US3846798A

US3846798A - Integrated window, antenna, and waveguide with plasma alleviation

Info

Publication number: US3846798A
Application number: US00752082A
Authority: US
Inventors: J Carl
Original assignee: United States Department of the Air Force
Current assignee: United States Department of the Air Force
Priority date: 1968-08-12
Filing date: 1968-08-12
Publication date: 1974-11-05
Anticipated expiration: 1991-11-05

Abstract

A method and an apparatus for cooling an electromagnetic wave permeable antenna window, and for alleviating a boundary layer of dense plasma, particularly for use in high performance reentry space vehicles having a sharp or conical configuration. The window, in a shock mounting, is of multilayered construction, having alternating shock absorbent bonded layers with channels or apertures spaced throughout. Gas, such as silicon tetrafluoride or sulfur hexafluoride, flows through an associated waveguide and is introduced, through the channels or apertures, into and through the window. As the coolant gas passes through the window, the window is cooled and does not ablate. Shear forces are used to maintain the window/ablator mold line. The gas then flows into the boundary layer of dense plasma, reducing the electron concentration of the plasma, and increasing the capability of transmitting or receiving electromagnetic waves.

Description

United States Patent 1191 1111 3,846,798

Carl Nov. 5, 1974 INTEGRATED WINDOW, ANTENNA, AND

WAVEGUIDE WITH PLASMA Primary ExaminerMaynard R. Wilbur ALLEVIATION Assistant Examiner-Richard E. Berger [75] Inventor: James R. Carl, Bridgeton, Mo. gi z gq f iz or firm-Harry Herbert [73] Assignee: The United States of America as v represented'by the Secretary of the 57 ABSTRACT United States Air Force, Washington DC A method and an apparatus for cool ng an electromagnenc wave permeable antenna wmdow, and for [22] Filed: Aug. 12, 1968 alleviating a boundary layer of dense plasma, particularly for use in high performance reentry space vehi- [21] Appl' 752082 cles having a sharp or conical configuration. The window, in a shock mounting, is of multilayered construc- [52] U.S. Cl .L 343/705, 343/784, 343/872, tion, having alternating shock absorbent bonded layers 333/98 R, 3925/65 with channels or apertures spaced throughout. Gas, [5 1] Int. Cl. H0lq 1/28 such as silicon tetrafluoride or sulfur hexafluoride, [58] Ifield of Search 343/784, 783, 705; flows through an associated waveguide and is intro- 333/22 F, 98, 98 P; 313/35; 325/65 duced, through the channels or apertures, into and through the window. As the coolant gas passes [56] References Cited through the window, the window is cooled and does UN STATES PATENTS not ablate. Shear forces are used to maintain the win- 2577 463 12/1951 l-lansellm 343/784 dOw/ablato mold line' The gas thenflows into the 2:947:956 8/1960 Alexander et al. 333/98 boundary f w dense Plasma, g the electron 3,110,000 11/1963 Churchill 333/98 P ux cohcehtrahon 0f the Plasma, and mcreasmg the p 3,128,965 4/1964 Ziemer 325/65 ux bility of transmitting or receiving electromagnetic 3,277,375 10/1966 Nelson et al 325/65 waves.

315331223 5/1323 7 ib bifi'. 537/3; 10 cla-ms, s

INTEGRATED WINDOW, ANTENNA, AND WAVEGUIDE WITH PLASMA ALLEVIATION BACKGROUND OF THE INVENTION This invention relates to a method and an apparatus for cooling an electromagnetic wave permeable antenna window, and, additionally, for alleviating a boundary layer of dense plasma.

This invention is particularly well suited for use, generally, in high thermal and high shear environments and, more specifically, in high performance reentry space vehicles having a sharp or conical configuration.

Electromagnetic wave permeable windows are not new. They have been made of glass, mica and, more recently, of alumina ceramic. They have been vacuum sealed or otherwise affixed to antennas, such as the horn type, and to output waveguides. Their use has been extended, in fact, to cooling structures, but as far as is known, without great success. Cooling, for example, by air, water and even specific gases, has been attempted at or contiguous to the periphery of the window. The results have been uneven cooling of the window, particularly at the center thereof, and resultant cracking of the window. Even where cracking did not occur, the structure of the window or of the coolant carrier, or both, resulted in significant loss of transmission of electromagnetic waves from theantenna or output waveguide.

