Design Ammonia Gas Detection System by Using Optical Fiber Sensor

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International Journal of Electronics Communication and Computer Engineering Volume 4, Issue 4, ISSN (Online): 2249–071X, ISSN (Print): 2278–4209

Design Ammonia Gas Detection System by Using Optical

Fiber Sensor

Dr. Bushra. R. Mhdi, Nahlia. A. Aljbar, Dr. Shehab. A. Kadhim, Jamal. F. Hamode, Abeer. H. Khalid, Suad. M. Ali, Afrah. S. Mhdi

Abstract–Design study and construction of Ammonia gas detection using a fiber as a sensor to based on evanescent wave sensing technique was investigated. Multi-mode fiber type (PCS) with core diameter (600μ m) and (50cm) length used where plastic clad was removed by chemical etching for effective sensing area which coated with sol-gel film to enhance its absorption characteristics to evanescent wave around the optical spectrum emitted from halogen lamp measurements through different temperature rang (25-60oc) with and without air using as a carrier to ammonia molecules are investigated. Finally sensing efficiency are monitored to ammonia gas it affected to different temperature and environmental condition are studied and our result are compatible to scientific publishes.

Keyword–Chemical Sensor, Fiber Sensor, Sol-Gel.

I. I

NTRODUCTION

Optical fiber chemical sensors (OFCSs) have some distinctive characteristics. The small size and flexibility of the sensor design makes them ideal tools for in situ and in vivo analysis، Because optical fiber can easily transmit Chemically encoded information between the spectrometer and a remote sample, optical fiber sensors are particularly suitable for monitoring various environmental hazards including either hostile or not easily accessible events[1] In addition optical fibers are relatively insensitive to sources of noise, such as radioactivity and electric fields[2] These devices utilize the reaction of ammonia vapor with either a dependent dye material or a pH-sensitive film which undergoes a suitable color change or an absorption change[1].

(OFCSs) based on dye indicators do have some limitations that should be recognized in applications of sensors. First of all, almost all dyes are temperature sensitive in their response characteristic and most dyes have a critical temperature above which they tend to cease response completely and they may get irreversibly dissociated. Secondly, the dye indicators have their own chemical properties and natural lifetimes that usually decrease with increasing temperature, and their behaviors may be largely dependent upon the ambient optical conditions, particularly in the presence of ultraviolet light [3]. Because evanescent field reduces the amount of light impinging on the dye by many orders of magnitude, optical fiber sensors based on evanescent field can overcome this problem. In addition, if the chemical reactions involved in the sensing process are too slow or irreversible, the sensor cannot be used to provide a fast, continuous, and accurate response.

In this kind of sensors, the parameter measured is the light intensity carried by the fiber that is modulated by the change in the absorption spectrum of the

chromospheres sensitive to NH3[4]. in this paper, we have designed and construction an optical fiber-based evanescent wave sensor for gaseous ammonia sensing. Sol–gel film is used to encode bromo cresol purple on the surface of a bared fiber core, and evanescent absorption is measured through a spectrometer. Gas sensing properties of the optical fiber evanescent sensor and ammonia responses versus temperature are reported. Meanwhile, the effects of carrier gas such as air on signal intensity and response time are also thoroughly investigated and compared

II. T

HEORY

Light can be guided in an optical element, or wave guide, at very high efficiencies by total internal reflection. The phenomenon occurs when light, traveling in a medium of refractive index nl, strikes the boundary of a second, relatively lower refractive index, medium, n2, at an angle, measured with respect to normal, greater than the critical angle, defined as [5,3]:

) 1 ( sin

1 2 1

n n c

  

When light undergoes this total internal reflection, a small amount of energy penetrates into the second medium. Known as the evanescent wave it has a depth of penetration (dP), defined as distance from the interface where intensity of the electric field is reduced to in verse exponentially amount of( e-l) the intensity at the interface. This depth into the second medium is [7]:



sin



(2)

2

/ 12 1/2

2

1 n

dp   

where θ is the angle of incidence at the interface with respect to normal, λl is the wavelength of light in the waveguide medium, λ/nl, and n12 is the refractive index

ratio of the waveguide and surrounding medium, nl/n2 Absorbing species at the interface will interact with the evanescent wave. Resultant changes in guided light intensity provides qualitative and quantitative information about species present in the evanescent field. Infrared spectroscopy is performed in this format when the sample to be examined is highly absorbing. Traditionally known as attenuated total reflection, ATR, the planar optical elements transport light in a narrow range of angles. Therefore, light strikes the interface between the optical element and sample at a discrete range of angles. However, when the light guiding element is an optical fiber this sampling technique is known as evanescent wave spectroscopy, EWS[7].

