG ROBERT M. ASHBY ATTORNEY Unite States Patent ULTRASONIC DELAY LINES David L. Arenberg, Rochester, Mass., and Robert M. Ashby, Pasadena, Calif.

Application November 6, 1951, Serial No. 255,128

23 Claims. (Cl. 333-30) (Granted under Title 35, U. S. Code (1952), see. 266) Thi invention relates in general to the art of delaying in time, electrical signal transmission, and more particulariy to ultrasonic delay lines employing multiple reflections of a directed acoustical beam.

In the electronic art, it is frequently desirable to delay signal transmission for periods of time ranging up to several milliseconds in duration. It is usually not feasible to employ electromagnetic delay lines for delays of such magnitudes especially with short pulse signals requiring wide band-widths. To attain a longer delay time than is possible with comparable electromagnetic delay lines, various types of ultrasonic delay lines have come into general use. These ultrasonic delay lines operate as follows: The signals to be delayed a small, finite time are caused to modulate a high frequency carrier. The frequency of the latter signal may be of the order of several megacycles per second. This modulated high frequency signal is converted to an acoustical (sound) signal which is made to traverse a given path as ultrasonic energy. At the end of this path, some or all of the acoustical energy is reconverted to electrical energy, amplified and detected to yield the original modulation signal. The relatively low velocity of propagation of sound Within the delay line results in longer delay times in this type than is possible with electromagnetic delay lines. The delay time in such an ultrasonic delay line is proportional to the total path length from the input to the output of the device.

Even with the relatively low velocity of the propagation of sound, it frequently happens that the path length required is so great that it is difficult or impractical to construct a delay line having a single straight path from the input to the output. To reduce the over-all length of ultrasonic delay lines, for the longer delay times, tubes containing a liquid propagation medium have been arranged in various patterns with reflectors placed at the junctions of the tubes to direct the energy from one tube to another. Delay lines of this type have a relatively large size, are relatively difficult to construct, and are subject to leakage of the propagation medium.

A second type of delay line using multiple reflection paths consists of a tank containing a liquid propagation medium with reflectors placed at certain points in the tank and in the path of the ultrasonic beam. These reflectors cause the ultrasonic beam to traverse the length and width of the tank a number of times before arriving at the output of the delay line. Delay lines of this type are also diflicult to construct, are frequently unstable in their operation, and are apt to produce unwanted signals due to the fact that multiple reflections in the medium present alternative paths for the reflected beam.

A third type of delay line using multiple reflection paths consists of either rectangular solids or rectangular forms containing a liquid propagation medium wherein a beam of energy is introduced at one corner of the rectangle and is directed at a point on the rectangle wall close to the corner opposite the point of introduction. Reflection of the beam takes place and a path is 2,777,997 Patented Jan. 15, 1957 traced across the last-mentioned corner to another wall of the rectangle. A second reflection takes place at this point and the beam is reflected back to a point on a Wall of the rectangle close to the corner where the beam originated. Successive reflections continue until the path traced by the beam comprises two series of parallel lines diagonally disposed across the rectangle, with'one series of lines being perpendicular to the other series, the path terminating at a corner adjacent to the original corner in a suitable receiver. Delay lines of this type are said to have rectangular symmetry. The primary disadvantage of a rectangularly symmetrical design is that reflection must take place several times from any given wall of the structure to provide sufficient path length. For eflicient use of the delaying medium, successive points of reflection on each wall must necessarily be closely spaced. Since the energy is not usually confinable to a beam of small diameter because of diffraction effects, the desired energy path is not followed by all of the energy. Some paths are of greater or shorter length than the desired path. The ultimate result i that the major signal reaching the receiver is accompanied by several unwanted or secondary signals.

Therefore, it is an object of. the present invention to provide a delay line employing multiple reflection paths which is of particularly compact, simple, and rugged mechanical construction and which has comparatively small secondary signals.

A further object of theinvention is to provide a delay line which is light in weight and which possesses great mechanical stability under adverse conditions of operation.

