US3748606A

US3748606A - Waveguide structure utilizing compliant continuous support

Info

Publication number: US3748606A
Application number: US00208207A
Authority: US
Inventors: S Kaufman; R Sabia; M Lutchansky; M County
Original assignee: Bell Telephone Laboratories Inc
Current assignee: AT&T Corp
Priority date: 1971-12-15
Filing date: 1971-12-15
Publication date: 1973-07-24
Anticipated expiration: 1990-07-24

Abstract

A waveguide structure is formed by supporting a waveguide section within a section of conduit by a low modulus continuous support material such as oil extended rubber which fills the space between the waveguide and conduit. This continuous support material eliminates distortions from weight loading induced deflections and provides substantial corrosion protection to the waveguide.

Description

United States Patent [1 1 Kaufman et a1.

WAVEGUIDE STRUCTURE UTILIZING COMPLIANT CONTINUOUS SUPPORT [75] Inventors: Stanley Kaufman, Flanders; Milton Lutchanslty, Randolph Twp., Morris County; Raffaele Antonio Sabia, Lincroft, all of NJ.

[73] Assignee: Bell Telephone Laboratories Incorporated, Murray Hill, NJ.

[22] Filed: Dec. 15, 1971 [21] Appl. No.: 208,207

[52] US. Cl. 333/95 R, 333/98 R, 333/98 M, 174/98, 260/33.6 A [51] Int. Cl. 1101p 1/00, 1101p 1/30, 1101p 3/12 [58] Field-of Search 0333/98 R, 95 R, 95, 333/98; 174/98; 260/36.6 A0, 77.5 AT

[56], 5 References Cited.

UNITED STATES PATENTS 3,605,046 9/1971 Miller 333/98 RX 3,434,994 3/1969 Smitet a1. 260/29.7 GP

366,174 7/1887' Kruesi "174/29 X 3,359,351 12/1967 Bender.. 139/149 X' 327,477 9/1885 'Spalding 174/98 1,959,368 5/1934 Kennedye 138/112 X 2,764,565 9/1956 Hoppe et a1... 260/2.5 AC 2,848,696 8/1958 Miller 333/95 R 2,966,643 12/1960 Kohman et a1... 333/95 R 3,007,122 10/1961 Geyling 333/95 R 3,108,980 10/1963 Gwin et a1 260/33.6 AQ

[ July 24, 1973 3,121,206 2/1964 Mandel 333/ R 3,246,073 4/1966 Bouche et a1... 174/42 3,345,245 10/1967 l-lanusa 138/111 X 3,479,621 11/1969 Martin 333/95 R 3,492,607 1/1970 Effemey 333/95 R OTHER PUBLICATIONS Verdol et al., Liquid Castabl e Elastomers from l-lydroxl-Terminated Polybutadienes, Parts 1 AND 11, Rubber Age, July & Aug. 1966, pp. 57-64, 62-68 Albersheim, W. J., Propagation of TE Waves in Curved Wave Guides, B.S.T.J., V01. 28, 1-1949, pp. 26-32 Unger, H. 3., Circular Electric Wave Transmission Through Serpintine Bends, B.S.T.J., V01. 36, 9-1957, pp. 1279-1291 Primary Examiner-Rudo1ph V. Rolinec Assistant Examiner-Wm. H. Punter Attorney-W. L. Keefauver and Edwin E. Cave [57] ABSTRACT A waveguide structure is formed by supporting a waveguide section within a section of conduit by a low modulus continuous support material such as oil extended rubber which fills the space between the waveguide and conduit. This continuous support material eliminates distortions from weight loading induced deflections and provides substantial corrosion protection to the waveguide.

5 Claims, 2 Drawing Figures PATENIEDJuL24|91a FIG. 2

SUPPLY FIG.

WAVEGUIDE STRUCTURE UTILIZING COMPLIANT CONTINUOUS SUPPORT BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to waveguide transmission systems and more particularly to a waveguide structure having a compliant continuous support for supporting the waveguide within a conduit, isolating it from disturbances in the surrounding environment and eliminating weight loading induced deflections and deflections due I to axial forces in the waveguide.

