Apparatus for detecting radiation and munition incorporating same

An apparatus for detecting radiation includes an entry window configured to receive radiation from a target, the entry window having an outer surface and an inner surface, such that the outer surface is not parallel to the inner surface. The apparatus further includes a radiation transmission assembly configured to receive at least a portion of the radiation received by the entry window. The apparatus further includes a radiation sensor configured to receive at least a portion of the radiation from the radiation transmission assembly.

BACKGROUND

1. Field of the Invention

The present invention relates to an apparatus for detecting radiation and a munition incorporating the apparatus.

2. Description of Related Art

Advances in technology have led to improvements in the precision of guided munitions. However, as guidance systems have become more sophisticated, the need for even greater precision is apparent. As military targets are frequently found in civilian surroundings, highly precise guidance systems are required to destroy these military targets while minimizing collateral damage to the civilian surroundings. One approach to increasing the precision of guided munitions is through using a laser designator to illuminate the desired target. The laser signal reflected from the target propagates through a radome of the guided munition. A quadrant detector within the radome of the guided munition then guides the munition to maximize the reflected laser signal received from the illuminated target. Other types of guided munitions sense types of radiation other than light.

While such laser guided munitions have been in operation for quite some time, the radome/detector design limits the velocity of these guided munitions. In particular, many of the radome/detector designs include a hemispherical radome. The velocity of a guided munition having a hemispherical radome is limited due to the radome's aerodynamic drag. In an effort to reduce this aerodynamic drag, the use of more conic-shaped radomes has been attempted. However, this change in radome shape has created problems for the detector system used to guide the munition. For example, such conic-shaped radomes typically suffer from limited field of view and poor detection of small and/or distant targets. Some designs include windows or waveguides that must conform to the outer surface of the munition or radome. Such designs suffer from the same problems, however, as conic-shaped radomes.

There are many designs of apparatuses and methods for directing electromagnetic waves well known in the art, however, considerable shortcomings remain.

SUMMARY OF THE INVENTION

There is a need for an improved apparatus for detecting radiation and a munition incorporating the apparatus.

Therefore, it is an object of the present invention to provide an improved apparatus for detecting radiation and a munition incorporating the apparatus.

This and other objects are achieved by providing an apparatus for detecting radiation. The apparatus includes an entry window configured to receive radiation from a target, the entry window having an outer surface and an inner surface, such that the outer surface is not parallel to the inner surface. The apparatus further includes a radiation transmission assembly configured to receive at least a portion of the radiation received by the entry window. The apparatus further includes a radiation sensor configured to receive at least a portion of the radiation from the radiation transmission assembly.

In another aspect, the present invention provides a munition. The munition includes a body and an apparatus for detecting radiation. The apparatus includes an entry window configured to receive radiation from a target, the entry window having an outer surface exposed from the body and an inner surface, such that the outer surface is not parallel to the inner surface. The apparatus further includes a radiation transmission assembly configured to receive at least a portion of the radiation received by the entry window. The apparatus further includes a radiation sensor configured to receive at least a portion of the radiation from the radiation transmission assembly.

The present invention provides significant advantages, including: (1) detecting radiation within a greater field of view; (2) reducing radiation loss during detection; (3) increasing the aperture within which radiation can be detected; and (4) providing a means for efficiently detecting radiation incorporated with a generally conic-shaped munition section or radome.

Additional objectives, features and advantages will be apparent in the written description which follows.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

The present invention represents an apparatus for detecting radiation and a method of using the apparatus. The apparatus is particularly useful in a guidance system of a munition for detecting light radiating from a target.

FIG. 1depicts a first illustrative embodiment of an apparatus101for detecting radiation according to the present invention. In the illustrated embodiment, apparatus101comprises an entry window103, a reflective conduit105, a filter107, a waveguide109, and a radiation sensor111. Radiation113, such as light, propagates through entry window103and may be reflected by reflective conduit105depending upon the propagation direction of the radiation upon exiting entry window103. Radiation having certain predetermined characteristics, such as a particular wavelength or range of wavelengths of light, is allowed to propagate through filter107. The filtered radiation then enters waveguide109, which directs the filtered radiation toward radiation sensor111. Radiation sensor111detects one or more characteristics of the filtered radiation, such as the intensity of the radiation, and converts the one or more characteristics of the filtered radiation into signals that are then transmitted via one or more contacts115(only one labeled for clarity).

