Design and Analysis of a Smart Multi Purpose Electronic Nose System

Transcription

1 Journal of Computer cence (): 63-7, 5 IN cence Publcatons, 5 Desgn and Analyss of a mart Mult Purpose Electronc Nose ystem Mahmoud Z. Iskandaran and Ndal F. hlbayeh Faculty of cence and Informaton Technology, Al-Zaytoonah Prvate Unversty of Jordan P.O. Box 9597, Post Code 9, Jordan Faculty of Computer cence and Informaton Technology, Appled cence Unversty P.O. Box 4, Post Code 93, Amman, Jordan Abstract: An electronc nose system for mult applcaton purposes s desgned and tested. Our hardware desgn allows varous types of sensors to be used for dfferent applcatons. The system s capable of beng nterfaced to both analog and dgtal nstruments wth specal flterng devces that solate the system from surroundng sgnals. The desgn of the system s dstngushed through the use of two logc controlled mcro fans that stablze the system atmosphere, whch surrounds the smellng sensor and also serves an mportant functon of removng any adsorbed odors on the surface of the sensor. Comprehensve mathematcs are used to desgn and descrbe each part of the presented system, whch allows methodcal development and changes of the system parameters for future advances. Testng of the hardware was carred out under computer control usng varous TG sensors such as TG8, and TG84 and TG3. Database based software wth neural network faclty was desgned to nterface the bult hardware and to process the electronc nose sgnals before beng classfed. Key words: Electronc Nose, Olfactory, Gas ensor, Hardware, oftware, Neural, Back-Propagaton INTODUCTION 63 The man motvaton for electronc noses s the development of qualtatve, low-cost, real-tme, and portable methods to perform relable, objectve, and reproducble measures of volatle compounds and odors. In order to develop an electronc nose, t s useful to examne the physology behnd olfacton snce bologcal olfactory systems contan many of the desred propertes for electronc noses. Also, the contrast between an artfcal system and physology s necessary to acheve a relable, subjectve, and analytcally acceptable system []. The potental uses of nose-machnes, whch essentally mmc the functons of human noses but wth more precson, are endless. Perfume makers are already usng them to protect ther patented smells aganst fakefragrance merchants, and U docksde nspectors have used a hgh-tech snout to resolve dsputes wth fshermen over the gradng of ther catch. More exctng are the possble medcal applcatons. centsts are researchng the use of electronc noses to dagnose llness by smellng patents breath wth the possblty of nstallng tny electronc noses n phone recevers, so that patents can smply breathe nto the phone and wat for a dagnoss. A smlar smelltransmsson devce may soon allow surfers on the Internet to wake up and smell the coffee qute lterally. esearchers are nvestgatng the use of breath analyss to dentfy the stages of the female menstrual cycle: the ablty of electronc noses to detect ovulaton could beneft both fertlty treatment and brth control. Hghtech snffers may be used not just for breath smellng but also to detect other subtle changes n body odor that can ndcate dsease condtons. Our unque personal body-odor may also become an alternatve form of dentfcaton, sgnalng the end of credt-card fraud, forgotten or msapproprated PIN numbers, fake ID cards, etc. The Assocaton for Payment Clearng ervces, an organzaton set up to fnd solutons to these problems, s nvestgatng the use of electronc noses n banks, and companes may soon be able to replace securty entry systems nvolvng cards and codes wth a devce that recognzes each employee s personal odor []. o far, the electronc noses avalable are no more senstve than the average human nose - although specalst noses are beng developed - but electronc noses do have sgnfcant advantages over those attached to humans. Electronc noses do not get bored wth repettve smellng tasks, or de-senstzed through habtuaton to partcular odors. Unpleasant smells such as ndustral chemcals and sewage do not make electronc snffers feel sck, and ther performance on smellng tasks does not fluctuate accordng to mood, hormone cycles or other unpredctable human factors [3]. In ths study, a fully operatonal electronc nose system for general smellng applcatons, whch models the functon of the bologcal nose, s presented. Background: The mammalan olfactory system uses a varety of chemcal sensors, known as olfactory receptors, combned wth automated pattern recognton