2. Description of the Prior Art The ever increasing demand for communications facilities is producing an increasing interest in the use of waveguide transmission lines as extremely broad frequency band long distance transmission media. One requirement for such a waveguide transmission system is that the waveguide tube be isolated from disturbances in the surrounding environment because the performance of the waveguide is critically dependent upon the maintenance of a high degree of straightness of the waveguide tubes. Thus, buried waveguide in particular must be isolated from disturbances in the surrounding environment such as irregularities in the trench bottom as well as earth tremors, vibrations, and faultings.

A limited degree of isolation may be achieved by simply enclosing the waveguide in a relatively large diameter conduit. When disturbances in the surrounding environment distort the conduit, the waveguide can move away from the conduit walls and thereby maintain its straightness.

A waveguide structure having an improved waveguide support system is disclosed in U.S. Pat. No. 3,007,122 issued to F. T. Geyling on Oct. 31, 1961. This patent teaches mounting the waveguide on fluid filled flexible members or bellows which are interconnected by a feeder tube and supported within a protective conduit.

Another waveguide structure having a support system utilizing a pulley and interconnecting cord arrangement is disclosed in US. Pat. No. 3,609,603 issued to M. Lutchansky on Sept. 28, 1971, and assigned to the assignee of this application.

Still another waveguide structure having a support system which places the waveguide under tension within the conduit thereby to maintain the straightness is shown in 'U.S. Pat. No. 3,605,046 issued to S. E. Miller on Sept. 14, 1971., and assigned to the assignee of this application.

Despite the substantial improvements disclosed in the foregoing waveguide structures, the support systems of these structures remain more complex than desired for a system which must be quickly and economically installed underground.

The result of distortions or deflections which occur in presently known waveguide structures is to produce electrical loss through mode conversion. Significant distortions can be produced by weight loading and by the large lateral loads that occur in a route bend due to thermally induced axial tensions when expansion joints are not used in the system. Such deflections occur between the discrete support points utilized in the previously disclosed support systems.

SUMMARY OF THE INVENTION The foregoing problems are solved in accordance with the principles of the invention by utilizing a waveguide 'structure in which the waveguide is supported within a conduit by a low modulus continuous support material such as an oil extended rubber. The waveguide is centered in the conduit and a suitable composition of material is poured into the conduit completely surrounding the waveguide. The material is then cured in place thereby providing a continuous low modulus support for the waveguide. The material prevents moisture and other corrosion producing forces from reaching the waveguide in the event of a failure in the conduit. The low modulus material isolates the waveguide from disturbances in the surrounding environment and eliminates weight and thermal loading induced deflections because of the continuous nature of the support.

DESCRIPTION OF THE DRAWING The invention will be more fully comprehended from the following detailed description and accompanying drawing in which:

FIG. 1 is a longitudinal sectional view of a waveguide structure made in accordance with the invention; and

FIG. 2 is a sectional schematic representation of a method for fabricating the structure of FIG. 1. The same numbers are used throughout to refer to similar elements.

DETAILED DESCRIPTION FIG. 1 shows a sectional view of a waveguide structure 101 comprising a waveguide 2supported within a surrounding protective conduit 4. Waveguide 2 can comprise any of the various well known types of waveguide including helix waveguide, dielectric-lined waveguide, etc., each of which types normally includes a metal tube as its outer jacket. Conduit 4 is substantially larger than waveguide 2. Conduit 4 can comprise a tube of metal such as steel, plastic such as polyvinyl chloride (PVC) or cement-asbestos or the like. Structure 101 is joined with like structures by known coupling apparatus to fonn a long distance transmission line. That is, waveguide 2 is joined on its ends 1 and 3 to respective ends of adjacent waveguide sections and likewise conduit 4 is joined on its ends 5 and 7 to the respective ends of adjacent conduit sections. When connecting waveguide structures 10! to form a continuous line, it is normally necessary to have access to the respective ends 1 and 3 of waveguide 2. Since no substantial relative motion of conduit 4 with respect to waveguide 2 can be obtained as will become apparent subsequently, it is desirable to have ends 1 and 3 of waveguide 2 extend beyond the ends 5 and 7, respectively, of conduit 4 a distance sufficient to allow working room for connecting ends I and 3 with the adjacent waveguide. After the waveguide ends are connected a short conduit coupling section can be installed to bridge between the recessed ends of the adjacent conduit sections 4. This conduit coupling section can be filled with material 6 if its length is significant or if otherwise desired.

