US 3797395 A
A compact thermal radiation signalling device employing infrared radiations, the device comprising a pattern of alternating high thermal emissivity zones with low emissivity zones, with a similarly patterned squirrel cage rotatable therearound to expose, to detecting means, at any given instant, emissivities of a predetermined wavelength. The heat causing the alternating emissivity zones to radiate is generated by a suitable chemical charge controllably ignitable within the device itself and carried thereby.
Claims available in
Description (OCR text may contain errors)
0 United States Patent [191 [111 3,797,395 Tyroler Mar. 19, 1974 [5 SIGNALLING DEVICE 3.702.391 11/1972 Wellnite et al. 250/495  Inventor: Jesse F. Tyroler, Dover, NJ. Primary Emminer Maynard R. Wilbur  Assignee: The United States of America as Assistant Examiner-N. Mosko'witz represented by the Secretary of the Attorney, Agent, or Firm--Edward J. Kelly; Herbert Army, Washington, DC. Ber] 2 Fl d: A .1 1966 [2 1 pr 57 ABSTRACT [211 540168 A compact thermal radiation signalling device employing infrared radiations, the device comprising a  US. Cl 102/37,], 250/495, 250/498, pattern of alternating high thermal emissivity zones 102/35.4 with low emissivity zones, with a similarly patterned Y  Int. Cl C06d 1/10 squirrel cage rotatable therearound to expose, to de-  Field of Search 250/ 199, 85, 105, 495, tecting means, at any given instant, emissivities of a 250/496, 498; 102/37.l, 35.4 predetermined wavelength. The heat causing the alternating emissivity zones to radiate is generated by a  References Cited suitable chemical charge controllably ignitable within UNITED STATES PATENTS the device itself and carried thereby.
3.697.329 10/1972 Bunker et al. 250/496 8 Claims, 7 Drawing Figures PATENTEU MAR l 9 I974 SHEET 1 BF 3 JE SSE E TYROLER PATENTEUMAR 19 I974 SHEEI 2 BF 3 350x393. e Y
Swucmtm JESSE E TYROLER 2 W M flttowwd SIGNALLING DEVICE The invention described herein may be manufactured and used by or for the Government for govern mental purposes without the payment to me of any royalty thereon.
This invention relates to a signalling device, and particularly to a thermal radiation signalling device for nocturnal use.
An object of the present invention is to provide a signalling device which uses thermal radiation and particularly having infra-red spectral wave length characteristics, as its source of identification.
Another object of the present invention is to provide a device of the above type which cannot be detected at night by an unaided eye.
A further object of the present invention is to provide a device of the above type which transmits its radiation at a predetermined modulated frequency, consequently permitting detection by a radiation detector system tuned to that frequency.
Still another object of the present invention is to provide a device of the above type which can be adapted for transmitting radiation waves over a wide range of frequencies while maintaining a small and compact size.
A still further object of the present invention is to provide a device of the above type which can be further adapted for radiation in the visible spectral range by a simple change of a single component.
Yet another object of the present invention is to provide a device of the above type which can be detected from any direction when it descends from a height above the earths surface.
It is also an object of the present invention to provide a device of the above type which uses a container having a thermal radiation surface defining an array of alternating high and low emissivity zones, a rotatable shell coaxial with the array and having spaced teeth in a pattern similar to the array, and a heat producing charge in the container for providing the necessary thermal radiation.
Further objects of the present invention will in part be obvious and will in part appear hereinafter.
For a fuller understanding of the nature and objects of the present invention, reference should be had to the following detailed description taken in connection with the accompanying drawings wherein:
FIG. 1 is a perspective view, partly broken away of a signalling device embodying the present invention in one form thereof;
FIG. 2 is a fragmentary view in elevation and partly in section of the signalling device of FIG. 1 showing further details of construction;
FIG. 3 is a diagrammatic representation of an application of the device of FIG. 1;
FIG. 4 is a diagrammatic representation of a method used in the prior art for modulating a signal by using thermal radiation;
FIGS. 5A and 5B are Intensity-Time diagrams representing qualitatively the principles of operation of the present invention; and
FIG. 6 is a perspective view showing, diagrammatically, another form of the present invention.
Radiation signalling devices are either of two types, electrical or pyrotechnic (flares). Flares, or, other type thermal radiation signalling devices, exhibit certain advantages over electrical radiation devices, which advantages render their use more prevalent. A few of these advantages are that they produce greater orders of magnitude of radiation for a given weight device, are more enduring and much cheaper to manufacture than the comparable electrical devices. Furthermore, there are certain military applications where thermal radiation devices are more practicable than are electrical devices, namely the illuminating of specific areas on a battlefield, use in firing from guns, or in aircraft dropping. However advantageous these thermal radiation devices are, they are still encumbered by a distinct dis advantage when it is desirable to use such devices for clandestine signalling purposes. This disadvantage is that these devices are visible and can be readily detectable by the enemy.