2 J. Comp., c., (): 63-7, 5 ncorporated n the olfactory bulb and olfactory cortex n the bran [4-5]. No one-receptor type alone dentfes a specfc odor. It s the collectve set of receptors combned wth pattern recognton that results n the detecton and dentfcaton of each odor. Fg. llustrates the major components and functon of the mammalan olfactory system and ts sensory components. Odor molecules arrve at the olfactory receptors stmulatng an electro-chemcal response that s transmtted through the crb form plate to the olfactory bulb and ultmately the olfactory cortex. The major operatons olfacton can be broken nto snffng, recepton, detecton, recognton, and cleansng of odors. The olfacton process begns wth snffng, whch brngs odorant molecules from the outsde world nto the nose. Wth the ad of turbnated (bony structures n the nose whch produce turbulence), snffng also mxes the odorant molecules nto a unform concentraton and delvers these molecules to the mucus layer lnng the olfactory epthelum n the upper porton of the nasal cavty. Next, the odorant molecules dssolve n ths thn mucus layer whch then transports them to the cla (har lke fbers) of the olfactory receptor neurons. The mucus layer also functons as a flter to remove larger partcles. Fg. : Major Components of the enses of Olfacton n the Human Fg. also llustrates the major components of the senses of olfacton and taste n the human. The major olfactory components are the olfactory receptors (sensors), the olfactory bulb (sgnal pre-processng), and the olfactory cortex (odor dentfcaton). The NO s the vomero nasal organ and s assocated wth pheromone detecton. ecepton nvolves bndng the odorant molecules to the olfactory receptors. These olfactory receptors respond chemcally wth the odorant molecules. Ths process nvolves temporarly bndng the odorant molecules to protens that transport the molecules across the receptor membrane. Once across the boundary, the odorant molecules chemcally stmulate the receptors. eceptors wth dfferent bndng protens are arranged randomly throughout the olfactory epthelum. The chemcal reacton n the receptors produces an electrcal stmulus. These electrcal sgnals from the receptor neurons are then transported by the olfactory axons through the crb form plate (a perforated bone that separates the cranal cavty from the nasal cavty wthn the skull) to the olfactory bulb (a structure n the bran located just above the nasal cavty). From the olfactory bulb, the receptor response nformaton s transmtted to the olfactory cortex where odor recognton takes place. After ths, the nformaton s transmtted to the lmbc system and cerebral cortex. There are no ndvdual olfactory receptors or portons of the bran that recognze specfc odors. It s the bran that assocates the collecton of olfactory sgnals wth the odor. Fnally, n order for the nose to respond to new odors, the olfactory receptors must be cleansed. Ths nvolves breathng fresh ar and the removal of odorant molecules from the olfactory receptors. The mart Electronc Nose ystem (EN): The two man components of the EN are the sensng system and the automated pattern recognton system as shown n Fg.. Ths combnaton of broadly tuned sensors coupled wth sophstcated nformaton processng makes the electronc nose a powerful nstrument for odor analyss applcatons. The sensng system can be an array of chemcal sensors where each sensor measures a dfferent property of the sensed chemcal, or t can be a sngle sensng devce (e.g., gas chromatograph, spectrometer) that produces an array of measurements for each chemcal, or t can be a hybrd of both. Each odorant or volatle compound presented to the sensor array produces a sgnature or characterstc pattern of the odorant [5-7]. By presentng many dfferent odorants to the sensor array, a database of sgnatures s bult up. Ths database of odorant sgnatures s then used to buld the odor recognton system. The goal of ths process s to tran or confgure the recognton system to produce unque classfcatons or clusterng s of each odorant so that an automated dentfcaton can be mplemented. Lke bologcal systems, electronc noses are qualtatve n nature and do not gve precse concentratons. Unlke bologcal systems, current electronc noses are usually traned to dentfy only a few dfferent odors or volatle compounds. Also, current systems lack the temporal dynamcs found n bologcal systems and neuromorphc models. Durng operaton, a chemcal vapor or odor s blown over the sensor array, the sensor sgnals are dgtzed and fed nto the computer, and the Artfcal Neural Networks [3] (mplemented n software) then dentfes the chemcal as shown n Fg