It should be noted that, in some embodiments, filter107is omitted. In such an embodiment, the radiation propagates through entry window103and may be reflected by reflective conduit105depending upon the propagation direction of the radiation upon exiting entry window103. The radiation then enters waveguide109, which directs the radiation toward radiation sensor111. Radiation sensor111detects one or more characteristics of the radiation, such as the intensity of the radiation, and converts the one or more characteristics of the unfiltered radiation into signals that are then transmitted via one or more contacts115.

In embodiments wherein filter107is present, reflective conduit105, filter107, and waveguide109form a radiation transmission assembly116according to the present invention. In embodiments wherein filter107is omitted, reflective conduit105and waveguide109form a radiation transmission assembly according to the present invention, corresponding to radiation transmission assembly116omitting filter107.

Still referring toFIG. 1, entry window103includes an outer surface117and an inner surface119. In the illustrated embodiment, outer surface117and inner surface119are substantially planar. The plane defined by outer surface117, however, is not parallel to the plane defined by inner surface119. In other words, the planes defined by outer surface117and inner surface119intersect. Thus, entry window103exhibits a first thickness t1proximate radiation sensor111and exhibits a second thickness t2, which is different from thickness t1, distal from radiation sensor111. It should be noted that, while outer surface117and inner surface119of entry window103are substantially planar in the illustrated embodiment, the scope of the present invention is not so limited. Rather, one or both of outer surface117and inner surface119may be nonplanar.

Entry window103may comprise any material that will allow radiation of the desired wavelength or range of wavelengths to propagate therethrough. In other words, entry window103is radiolucent at the particular wavelength or range of wavelengths of interest. For example, if the radiation of interest is light, entry window103may comprise a material such as glass, acrylic, or the like.

Still referring toFIG. 1, reflective conduit105reflects some of the radiation that propagates through entry window103, depending upon the propagation direction of the radiation upon exiting entry window103, as will be discussed in greater detail below. Reflective conduit105defines an inner surface121that is configured to reflect a substantial portion of the radiation striking inner surface121. In a preferred embodiment, inner surface121is polished. Reflective conduit105may comprise any suitable material, such as aluminum or the like. Moreover, reflective conduit105may be a separate element or may be incorporated into another element, as will be discussed in greater detail below.

Filter107, if present, receives radiation from reflective conduit105through entrance123and radiation that is allowed to propagate through filter107propagates through exit125. Filter107may comprise any suitable filter for the particular implementation of apparatus101. For example, filter107may substantially exclude or reflect all radiation except radiation exhibiting a particular wavelength or range of wavelengths. In one embodiment, filter107comprises a Fabry-Perot filter, which can be characterized as an interference filter and as a resonant optical cavity. A Fabry-Perot filter comprises a cavity bounded by partially reflective, low-absorption mirror coats on two substantially flat, substantially transparent plates. Such filters exhibit high spectral resolution and, thus, are known as narrow-band-pass filters. Other types of filters for filter107, however, are contemplated by the present invention.

Still referring toFIG. 1, waveguide109receives radiation that is allowed to propagate through filter107from exit125of filter107, if filter107is present. If filter107is omitted, waveguide109receives radiation from reflective conduit105. Waveguide109comprises a structure having the ability to guide the flow of radiation, such as light, along a path parallel to the structure's optical axis and having the ability to contain the energy within or adjacent to the structure's surface. Examples of waveguides configured to guide light include optical fibers, light pipes, and the like. Such optical waveguides often comprise materials such as glass, acrylic, or the like.

In the illustrated embodiment, waveguide109comprises an entrance127and an exit129. Waveguide109tapers from a larger dimension at entrance127to a smaller dimension at exit129. Radiation enters waveguide109via entrance127and exits waveguide109via exit129. Radiation exiting waveguide109via exit129enters radiation sensor111, wherein one or more characteristics of the filtered or unfiltered radiation, such as the intensity of the radiation, are converted into signals that are then transmitted via one or more contacts115(only one labeled for clarity).

FIGS. 2-4depict exemplary rays of radiation, such as light rays being visible to the human eye or non-visible to the human eye, propagating into apparatus101. The exemplary rays have different angles of incidence with respect to entry window103in each of the figures.FIG. 2depicts a ray201propagating substantially parallel to a boresight axis203of a munition, such as munition601ofFIG. 6(not shown inFIG. 2).FIG. 3depicts a ray301propagating at an angle A1with respect to boresight axis203.FIG. 4depicts a ray401propagating at an angle A2with respect to boresight axis203.