One way of maintaining the aforementioned advantages of thermal radiation signalling devices while avoiding the disadvantages of visibility is to cause such a device to emit radiation waves in the infrared spectral range. Although the most common thermal radiation signalling device, the flare, emits significant amounts of infrared radiation (i.e. amounts readily detected by infrared detectors) they are unable to do so without producing visible light. Chemical compositions have been used to produce all infrared signals by enclosing them in containers made of metal, graphite, or some ceramic material. The chemical would cause the container to be heated to a temperature just below where there would be any significant radiation (approximately 600C).
However, any reasonably sized device using the enclosed chemical composition for producing infrared radiation is limited in intensity and consequently limited in its detectable range. A reasonably sized device, as used here, is one which can be readily and conveniently carried by a person and/or launched from a small hand gun. A technique that is used which significantly extends the detectable range of an infrared source is-to modulate (or chop) it at some fixed frequency. This technique allows the signal to be detected at a much greater range since the detector system can be made to be blind to all other frequencies by electronic means and consequently detects these modulated signals at a much greater range. As is illustrated by FIG. 4, the usual or conventional technique of chopping a source is by means of a rotating, slotted disc 10 positioned forwardly of a radiation source 12.
Reference to FIGS. 5A and 58 together with the following description will explain qualitatively, how a modulated signal improves the range of detection of an infrared signal. An infrared detector system seeking an infrared signal will oftentimes be looking at some background such as trees, buildings, automobiles, etc., or on any combination of these objects. If you examined the D.C. signal from this background you may see a signal as a function of time comparable to the dashed line a of FIG. 5A. The actual signal sought, if viewed without background, may have the signal indicated by the dotted line b. The true signal in this case, when viewed by the detector system, would look like the solid line C and the operator would not be able to determine or recognize that the signal which is to be detected is radiating since the natural random fluctuation of background is of the same magnitude as the infrared signal.
If the infrared signal is modulated at a fixed frequency having the same intensity as the original infrared signal, this signal represented by the dotted line d of FIG. 5B, in combination with the same background, now appears to the detector system as solid line e of FIG. 58. Such a detector system could utilize a wide band A.C. responding electrical system which would blend out all the DC. or slow frequency transients. If this desired fixed frequency signal was gradually made lower in intensity, it would again get confused with the background signal. This signal can be further discriminated from the background signal by utilizing a detector system with a narrow frequency response centered around the known frequency of the desired source (i.e., the detector system is made blind to all frequencies except those very close to the modulated frequency of the source). Then all of the frequency components of background signal other than those which correspond to desired modulated signal would be ignored by the detector and the ability of the detector system to see this modulated source would be further improved.
In addition to the background noise the detector electronic system itself adds electrical noise of all frequencies and the filtering described above aids in eliminating this electrical noise in a similar manner as the background noise. Generally, both background and electrical noise decrease at higher frequencies. Therefore, it is advantageous to chop or modulate the desired infrared signal at as high a frequency as possible.
The conventional modulated systems illustrated by FIG. 4 are limited in range of frequencies practicably available. This will be demonstrated by the following example:
When an arrangement such as that of FIG. 4 is used, two methods are available for increasing the chopping rate, namely, increase the angular velocity of the disc 10, or increase the number of openings 14 in the disc. In order to let detectable amounts of radiation through the openings 14 it is essential that the size of the open ings 14 be approximately the same as that of the source 12. Otherwise, there would be significant blocking of the chopped radiation. Therefore, for any given source 12 and size disc the number of openings 14 are limited. Consequently, for any size source, in order to chop at high constant frequencies, it is necessary to have the disc 10 many times the area of the source 12 for practical angular velocities of the disc 10. By way of illustration, assume that the source 12 is circular in shape and one inch in diameter (the following results will actually be. independent of the size of the source) and the disc rotates at 3,600 RPM, and it is desired that the apparent chopping rate of the source 12 by 1,200 cycles/ second or 72,000 cycles/minute. This would mean that it would be necessary to have openings on the disc 10. In order to have the whole surface of the source 12 completely open and closed, it would require a disc diameter at least 13.7 inches. This would make the area of the disc 10 over one hundred times that of the area of the source. This large disc size would render this type of chopping system impractical for many type systems.
