Chemistry: analytical and immunological testing – Including sample preparation – Gaseous sample or with change of physical state
Reexamination Certificate
1998-01-23
2001-02-13
Tung, T. (Department: 1743)
Chemistry: analytical and immunological testing
Including sample preparation
Gaseous sample or with change of physical state
C422S098000, C436S149000, C436S152000
Reexamination Certificate
active
06187597
ABSTRACT:
BACKGROUND OF THE INVENTION
Gas sensors sensitive to different molecules are known. Such sensors are normally not totally selective but have different selectivity patterns. It is known to combine such sensors in order to analyze gas mixtures and odors. By comparing the obtained response patterns with previous test results using a computer remarkably precise results can be obtained regarding the identification, classification and also quantification of gas mixtures and odors.
The combination of a number of sensors and a pattern recognition routine is known as an “electronic nose” [Sensors and Sensory Systems for an Electronic Nose, (J. W. Gardner and P. N. Bartlett, eds.) Nato ASI Series E, vol. 212, Kluwer Academic Publishers, 1992]. Electronic noses have numerous applications within the and food processing industry, medical diagnosis, control of combustion, processes and monitoring of the environment, to mention a few.
Modern computers have improved upon the use of pattern recognition methods to identify the response pattern from different sensor to different odors. Many different sensors are available and in many cases a number of set ups may have to be tested and even combined to provide a correct analysis in the end. This is particularly important since it is not only desirable to know which molecules, but it is also in many cases important to know their actual concentrations. This presents a problem since the sensors may have to detect very small quantities of material or very large quantities of the same. Sensors that are too sensitive will not be able to measure large quantities correctly and sensors that are not sensitive enough will not give any indication at all of low concentrations. Thus, in order to obtain arcuate readings taking into consideration amount, concentration and identification, a versatile electronic nose sensor with a range of selectivities and sensitivities is necessary. Furthermore, the choice of the sensors will depend on the particular application. As a result of the above difficulties the electronic noses of today are not very versatile and may in some instances require very large number of sensors and data power making them rather expensive and slow.
Another problem encountered is the lack of selectivity, that is, many sensors react on many gases almost identically, making it difficult to tell them apart and necessitating additional sensors etc.
The object of the present invention is to provide a method by which the analyzing power of chemical sensor arrays can be expanded and a more exact as well as a more versatile device for the monitoring of gas mixtures and odors.
SUMMARY OF THE INVENTION
In accordance with the invention this is achieved by using a new sensing principle based on a geometrical distribution of sensors and catalysts. This arrangement gives a number of possibilities for the enhancement and control of the signal pattern from a sensor array for a given gas mixture.
In this new sensing method according to the invention the gas or gas mixture that is to be analyzed is brought to pass a catalyst simultaneously with detection by sensors. Many of the gas components that are desirable to monitor react in one way or the other in the presence of a catalyst. This means that the gas passing over the catalyst will change in its proportions of different molecules. This in turn can be detected since sensors placed along the catalyst will give different readings. Since different molecules react in different ways in the presence of a specific catalyst a recognizable pattern specific to the mixture will be obtained in the gas flow direction along the catalyst.
The sensors can be arranged in the catalyst itself, or catalysts and sensors may constitute for example, the top and bottom surfaces in a gas analyzing flow cell, provided that the height is not too large, since the change in the composition due to chemical reactions at the catalyst must also influence the sensors in order to provide the recognizable pattern. Such a measuring cell can be provided with a varying set up of catalysts or catalytic surfaces, and indeed several different catalytic materials can be used in, for instance, strips in the cell and also different sensors can be used. A set up change can however be obtained in other interesting ways. To start with, the thickness of the layers of catalytic materials can vary along the flow path. Also the temperature of the sensors and/or the catalytic materials may vary along the flow path or crosswise of the flow path in order to provide suitable recognizable patterns. The size of the catalytic areas and the temperature of these areas will influence the concentration/alteration of the gas components. The temperature at the sensors will influence the sensitivity of the sensors. Suitable catalytic materials are platinum, palladium, iridium as well as other organic or inorganic materials, including semiconducting materials.
The presence of a catalyst may change gas components that are not otherwise measurable with the sensors used into components that can be measured or sensed by the sensors. Conversely and at the same time, for example, other components that can be sensed can be changed into components that are not sensed by the used sensors if desired.
One of the major advantages of the invention is the above mentioned possibility to construct in a simple way sensor cells that can easily be switched between a number of different selectivity patterns. It gives the possibility to use a modular system comprising one or two dimensional sensor matrices or arrays and a catalytic surface or even an array of matrix of catalysts comprising areas of different catalytic materials that can be combined to give a device with a great number of different selectivity patterns. Top and bottom in an analyzing cell can be combined to provide the desired selectivity and sensitivity, which efficiently reduces the number of sensor arrays that has to be kept in store. Since the catalytic part (for instance top) need no or only few (temperature control) electrical connections, substitution can be carried out in simple mechanical ways. Further advantages and features of the invention are apparent from the following description of preferred embodiments.
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Schweizer-Berberich et al, Characterisation of Food Freshness with Sensor Arrays, Sensors and Actuators, vol. 18-19, 1994, pp. 282-290.
Lundstrom Ingemar
Sundgren Hans
Hayes Soloway Hennessey Grossman & Hage PC
Nordic Sensor Technologies AB
Tung T.
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