Title of Invention

AN ELECTRONIC EXPLOSIVE DETECTOR

Abstract

An electronic explosive detector (1A) comprising an active sensor (2) and a reference sensor (3). Each of the sensors comprises of a microheater (5) micromachined from a dielectric material having low thermal capacity and high adsorbing capacity for high energy materials. The microheater comprises an air suspended platform (4) and a heater element patterned on the air suspended platform. Each of the microheaters is connected to a voltage pulse generator (6) and a resistor (7) in series and a data acquisition unit (8) connected across the resistors (Figs 1 and 2). 25 JUL 2008

Full Text

FORM 2 THE PATENTS ACT, 1970 (39 of 1970) As amended by the Patents (Amendment) Act, 2005 & The Patents Rules, 2003 As amended by the Patents (Amendment) Rules, 2006 COMPLETE SPECIFICATION (See section 10 and rule 13) TITLE OF THE INVENTION An electronic explosive detector APPLICANTS Indian Institute of Technology, Bombay, an autonomous research and educational institution established in India by a special Act of the Parliament of the Republic of India under the Institutes of Technology Act 1961, Powai, Mumbai 400076, Maharashtra, India INVENTORS Mukherji Soumyo, Khanna Vibhor and Shankar Prasanth, all of School of Biosciences and Bioengineering, Indian Institute of Technology, Bombay, Powai, Mumbai 400076, Maharashtra, India and Rao Valipe Ramgopal and Verma Tushar both of Department of Electrical Engineering, Indian Institute of Technology, Bombay, Powai, Mumbai 400076, Maharashtra, India, all Indian nationals PREAMBLE TO THE DESCRIPTION The following specification particularly describes the nature of this invention and the manner in which it is to be performed: 25 JUL 2008 FIELD OF THE INVENTION This invention relates to an electronic explosive detector. BACKGROUND OF THE INVENTION Detection of explosives like trinitrotoluene (TNT), pentacrythritoltetra nitrate (PETN) or cyclotrimethylene trinitramine (RDX) is extremely important, especially because of their gross misuse and abuse by unscrupulous and antisocial elements for wanton destruction of life and property. There are bulk detectors for detection of explosives based on X-ray, neutron imaging or laser (infra red), which identify the explosives on the basis of their atomic numbers [Anna P., Sara W., Birgit B., Carina E., Erik H., "Explosives Detection- A Technology Inventory", FOI, Weapons and protection, User report (Sep 2006),2030.]. Bulk detectors are costly and bulky and occupy large area and are not portable. X-ray and neutron imaging type detectors are also not safe. Detectors of explosives based on trace detection technology generally use gas chromatography coupled with various devices like chemiluminescence or electron capturer [Sameer S., Maneesha S., "Explosives detection systems (EDS) for aviation security", Signal Processing 83, 2003, 31 - 55]. A main disadvantage of such detectors is their inability to detect explosive compounds with low vapour pressure and low volatility. Ion mobility spectroscopy is also used for detection of explosives ("Trace and Bulk Detection of Explosives by Ion Mobility Spectrometry and Neutron Analysis" by D. Rondeshagen, G. Arnold, S. Bockisch, K. -P. Francke, J. Leonhardt and A. Kiister in Detection of Liquid Explosives and Flammable Agents in Connection with Terrorism, Published by Springer Netherlands, May 2008). It is bulky and very expensive. Micro-electro-mechanical systems (MEMS) are also used for detection of explosives. (L. A. Pinnaduwage et al.,"A microsensor for 2 trinitrotoluene vapour", NATURE,Vol. 425, OCTOBER 2nd, 2003, p. 474). Microcantilevers have been the traditional choice of researchers for detection of explosives because of their advantages like improved dynamic response, greatly reduced size, high surface-to-volume ratio, high precision and increased reliability as compared to the other MEMS. An array of microcantilevers is coated with different sensor materials like SXFA [poly(l-(4-hydroxy-4-trifluoromethyl-5,5,5-trifluoro)pent-1 -enyl)methylsiloxane] or carbowax-1000. Adsorption of target molecules on the different sensor materials causes differential stresses in the respective cantilevers causing them to bend, which in turn will cause the output signals to vary in various forms such as change in deflection in reflected laser beam from the cantilever surface on the PSD / quadrant detectors / lateral effect detectors or change in vibrational resonance frequency caused either by adsorption of molecules on the cantilever surface or due to thermal characteristics of analyte. In order to avoid optical readout systems, piezoresistive cantilevers are used to give a direct electrical readout depending upon the change in electrical resistance proportional to analyte concentration. Microcantilevers have disadvantages like use of chemical coatings which are responsive to particular groups found in explosive and hence, would respond to any compound present in atmosphere having those groups and give erroneous detection. Microcantilevers employ frequency measurement equipments which render them bulky and expensive. Microcantilevers may require optical systems