Referring now to the drawings, in which like reference characters refer to like parts throughout the vari ous figures, and referring particularly to FIGS. 1 and 2, 11 is generally a thermal radiation signalling device comprising a main body 16 or container, having closed upper and lower ends. The body 16 defines an outer thermal radiation signalling surface having an array of alternating high and low emissivity zones, 18 and 20 respectively. The zones 18 and 20 are equal in configuration, and in this embodiment, extend longitudinally along the peripheral surface of the body 16 from end to end, and further extends along the lower end of the body 16 a fixed distance. The significance of this will become apparent further on in the course of this description. The body 16 of this embodiment is made of steel, and the high emissivity zones 18 are oxidized portions of this steel body 16. This will provide an emissivity of approximately 0.80 at 600C. If a higher emissivity is desired, other materials may be applied to the surface of the body 16. The low emissivity zones 20 are silver platings displaying an emissivity approximately 0.04 at 600C. Other materials and methods of application thereof to the body may be used to vary the emissivity as desired. As in the high emissivity zones 18, the body 16 itself could be used for the low emissivity zones. The importance here, however, is that the array of alternating high and low emissivity zones be presented on the thermal radiation surface.
A shell 22 is rotatably mounted on the body 16 in fixed space relationship thereto. The shell 22 here is related to the body 16 in a fashion commonly known as a squirrel cage arrangement. The shell 22 will, thus, be referred to as the squirrel cage 22 hereinafter. The squirrel cage 22 conforms in shape to that of the thermal radiation signalling surface of the body 16, and is mounted to the body so that it is coaxial with the highlow emissivity zones, 18 and 20, array. In this embodiment the body 16 is cylindrical in shape, with the zones 18 and 20 extending longitudinally over the surface of the body 16. Consequently, the pattern of the array is cylindrical, therefore the squirrel cage 22 is cylindrical, coaxial and coextensive with body 16. FIG. 6 shows, diagramatically, another arrangement of a body 24 having high and low emissivity zones 26 and 28, and a squirrel cage or shell 30 coaxial with the thermal radiation signalling surface.
The squirrel cage 22 has a continuous upper portion 32 with a plurality of spaced teeth 34 extending longitudinally therefrom. The teeth 34 bend radially inwardly at their lower ends terminating in a continuous ring 36 having a diametrical strip 38 extending across the ring 36 and having its midpoint passing through the axis of the body 16. The teeth 34 and the spaces or opening therebetween form a pattern substantially the same as that of the high-low emissivity zone, 18 and 20, array. Thus at one instance the high emissivity zones 18 will be exposed, and at another the low emissivity zones 20 will be exposed. The same relationship exists in the embodiment of FIG. 6 except that the significant geometry are sectors of circles, the high and low emissivity surface 26 and 28 are radiating outwardly through shell 30 which is rotated through the center.
A pivot pin 42 or the like passes through the midpoint of the strip 38 and is fixed to the lower end of the body 16. A hollow tube 44 passes through the midpoint of the upper end of the squirrel cage 22 and into the body 16 by this arrangement.
Drive means are provided for providing energy for rotating the squirrel cage 22. The embodiment of FIGS. 1 and 2 is adapted for atmospheric descent to the earths surface. Thus, vanes 46, suitably designed for providing the desired rotational speed to the squirrel cage 22, are fixed to the continuous upper portion 32 of the squirrel cage 22. Other type drive means, such as motors, spring drives, or the like, can be substituted for the vanes 46 as those skilled in the art can readily discern. The vanes 46 of this embodiment or collapsible and spring loaded, for convenience of carrying or launching from a gun.
Body 16 contains a heat producing charge 50 for providing heat energy to the body 16. The composition of the charge 50 is selected so as to produce a minimum amount of gas when it is ignited, so that no visible sparks are created. The composition of the charge 50 is also selected so that it heats the body 16 to a temperature just below where it emits visible light on the signalling surface thereof. For steel this temperature is 600C. Thus, the signalling surface of the body 16 will emit thermal radiation waves in the infrared spectral range. An igniter 52 situated in the tube 44 will cause ignition of the charge 50. The igniter 52 can be any of the commonly used types, either electrical or chemical.
