Reflected radiance sensors for detection of reflected radiation

Details Reflected radiance sensors for detection of reflected radiation Reflected radiance sensors for detection of reflected radiation

1998-09-09

2001-06-12

Lee, John R. (Department: 2878)

Radiant energy

Photocells; circuits and apparatus

Optical or pre-photocell system

C250S239000, C356S218000

Reexamination Certificate

active

06246045

ABSTRACT:

FIELD OF THE INVENTION
The present invention generally relates to radiation sensors, and more particularly, to radiation sensors that detect and measure surface reflected radiation.
BACKGROUND OF THE INVENTION
Radiation sensors provide a wide variety of functionality in both military and commercial applications. For example, radiation sensors are utilized in communication systems, in lighting control systems, and in imaging systems, just to name a few. In many applications, the radiation sensor is mounted to a surface so that the angular field of view (FOV) of the sensor does not intersect the surface, that is, the sensor is configured to detect radiation incident on the surface to which the sensor is mounted. The sensor is typically configured so that its FOV is directed into open space for the detection of incident radiation, without reflection off the surface to which the sensor is mounted. Examples of such sensors can be found in one or more of U.S. Pat. Nos. 2,964,636, 4,636,631, and 5,308,985.
Nonetheless, it may be desirable in many applications to detect and measure radiation reflected off a surface to, for instance, control the reflected radiation intensity (radiance) or characterize the reflectivity of the surface. For example, in a radiant heating system where reflective surfaces are utilized to redirect the radiant heat flux it may be desirable to precisely monitor the intensity of the radiation reflected at several points on the surfaces. Monitoring the intensity of the reflected radiation or changes in reflectivity may be important in order to accurately establish and control radiant intensity or uniformity, or to establish and maintain a desired spatial intensity pattern. It may also be desirable to monitor the degradation in the reflectivity of the reflective surfaces over time, especially where the cumulative effect may be significant. This would be possible using a known incident radiant intensity and a calibrated reflected radiance sensor.
As another example, it may be desirable to precisely control the intensity (luminance) reflected off of surfaces in lighting systems used in a factory, office, aircraft, etc. The reflectivity of surfaces degrade through exposure to the elements of nature and normal use, which may decrease their ability to effectively reflect light onto the subject of interest. In addition, the intensity of the light source may change over time, and thus causing a reduction in reflected luminance. Source intensity degradation also applies to radiant heating systems. By monitoring the reflected radiance or luminance, the source intensity can be precisely controlled to compensate for source intensity changes and surface reflectance changes. These are just two examples of the many circumstances in which it may be desirable to measure the radiance or luminance reflected off a surface, and it will be appreciated by those of ordinary skill in the art that numerous other circumstances exist in which it would be desirable to measure reflected radiation.
However, in order to detect the radiation reflected off a surface, a probe or other means is typically utilized to position the sensor over the surface so the FOV of the sensor is directed toward the general area of interest of the surface. However, the probe or other means used to position the sensor may interfere with or possibly block a portion of the incident radiation. Moreover, the reflected radiation incident on the sensor may be redirected toward the surface in a manner that produces multiple reflections before reaching the sensor, which may cause inconclusive sensor readings. The probe may also not be capable of being precisely and consistently positioned over the surface so as to render conclusive measurements. Thus, the amount of radiation reflected off the surface may not be accurately measured, and therefore, may be irrelevant. Usually, reflected radiation is remotely measured with radiometer instruments, which are expensive, bulky, and can block some of the incident radiation. Furthermore, they are not integrated with the surface so that they may be operated continuously for uninterrupted monitoring which advantageous in critical control situations.
Therefore, an unsatisfied need exists in the industry for a sensor for accurately and consistently measuring the radiation reflected off a surface.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide an improved radiation sensor.
It is another object of the present invention to provide an improved radiation sensor for measuring the radiation reflected off the surface to which the sensor is mounted.
It is another object of the present invention to provide an efficient surface mounted radiation sensor.
These and other objects are provided according to the present invention by a reflected radiance (i.e., luminance) sensor that is held in a spaced-apart relationship with a surface which intersects the field of view of the sensor so that the radiation reflected off the surface can be measured. The sensor is configured to detect only reflected radiation so that the reflected radiation is accurately measured without any direct incident component. A support structure is utilized to hold the sensor in place. The support structure is preferably made of material that is substantially invisible (i.e., transparent) to the radiation wavelength band of interest. The design of the support structure in accordance with the present invention is not limited to any one design, but may be designed for optimum performance in a particular application. For instance, a support structure may be contoured to the surface to which the sensor is mounted in order to reduce air resistance or disturbances along the surface where such disturbances may be undesirable. Advantageously, the reflected radiance sensor of the present invention is able to provide measurement data on a real-time or periodic basis without having to use a probe or other intrusive means which may affect the accuracy of the measured reflected radiation. Further, the reflected radiance sensor of the present invention is mounted to the surface so it is at a known, predetermined distance from the surface which renders consistent measurements.
In accordance with an aspect of the present invention, a sensor that measures the intensity of radiation reflected off a surface comprises a radiation detector and a support structure for positioning the radiation detector in a spaced-apart relationship with respect to the surface to which the sensor is mounted, so that the field of view of the radiation detector intercepts the surface. This support structure may take a frusto-conical shape, though it will be appreciated by those of ordinary skill in the art, that the support structure may take other suitable shapes. The reflected radiance sensor may further include a lens which is optically coupled to the radiation detector. In one embodiment, the lens may comprise an immersion lens that may be attached to the radiation detector using an optical adhesive.
The support structure may define a cylindrical cavity, wherein the lens is disposed in the cavity adjacent to the radiation detector. The lens may take any number of shapes, such as hemispherical, quasi-hemispherical, cylindrical, or half-cylindrical. Preferably, the lens comprises a material having a refractive index greater than 1.25. The radiation detector may be positioned at a focal point of the lens in order that a smaller diameter detector may be utilized. Further, the lens preferably includes means of preventing direct radiation from being incident on the radiation detector. The means for preventing direct light incidence on the detector may take many forms, such as a black mask at the apex of the lens, or a planar surface at the bottom of the lens opposite the radiation detector.
Nonetheless, regardless of whether or not a lens is utilized, the radiation detector is disposed in a position by the support structure that essentially prevents direct incident radiation from being detected by the radiation detector. Thus, the radiation de

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