Title of Invention

A SENSOR SYSTEM FOR DETECTING PRESENCE OF DEOXIDIZING GASES

Abstract

A sensor system for detecting the presence of deoxidizing gases, in particular, to a metal-oxide semiconductor based sensor adapted to undergo change in conductivity in presence of deoxidizing gases such as dimethylamine and trimethylamine vapours evolving out of the decaying fish. The said system can be used to monitor presence of deoxidizing gases and thereby monitor the quality of fish in a rapid and non-destructive way. The sensor system is adapted for operative connection to any suitable output device to generate indicator signals on detection of the said gases emanating from degenerating fish. The system is compact, portable, user-friendly and capable of detecting deoxidizing gases emanating from degenerating fishes from remote locations.

Full Text

The Field of Invention The present invention relates to sensor system for detecting the presence of deoxidizing gases, in particular, to a metal-oxide semiconductor based sensor system for detection of deoxidizing gases such as dimethylamine and trimethylamine vapours evolving out of the decaying fish. The system of the present invention can be used to monitor presence of deoxidizing gases and thereby monitor the quality of fish in a rapid and non-destructive way. Background Art The traditional method for estimating the freshness of fish is to go by the microbial counts of pathogenic relevance in the degraded fish. Of late, fish freshness studies have been performed using different approaches such as amperometric biosensors for determinations of amines, enzyme reactor based systems, GC (Gas Chromatography) analysis of amines, Mass spectrometry, F!A (Flow Injection Analysis) etc. Most of these methods are relatively time consuming, required experienced personal and expensive apparatus. "Total Volatile Basic amines" (TVB) is one of the most widely used measurements of seafood quality. It is a general term, which includes the measurement of trimethylamine (produced by spoilage bacteria), dimethylamine (produced by autolytic enzymes during frozen storage), ammonia and other volatile basic nitrogenous compounds associated with seafood spoilage. Gas Chromatography is a method for the separation and analysis of complex mixtures of volatile organic and inorganic compounds. The apparatus used in gas chromatography consists of four basic components: a carrier-gas supply and flow controller, a sample inlet system providing a means for introduction of the sample, the chromatographic column and associated column oven, and the detector system. When a mixture of components is injected into a chromatograph equipped with an appropriate column, the components travel down the column at different rates and therefore reach the end of the column at different times. A detector is positioned at the end of the column to quantify the concentrations of individual components of the mixture. Though the gas chromatographs can provide superior discrimination capabilities with reasonably high precision, sensitivity and reproducibility these are not portable and hence cannot be used in-situ. Moreover, the chromatographs are 2 expensive (the price for the bench-top model varies in the range of $20,000 to $50,000) and require skilled personnel to operate. Solid-phase micro extraction (SPME) is relatively a new method that allows trace analytes to be introduced into the chromatographic system without the need for solvents. This method involves exposing a small segment of fused silica fiber coated with a non-volatile polymeric material. The coated fiber is mounted in a syringe-tike device that can expose the fiber to the desired environment and also withdraw it for protection during transfer to GC. The analyte of the interest adsorbs on the fiber coating and is thermally desorbed when introduced into the chromatographic injection port. The direct SPME determination is also a time consuming and destructive method as in a typical process finely ground fish fillet is weighed in a vial equipped with a magnetic stirrer bar and alkaline solution is added. The stirred sample is then heated to liberate the volatile bases and then cooled to near room temperature. For measurement, the SPME fiber is exposed for a couple of minutes in the headspace of the vial and-inserted in the measuring device equipped with Flame Photometric Detector (FID). The throughput of the analysis is about 10 samples/hour. In Mass Spectrometry the sampled gas mixtures are ionized and charged molecular fragments are produced. These fragments are sorted in a mass filter according to their mass to charge