to detect bending of microcantilevers, which further render the microcantilevers bulky and fragile and unsuitable for field applications. MEMS comprising SAW (Surface Acoustic Waves) sensors, SPR (Surface Plasmon Resonance) sensors or immunosensors cannot be miniaturized enough to be incorporated as arrays (necessary to achieve selectivity) and require frequency 3 measuring equipments which are large and expensive. Microcanti levers are also sensitive to shock and vibrations and prone to measurement errors resulting therefrom. In the abstract quoted from Proceedings of 2004 International Conference on Information Acquisition there is described a Micro-Electro-Mechanical System (MEMS) sensor array which is capable of detecting explosive particles. The array consists of 12 silicon beams and on each beam there are a heater and a temperature sensor. The silicon beams can be heated up to the melting point of particular kind of explosive by the heaters while each sensor is used to measure the temperature change of each beam caused by heat absorption of the explosive particles when they melt. Experimental results showed that the array was capable of detecting (TNT) and (RDX) samples as little as lug. (A MEMS Sensor Array for Explosive Particle Detection by Deyi Kong, Tao Mei, Yongchun Tao, Lin Ni, Tao Zhang, Wei Lu, Zhengyong Zhang and Rui Wang). The detection limit of this detector is significantly high but it suffers from the various other disadvantages discussed earlier. In the abstract quoted from Proceedings of the 2007 International Conference on Information Acquisition describes deflagration experiments of trace explosive. A kind of sensitive silicon beam for detecting radiation in the deflagration of trace explosive was designed. The silicon beam had a heating and a thermal resistor on it, used as stimulating and detecting elements respectively. Thermal -Electric simulation of the silicon beam was carried out by finite element analysis software ANSYS (Design of a Silicon Beam for Detecting Deflagration of Trace Explosive by Yongguang Qil, Jianbin Zhu, Deyi Kong and Xiaohua Wan). The beam is fabricated with silicon 4 having a very thin oxide layer as a mask for protection while releasing the.beam by etching the backside of the wafer. A thin oxide layer and a structural layer of silicon can result in very high heat conductivity to the rest of the detector and hence overall high heat capacity for transient or high speed / pulse measurements. Due to the high conductive heat loss to active surface area ratio of the silicon beam, it has low sensitivity. The silicon beam also has the other disadvantages as discussed earlier. OBJECTS OF THE INVENTION An object of the invention is to provide an electronic explosive detector which is simple in construction, reliable and accurate and easy and convenient to operate. Another object of the invention is to provide an electronic explosive detector which is of low cost and which can be miniaturised and mass produced. Another object of the invention is to provide an electronic explosive detector which is portable and can be handheld and which is rugged and which can be maintained easily. Another object of the invention is to provide an electronic explosive detector which is self cleaning and reusable and which is not sensitive to shock and vibrations. DETAILED DESCRIPTION OF THE INVENTION According to the invention there is provided an electronic explosive detector comprising an active sensor and a reference sensor each of the sensors comprising a microheater micromachined from a dielectric material having low thermal capacity 5 and high adsorbing capacity for high energy materials, the microheater comprising an air suspended platform and a heater element patterned on the air suspended platform, the microheaters each being connected to a voltage pulse generator and a resistor in series and a data acquisition unit connected across the resistors. According to the invention there is also provided an electronic explosive detector comprising an active sensor and a reference sensor, each of the sensors comprising a microheater micromachined from a dielectric material having low thermal capacity and high adsorbing capacity for high energy materials, the microheater comprising an air suspended platform and a heater element patterned on the air suspended platform and further comprising a resistance temperature device (RTD) patterned on the air suspended platform in the proximity of the heater element, the microheaters being connected to a voltage pulse generator and the RTDs each being connected to a resistor and a constant voltage source in series and a data acquisition unit connected across the resistors. The following is a detailed description of the invention with reference to the accompanying drawings, in which : Fig 1 is a schematic view of the electronic explosive detector according to an embodiment of the invention; Fig 2 is an isometric view of the microheater of the explosive detector of Fig 1; 6 Fig 3 is a schematic view of the electronic explosive detector according to another embodiment of the invention; Fig 4 is an isometric view of the microheater of the explosive detector of Fig 3; and Figs 5, 6, 7, 8, 9, 10 and 11 are graphical representations of experimental results obtained by a typical explosive detector of the invention. The electronic explosive detector 1A as illustrated in Figs 1 and 2 of the accompanying drawings comprises an active sensor 2 and a reference sensor 3. Each of the sensors comprises of a microheater (5) micromachined from a dielectric material having low thermal capacity and high adsorbing capacity for high energy materials like explosives. The microheater comprises an air suspended platform (4) and a heater element patterned on the air suspended platform. The platforms are suspended over a pit 4a. Each of the microheaters is connected to a voltage pulse generator 6 and a resistor 7 in series. 