An additional object is to provide a delay line which avoids the disadvantages of rectangular symmetry.

in general, the present invention consists of a polygonal 0r polyhedral structure having approximately the shape of either a circular disc or a sphere, modified to provide a plurality of surfaces for multiple reflection of the sound beam. The structure may be either a solid or a container filled with a suitable fluid propagation medium. Either two or three dimensional paths may be used in both the spherical and circular structures. For purposes of explanation, however, the embodiments utilizing a solid thin polygonal structure and two or three dimensional paths will be described.

In general, the number of facets on the polygon is odd or a multiple of four, the top and bottom surfaces being left flat. Except for the case of pairs of facets carrying the generating and receiving transducers, each of the facets makes equal angles with those adjacent thereto and is normal to the top and bottom polygon surfaces. The facets on which the transducers are mounted are maintained normal to the top and bottom surfaces of the polygon, but are tilted through an angle of int/4 from the position which would be found in an entirely regular polygon where a is the angle between adjacent reflecting facets and is equal to 21r/n, where n=the total number of facets. Although it is convenient to construct the invention from stock of circular crosssection shaped into a regular polygon (except for the facets on which the transducers are mounted) this feature is not necessary and the polygon need not be regular but the angles between facets must be as defined above. Thus, in general, the angles between adjacent facets are always small integral multiples of 06/4. For a better understanding of the invention, together with other and further objects, features, and advantages, refer ence should be made to the following description which is to be read in connection with the accompanying drawings in which:

Fig. 1 is' a perspective schematic view of one embodiment of the delay line; and

Fig. 2 is a section viewofa second embodiment of the invention.

The embodiment shown in Fig. 1 comprises a thin regular polygon 29 of-solid material such as quartz, flat on its top and bottomsurfaces and having a series of facets A through I on its perimeter as 'shownin the drawing. For convenience the over-all structure will be referred to as polygonal. The polygonal structure is modified as shown to provide bilaterally symmetrically placed transducer facets A and F, the details of which will be found below. Facet A has a crystal transducer 21 mounted thereon and is normal to the top and bottom polygon surfaces, and makes an angle of or with facet B and A a with facet I. Facet F has mirror symmetry with facet A making an angle of A a. with facet E and a with G. Facet F also has a transducer 22 mounted thereon. The remaining facets B, .C, D, E, G, H, and l are hereinafter calledregular facets since each is normal to the top and bottom surfaces of polygon 20 and at an angle a with respect toadjacent regular facets.

When electrical energy is introduced into the transducer 21 mounted on facet -A, an acoustical wave will be set up which will trace a path to facet E, which is along the normal to the center of facet A. The energy impinging on facet B will be incident thereon at an angle of 90/:1 degrees to the normal erected at the center of facet E and will be reflected at an angle to this normal which is equal to the incident angle. The result is that a path will then be traced to facet 1. Another reflection similar to the first will occur at this facet and a path will be traced to facet D. The process continues and a path is traced successively to facets H, C, G, B, and F, as shown by the dashed lines of Fig. 1. Since facet F is tilted, as noted hereinabove, energy incident on that facet will strike this facet along the normal and will be either reflected back toward facet B, or, preferably, absorbed in exciting the transducer mounted on facet F.

The embodiment shown in Fig. 1 includes a regular polygon, and its operation has'been described in terms of relating to a regular polygon for the sake of convenience of illustration. Irregular polygons may also be used, and the operation thereof would be similar to that of the regular polygonal structure. Also, the path may be terminated at facets other than F with appropriate tilting of the terminating facet.