In addition, in connection with the use of electromagnetic permeable windows in antenna or output waveguides for use in airborne vehicles, particularly sharp or conical configurated high performance reentry vehicles, there is the problem of dense plasma which can prevent, or at least severly limit, propagation or transmission of electromagnetic waves to or from the vehicle. This transmission limitation is well-known not only to those skilled in the art, but also to the general public and to commercial communications mass media, such as television, which often refers to this phenomena, in connection with coverage of space flights, as communications interference or communications blackout caused by a plasma layer or a plasma sheath.

My invention cools electromagnetic wave permeable windows without deleterious effect and, concurrently, eliminates or at least minimizes the problem of transmission limitation caused by the dense plasma in, near, or about the window, when the window is used in an airborne vehicle.

SUMMARY OF THE INVENTION My invention pertains to a method and an apparatus for cooling an electromagnetic wave permeable antenna window and for alleviating a boundary layer of dense plasma. More particularly, this invention relates to an integrated electromagnetic wave permeable window, antenna, and waveguide, with plasma alleviation, for use, for example, in high performance reentry space vehicles having a sharp or conical configuration.

Thus, an object of my invention is to provide a novel electromagnetic wave permeable window for use with an antenna or a waveguide.

Another object of my invention is to provide an electromagnetic wave window which can be simply and economically constructed and which can be efficiently cooled without any deleterious effect.

Still another object of my invention is to provide an electromagnetic wave permeable window which can be used in high thermal and high shear environments.

A further objectof my invention is to provide an electromagnetic wave permeable window for use in high performance reentry space vehicles having a sharp or conical configuration.

A still further object of my invention is to provide a novel method of cooling an electromagnetic wave permeable wave window.

An additional object of my invention is to provide a method for alleviating a boundary layer of dense plasma in, near and about an electromagnetic wavepermeable window to eliminate, or at least uminimze, the problem of transmission limitation caused by said dense plasma.

These, and still other, objects of my invention will be-- come readily apparent after a consideration of the description of my invention and reference to the drawings.

DESCRIPTION OF THE DRAWINGS FIG. 1 is a top plan view, in schematic form, ofa portion of a sharply configurated reentry space vehicle showing an embodiment of my invention;

FIG. 2 is a cross-sectional view, in schematic form, taken along line I-I of FIG. 1;

FIG. 3 is also a cross-sectional view, in schematic form, buttaken along line IIII of FIG. 1;

FIG. 4 is a top plan view, in schematic form, of a portion of a sharply configurated reentry space vehicle showing another embodiment of my invention; and

FIG. 5 is a cross-sectional view, in schematic form, taken along line III-Ill of FIG. 4.

DESCRIPTION OF THE EMBODIMENTS With reference to FIG. 1, wherein a portion of a sharply configurated reentry space vehicle 10 is shown, the electromagnetic wave permeable window 21 is flush, or essentially level with, the ablative surface or shield 11 of space vehicle portion 10. Window 21 is a part of an integrated window-antenna-waveguide assembly 20, of which the antenna and waveguide component parts are not shown in FIG. I.

In FIG. 2, the ablative surface or shield 11, the window 21, and the antenna-waveguide portion of the integrated window-antenna-waveguide assembly 20, and their relative positioning are better seen. The window 21 is at the antenna (or output waveguide) interface 24 and said window is of the multilayered type, i.e., layered construction, with alternating bonded layers, such as 22 and 23, preferably of fused silica layers with less dense layers which are sintered until bonds are formed.

seen. It is to be noted that the alternating

bonded layers

22 and 23 of window 21 are also contoured.

Window 21 is in a suitable shock mounting (not shown).

In FIGS. 4 and 5 are depicted views of another embodiment of my invention.