3 J. Comp., c., (): 63-7, 5 base whch s hghly resstant to severe envronments. The sensng unt s shown n Fg. 5. The relatonshp between sensor resstance and the concentraton of detected odor can be expressed by the followng equaton over a predetermned range of odor concentratons. A[C] B () Where: electrcal resstance of the sensor A, B constant [C] Odor concentraton Fg. : chematc of EN The nput to the odor sensor(s) can ether be AC or DC of maxmum value of 4 maxmum power s 5mW. The maxmum nput to the heater s 5. The outputs of the sensor(s) are: * Usng DC nput: only change of the voltage ampltude of the output wth change gas. * Usng AC nput: the change wll be n the ampltude and phase. The sensor resstance () s calculated usng the followng formula: - C L () L Fg. 3: Neural Networks ecognton Engne ystem Hardware Desgn: The mart Electronc Nose system (EN) s a system that converts the sensed odor n ar to an electrcal sgnal that s condtoned and sent to a computer to be nterpreted and classfed usng a specfcally desgned Neural Network algorthms. Fg. 4 shows the degned and bult EN crcut, whch conssts of the followng parts: ensng Unt: The used sensng element s a Fgaro gas sensor, whch conssts of a Tn Oxde (no ) semconductor [8], whch has low conductvty n clean ar. In the presence of a detectable gas, the sensor's conductvty ncreases dependng on the gas concentraton n the ar. A smple electrcal crcut can convert the change n conductvty to an output sgnal, whch corresponds to the gas concentraton. The used TG83 has hgh senstvty to the vapors of organc solvents as well as other volatle vapors. It also has senstvty to a varety of combustble gases such as carbon monoxde, makng t a good general-purpose sensor. The sensor s also manufactured wth a ceramc Wth Power dsspaton across sensor electrode (P) gven by: P * (3) C ( + ) L In ths study an AC source wth KHz frequency s used. Functon Generator Unt: Fg. 6 shows the functon generator used to nput sgnal to the sensng unt where t gets modulated the smelled odor. The Unt employs the X-6 monolthc functon generator (Fg. 7), whch s capable of producng accurate snusodal, square, trangular, and ramp waveforms. Ths makes ths generator deal for communcaton and nstrumentaton purposes specally for our electronc nose applcatons that may requre dfferent types of sgnals that can also be pre-modulated before ts nputted to the sensor usng analogue or dgtal modulaton technques. The output waveforms of the X-6 can be both ampltude of frequency 65

4 J. Comp., c., (): 63-7, 5 Fg.4: The EN Crcut 66

5 J. Comp., c., (): 63-7, 5 Fg. 5: mell ensor and Equvalent Electrcal Crcut Fg. 6: The Functon Generator Unt Fg. 7: X-6 Functon Generator modulated by an external sgnal. The operatng frequency can be selected over the range. Hz to MHz. When used n our system Fg. 6, at pn 7 provdes the desred frequency tunng. The harmonc content of the used snusodal output can be reduced by addtonal adjustment as shown n Fg. 6. a adjusts the shape of the sne wave wth b provdng the requred adjustment to mantan waveform symmetry. The frequency of operaton f o s determned by an 67