ratio. The ions are detected as electrical signals with an electron multiplier or a Faraday plate. Though the mass spectrometers have good discrimination capabilities and can detect a wide range of chemicals, the units appear to be quite expensive (more than $40,000) and spectral overlaps can be a problem in detecting mixtures of unknown composition. Moreover these are often not portable enough to carry into the site of application. Objects of the Invention It is thus the basic object of the present invention to provide a sensor system for detecting presence of deoxidizing gases in particular a metal-oxide semiconductor based sensor adapted to undergo change in conductivity in presence of trace amount of such deoxidizing gases 3 Another object of the invention is to provide a sensor system for detecting presence of deoxidizing gases, more particularly dimethyl amine and trimethyl amine emanating from decaying fish, to monitor the quality of the fish, after harvesting, in a rapid, continuous and non-destructive way. Yet further object of the present invention is directed to provide a sensor system for sensing deoxidizing gases which would be compact and readily portable and thus user friendly. Yet another object is directed to provide a gas sensor system, which would be cost effective as compared to the Gas Chromatographs or Mass Spectrometers. Yet further object is directed to provide a sensor system that would be operable, for monitoring the quality of the fish, at ease even without any skilled personnel. Yet further object of the present invention is to provide a sensor system for sensing deoxidizing gases which can be adapted for large-scale applications such as sensing of deoxidizing gases at remote locations. Summary of the Invention Thus according to the present invention there is provided a sensor system for detecting presence of deoxidizing gases comprising: i) substrate having a metal-oxide coating adapted to adsorb oxygen on heating and resist current flow there through and to allow current flow there through in presence of deoxidizing gases; ii) heating means to provide requisite operating temperature for said oxide coating; and iii) electrodes operatively connected to facilitate current flow through said metal oxide in the presence of a deoxidizing gas to thereby sense the presence of such deoxidizing gases. According to an aspect of the present invention there is provided a sensor system for detecting presence of deoxidizing gases comprising: 4 i) substrate having a metal-oxide coating adapted to adsorb oxygen on heating and resist current flow there through and to allow current flow there through in presence of deoxidizing gases; ii) heating means to provide requisite operating temperature for said oxide coating; iii) electrodes operatively connected to facilitate current flow through said metal oxide in the presence of a deoxidizing gases; and iv) an associated circuitry adapted to generate signals as and when said flow of current through said metal oxide coating resulting from said deoxidizing gases exceeds a preset value. In accordance with a preferred aspect of the present invention the said substrate with metal oxide coating, the heating means and the electrodes are housed in a composite unit adapted to be operatively connected to a power source. Detailed Description The sensor system of the present invention is directed to detect presence of deoxidizing gases, more particularly dimethyl amine and trimethyl amine emanating from decomposing fishes, by change in electrical conductivity of the said-metal oxide coating in presence of such gases. The said sensor system monitors fish freshness in a rapid, continuous, nondestructive and user-friendly' manner from close as well as remote areas. The substrate of the said sensor system is made of glass or quartz or AI2O3: Such substrate comprises 0.8 mm to 1.5 mm in thickness, preferably 1 mm, 4.5 mm to 5.5 mm in width and preferably 5 mm and 7 mm to 9 mm in length, preferably 8 mm. The electrodes of the said sensor system are a couple of parallel electrodes made preferably of gold or platinum. Their thickness ranges from 0.8 µm to 1.2 µm and preferably 1µm and the width from 0.9 mm to 1.1 mm and preferably 1 mm deposited on the substrate by e-beam evaporation. In the bonding pad region the width of the electrodes is from 1.9 to 2.1 mm, preferably 2 mm. 5 The metal oxide is deposited as a thin film of said oxide, preferably of ZnO and TiO2 on the substrate and at least partially on the parallel electrodes. Such deposition of the metal oxide on the substrate can be carried out involving CVD methods. Preferably, the