Conduit 4 may be deformed by disturbances in the surrounding environment. Thus waveguide 2 must be supported within conduit 4 in such a manner as to be isolated from these deformations. Additionally, the deflections or deformations of waveguide 2 because of its own weight loading and lateral loading caused by the effects of temperature changes must be held to a minimum. A support providing isolation and eliminating weight loading and temperature change induced deflections is obtained by using a very low modulus continuous support material 6 to surround and support waveguide 2 within conduit 4. The low modulus material 6 permits the axis of conduit 4 to readily deform with respect to the axis of waveguide 2 without transmitting a significant portion of the deforming forces to waveguide 2. The continuous support provided by material 6 eliminates weight loading induced deflections by eliminating discrete support points between which such deflections can occur.

Material 6 advantageously can be in a liquid form initiallyto permit the manufacture of waveguide structures as discrete units as illustrated in FIG. 2. A waveguide 2 is placed within a conduit 4 and substantially centered therein about the longitudinal center line 24. This is accomplished by inserting the ends of waveguide2 into concentric flanges 16 on caps 14 which fit over the ends of conduit 4. Caps 14 seal the ends of conduit 4. An appropriate low modulus material 6 in liquid form is pumped from a source 22 via pipe 20 through an opening 18 in one cap 14 into the space between waveguide 2 and conduit 4. An opening 17 is provided in the top cap 14 to permit the escape of gasses during the filling operation. The material 6 is then allowed to cure in place forming the low modulus continuous support previously discussed. Caps 14 are then removed. In order to eliminate weight loading distortions in the waveguide, the assembly shown in FIG. 2 must be vertical. To fabricate long sections it may be desirable to utilize a horizontal process. In this case it is necessary to center the waveguide within the conduit with a compliant virtually continuous initial support that allows the filling of the conduit while not permitting distortions due to weight loading. The initial support will be encased in the low modulus material and the effective modulus of the combination will be somewhat higher than the modulus of either constituent support acting independently. An initial support which could'be utilized for this purpose is a length of compliant tubing wrapped in the form of a helix around the waveguide as described in the copending application of J. C. Bankert et al., Ser. No. 205,796, filed 12-8-71 and assigned to the assignee of this application. It is apparent that waveguide structure 101 can be mass fabricated in a factory and shipped as a unit to the field where it can be quickly installed.

The most important property of material 6 is its foundation modulus or equivalent spring constant per unit length of waveguide 2. Material 6 eliminates deflections due to the weight loading of waveguide 2 by providing a continuous support along waveguide 2. However, deformations of conduit 4 must be isolated or filtered to prevent resulting deflections in waveguide 2. In particular deformations of conduit 4 having mechanical wavelengths corresponding to the beat wavelengths between the primary wave mode being transmitted and degenerate or spurious modes must be filtered. The mechanical wavelengths which are most important at a given operating frequency increase in proportion to the square of the inside diameter of waveguide 2. A material having an equivalent spring constant of no greater than 30 pounds per inch of compression of material 6 per inch of length of waveguide 2 will sufficiently filter or isolate most deformations having mechanical wavelengths of interest from waveguide of sizes presently deemed practical. On the other hand, a foundation modulus of pounds per inch of compression per inch of length is a practical lower bound for limiting the radial deflection of the curved sections of waveguide sufficiently to avoid contact with the protective jacket when the waveguide is subjected to thermal stresses. For example, with material 6 having an equivalent spring constant within the above stated range of 10 to 30 pounds per inch of compression per inch of length,

the losses in a 2 inch inner diameter waveguide enclosed is a steel conduit 4 resulting from deformations of conduit 4 should be no greater than 0.1 db per mile if reasonable manufacturing and installation methods are followed.