The operation of the present invention can be best described and understood by considering the following application (refer to FIG. 3). In a nocturnal landing of paratroopers it is desired to collect the troops without enemy detection. The leader of the group carries an infrared signal device 11 as described and a small hand gun for launching same. The rest of the troops are equipped with infrared detectors 54. The leader launches the device 11 to a predetermined height above the earths surface. This launch is timed so that the rest of the troops know when to turn on the detectors 54. A parachute 56 connected to the device 11 by a suspension cable 58 or the like assists the device 11 to descend at a relatively slow rate. The igniter 52 ignites the charge 50 which produces heat energy causing the signalling surface of the device to emit infrared radiation waves. The wind vanes 46 rotate the squirrel cage 22 at a fixed speed thereby causing the infrared waves to be emitted at a fixed frequency known only to the troops. The detectors 54 are tuned into the emission frequency, and are rotated 360 to determine the direction of the infrared signal and simultaneously determine the approximate angle from horizontal for maximum signal so an estimate of the approximate distance to the leader can be made. A rough check on distance would also be made by the strength of the signal. Thus, the troops can be conveniently collected without the danger of enemy detection. This invention can be readily used for many other applications, such as marking parachute drop zones or identifying points on shore lines for clandestine landing operations.
Since the high and low emissivity zones 18 and 20 bend onto the lower end of the body 16 the infrared signal can be detected from any direction including a position directly below the device 11.
The modulation of the infrared signal is determined by the rate of rotations of the squirrel cage 22 and the spacing of the teeth 34 thereon. The frequency or chopping rate would be the cycles per second that the squirrel cage 22 rotates multiplied by the number of spacings between the teeth 34. The chopping rate can be increased by putting more and thinner zones 18 and 20 on the body 16 and accordingly change the spacing and number of teeth 34 of the squirrel cage 22. This modification can be made without changing the overall dimensions of the device 11 and without significantly decreasing the peak output of the modulated signal (since the emitting surface would always be proportional to one-half the projected area of the cylinder regardless of the number of zones used).
As those skilled in this art can readily see the present invention is applicable for producing radiation signals in the visible spectral range also, and a similar device would work for high temperatures and/or visible light if a modulated source of this type was desirable. Since equivalent ranges could be obtained with much smaller signals for modulated than unmodulated, it would be much more difficult for the enemy to detect than an unmodulated signal unless he knew the exact frequency of transmission.
Furthermore, it is not necessary for the zones 18 and 20 or zones 26 and 28 to be limited to the configurations described. Various other patterns can be applied so long as the squirrel cage 22 or shell 30 used displayed a matching pattern.
Since certain changes may be made in the above devices without departing from the scope of the invention herein involved, it is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.
1. A thermal radiation signalling device comprising a hollow body defining an outer thermal radiation surface;
means on said surface defining an array of alternating high and low emissivity zones;
a heat producing charge within said body;
means for igniting said charge;
a rotatable shell coaxial with, and in spaced relationship with said array means, said shell defining a plurality of spaced teeth; and
means for rotating said shell at. a predetermined speed.
2. A device according to claim 1 wherein said hollow body is heat conductive,
said emissivity zones are substantially equal in area and configuration; and
said teeth are equally spaced, said teeth and the spaces therebetween defining a pattern substantially similar to that of said array means.
3. A device according to claim 2 wherein said body is cylindrical,
said emissivity zones extend longitudinally along said surface,
said shell is cylindrical and mounted on said body,
said plurality of teeth extend longitudinally.
4. A device according to claim 3 wherein said body has closed upper and lower ends,
said emissivity zones extend between said ends and further extend along the surface of said lower end to a fixed point thereon,
said shell is coextensive with said body and mounted on one of end thereof, and
said teeth have radially inwardly extending lower portions.
5. A signalling device as set forth in claim 4 wherein said heat producing charge ignites without generating visible products of combustion and transfers heat energy to said surface without visible glow thereof.
6. A signalling device as set forth in claim 4 wherein said high emissivity zones are provided by said surface and said low emissivity zones are provided by layers of silver metal plated on said surface.
7. A signalling device as set forth in claim 4 wherein a parachute is fixed to said body upper end for aiding atmospheric descent of said device.
8. An infrared radiation device for nocturnal signalling, comprising a hollow, cylindrical steel body having closed upper and lower ends and defining an outer thermal radiation surface; said surface having an array of high and low emissivity zones of equal area and configuration, each of said zones extending longitudinally along said peripheral surface between said ends and further extending along the surface of said lower end to a fixed point thereon, said high emissivity zones being provided by said body surface and said low emissivity zones being provided by thin strips of highly reflective metal;
a heat producing charge in said body for producing heat energy without generating visible products of combustion and transferring heat energy to said body surface without visible glow thereof;
means for igniting said charge;
a rotatable cylindrical shell coaxial and coextensive with said body and mounted on one of said ends of said body, said shell having a continuous portion and a plurality of longitudinally extending equally spaced teeth having radially inwardly extending lower portions, said teeth and said spaces therebetween together defining a pattern substantially similar to that of said array;
and means for rotating said shell at a predetermined speed.