8 is a data acquisition unit connected across the resistors. 9 is a display unit and /or an alarm unit connected to the data acquisition unit. Preferably the data acquisition unit is a data acquisition card (DAQ). Preferably the air suspended platform is micro machined from silicon and the heater element is patterned with platinum. Contacts, preferably gold contacts, of the microheater are marked 11a and 1 lb. Contacts 1 la and 1 lb are connected to the pulse generator 6 and resistor 7, respectively. Traces of an explosive material (not shown) to be detected are introduced on the heater element of the active sensor and a voltage pulse is introduced across the heater elements. As a result, a current flows 7 through the heater elements and the heater elements get heated up. Due to the deflagration (rapid burning) property of the explosive, the temperature of the heater element of the active sensor rapidly increases to the deflagration temperature characteristic of the explosive. The difference in temperature as experienced by the heater element of the active sensor changes the IV or resistance characteristics of the resistor of the active sensor accordingly. The DAQ card senses the differential IV characteristics and processes the change in the IV characteristics into a corresponding voltage / current signal and outputs the signal to drive the display unit and/or alarm unit. The electronic explosive detector IB as illustrated in Figs 3 and 4 of the accompanying drawings further comprises a resistance temperature device (RTD) 12 patterned on the air suspended platform? in the proximity of the heater element in the case of both the active and reference sensors. There are four contacts, preferably gold contacts, 11a, l1b, l1c and l1d. The microheaters are connected to the pulse generator at contact 11a and ground at contact l1b. The RTDs are connected to a constant voltage source 13 at contact l1c and series resistors at contact l1d. The voltage source 13 delivers a constant voltage to the RTDs. The voltage applied to the RTDs does not heat up the RTDs significantly and the temperature change of the RTDs is due to heat generated by the microheaters and deflagration. As a result, measurement errors due to variations in the pulse generator and current through the microheaters will not occur. Preferably the RTDs are patterned with platinum. The RTDs will sense the temperatures of the respective heater elements. The IV or resistance characteristics of the RTD of the active sensor changes depending upon the temperature of the respective heater element which in turn depends upon the deflagration temperature of the explosive. The differential IV characteristics of the resistor of the active sensor will be processed by the DAQ as described earlier to 8 detect the explosive. The air suspended platform thermally isolates the heater element and the RTD against noise and other interferences so as to eliminate measurement errors and improve the reliability and accuracy of the detector. A typical microheater was fabricated by oxidizing a silicon memberane into SiO2- A heater element of 30 microns width and RTD of 30 microns width were patterned on the surface of the membrane by sputtering Ti/Pt by optical lithography. Excess metal was removed from the surface by Lift-Off. Air suspended platform was etched on the membrane by formation of a pit or "etch window" using optical lithography and TMAH (Tetramethyl ammonium hydroxide solution). The resistance of the heater element and RTD were 170 ohms and 130 ohms respectively. Gold contacts were deposited on the microheater by sputtering or vapor deposition. Using the above typical microheater in a detector of Fig 1 and using a solution of RDX in acetone (5 mg/ml) experiments were carried out. A voltage pulse was applied across the heater elements. Pulse across the heater elements with and without the RDX were as shown in Fig 5 of the accompanying drawings. In experiments with RDX, drops of the RDX solution were introduced on the heater element of the active sensor. The pulses in Fig 5 have been amplified in Fig 6 of the accompanying drawings. Fig 6 clearly shows that there was a drop or decrease in the voltage pulse when RDX was applied on the heater element. This indicates that the IV characteristics of the heater element changed with the introduction of RDX on the heater element due to deflagration of RDX. Change in voltage was observed