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angles that are present at the core/cladding interface. The cone of light that an optical fiber can accept and guide from an infinite source is referred to as the numerical aperture, NA, and is defined as [8]:





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sin n₁2 n₂21/2 n

N_A _ext  

where next is the refractive index of the external medium,

θa is acceptance angle of the fiber, and nl and n2 are the

refractive indices of the core and cladding, respectively If infrared active species are present in the evanescent field of an optical fiber, light intensity will decrease according to the following relationship [9]:



/



log



/



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logI I₀ _eL_c NA₀2 NA2

where I is transmitted light intensity after analyte exposure, Io is reference intensity with no analyte present, L is fiber length, c is molar concentration, and NA and NAO are numerical apertures of the fiber with and without analyte present, respectively. Effective molar absorptivity,

αe , is defined,

) 5 ( p

e   

where ε is molar absorptivity of infrared active species and

ηpis the fraction of light entering the fiber that is present in the cladding,

) 6 ( /V

K p  

In equation 6, k is a proportionality constant, determined by Gloge (10) to be (1.89) for equilibrium mode distribution in a fiber. The denominator, known as the V aerometer, determines the number of optical modes a fiber can support and is defined as,





) 7 ( 2 ₁2 ₂2 1/2

 

  

 _



n n r V

where r is the fiber radius.

III. E

XPERIMENTAL

W

ORK

Plastic Clad Silica (PCS) multi-mode optical fiber with core diameter of 600μ m was cut into 50 cm length and

both ends were polished. The revealed cladding was removed by chemical etching through immersing the fiber in a 50% HF solution for 10 min. In the present investigation,(Na2 O3 Si ) was used as the precursor for the sol preparation since the refractive index of the porous silica film produced is less than that of the fiber core. The ammonia sensitive dye used in the present case is bromocresol purple (BCP, Arcos Organics, Indicator Grade), as it is chemically more stable and is more resistant to oxidation than other indicators[11].

A magnetic stirrer was employed to mix the sol–gel reagents. Experimental set up for the sensing system is shown schematically inFig.1. A cylindrical chamber with inner diameter of 2.5 cm and thickness of 0.2 cm was customized. Gas inlet and outlet were positioned opposite as shown inFig.1. The photograph of experimental set up is shown in Fig (2). The upside channel is used as gas inlet and the downside channel as outlet. Because the analyte gas, ammonia is lighter than any carrier gases used this design will help the analyte gas evenly pass through the test chamber when ammonia gas was introduced from the

up to down way. The test chamber was heated by using an electrical resistance heater for temperature influence testing. The inner temperature of the chamber was calibrated and monitored using a digital thermometer. A LS-1 Tungsten Halogen Light Source and USB2000 Miniature Fiber Optic Spectrometer (Ocean Optics Inc.) were employed to characterize the absorption properties of the analyte gas. The air pumping was used to pump the air flow in the cavity.

Fig.1. Schematic of the experimental setup for optic fiber ammonia gas sensor

Fig.2. Shows the photograph experimental set up.

IV. R

ESULTS AND

D

ISCUSSION

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Fig.3.Shows the spectrum of Intensity at different temperature of ammonia gas at a Halogen lamp

wavelength.

The relation between the wavelength and intensity shown in fig.3 at different temperature. The intensity of absorption increases with decrease temperature,the peak at wavelength of (596 nm) was identified for all the temperature tested.

Fig.4. Shows the relation between the Intensity virus temperature in air flow.

The response of the optical fiber evanescent sensor versus different temperature of ammonia is plotted in Fig. 4. The dyes are temperature sensitive in their response characteristic. The effect of temperature on the sensing property of optical fiber sensors has been investigated with the air carrier gas. In the case of air as carrier gas, the response curves of the sensor to ammonia at temperatures of Range (25-60)◦C, are plotted in Fig.4. When the temperature increase from 25 to 60 ◦C, the intensity

quickly reduces from 215.2 to about 107.6 The relation between wavelength and output intensity with and without air flow is shown in fig.5. The upper curves are the prescience of without air flow ,where the intensity is

highest. The lower curves are with the presence of air flow, where the intensity is the lowest.