The embodiment of the invention illustrated in Fig. 2 is essentially a sectional view of Fig. 1 taken along the beam path from A to E, except for two modifications. The facets on the perimeter of the structure of Fig. 2, except for those facets on which the transducers for introducing and extracting energy are mounted, for example, A, are normal to the top and bottom surfaces of the structure. Also, as in. Fig. 1, these facets make angles of 360/ n with adjacent facets. In other words, a plan view of the embodiment of Fig. 2 would be practically identical to the view of 'Fig. 1. However, the facets on which the transducers are mounted are not only tilted in one plane at an angle of 06/4 to the normal facet direction of a regular polygon (as in Fig. l) but, further, the plane is rotated about its top edge through an angle of 45 Hence, the facet lies in a plane which is at an angle of 45 to the top and bottom surfaces of the structure and at an angle of :m/ 4 to the usual facet direction. Thus, the beam of energy in this embodiment, starting at A, follows the same projection in a plane parallel to the top and bottom surfaces between facets as the beam in Fig. 1, but each leg of the energy path, for example, A to E in Fig. 2, includes, in addition, a series of reflections from the top and bottom surfaces caused by the introduction of the energy at the 45 angle. The energy is then reflected at a solid angle from the facet E in a direction towards a facet corresponding to I of Fig. 1, but again beingreflected from the bottomand top surfaces tracing a psmsrmsartstheipsm A? to .E' previously described. This process "continues until the beam has been reflected from .all the regular facets and arrives normal to the second 45 facet on which the receiving transducer is mounted. The energy is then absorbed by the transducer and transmitted to further electrical apparatus. One advantage of this design is that the delay obtained is multiplied by 1.414 over the design of Fig. l.

The foregoing description relates only to a simple form of the present invention. It is, of course, understood that a polyhedrai structure having facets on the surface thereof, or either polygonal or polyhedral structures having reflecting facets curved to provide focusing of the beam as it is reflected are within the scope of the present invention.

The invention described herein may be manufactured and used by or for the Government of the United States of America for governmental purposes without the payment of royalty thereon or therefor.

What is claimed is:

1. An ultrasonic delay line comprising, a regular polygonal fused quartz propagation medium having it facets on the edge thereof, it being an odd integer, all of said facets lying in planes normal to the top and bottom surfaces of said medium, two of the facets lying in planes at an angle of /11 to radii to the points of tangency between said polygon and the inscribed circle of said polygon, the remaining facets being located in planes normal to radii to the points of tangency between said polygon and the inscribed circle of said polygon.

2. Au ultrasonic delay line comprising, a propagation medium having characteristics substantially the same as those of fused quartz and formed into a flat polygon having 11 facets on the edge thereof, It being a multiple of 4, all of said facets lying in planes normal to the top and bottom surfaces of said flat polygon, two of the facets lying in planes at an angle of 90/ rz to radii to the points of tangency between said polygon and the inscribed circle of said polygon, the remaining facets being disposed s'uch that they lie in planes normal to radii to the points of tangency between said polygon and said inscribed circle.

3. An ultrasonic delay line comprising a solid propagation medium having characteristics similar to those of fused quartz in the form of a flat prism having in facets with top and bottom surfaces parallel, all of said facets lying in planes normal to the top and bottom surfaces of said prism, the angle between any two of m-2 of said facets corresponding'to r times those of a regular polygon with n sides, or 360r/n, where r is an integer less than n, and n is an odd integer equal to or greater than m, while the angle between either of the two excepted facets and any one of the m-2-others is 90(4r:1)/n, first and second crystal transducers respectively mounted on said two facets, means for applying an electrical signal to said first crystal transducer, and means connected to said second transducer for receiving a signal therefrom.

4. Anultrasonic delay line comprising a propagation medium having the characteristics of fused quartz in the found a flat prism having m facets with top and bottom surfaces parallel, all of said facets lying in plane normal to the top and bottom surfaces of said prism, the angle between auytwo of m-2 of said facets corresponding to r times those of a regular polygon with n sides, or 360r/n, where r is an integer less than n, and n is a multiple of 4 equal to or greater than m, while the angle between either of the two excepted facets and anyone of the 'm2 others is 90(4r:L-l)/n, first and second crystal transducers respectively mounted on said two facets, means for applying an electrical signal to said first crystal transducer, and means connected to said second transducer for receiving a signal therefrom.

5. An ultrasonic delay line comprising a solid propagation medium having the characteristics of fused quartz in the form of a flat prism having in facets with top and bottomj'surfaces. parallel, all of said facets lying in planes normal to the top and bottom surfaces of said prism,

- '5 the angle between any two of m2 of said facets corre sponding to r times those of a regular polygon with n sides, or 360 r/n, where r is an integer less than n, and n is an odd integer equal to or greater than m, while the angle between either of the two excepted facets and any one of the m2 others is 90 (4r:1)/n, a first crystal transducer mounted on one of said two excepted facets, means for applying an electrical signal to said first crystal transducer, a second crystal transducer mounted on the other of said two excepted facets, and means connected to said second crystal transducer for receiving a signal therefrom.