CVD method disclosed and claimed in co-pending application no 512/CAL/2001 may be followed. The thickness of the metal oxide layer-ranges from 0.8 µm to 1.2 µm, preferably 1mm, width is of 4.5 mm to 5.5mm, preferably 5 mm and length is 4.5 mm to 5.5mm, preferably 5 mm. This metal-oxide layer acts as the gas-sensing element based on its resistivity change upon exposure to the test gas such as hydrogen, dimethyl amine, trimethyl amine at selective operating temperatures. It has been found by way of the present invention that metal oxide-layers such as ZnO layer shows sensitivity to dimethylamine from decomposing fish at a temperature of 200 to 400°C. However, the ZnO has highest sensitivity to the said gas is found to be at 300°C. The ZnO coating is adapted to adsorb oxygen when heated to the said optimum' temperature in air and this adsorbed oxygen forms a potential barrier increasing, resistance to current flow. In presence of deoxidizing gas, such as dimethyl amine emanating from decomposing-fish, this oxygen is consumed for total oxidation of the said gas following the reaction below: (CH3)2 NH + O- NO2 + CO2 +H2O + e-. and e", the free electron thus released enhances the electrical conduction of the ZnO coating. The heating means used is preferably meander-shaped platinum heater attached to the backside of the substrate. This heating arrangement provides requisite temperature for the optimum operation of the sensor. It varies in thickness from 1.5 µm to 2.5 µm and is preferably 2 µm. 6 As discussed above the sensor system can be housed in a suitable composite unit obtained of preferably high impact polycarbonate housing having at a surface portion thereof a double gauze for easy passage of the said deoxidizing gas to said metal oxide coating and electrical connection means to operatively connect the same to power source. Such a composite unit is portable and can be connected to an associated circuitry that may be closely or remotely placed for desired indication of decay of fish and the like. The said associated circuitry may be integrally formed along with said composite unit of said substrate with said metal oxide coating, heating means and electrodes or can be operatively connected to said composite unit from separate remote locations. The associated circuitry can be any conventional circuitry adapted to monitor the variance in current flow due to change in the resistivity of the metal oxide due to presence of deoxidizing gases and generate corresponding output signals to indicate the presence of such gases. The sensor system can be connected in series with a potentiometer which in turn is connected to the potential divider. The potential dividers are operatively connected to the comparator. The comparator sends output signals via the transistor to the signal out put device to generate indicator signals such as audible buzzer beeps, visual signals, voice signals and the like, preferably audible buzzer-beeps. The details of the invention its objects and advantages are described hereunder in greater detail with reference to the non-limiting exemplary illustrations as per the accompanying figures wherein: Fig 1a and 1b illustrates the front and rear view respectively, of the substrate supporting the metal oxide layer, the heating means and the operating connections of the system of the invention. Fig 2a; illustrates the system of fig 1 a/1 b above housed in a composite unit; 7 Fig 2b:il!ustrates in top plan view the composite unit of Fig 2a with its top gauze removed ; Fig 3: illustrates the associated circuitry of Sensor System for generating output signals. Description of Figures Fig 1a and 1b illustrates the front and rear view respectively of the substrate supporting the metal oxide layer, the heating means and the operating connections of the system of the invention comprising of - The substrate (1) of the sensor system is made of glass or quartz or alumina .The said substrate is 1 mm thick, 5 mm wide, and 8 mm long. A couple of parallel electrodes (3) made of gold or platinum are attached to the said substrate. They are 1µm thick and 1 mm wide and deposited on the substrate by e-beam evaporation. In the bonding pad region the width of the electrodes are 2 mm. A thin film of metal-oxide semiconductor layer (2) made typically ZnO and TiO2 is deposited on the substrate and partially on the parallel electrodes by a CVD method. The said layer is 1µm thick, 5 mm wide and 5 mm long. This semiconducting metal-oxide layer acts as the gas-sensing element based on its resistivity change upon exposure to the test gas. A heating means (4) which is 2 µm thick meander-shaped platinum heater is attached to the backside of the substrate in order to provide requisite temperature for the optimum operation of the sensor. Fig 2a: illustrates the system of fig 1 a/1b above housed in a composite unit comprising of top gauze (6), the housing (5) and the pins (7) for electrical connection. 