The foundation modulus can be lowered for a given material composition by increasing the diameter of conduit 4. The manner in which the foundation modulus varies with the material and geometric parameters is given approximately by the following formula where k is the formulation modulus in pounds per inch of compression per inch of length, E is Young's modulus in pounds per square inch, 1/ is Poisson's ratio, and r, and r refer to the inner and outer radii or material 6, respectively. This formula was derived from results presented by W. A. Gross in an article entitled The Second Fundamental Problem of Elasticity Applied to a Circular Ring in Zeitschrift fuer Angewandte Mathematik und Physik (ZAMP), Vol. III, pp. 71-73, 1957.

The creep properties of material 6 must be such that the increase in deflection under sustained load will not exceed 50 percent of the initial deflection from that load over an expected life of approximately 40 years.

In addition to the foundation modulus and creep requirements discussed above, material 6 must also meet other requirements. For example, it must be compatible with waveguide 2 which typically has a steel outer jacket and conduit 4 which may be steel, polyvinyl chloride, etc. Material 6 must be resistant to attack from agents such as water, oil, micro-organisms, vermin, etc., which can access material 6 is failures occur in conduit 4. Material 6 should have high electrical resistivity, and good tear resistant properties. The proper ties of material 6 must remain stable with time, temperature, and the stresses placed thereon because of deformations in conduit 4. Since material 6 advantageously is in a liquid form initially, the formulation of material 6 should be such that it cures in place at room temperature to provide the low modulus support. Room temperature curing minimizes shrinkage and thereby minimizes stresses resulting from shrinkage.

One material having the foregoing properties is a highly extended or plasticized rubber. Thus a suitable rubber plasticized with a compatible diluent such as a solvent oil can be used for material 6. Rubbers which can be used include the rubbers containing unsaturation such as natural rubber, styrene butadiene rubber, ethylene propylene diene rubber as well as rubbers often used in casting compounds such as silicons, epoxies, and urethanes. Urethane rubbers are preferable and polybutadiene based urethanes are the most preferable. Plasticizers or diluents which can be used include aromatic and aliphatic petroleum oils, dioctal pthalate or other aromatic esters with the aromatic type petroleum oil or plasticizers being required when etc., can also be added to the composition as desired.

Typical composition for material 6 will contain between 5 and percent rubber and 85 to 95 percent diluent.

One example of a plasticized polyurethane rubber is a 7 percent rubber composition, i.e., containing approximately 7 percent rubber polymer in the final formulation, formed from a solution comprising: 50 grams per liter of solution of hydroxyl terminated liquid polybutadiene having a hydroxyl functionality between 2.2 and 2.4 and a hydroxyl content between 0.75 and 0.90 equivalents per kilogram, such as that available under the trademark R-45 HT Poly bd from ARCO Chemical Company as the rubber polymer; grams per liter of solution of MDl (diphenylmethane diisocyanate) prepolymer of R-45 HT Poly bd hydroxyl terminated liquid polybutadiene containing 8 to 10 percent isocyanate (NCO) as the crosslinking rubber polymer; 20 milliliters per liter of solution of dibutyl tin dilaurate such as that available under the trademark Catalyst T-lZ from M&T Chemicals, lnc., as the catalyst; and an aromaticpetroleum oil containing more than 90 weight percent of aromatic molecules, such as that available under the trademark Kenplast G from Kenrich Petrochemicals, lnc., in which the above components are all dissolved. The foregoing solution cures at room temperature to form a low modulus composition. When utilized to support a waveguide having an outer diameter of approximately 2.3 inches in a conduit having an inner diameter of approximately 4.25 inches, the above composition provides a continuous support having a foundation modulus of approximately 20 pounds per square inch. The same material provides foundation modulus of approximately 12 pounds per square inch if the conduit inner diameter is increased to 5.0 inches.