6 J. Comp., c., (): 63-7, 5 external tmng capactor C across pns 5 and 6 and by a resster connected to ether pn 7 or 8. The operatng frequency s gven by: f o Hz (4) * C And can be adjusted by varyng ether or C. tablty s optmum for 4K<<K wth values of C n the range of pf<c<uf. Our snusodal carrer frequency of KHz s chosen to derve the system wth 4.34K and CuF whch when substtuted n equaton 4 gves an operatng frequency of.473khz. the maxmum ampltude of the output sgnal of the generator s nversely proportonal to the resstor 3 (Fg. 6) connected to pn 3. Hence, by usng 3 5K would obtan an approxmate value of 6 volts for our generated sne wave. The Flterng Unt: Fg. 8 shows the multstage BPF used to nose remove and frequency specfy the sensng unt output sgnal. Ths means that any sgnal outsde the prescrbed bandwdth wll not be accepted. Ths s essental for medcal and securty sgnatures. Ths crcut, whch s based on the concept of two ntegrators, cascaded together wth an overall feedback loop (two ntegrator loop b-quad) possesses hgh selectvty necessary for our applcatons. Dvde both sde of equaton (6) by gves: K (7) + + In equaton (7) we observe that the sgnal can be obtaned by passng through an ntetegrator wth a tme constant equal to. Furthermore, passng the resultng sgnal through another dentcal ntegrator results. Fg. 9 shows the block dagram from such a two ntegrator arrangement. Fg. 9: Two Integrator Arrangement In order to obtan (the nput sgnal feedng the two cascaded ntegrators), equaton (7) s rearranged whch gves: K (8) Whch suggests that can be obtaned by usng the weghted summer as shown n Fg.. Fg. 8: BPF ystem To mathematcally descrbe the flterng crcut we consder frst the second order hgh pass transfer functon gven by: K (5) + + Where: K s a gan constant. : s a qualty factor. Cross multplyng equaton (5) gves v + + K (6) 68 Fg.: The Weghted ummer Consderng Fg. 9 and we obtan Fg. whch s descrbed by the followng expresson:

7 J. Comp., c., (): 63-7, K Fg.: Two Integrator Bquad + lp (9) Equaton 9 ndcates that the output sgnal of the frst ntegrator s bp wth a center frequency gan of the realzed band pass flter equals to K. the requred samplng frequency, external components are needed. Fg. 4 shows the necessary connectons for our system ADC. The desgn of analog to dgtal converter unt (Fg. 4) s based on frequency samplng wth voltage reference as carred out by the ADC 84 (Fg. 3). For our applcaton a 64 KHz frequency s selected wth an external clock suppled to the ADC unt by our computng system CPU. As shown n Fg. 4 an external capactor and resster are requred for crcut operaton. Usng the expresson F clk and knowng the value of the capactor C 5pF wll gve us a resstance value of K. A reference voltage of.5 volts s used. Amplfcaton Unt: After the sgnal passes through the b-quad BPF t needs smple amplfcaton process to enhance the voltage level of the modulated snusodal sgnal comng out of the sensor. Fg. shows the Op- Amp used enlarge the sensng unt fltered sgnal. Fg. : Amplfcaton Unt Fg. 3: ADC84 The output voltage of the crcut descrbed n Fg. s gven by: f () Where, f K and.k. Ths substtutng the above values wll gve K5. Ths value of K s used together wth a value of to obtan the requred center frequency gan of the band pass flter. Analogue to Dgtal Converter Unt: Ths unt s used to enable the samplng and processng of the electronc nose sgnal by the specfcally desgned software and neural engne. It nterfaces the system hardware to ts nterpretng and classfyng software. Ths s carred out usng the ADC84 devce shown n Fg. 3. To select 69 Fg. 4: ADC84 Unt