In this embodiment, and specifically with reference to FIG. 4, there is a coolant fluid outlet 55 disposed adjacent to the electromagnetic wave permeable window 51, of integrated antenna-window-waveguide assembly 50, in ablative surface or shield 41 of space vehicle portion 40.

In FIG. 5 is shown window 51 with alternating bonded layers such as 52 and 53, preferably of fused silica layers with less dense layers which are sintered until bonds are formed, antenna 54, and coolant fluid flow conduit 55, just upstream of window 51, as they are relatively positioned in ablative shield 41.

It is to be noted that in this embodiment, window 51 does not have any artificially constructed channels, such as 25, FIGS. 2 and 3.

The coolant fluid, such as silicon tetrafluoride gas or sulfur hexafluoride gas 56, flows through conduit 55.

Window 51 and coolant fluid flow conduit 55 are flush with the contouring of ablative shield 41 at the air flow boundary surface 57.

Window 51 is in a suitable shock mounting (not shown).

MODE OF OPERATION OF THE PREFERRED EMBODIMENT As to the embodiment shown in FIGS. 1, 2 and 3, the gas coolant 28, such as silicon tetrafluoride or sulfur hexafluoride, is introduced through conduit 26 which in this case serves the dual purpose of coolant delivery system and waveguide. The flow of the gas coolant through the waveguide, as such, protects the waveguide from high voltage breakdown.

Coolant gas 28 leaks into electromagnetic wave permeable window 21 through artifically constructed channels 25, cooling the window. As a result, window 21 does not ablate. Shear forces are used to maintain the window/ablator mold line or air flow boundary 27, so that if the shearing forces are sufficiently strong, window 21 will shear at the bond lines between alternating bonded layers, such as 22 and 23, as a particular bond line is reached and is acted upon by the shearing forces. It is here to be noted that the multilayered construction of window 21 with shock absorbent bonding layers, such as 22 and 23, preferably of fused silica layers with less dense layers which are sintered until bonds are formed, together with the shock mounting (not shown) of window 21, permits window 21 to withstand much higher shock levels than any known conventional solid electromagnetic wave permeable window. The layered construction, with alternating bonding layers, of window 21 serves as acoustical mismatch for the attenuation of shock waves.

Coolant gas 28, after flowing through artifically constructed channels 25, passes into boundary layer 27, a region of high temperature and high electron concentration, cools that boundary layer 27 and, thereby, reduces the electron concentration, or dense plasma, and eliminates, or at least minimizes, the problem of transmission limitation caused by the dense plasma.

As to the embodiment shown in FIGS. 4 and 5, the

6 coolant gas 56, such as silicon tetrafluoride or sulfur hexafluoride, is introduced through conduit 55 into boundary layer 57, which is a region of high temperature and high electron concentration. There, the coolant gas 56, moving downstream, cools window 51 by cooling boundary layer 57. Additionally, and as a result of cooling of boundary layer 57, the electron concentration or dense plasma is eliminated, or at least minimized, so that transmission of electromagnetic waves is significantly improved.

Window 51 is structured similarly to window 21, FIGS. 2 and 3, except of course that it does not have artificially constructed channels 25, FIGS. 2 and 3. In

essence, it does not ablate; shear forces are used to maintain the window/ablator mold line or air flow boundary 57; window 51 will shear at the particular or appropriate bond line if sufficient shearing force is applied; and, window 51 will withstand much higher shock levels than conventional solid electromagnetic wave permeable windows because, in addition to the foregoing, it is also shock mounted (not shown) and its layered construction, with alternating bonding layers, serves as acoustical mismatch for the attenuation of shock waves.

While there has been shown and described the fundamental novel features of my invention, as applied to the preferred embodiments, it is to be understood that various substitutions and omissions may be made by those skilled in the art, without departing from the spirit of the invention. For example, the window may be used as waveguide window, rather than an antenna window; the configuration or periphery of the window may be circular, or otherwise configurated as necessary or desired; the artifically constructed coolant flow channels through the window may be replaced by natural channels, simply by using gas-pervious electromagnetic wave permeable materials as the bonded layers; the window laminates may be flat, rather than contoured; and the window laminates may be of pyrolytic boron nitride layers with hot pressed boron nitride as bonding layers.