Another example of a plasticized polyurethane rubber is a composition containing approximately 7.7 percent rubber polymer in the final formulation formed from a solution comprising: 55 grams per liter of R-45 HT Poly bd hydroxyl terminated liquid polybutadiene; 22 grams per liter of the MD] prepolymer of the liquid polybutadiene; 20 milliliters per liter of Catalyst T-l2 dibutyl tin dilaurate; and Kenplast G plasticizing solvent oil. This composition provides a material having a foundation modulus of approximately 20 pounds per square inch when used to support a waveguide having an outer diameter of approximately 2.3 inches in a conduit having an inner diameter of approximately 5.0 inches. In the two foregoing examples, the amounts of the hydroxyl terminated polybutadiene can be varied between 50 and 60 grams per liter and the amounts of the MDl prepolymer of the polybutadiene can be varied between 20 and 25 grams per liter.

Another example is a seven percent rubber composition formed from a solution comprising: 70 grams per liter of R-45 HT Poly bd hydroxyl terminated liquid polybutadiene; 8.5 grams per liter of isocyanate (MDI) 65 from The Upjohn Company as the crosslinking agent; 10 milliliters per liter of stannous oleate such as that available under the trademark Catalyst T-6 from M&T Chemicals, lnc., as the catalyst; and Kenplast G plasticizing solvent oil. This composition provides amaterial having a foundation modulus of approximately 10 pounds per square inch when used to support a waveguide having an outer diameter of approximately 2.3 inches in a conduit having an inner diameter of approximately 5.0 inches.

Still another example is an eight percent rubber composition formed from a solution comprising-80 grams per liter of R-45 HT Poly bd hydroxyl terminated-polybutadiene; 9.75 grams per liter of lsonate l43L MDI; l0 milliliters per liter of Catalyst T-6 stannous oleate; and Kenplast G plasticizing solvent oil. This composi tion provides a material havinga foundation modulus of approximately 30 pounds per square inch when used to support a waveguide having an outer diameter of approximately 2.3 inches in a conduit having an inner diameter of approximately 5.0 inches. In the two'foregoing examples, the amounts of the isocyanate can be varied between 8 and 10 grams per liter. ii

In the foregoing examples, the aromatic oil used is available as mentioned from Kenrich Petrochemicals, lnc., under the trademark Kenplast G. Its main properites are:

Specific gravity 1.02

Viscosity at 25 C. l l cps Pour point of F. 40

Mixed analine point F. 60

Flash point F. 290

Hydrocarbon analysis,wt (Clay-Gel analysis) Polar resins 4 Aromatics 95 Saturates l A high flash point is desirable from safety considerations.

The polybutadiene used is a hydroxyl terminated liquid polybutadiene obtainable under the trademark R- HT Poly-bd from the ARCO Chemical Company. Its main properties are:

Polybutadicne isomer content:

Trans l, 4

Cis l, 4 20% Vinyl l 2 20% Viscosity at F. poise Moisture wt 0.05

Iodine Number 398 Hydroxyl Content 0.85 equivalents/kgm Although the foregoing discussion primarily has dealt with the use of a low modulus support material as a distinct support system, the material can also be utilized in conjunction with an initial support system as previously mentioned. The factory assembled unit could include only the initial support system. After installation of such a waveguide unit in the ground, a liquid which would cure to a low modulus material in accordance with this invention could be injected into the conduit surrounding the waveguide. This material would then provide the continuous support necessary to carry the lateral loads associated with temperature changes as well as provide waterproofing and corrosion protection as previously discussed. The initial support system provides for disturbances caused by the initial trench bottom irregularities, etc., and thus the combined support system would need to eliminate only the long term disturbances. The somewhat stiffer support resulting from such a combined support system would be acceptable. Although the support material offers advantages, such as preventing the axial migration of water, when it bonds to both the waveguide and conduit, it is not essential that such bonding be obtained to either the conduit or the waveguide. Without bonding, the material still provides an effective low modulus continuous support even though less corrosion protection may be provided to the waveguide; The equivalent spring constant provided by the support material will tend to be higher in bonded situations than in unbonded applications.

