Radiant energy – Photocells; circuits and apparatus – Optical or pre-photocell system
Reexamination Certificate
2001-01-23
2003-08-12
Allen, Stephone B. (Department: 2878)
Radiant energy
Photocells; circuits and apparatus
Optical or pre-photocell system
C250S226000, C356S402000, C422S086000, C436S167000
Reexamination Certificate
active
06605804
ABSTRACT:
BACKGROUND INFORMATION
There is a plurality of fields of application for sensors. These include the use of gas sensors for early fire detection. Thus, prior German patent application 197 41 335.8 describes optical gas sensors which are based on an interaction of specific gases with a semitranslucent layer, an absorption factor of light of a specific wavelength being dependent on the gas concentration. Disadvantageous in the known optical gas sensors are the relatively complex and voluminous measurement set-ups since, apart from an optical transmitter and an optical receiver, it is required to arrange a gas-sensitive layer within a beam path between these two components. In particular, measurements where the intention is for gas concentrations to be measured at points which are spatially distant from the optical components and which are, for example heavily thermally stressed, are possible only with difficulty.
SUMMARY OF THE INVENTION
The optical sensor according to the present invention offers the advantage that very compact and inexpensive, integrated components are picturable because of the spatial separability of the at least one optical transmitter and the at least one optical receiver and because of a sensitive layer which interacts with a sample, for example, a gas or a gas mixture, and which changes the transmission of light of a specific wavelength. If an integrated module preferably composed of an optical transmitter and of an optical receiver, is coupled via optical waveguides to the sensitive layer, which can be installed at any distant location, these units can completely be spatially separated from one another and, consequently, the gas-sensitive layer can be positioned at locations where, due to the spatial conditions or because of the thermal or mechanical conditions, no sensitive optical and/or electronic components can be installed.
By using, as the sensitive element, a gas-sensitive layer or membrane, also designated as optode, which is substantially permeable to electromagnetic radiation, and which changes its absorption properties and/or its refractive index for electromagnetic radiation in response to a contact with a gas or a gas mixture, very compact and miniaturizable gas sensors can be manufactured in simple manner. Understood by an optode in connection with the present invention, are, in particular, polymer layers which, due to indicator substances intercalated therein, exhibit a dependency of the light transmission on the concentration of a specific gas in the atmosphere surrounding the optode. Optodes which are used according to the present invention respond to the concentration of a specific gas in a selective and reversible manner. By measuring the absorption properties of the indicator substance which is present in the gas-sensitive layer or membrane, and which is exposed to and interacts with the gas, it is possible for very low gas concentrations to be measured and detected using relatively simple optical devices. The indicator substance present in the gas-sensitive layer and preferably intercalated in a polymer matrix, preferably responds only to a specific gas so that, using different indicator substances, sensors acting in a gas-specific manner are picturable, respectively.
In an advantageous embodiment of the optical sensor, a gas-sensitive layer having an applied or integrated indicator substance is interpositioned in the beam path of at least one source for electromagnetic radiation, preferably an optical transmitter, and of at least one detector for electromagnetic radiation, preferably an optical receiver, the gas-sensitive layer changing the transmission or absorption properties for the electromagnetic radiation depending on the physical and/or chemical interaction with a specific gas. The gas-sensitive layer is coupled to the transmitter and to the receiver via at least one optical waveguide. The source for electromagnetic radiation can be, for example, a light-emitting diode as optical transmitter, the light-emitting diode emitting light having a suitable wavelength. Accordingly, a photodiode is possible as optical receiver having a frequency range matched to the emitted wavelength of the light-emitting diode. Such a design can be implemented in simple manner with very inexpensive component parts. The gas-sensitive layer with the indicator substance contained therein or applied thereto, which is arranged in the beam path between optical transmitter and optical receiver is quantitatively calibrated at specific light wavelengths, preferably in a manner corresponding to its absorption properties, so that different gases can be detected using different light wavelengths with differently responding indicator substances.
Furthermore, it is advantageous to combine a plurality of optical transmitters with a plurality of gas-sensitive layers capable of detecting different gases, respectively, so that different gases can be detected using a single device. It can also be advantageous for the at least one optical transmitter and/or the at least one optical receiver to be directly provided or coated with a gas-sensitive layer. In this manner, a plurality of optical receivers provided with layers which are sensitive to different gases, respectively, can be irradiated by a plurality of optical transmitters or also by only one optical transmitter which, in this case, covers the entire required wavelength range.
The beam path between optical transmitter and optical receiver, including the intermediate gas-sensitive layer, can be extended in advantageous manner by using optical waveguides as optical coupling elements. In this manner, at least two optical transmitters and receivers positioned at different locations can be optically coupled with a gas-sensitive layer. Also possible is a spatial assembly of optical transmitter and optical receiver at the same location as well as an optical coupling over a very large distance using two optical waveguides led in parallel. The optical waveguides can be diverted or bent at their coupling point to the gas-sensitive layer in such a manner that their end faces, at which the light emerges or enters perpendicularly, are located in a parallel manner opposite each other, the gas-sensitive layer lying in between in the optical axis.
In an advantageous embodiment, the ends of the optical waveguides to be optically coupled to the gas-sensitive layer are chamfered at their sides facing away from the gas-sensitive layer in such a manner that the light beam guided in the optical waveguides is reflected toward the air at these interfaces (boundary surfaces). If the ends of the optical waveguides are chamfered to 45°, the light is reflected by 90° correspondingly, and exits the respective optical waveguide perpendicularly to the longitudinal direction thereof. If one end of the optical waveguide or both ends are coated with a gas-sensitive layer in a manner that the gas-sensitive layer is located in the beam path of a light beam running between the optical waveguides in the medium to be examined, it is possible for an optical detecting device for gases which has an extremely compact and simple design to be implemented at an arbitrary mounting location.
In a further advantageous embodiment, provision is made to use only one optical waveguide which, due to its special design including a conical peak and a gas-sensitive layer applied thereto, allows gases to be effectively detected also at locations which can be very far away from optical transmitter and receiver. In this context, at one end of the optical waveguide, the optical transmitters and receivers are arranged in such a manner that the light beam emanating from the optical transmitter runs parallel to the light beam guided toward the optical receiver within the optical waveguide. Therefore, the optical waveguide used in this connection expediently has a diameter which allows optical transmitters and receivers which can be considerably miniaturized to be arranged side by side. At the other end, the optical waveguide expediently has a conical peak which is partially o
Bernhard Winfried
Hensel Andreas
Mueller Andre
Mueller Lutz
Muller-Fiedler Roland
Allen Stephone B.
Robert & Bosch GmbH
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