6. An ultrasonic delay line comprising a propagation medium having substantially the characteristics of fused quartz in the form of a fiat prism having in facets with corresponding to 1' times those of a regular polygon with n sides, or 360 r/ n, where r is an integer less than n, and n is a multiple of 4 equal to or greater than 112, while the angle between either of the two excepted facets and any one of the m2 others is 90 (4ri1)/n, a first crystal transducer mounted on one of said two facets, means for applying an electrical signal to said first crystal transducer, a second crystal transducer mounted on the other of said two facets, and means connected to said sec ond crystal transducer for receiving a signal therefrom.

7. An ultrasonic delay line comprising, a flat prism having m facets with top and bottom surfaces parallel, all

of m2 of said facets corresponding to r times those of a regular polygon with n sides, or 360 r/n, where r is an integer less than n, and n is an odd integer equal to or greater than m, while the angle between either of the two excepted facets and any one of the m2 others is 90 (4r:l)/n, first and second crystal transducers, said first crystal transducer being mounted on said first facet for directing an ultrasonic wave substantially across said polygon to a second of said facets, said second facet resecond crystal transducer for receiving a signal therefrom. 8. An ultrasonic delay line comprising, a flat prism having m facets with top and bottom surfaces parallel, all

of m2 of said facets corresponding to r times those of a regular polygon with n sides, or 360 r/n, where r is an integer less than n, and n is a multiple of 4 equal to or greater than m, while the angle between either of the two excepted facets and any one of the m2 others is 90 (4r:l)/n, first and second crystal transducers, said first crystal transducer being mounted on said first facet for directing an ultrasonic wave substantially across said polygon to a second of said facets, said second facet reflecting said ultrasonic wave substantially across said polygon to a third of said facets, similar reflections continuing successively until the ultrasonic wave impinges on said m facet, said second crystal transducer being mounted on said m facet, and means connected to said second crystal transducer for receiving a signal therefrom.

9. An ultrasonic delay line comprising, a flat prism having m facets with top and bottom surfaces parallel, m2 of said facets lying in planes normal to the top and bottom surfaces of said prism, the angle between any two of m2 of said facets corresponding to r times those of a regular polygon with n sides, or 360 r/n, where r is an integer less than n, and n is an odd integer equal to or greater than m, while the angle between either of the two excepted facets and any one of the m2 others is (4ri- 1)/n, first and second crystal trans; ducers, said first crystal transducer being mounted on said first facet for directing an ultrasonic wave downwardly to: ward the bottom surface of said polygon, the bottom surface reflecting said' wave to the top surface, successive reflections continuing from the bottom and top surfaces until said wave occurring at said second facet, further reflections similar to those between said first and said second facets occurring until said wave impinges on a third of said facets,the process being continued until said wave impinges on said m facet, said second crystal transducer being mounted on said m facet, and means connected to said second crystal transducer for receiving a signal therefrom.

10. An ultrasonic delay line comprising, a flat prism having 212 facets with top and bottom surfaces parallel, m2 said facets lying in planes normal to the top and bottom surfaces of said prism, the angle between any two of m2 of said facets corresponding to r times those of a regular polygon with n sides, or 360 r/n, where r is an integer less than n, and n is a multiple of 4 equal to or greater than m, while the angle between either of the two excepted facets and any one of the m2 others is 90 (4r1-1)/n, first and second crystal transducers, said first crystal transducer being mounted on said first facet said wave occurring at said second facet, further reflecfacets, the process being continued until said wave impinges on said m facet, said second crystal transducer being mounted on said m facet, and means connected to said second crystal transducer for receiving a signal therefrom.

11. An ultrasonic delay line comprising a propagation medium having more than 6 surfaces, at least 5 of said and second electro-acoustical transducers, said transducers mounted in contact with first and second perimetrical surfaces, respectively, means for applying an electrical signal to one of said transducers whereby a beam of acoustical energy is directed through said medium to a third surface and reflected therefrom to another of said surfaces, further reflections occurring until said acoustical energy impinges on said second surface having the second transducer, and means connected to said second transducer for receiving a signal therefrom.