8 J. Comp., c., (): 63-7, 5 To help the sensng unt recover to ts orgnal status after smellng odors, and to elmnate problems connected to mxtures of odors and msclassfcaton, a computer controlled ventlaton and extracton system s mplemented, whereby two mcro fans are used to stablze the ar over the sensng unt and extract any remaned molecules on the surface of the sensor element. Followng are the man parts of the extracton and ar stablzaton system. Tmng Unt: Fg. 5 shows the used 555 Tmer, whch s used to start and stop the mcro fans under computer control. The 555 tmer needs external components to set ts swtchng tme characterstcs as shown n Fg.6. The output pulse frequency of the tmng unt shown n Fg. 6 and generated by 555 tmer n Fg. 5 s controlled by,, and C the perod of the pulse can be adjusted usng and C usng the followng expresson T ch *C *ln. Ths functon s used to cover the rsng part of the waveform wth the dsgorgng part gven by T ds *C ln. Countng and Logc Control Unt: Fg. 7 shows the countng crcut, whch s necessary to produce the followng codes to control the nternal process of the desgned hardware. The unt wll produce codes from to. These codes are programmed as shown n table.. Fg. 8 shows the mplementaton of counter and logc n our system. The 7493IC conssts of 4 flp-flops. The flp-flops can be connected to count n bnary, PCD or other countng formats. It can be connected to count from to dfferent maxmum values. Yhs s done by connectng or of the outputs to reset nputs at and (pns and 3). Fg.8 shows A (pn) and B (pn 9) havng a NAND gate nput and an output whch connects wth and. the output from the tmng unt s connected to the nput of the counter (pn 4). The overall crcut shown n Fg. 8 s used to derve the mcro fans wth a drvng current obtaned through the crcut n Fg. 9 and descrbed by the followng equaton: I + I () Fg. 5: The Used 555 Tmer Table : Control Codes of Desgned Hardware Code Control Functon Operate Fan Number eset Interval ADC Converson Operate Fan Number Not used eset Fg. 6: The 555 Tmng Unt Fg.7: 7493 Countng Crcut 7

9 J. Comp., c., (): 63-7, 5 Fg.8 Countng and Logc Control Unt Fg. 9 shows the drvng unts for the mcro fans. Ths crcut s necessary to pull the voltage and current levels to ther rght values for the fans to be drven correctly. Fg.9: Fans Drvng crcut CONCLUION The desgned and bult TG 8 seres mart Electronc Nose ystem (EN) proved to be an excellent system for the general purpose applcatons as t allows any of the 8 seres sensors to be nterfaced wthout the need for any hardware modfcaton or adjustment. The extensve use of mathematcal equatons descrbng each step of the desgn s a major advantage n our desgned system as t allows easy modfcaton and development of the system to ncorporate any newly presented deas and components on the market. The ntal choce of the TG type of sensors s due to there smple desgn and the advantage of havng an ntegrated heater whch helps n stablzng detectng element temperature and evaporaton of adsorbed odors molecules, hence provdes acceptable results that s mproved through the use of hardware flterng and dgtzng devces and an ntellgent software whch provdes excellent classfcaton. The overall desgned system performance s further mproved through the use of our specally controlled mcro fans that enable rapd recovery of detected sgnals to ts ntal levels. Further mprovement could be ntroduced to our effcent system by ntegratng all sensors onto one devce where by ntegraton and mnaturzaton wll mprove the electrcal characterstcs of the sensng part of the desgned system. EFEENCE. Nagle, H. T., 998. The How and Why of Electronc Noses. IEEE pectrum, pp: taples, E. J., 998. Doxn/Furan Detecton and Analyss Usng a AW-Based Electronc Nose. Proc. IEEE Internatonal Ultrasonc ymposum, enda, Japan. 3. Keller, P., 994. Three Neural Network Based ensor ystems for Envronmental Montorng. Proc. IEEE Electro94 Conference, Boston. 4. Merler,., C. Furlanello, B. Larcher and A. boner,. Tunng Cost enstve Boostng and ts Applcaton to Melanoma Dagnoss. In MC, Cambrdge, UK, ol 96 of LNC, pp: Pardo, M. and G. Nederjaunfner,. Data Preprocessng Enhances the Classfcaton of Dfferent Brands of Espresso Coffee wth an Electronc Nose. ensors &Actuators B, Deveza,., D. Thel,.A. ussel and A. Mackay-m, 994. Odor ensng for robot gudance. The Int. J. obotcs es., 3: hlbayeh, N. and M.Iskandaran, 3. Dscrmnaton of Perfumes Usng an Electronc Nose ystem. WEA Trans. On Crcuts and ystems, : Fgaro sensors ( 7