Referring now toFIG. 2, ray201, or at least a portion of ray201, propagates through entry window103. As noted above, ray201, prior to encountering entry window103, propagates in a direction substantially parallel to boresight axis203. Because inner surface119of entry window103is not parallel to outer surface117of entry window103, ray201is refracted at a different angle at inner surface119than at outer surface117. It should be noted that the embodiment of entry window103illustrated inFIGS. 1-4has been generally optimized to allow ray201to propagate through entry window103and strike entrance123of filter107at an angle B1that is substantially perpendicular to entrance123of filter107. Having ray201enter filter107from a direction substantially perpendicular to entrance123of filter107is particularly advantageous when filter107is a Fabry-Perot filter. Generally, Fabry-Perot filters exhibit significant losses when rays enter such filters at incidence angles that vary significantly from about 90 degrees. It should be noted, however, that the present invention contemplates tailoring the configuration of entry window103to affect the propagation direction of rays exiting entry window103, for example, as discussed herein with respect toFIG. 5.

Still referring toFIG. 2, a portion of ray201propagates through filter107, depending upon the particular characteristics of filter107. Ray201enters waveguide109and, in the illustrated example, is reflected from a wall131of waveguide109. Preferably, for rays such as ray201propagating through waveguide109, the rays are totally internally reflected within waveguide109. Total internal reflection occurs when light is refracted or bent at a medium boundary enough to send it backwards, effectively reflecting the entire ray. When a ray propagates across a boundary surface, e.g., at wall131of waveguide109, between materials with different refractive indices, the ray will be partially refracted at the boundary surface and partially reflected. However, if the angle of incidence, e.g., angle C, is shallower (closer to the boundary) than the critical angle, then the ray will stop crossing the boundary altogether and, instead, totally reflect back internally within waveguide109. The critical angle is the angle of incidence wherein a ray is refracted so that the ray travels along the boundary between the media and is defined as:

θc=sin-1⁡[n1n2],
wherein θcis the critical angle, n1is the refractive index of the less dense material, and n2is the refractive index of the more dense material. Total internal reflection can only occur where a ray propagates from a denser medium to a less dense medium, i.e., from the medium with a higher refractive index to a medium with a lower refractive index. For example, total internal reflection will occur when a ray propagates from glass to air, but not when the ray propagates from air to glass.

In the example illustrated inFIG. 2, the portion of ray201that enters entrance127of waveguide109substantially, totally internally reflects from wall131of waveguide109into radiation sensor111. A reflective layer (not shown) may, in some embodiments, be applied to wall131. Thus, rays that exceed the critical angle with respect to wall131are substantially, totally reflected back into waveguide109, rather than a portion of the ray being refracted at wall131.

Referring now toFIG. 3, ray301, or at least a portion of ray301, propagates through entry window103. As noted above, ray301, prior to encountering entry window103, propagates at an angle A1with respect to boresight axis203. In the example provided inFIG. 3, the source of ray301is “above boresight.” Because inner surface119of entry window103is not parallel to outer surface117of entry window103, ray301is refracted at a different angle at inner surface119than at outer surface117. Ray301strikes entrance123of filter107at an angle B2that, while not substantially perpendicular with respect to entrance123, provides improved operation over conventional radiation detectors.

It should be noted that the portion of ray301that propagates through exit125of filter107may or may not be substantially, totally internally reflected from wall131of waveguide109into radiation sensor111. If the portion of ray301that propagates through exit125of filter107is not substantially, totally internally reflected from wall131, some losses will result. In an alternative embodiment, however, wall131of waveguide109exhibits a complexly-contoured configuration, such as described in commonly-owned, co-pending U.S. patent application Ser. No. 11/327,562, which is hereby incorporated by reference for all purposes. Such a configuration, in some implementations, lessens the likelihood of attenuation or loss of the amplitude of the portion of ray301allowed to propagate through filter107due to a lack of total internal reflection at wall131of waveguide109. While the use of a waveguide having a complexly-contoured configuration is described concerning the embodiment and example ofFIG. 3, the scope of the present invention is not so limited. Rather, a waveguide having a complexly-contoured configuration may be utilized in any embodiment of the present invention.

Referring now toFIG. 4, ray401, or at least a portion of ray401, propagates through entry window103. As noted above, ray401, prior to encountering entry window103, propagates at an angle A2with respect to boresight axis203. In the example provided inFIG. 4, the source of ray401is “below boresight.” Because inner surface119of entry window103is not parallel to outer surface117of entry window103, ray401is refracted at a different angle at inner surface119than at outer surface117. Ray401strikes entrance123of filter107at an angle B3that, while not exactly 90 degrees with respect to entrance123, is sufficiently close to 90 degrees to allow acceptable operation of filter107. The portion of ray401that propagates through exit125of filter107is substantially, totally internally reflected from wall131of waveguide109into radiation sensor111.