as shown in Fig 5 and Fig 6 of the drawings. A visible plume of smoke arising out of the heater element was also observed. Fig 7 indicated a sharp peak on introduction 9 of the RDX characteristic of the deflagration property of the RDX. Whereas Fig 8 which is without RDX did not show any such sharp peak. Figs 9 and 10 of the accompanying drawings represent characteristic peaks obtained by introducing benzoic acid and para nitro benzoic acid respectively. Figs 9 and 10 clearly show that the characteristic peak of RDX was not exhibited by the acids. Fig 11 of the accompanying drawings represents experimental results with RDX vapour in nanogram level (2 nanograms). Fig 11 also showed the characteristic peak of RDX at the deflagration temperature thereof. It is evident from the above experimental examples that the electronic detector of the invention is very accurate in detecting explosives making use of their deflagration property and deflagration temperature. It is very sensitive upto nanogram levels of 2 of the explosives. It is not sensitive to vibrations and shock and is reliable, simple in construction and is of low cost. The fabrication time of the detector is reduced and its productivity is increased and it can be mass produced. It can be easily miniaturised and is portable and can be handheld. It is rugged and can be installed and maintained easily. It can be easily operated by any persons and the results can be seen or read easily. It eliminates expensive optical systems and highly sensitive electronics and chemicals. As the explosive is adsorbed on the microheater surface, the detector of the invention is self cleaning and reusable. It is ideal for field applications and can be installed with ease where valuables are stored or kept or where people assemble like public places meeting places, airports, bus or train stations, trains or buses, offices or buildings or the like. It can also be used by security personnel to screen explosives or people. It can also be used for detection 10 of other chemicals like organic acids like benzoic acids or nitro derivatives thereof like paranitrobenzoic acids which burn slowly unlike explosives which burn rapidly. It is to be understood that the microheater can be fabricated from any dielectric material having low thermal capacity and high adsorbing capacity for high energy materials. The microheater and RTD also can be formed using other metal / adhesion layer combination. The air suspended platform also can be made by backside etching using double side air aligner (DSA). Etching of the platform also can be done by other solutions like KOH. The display unit and/or alarm unit and RTD are optional. The signal from the DAQ can also be taken to a different device or instrument for further processing. It can also be taken to a personal computer or personal assistant (PDA) for further processing. Such variations of the invention are obvious to those skilled in the art and are to be construed and understood to be within the scope of the invention. 11 We claim: 1. An electronic explosive detector comprising an active sensor and a reference sensor each of the sensors comprising a microheater micromachined from a dielectric material having low thermal capacity and high adsorbing capacity for high energy materials, the microheater comprising an air suspended platform and a heater element patterned on the air suspended platform, the microheaters each being connected to a voltage pulse generator and a resistor in series and a data acquisition unit connected across the resistors. 2. The detector as claimed in claim 1, which comprises a display unit and /or an alarm unit connected to the data acquisition unit. 3. The detector as claimed in claim 1 or 2, wherein the data acquisition unit is a data acquisition card (DAQ). 4. The detector as claimed in anyone of claims 1 to 3, wherein the air suspended platform is micromachined from silicon and the heater element is patterned with platinum. 5. An electronic explosive detector comprising an active sensor and a reference sensor, each of the sensors comprising a microheater micromachined from a dielectric material having low thermal capacity and high adsorbing capacity for high energy materials, the microheater comprising an air suspended platform and a heater element patterned on the air suspended platform and further comprising a resistance 12 temperature device (RTD) patterned on the air suspended platform in the proximity of the heater element, the microheaters being connected to a voltage pulse generator and the RTDs each being connected to a resistor and a constant voltage source in series and a data acquisition unit connected across the resistors. 6. The detector as claimed in claim 5, which comprises a display unit and /or an alarm unit connected to the data acquisition unit. 7. The detector as claimed in claim 5 or 6, wherein the data acquisition unit is a data acquisition card (DAQ). 8. The detector as claimed in anyone of claims 5 to 7, wherein the air suspended platform is micromachined from silicon and the heater element is patterned with platinum. Dated this 25th day of July 2008 of Khaitan & Co Agent for the Applicants 13

