Radiant energy – Photocells; circuits and apparatus – Optical or pre-photocell system
Reexamination Certificate
2001-11-15
2003-07-15
Le, Que T. (Department: 2878)
Radiant energy
Photocells; circuits and apparatus
Optical or pre-photocell system
C204S557000
Reexamination Certificate
active
06593588
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to sensors for detecting changes in a variety of conditions, including temperature, chemical conditions including pH changes and levels of specific ions, levels of biological antigens, radiation levels, and electrical field strength. Sensors for detecting these parameters are based on the principle wherein the integrated intensity of light (or other wave energy) in the vicinity of a light source, diffused and scattered within an optical scattering medium, will increase as the effective concentration of the scattering centers within the medium increases, i.e., as the average distance between scattering centers decreases or as the scattering centers change their light-scattering properties. The sensors and detectors of the present invention may be used in a wide variety of applications, including laboratory and clinical instrumentation as well as industrial uses in a variety of applications wherein detection of these parameters is required.
BACKGROUND OF THE INVENTION
The present invention relies on the principle whereby the intensity of light or other wave energy from a source, which is diffused and scattered within a scattering medium such as translucent foam, is increased in the vicinity of the light source as the effective concentration of scattering centers within the medium increases, i.e., the average distance between scattering centers decreases or their light-scattering properties are enhanced.
The region within the medium which contains scattered light from the source is known as a “virtual optical cavity”, in that the properties of an optical cavity are emulated. For convenience, the term “optical cavity” will refer to a virtual optical cavity. The intensity of scattered light at any particular position within an optical cavity is referred to as the “integrated intensity” of the light at that position. Thus, as the medium is compressed by, for example, the application of pressure, the integrated intensity of the light within the region immediately surrounding the light source increases in intensity. The increase is proportional to the increase in concentration of scattering centers. This in turn may be related increases in pressure applied to the medium. A consequent decrease in light intensity occurs within a more distant region within the medium. For example, U.S. patent application Ser. No. 08/895,268 (Reimer et al.) describes a pressure sensor based on this principle, in which the scattering medium may comprise either a material having scattering centers dispersed generally evenly therein, or a hollow deformable container, the inner surface of which diffuses light or other wavelike energy directed into the medium. The light source forms an integrated cavity within the medium, defined by a region containing fully scattered light from the source. When pressure is applied to the medium, the medium compresses and increases the concentration of scattering centers in the region surrounding the light source. The resulting increase in light intensity is detected by a receptor and communicated to an information processor. In one version, a multiplicity of light sources and receivers permits the general location of the pressure to be resolved. Within an apparatus of this type, one or more light sources and detectors are provided, with each source and its corresponding detector being generally adjacent to each other or close together. Most conveniently, the scattering medium comprises a compressible, translucent material such as plastic foam. An array of source/detectors pairs may be provided to provide localized pressure detection means. The detector or detectors are associated with a signal processing unit, which receives information from the detectors corresponding to the detected integrated light intensity levels, and resolves this information into a corresponding pressure level experienced by the scattering medium.
It has not been previously proposed to provide an apparatus which makes use of an integrating optical cavity of the above type for the detection of parameters other than pressure. Thus, any phenomenon, condition or parameter which increases the concentration of scattering centers within a scattering medium, may be detected by means of detecting an increase or decrease in integrated light intensity within the scattering medium, wherein the light is provided by a source of known intensity.
It has been observed that polymer gels, which are generically referred to as hydrogels, can be adapted to serve as a light-scattering medium. An example of such a gel is polyacrylamide. These gels can be engineered to swell or shrink in response to specified chemical or physical changes in their environment. For example, a hydrogel graft copolymer of PMMA (polymethylmethacrylate) and PEG (polyethylene glycol) is pH sensitive. Carboxylic acid groups of the PMMA tend to be protonated at low pH. Hydrogen bonds form between carboxylic acid groups and the ether oxygens on the PEG chain. This reversible ionic polymerization increases the hydrophobicity of the polymer matrix, and water is expelled from the gel and the matrix tends to shrink or collapse. The total resulting volume change can be large, as much as a factor of 1000. If the collapsed gel is exposed to high pH values, the carboxylic acid group become ionized, and the gel becomes more hydrophillic; it then absorbs water and expands. Examples of such a gels have been described by Tanaka in U.S. Pat. Nos. 6,030,604; 5,801,221; 5,242,491; 4,732,930. It is also feasible to provide gels within which functional groups are contained.
It will be understood that within this specification, references to the term “light” apply to other wave energy sources, including sound and non-visible electromagnetic radiation, with suitable and obvious modifications to the apparatus and method embodiments described herein.
SUMMARY OF THE INVENTION
An object of the present invention is to provide an improved sensor which may be adapted to detect levels of various physical phenomena, including pH, temperature, ion level, radiation, electrical field strength, and biologically active antigens.
In one aspect, the invention comprises a sensor for detecting various physical or chemical changes within the environment surrounding the detector. In this aspect, the invention comprises a light source, translucent medium having light scattering centers dispersed therein to fully scatter light from the light source, a detector positioned in the vicinity of the source responsive to the integrated intensity of light from the light source, and an information processing means in communication with the detector for translating the detected light intensity into an electronic signal responsive to the level of a selected physical or chemical parameter. The translucent medium and/or the scattering centers are selected to respond to changes in various physical or chemical parameters by altering either the concentration or reflective properties of the scattering centers in the region surrounding the light source. This region is referred to herein as an “optical cavity”, and it is understood that this is defined by a region within the translucent material in the vicinity of the light source, within which light from the light source is fully scattered and an increase in the concentration of scattering centers produces a measurable increase in the integrated intensity of light. Outside the cavity, the intensity of scattered wave energy decreases as the dimension of the cavity decreases. The boundary of the cavity is related to the characteristic scattering length of the medium. Typically the interior of the cavity will be less then one characteristic scattering length removed from the energy source whereas the exterior of the cavity will be more then one characteristic scattering length removed from the energy source.
In one version, the invention comprises a temperature sensor having an electronic output responsive to the temperature of a selected medium. In this version, the scattering medium comprises a solid material
Canpolar East Inc.
Fincham Ian
Le Que T.
McFadden Fincham
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