What I claim is:

1. An electromagnetic wave transmitting and receiving structure, comprising:

a. an antenna;

b. an electromagnetic wave permeable window which includes:

(1). a plurality of alternating bonded layers; and

(2). a plurality of hollow channels, essentially parallel to each other and extending throughout said window.

c. means for supporting said electromagnetic wave permeable window within said antenna; and

d. a waveguide affixed to said antenna.

2. The apparatus, as set forth in claim 1, wherein said alternating bonded layers are of fused silica and of less dense silica which has been sintered.

3. The apparatus, as set forth inclaim 1, wherein said alternating bonded layers are of pyrolytic boron nitride and of hot pressed boron nitride.

4. An apparatus for cooling an electromagnetic wave transmitting and receiving structure, and for alleviating a boundary layer of dense plasma, in a high performance reentry space vehicle, comprising:

a. an antenna;

b. an electromagnetic wave permeable window, having a plurality of alternating bonded layers of fused silica and of less dense silica which has been sintered, and having a plurality of hollow channels essentially parallel to each other and extending throughout said window;

c. means for supporting said electromagnetic wave permeable window within said antenna;

(1. a waveguide affixed to said antenna;

e. a coolant fluid; and

f. means for conducting said coolant fluid to said hollow channels of said electromagnetic wave permeable window.

5. The apparatus, as set forth in claim 4, wherein the coolant fluid is silicon tetrafluoride.

6. The apparatus, as set forth in claim 4, wherein the coolant fluid is sulfur hexafluoride.

7. The apparatus, as set forth in claim 4, wherein the means for conducting said coolant fluid to said hollow channels of said electromagnetic wave permeable window is the said waveguide.

8. An apparatus for cooling an electromagnetic wave transmitting and receiving structure, and for alleviating a boundary layer of dense plasma, in a high perform- I ance reentry space vehicle, comprising:

a. an antenna;

10. The method of cooling an electromagnetic wave transmitting and receiving structure, and of alleviating a boundary layer of dense plasma, in a reentry space vehicle having an electromagnetic wave permeable window, comprising the step of flowing a coolant fluid through hollow channels in said window.

Claims

1. An electromagnetic wave transmitting and receiving structure, comprising: a. an antenna; b. an electromagnetic wave permeable window which includes: (1). a plurality of alternating bonded layers; and (2). a plurality of hollow channels, essentially parallel to each other and extending throughout said window. c. means for supporting said electromagnetic wave permeable window within said antenna; and d. a waveguide affixed to said antenna.

3. The apparatus, as set forth in claim 1, wherein said alternating bonded layers are of pyrolytic boron nitride and of hot pressed boron nitride.

4. An apparatus for cooling an electromagnetic wave transmitting and receiving structure, and for alleviating a boundary layer of dense plasma, in a high performance reentry space vehicle, comprising: a. an antenna; b. an electromagnetic wave permeable window, having a plurality of alternating bonded layers of fused silica and of less dense silica which has been sintered, and having a plurality of hollow channels essentially parallel to each other and extending throughout said window; c. means for supporting said electromagnetic wave permeable window within said antenna; d. a waveguide affixed to said antenna; e. a coolant fluid; and f. means for conducting said coolant fluid to said hollow channels of said electromagnetic wave permeable window.

8. An apparatus for cooling an electromagnetic wave transmitting and receiving structure, and for alleviating a boundary layer of dense plasma, in a high performance reentry space vehicle, comprising: a. an antenna; b. an electromagnetic wave permeable window, having a plurality of alternating bonded layers of fused silica and of less dense silica which has been sintered; c. means for supporting said electromagnetic wave permeable window within said antenna; d. a waveguide affixed to said antenna; e. a coolant fluid; and f. means for conducting said coolant fluid to the boundary layer.

9. The apparatus, as set forth in claim 8, wherein the means for conducting said coolant fluid to the boundary layer is a conduit upstream of said electromagnetic wave permeable window.