8 Fig 2b: illustrates in top plan view the composite unit of Fig 2a with its top gauze removed. The figures show the high-impact polycarbonate housing (5) for the said system. On one surface of the said housing is a 100 mesh SUS 316 double gauze (6) for passage of the test gas and on the other surface are 1 mm diameter nickel pins (7) for establishing connection with a power source. The metal oxide coating on the substrate forms the sensor chip (2a), which is provided with connection leads to micro-heater (4a) and connection leads to electrodes (3a-) and are visible on removal of the said gauze. Fig 3: illustrates the associated circuitry of Sensor System for generating output signals where S represents the Sensor System, which is connected in series with a potentiometer RL In presence of the test gas the resistance of the metal oxide changes causing a change in current flowing through RL. So the voltage drop VRL. across the load resistor (RL) is a function of the test gas concentration. R1 and R2 act as the potential divider. The voltage drop (Vref.) across R2 is the reference voltage. The comparator monitors whether VRL is greater than Vref. For VRL 9 WE CLAIM ,1. A sensor system for detecting presence of deoxidizing gases comprising: i) substrate having a metal oxide coating adapted to adsorb oxygen on heating and resist current flow there through and to allow current flow there through in presence of said deoxidizing gases, ZnO and TiO2, preferably ZnO. ii) heating means to provide requisite operating temperature for said oxide coating; and iii) electrodes operatively connected to facilitate current flow through said metal oxide in the presence of a deoxidizing gas to thereby sense presence of such deoxidizing gas. 2. The sensor system as claimed in claim 1 for detecting presence of said deoxidizing gases comprising: i) substrate having a metal oxide coating adapted to adsorb oxygen on heating and resist current flow there through and to allow current flow there through in presence of said deoxidizing gases; ii) heating means to provide requisite operating temperature for said oxide coating; iii) electrodes operatively connected to facilitate current flow through said metal oxide in the presence of said deoxidizing gas. iv) as associated circuitry adapted to generate signals as and when said flow of current through said metal oxide coating resulting from said deoxidizing gases exceeds a preset value. 3. The sensor system as claimed in claim 1or 2 wherein the said substrate having said metal oxide coating, heating means and said electrodes with or without the said associated circuitry are packaged in a composite unit. 4. The sensor system as claimed in claim 3 wherein the said composite unit comprises high impact polycarbonate housing having double gauze for easy passage of the said deoxidizing gas to said metal oxide coating and electrical connection means to operatively connect the same to power source. 3. 10 5. The sensor system as claimed in any one of the preceding claims wherein said metal-oxide semiconductor layer is selected from ZnO 6. The sensor system as claimed in claim 5 wherein said metal oxide layer is selected to have thickness of 0.8 18 µm to 1.2 µm, preferably 1µm; width of 4.5 mm to 5.5mm, preferably 5 mm and length of 4.5 mm to 5.5mm, preferably 5 mm. 7. The sensor system as claimed in claim 6 wherein said metal oxide layer comprise CVD deposited metal oxide layer on the substrate and partly on the electrodes. 8. The sensor system as claimed in claim 7 wherein said metal oxide senses presence of said deoxidizing gases selected from hydrogen, dimethylamine and trimethylamine. 9. The sensor system as claimed in any one of the preceding claims wherein said substrate is made up of material selected from glass, quartz, alumina. 10. The sensor system as claimed in claim 9 wherein said substrate is selected to have thickness of 0.8 mm to 1.5 mm, preferably 1mm, width of 4.5 mm to 5.5 mm, preferably 5 mm and length 7 mm to 9 mm, preferably 8mm. 11. The sensor system as claimed in any one of the preceding claims wherein said electrodes are selected from gold, platinum. 12. The sensor system as claimed in claim 11 wherein said electrodes are selected to have thickness of 0.8 µm to 1.2 µm, preferably 1µm; width of 0.9 mm to 1.1 mm, preferably 1mm and width in the bonding pad region of 1.9 to 2.1 mm, preferably 2 mm 12. 