FIG. 5depicts a second illustrative embodiment of an apparatus501for detecting radiation according to the present invention. Each of the components of apparatus501, except for an entry window503, corresponds to the components of the embodiment ofFIG. 1. In the illustrated embodiment, entry window503is tailored to refract ray301more perpendicularly toward entrance123of filter107. In the embodiment ofFIG. 2, entry window103exhibits a thickness t2, distal from filter107, that is greater than thickness t1, proximate filter107. In the embodiment ofFIG. 5, however, entry window503exhibits a thickness t3, proximate filter107, that is greater than a thickness t4, distal from filter107. While the incidence angle B4at which ray301strikes entrance123of filter107is not substantially 90 degrees, the configuration of entry window503provides an improvement in operation of filter107over the configuration of entry window103.

It should be noted that the scope of the present invention is not limited to the apparatuses101and501ofFIGS. 1 and 5, respectively. Rather, the present invention contemplates tailoring the configuration of at least an entry window, such as entry window103or503, according to one or more characteristics of rays of radiation to be detected by the apparatus of the present invention. For example, the scope of the present invention encompasses tailoring the configuration of an entry window, such as entry window103or503, according to the propagation direction of radiation rays of interest, such that the entry window does not exhibit total internal reflection.

FIG. 6depicts an illustrative embodiment of a munition601that includes one or more apparatuses for detecting radiation, such as apparatus101or501, according to the present invention. In the illustrated embodiment, munition601comprises four apparatuses101,501, or the like disposed in a nose603. The present invention, however, contemplates munitions wherein any suitable number of apparatuses101,501, or the like are disposed in a suitable portion of munition601. Preferably, a munition according to the present invention includes a plurality of apparatuses for detecting radiation, such as apparatus101or501, disposed about boresight axis203.

FIGS. 7 and 8depict a top, perspective view and a bottom, perspective view, respectively, of an illustrative embodiment of nose603of munition601(shown inFIG. 6).FIG. 9depicts a cross-sectional view of nose603taken along the line9-9inFIGS. 7 and 8. In the illustrated embodiment, nose603, which is generally conic in shape, includes four apparatuses101(only three apparatuses101shown inFIG. 9) radially disposed about boresight axis203. Entry windows103of apparatuses101are exposed through a body701of nose603to receive radiation. Radiation enters one or more of entry windows103, as discussed herein regardingFIGS. 1-5. Referring in particular toFIG. 9, the illustrated configuration of apparatuses101provides a clear space between apparatuses101for other components of munition601.

FIG. 10depicts an illustrative embodiment of a guidance system1001of munition601. In the illustrated embodiment, guidance system1001comprises four apparatuses101for detecting radiation coupled with a trajectory controller1003. In one particular operation, each apparatus101provides a signal, such as an optical signal or an electrical signal, to trajectory controller1003that is proportional to the amplitude of radiation, such as light, detected by radiation sensor111(shown inFIGS. 1-5). Trajectory controller1003controls a plurality of control surfaces, such as control surfaces605of munition601(shown inFIG. 6). If the amplitudes of the signals provided by each of apparatuses101is substantially equal, the radiation is propagating substantially along boresight axis203. In such a situation, munition601is traveling along a path toward the source of the radiation. If, however, the amplitudes of the signals provided by each of apparatuses101are unequal, trajectory controller1003calculates a desired trajectory for munition601directed toward the source of the radiation based at least upon the amplitudes of the signals. Trajectory controller1003accomplishes the change in trajectory by controlling one or more of control surfaces605of munition601(shown inFIG. 6).

The present invention provides improved field of view, lower radiation losses, and greater radiation aperture than conventional radiation detection apparatuses.

The particular embodiments disclosed above are illustrative only, as the invention may be modified and practiced in different but equivalent manners apparent to those skilled in the art having the benefit of the teachings herein. Furthermore, no limitations are intended to the details of construction or design herein shown, other than as described in the claims below. It is therefore evident that the particular embodiments disclosed above may be altered or modified and all such variations are considered within the scope and spirit of the invention. Accordingly, the protection sought herein is as set forth in the claims below. It is apparent that an invention with significant advantages has been described and illustrated. Although the present invention is shown in a limited number of forms, it is not limited to just these forms, but is amenable to various changes and modifications without departing from the spirit thereof.