Documents:

1590-MUM-2008-ABSTRACT(14-11-2014).pdf

1590-MUM-2008-ABSTRACT(14-2-2014).pdf

1590-mum-2008-abstract.doc

1590-mum-2008-abstract.pdf

1590-MUM-2008-CLAIMS(AMENDED)-(14-11-2014).pdf

1590-mum-2008-claims.doc

1590-mum-2008-claims.pdf

1590-MUM-2008-CORRESPONDENCE(11-9-2014).pdf

1590-MUM-2008-CORRESPONDENCE(21-11-2011).pdf

1590-MUM-2008-CORRESPONDENCE(21-11-2012).pdf

1590-MUM-2008-CORRESPONDENCE(25-3-2009).pdf

1590-MUM-2008-CORRESPONDENCE(27-6-2013).pdf

1590-MUM-2008-CORRESPONDENCE(28-6-2013).pdf

1590-MUM-2008-CORRESPONDENCE(29-9-2008).pdf

1590-MUM-2008-CORRESPONDENCE(8-8-2008).pdf

1590-mum-2008-correspondence.pdf

1590-MUM-2008-DEFENCE R & D ORAGANISATION(7-5-2013).pdf

1590-MUM-2008-DEFENCE R & D ORGANISATION(15-7-2013).pdf

1590-mum-2008-description(complete).doc

1590-mum-2008-description(complete).pdf

1590-MUM-2008-DRAWING(14-2-2014).pdf

1590-mum-2008-drawing.pdf

1590-MUM-2008-FORM 1(21-11-2011).pdf

1590-MUM-2008-FORM 1(29-9-2008).pdf

1590-mum-2008-form 1.pdf

1590-MUM-2008-FORM 13(21-11-2011).pdf

1590-MUM-2008-FORM 18(8-8-2008).pdf

1590-MUM-2008-FORM 2(TITLE PAGE)-(14-11-2014).pdf

1590-MUM-2008-FORM 2(TITLE PAGE)-(14-2-2014).pdf

1590-mum-2008-form 2(title page).pdf

1590-mum-2008-form 2.doc

1590-mum-2008-form 2.pdf

1590-MUM-2008-FORM 26(29-9-2008).pdf

1590-mum-2008-form 3.pdf

1590-MUM-2008-FORM 8(8-8-2008).pdf

1590-MUM-2008-MARKED COPY(14-11-2014).pdf

1590-MUM-2008-MARKED COPY(14-2-2014).pdf

1590-MUM-2008-REPLY TO EXAMINATION REPORT(14-2-2014).pdf

1590-MUM-2008-REPLY TO HEARING(14-11-2014).pdf

1590-MUM-2008-SPECIFICATION(AMENDED)-(14-11-2014).pdf

1590-MUM-2008-SPECIFICATION(AMENDED)-(14-2-2014).pdf

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Amended specification in track after attending hearing (2).pdf

Form 13.pdf

Revised abstract.pdf