11 13. The sensor system as claimed in any one of the preceding claims wherein said heating means comprise meander shaped platinum heater attached to the rear of the substrate and connected to power source. 14. The sensor system as claimed in claim 13 wherein the said heating means is selected to have thickness of 1.5 µm to 2.5 µm, preferably 2 µm 15. The sensor system as claimed in claim 13 wherein the said heating means is heated to a temperature of 200-400°C, preferably to 300°C for optimum sensitivity of the sensor. 16. The sensor system as claimed in anyone of preceding claim wherein the associated circuitry is closely or remotely placed in respect of the said composite unit. 17. The sensor system as claimed in claim 16 wherein said associated circulitry comprises potentiometer, potential dividers, comparator, transistor and signal output device. 18. The sensor system as claimed in claim 17 wherein said associated circuitry comprises the potentiometer adapted to record the change in the voltage drop in the sensor while the said comparator is adapted to compare this voltage drop with the reference voltage across the said potential divider and to transmit the output via the said transistor to the said signal output device to generate indicator signals. 19. The sensor system as claimed in claim 18 wherein the signal out put device is selected from audible buzzer beeps, visual signals, voice signals, other indicator signals; preferably audible buzzer beeps. 20. The sensor system as claimed in claim 8 for sensing fish odour wherein said metal oxide senses presence of dimethylamine or trimethylamine, the gases responsible for mal odour evolved out of decomposing fish. 12 21. The sensor system as claimed in any one of preceding claims for sensing fish odour comprising said metal-oxide preferably ZnO coated on said substrate adapted to adsorb oxygen on being heated at selective operative temperature whereby the resistivity of the metal oxide coating is increased ; said metal oxide coating further adapted to release the adsorbed oxygen in the presence of deoxidizing gases preferably dimethyl amine and trimethyl amine, emanating from decomposing fish to thereby provide for flow of current there through onto said associated circuit via said electrodes and thereby indicate the presence of deoxidizing gas from decomposing fish. 22. The sensor system as claimed in claim 21 wherein the associated circuitry comprises the potentiometer adapted to record the change in the voltage drop in the sensor while the said comparator is adapted to compare this voltage drop with the reference voltage across the said potential divider and to transmit the output via the said transistor to the said signal output device to generate indicator signals to indicate the condition of fish freshness 23. The sensor system substantially as herein described and illustrated with reference to the exemplary illustrations. 24. The method of detecting deoxidizing gas from decomposing fish using the system as claimed in claim 1 to 22. A sensor system for detecting the presence of deoxidizing gases, in particular, to a metal-oxide semiconductor based sensor adapted to undergo change in conductivity in presence of deoxidizing gases such as dimethylamine and trimethylamine vapours evolving out of the decaying fish. The said system can be used to monitor presence of deoxidizing gases and thereby monitor the quality of fish in a rapid and non-destructive way. The sensor system is adapted for operative connection to any suitable output device to generate indicator signals on detection of the said gases emanating from degenerating fish. The system is compact, portable, user-friendly and capable of detecting deoxidizing gases emanating from degenerating fishes from remote locations.

Documents:

00436-cal-2002 abstract.pdf

00436-cal-2002 claims.pdf

00436-cal-2002 correspondence.pdf

00436-cal-2002 description(complete).pdf

00436-cal-2002 drawings.pdf

00436-cal-2002 form-1.pdf

00436-cal-2002 form-18.pdf

00436-cal-2002 form-2.pdf

00436-cal-2002 pa.pdf

436-cal-2002-granted-abstract.pdf

436-cal-2002-granted-acceptance publication.pdf

436-cal-2002-granted-claims.pdf

436-cal-2002-granted-correspondence.pdf

436-cal-2002-granted-description (complete).pdf

436-cal-2002-granted-drawings.pdf

436-cal-2002-granted-form 1.pdf

436-cal-2002-granted-form 19.pdf

436-cal-2002-granted-form 2.pdf

436-cal-2002-granted-letter patent.pdf

436-cal-2002-granted-pa.pdf

436-cal-2002-granted-reply to examination report.pdf

436-cal-2002-granted-specification.pdf