12. An ultrasonic delay line of the type described in claim 11 wherein the surfaces are plane surfaces.

13. An ultrasonic delay line of the type described in claim 11 whereinthe propagation medium is a solid.

medium, each of said other surfaces comprising said polygonal perimeter being at an angle other than 90 with at least one immediately adjacent surface of said other surfaces comprising said polygonal perimeter, said other surfaces extending between said 2 parallel surfaces, first and second electro-acoustical transducers, said transtucers mounted in contact with first and second perimetrical surfaces, respectively, means for applying an electrical signal to one of said transducers whereby a beam of acoustical energy is directed through said medium to a third surface and reflected therefrom toward another of said surfaces, further reflections occurring until said acoustical energy impinges on said second surface having said .second transducer, and means connected to said second transducer for receiving a signal therefrom.

15. An ultrasonic delay line of the type defined in claim 14 wherein the propagation medium is a solid.

16. An ultrasonic delay line of the type defined in claim 14 wherein the perimetrical surfaces are normal to the 2 parallel surfaces.

17. An ultrasonic delay line of the type defined by claim 14 wherein the perimetrical surfaces on which the transducers are mounted are not normal to the two parallel surfaces.

18. An ultrasonic delay line comprising a polygonal fused quartz propagation medium having it facets between top and bottom surfaces thereof, 11 being an integer at least equal to live, two of said'facets lying in planes at an angle of 90/n to radii to the points of tangency between said polygon and the inscribed circle of said polygon, the remaining facets being located in planes normal to radii to the points of tangency between said polygon and the inscribed circle of said polygon.

19. An ultrasonic delay line comprising a solid propagation medium in the form of a flat prism having in facets with top and bottom surfaces parallel, all of said facets lying in planes normal to the top and bottom surfaces of said prism, the angle between any two of m-2 of said facets corresponding to 1' times those of a regular polygon with n sides, or 360r/n, where r is an integer less than a and n is an integer equal to or greater than in, while the angle between either of the two excepted facets and any one of the ru -2 others is 90 (4ril)/n, first and second crystal transducers respectively mounted on said two facets, means for applying an electrical signal to said first crystal transducer, and means connected to said second transducer for receiving a signal therefrom.

20. An ultrasonic delay line comprising a propagation medium having a reflecting facets disposed between the top and bottom surfaces and comprising a. polygonal perimeter of said delay line, a being an integer at least equal to five, the angular relationships among n-2 of said facets conforming substantially to the angular relationships among corresponding sides of an equi-angular polygon of at least it sides, the angular relationshipbetween each of two expected facets and said n2 facets differing from the angular relationship between corresponding sides of an equi-angular polygon of at least :2 sides by an amount equal to a multiple of /n.

21. The delay line of claim 20 further characterized by transducer means mounted on said polygonal perimeter for inducing supersonic energy within said delay line, whereby said energy is multiply reflected from said facets.

22. An ultrasonic delay line comprising a propagation medium having 11 reflecting facets disposed between top and bottom surfaces and comprising a polygonal perimeter of said medium, 11 being an integer at least equal to five, the angular relationships among 11-2 of said facets conforming substantially to the angular relationships among corresponding sides of an equi-angular polygon of at least it sides, the excepted two facets being tilted through an angle equal to lit/4 from the position they would occupy if said It facets formed an equi-angular polygon, where a is the angle between adjacent sides of an equi-angular polygon of at least n sides.

23. The ultrasonic delay line of claim 22 further characterized by first and second transducer means mounted on said first and second ones of said reflecting facets, means connected to said first transducer means for applying an electrical signal to said transducer means, and

means connected to said second transducer means for receiving a signal therefrom.

References Cited in the file of this patent 1 UNITED STATES PATENTS 2,472,600 Luboshez June 7, 1949 2,505,364 McSkimin Apr. 25, 1950 2,505,515 Arenberg Apr. 25, 1950 2,525,861 Carlin Oct. 17, 1950 2,540,720 Forbes Feb. 6, 1951 2,624,804 Arenberg Ian. 6, 1953