While the invention has been described in detail with respect to specific embodiments thereof, it is to be understood that various modifications thereto might be made by those skilled in the art without departing from the spirit and scope of the following claims.

What is claimed is: l. A waveguide structure comprising in combination: a section of waveguide; a section of rigid protective jacket surrounding said section of waveguide and spaced therefrom; and an initially low viscosity liquid material filling the space between said waveguide and said jacket and supporting said waveguide within said jacket, said material comprising a solvent oil gelled by the in situ catalytic reaction of a hydroxyl-terminated polybutadiene with a crosslinking agent, said hydroxyl-terminated polybutadiene having an average functionality sufficient to form a cross-linked network that gels said oil, said oil comprising the major fraction by weight of said material, and said material having an equivalent spring constant per inch of length along said structure of 10 to 30 pounds per inch of compression of said material. 2. Apparatus in accordance with claim 1 wherein said solvent oil is an aromatic solvent oil containing a major proportion of aromatic molecules; said hydroxylterminated polybutadiene is present in amounts from 50 to 60 grams per liter of said initially liquid material; said crosslinking agent comprises a diphenylmethane diisocyanate prepolymer of said hydroxyl-terminated polybutadiene; and said agent is present in amounts from 20 to 25 grams per liter of said material.

3. Apparatus in accordance with claim 2 wherein said hydroxyl-terminated polybutadiene has a hydroxyl functionality between 2.2 and 2.4 and a hydroxyl content between 0.75 and 0.90 equivalents per kilogram, and said oil contains at least 90 weight percent of aromatic molecules.

4.-Apparatus in accordance with claim 1 wherein said solvent oil is an aromatic solvent oil containing a major proportion of aromatic molecules; said hydroxylterminated polybutadiene is present in amounts from to grams per liter of said initially liquid material; and said crosslinking agent comprises isocyanate and is present in amounts from 8 to 10 grams per liter of said material.

5. Apparatus in accordance with claim 4 wherein said hydroxyl-terminated polybutadiene has a hydroxyl functionality between 2.2 and 2.4 and a hydroxyl content between 0.75 and 0.90 equivalents per kilogram, and said oil contains at least weight percent of aromatic molecules.

Claims

1. A waveguide structure comprising in combination: a section of waveguide; a section of rigid protective jacket surrounding said section of waveguide and spaced therefrom; and an initially low viscosity liquid material filling the spaCe between said waveguide and said jacket and supporting said waveguide within said jacket, said material comprising a solvent oil gelled by the in situ catalytic reaction of a hydroxyl-terminated polybutadiene with a crosslinking agent, said hydroxyl-terminated polybutadiene having an average functionality sufficient to form a cross-linked network that gels said oil, said oil comprising the major fraction by weight of said material, and said material having an equivalent spring constant per inch of length along said structure of 10 to 30 pounds per inch of compression of said material.

2. Apparatus in accordance with claim 1 wherein said solvent oil is an aromatic solvent oil containing a major proportion of aromatic molecules; said hydroxyl-terminated polybutadiene is present in amounts from 50 to 60 grams per liter of said initially liquid material; said crosslinking agent comprises a diphenylmethane diisocyanate prepolymer of said hydroxyl-terminated polybutadiene; and said agent is present in amounts from 20 to 25 grams per liter of said material.

4. Apparatus in accordance with claim 1 wherein said solvent oil is an aromatic solvent oil containing a major proportion of aromatic molecules; said hydroxyl-terminated polybutadiene is present in amounts from 70 to 80 grams per liter of said initially liquid material; and said crosslinking agent comprises isocyanate and is present in amounts from 8 to 10 grams per liter of said material.

5. Apparatus in accordance with claim 4 wherein said hydroxyl-terminated polybutadiene has a hydroxyl functionality between 2.2 and 2.4 and a hydroxyl content between 0.75 and 0.90 equivalents per kilogram, and said oil contains at least 90 weight percent of aromatic molecules.