The highest intensity without air flow was reason to take fixed sample from pollution environment saturation by ammonia but in the case of air flow the ammonia gas mixture with air, the concentration of ammonia gas is less than the first case. The reason for without air flow to have a better response for ammonia detection is clear.

Fig.5. Shows the relation between the Intensity virus wavelength with and without air flow.

However, a possible explanation in the view of reaction mechanism may help to understand the process. As it is well know that some high electroaffinity elements such as oxygen and nitrogen can form hydrogen bond with (O H) and (N H) structure, there is possibility that using nitrogen or air as carrier gas may help to stabilize the targeted ammonia molecules through forming hydrogen bond, which should have better interaction with the dye molecules immobilized on the sensing film[12] Since the dye molecule, BCP, has aromatic structure with three benzene rings that have double bonds and π electrons

which is mobile, it is helpful for interactions between the targeted ammonia molecule and the dye molecules with air flow ionic molecule forms a hydrogen bond with nitrogen or oxygen, since oxygen or nitrogen possesses either double or triple bonds andπ–π interaction is easier than π–

σ interaction when ammonia molecule alone (without hydrogen bond) [13].

V. C

ONCLUSION

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These experimental results have demonstrated that a fast response optical fiber evanescent gaseous ammonia sensor can be constructed by applying slightly elevated ambient temperature.

R

EFERENCES

[1] A. Messica, A. Greenstein, A. Katzir, U. Schiessl, M. Tacke, (1994) ,"Fiberoptic evanescent wave sensor for gas detection", Opt. Lett. 19 (15) 1167–1169.

[2] Z. Jin, Y.X. Su, Y.X. Duan, (2001) , " Development of a polyaniline based optical ammonia sensor", Sens.ActuatorsB72, 75–79.

[3] B. Culshaw, (2004) ," Optical fiber sensor technologies: opportunities and perhaps- pitfalls", J. Lightwave Technol. 22 (1) 39–50.

[4] J. Lin, (2000) , "Recent development and applications of optical and fiber-optic pH sensors", Trends Anal. Chem. 19 (9) 541–

552.

[5] DeGrandpre, M. D.; Burgess, L. W. ,(1990), App. Spec. 44,273-279.

[6] Snyder, A. W.; Love, J. D. , (1983);Optical Wave guide Theory,

Chapman and Hall: New York.

[7] Kapany, N S. , (1967); Fiber Optics, Academic Press: New York.

[8] B.H. Timmer, K.M.v. Delft, R.P. Otjes, W. Olthuis, A.v.d. Berg, (2004) ," A miniaturized measurement system for ammonia in air", Anal. Chim. Acta 507 (1) 139–145.

[9] P. Suresh kumar, C. P. G. Vallabhan, V. P. N. Nampoori, V N

Sivasankara Pillai and P. Radhakrishnan, (2002), “ A fiber optic

evanescent wave sensor used for the detection of trace nitrites in

water”,Journal of optics A: Pure and Applied Optic,Vol 4, 247-250

[10] Gloge, D.; (1971), Appl. Optics,10,2252-2258.

[11] Sunil K. Khijwania, Kirthi L. Srinivasan, Jagdish P. Singh,

(2005) , “An evanescent-wave optical fiber relative humidity

sensor with enhanced sensitivity”,Sensors and Actuators, B 104 217–222.

[12] V. Matejec, J. Mrázek, M. Hayer, I. Kašík, P. Peterka, J. Kaňka,

P. Honzátko, and D. Berková, (2006),“Microstructure fibers for gas detection”,Mater. Sci.Eng. C26, 317-321.

[13] Roberto Gravina, Genni Testa and Romeo Bernini, (2009)," Per fluorinated Plastic Optical Fiber Tapers for Evanescent Wave Sensing",Sensors,9, 10423-10433.

A

UTHOR’S

P

ROFILE

Bushra. R. Mhdi

was born in Bagdad ,Iraq in 1966, she received B.S degree in electrical Engineering from Technology University,in1987,M.S degree in Laser Application in Electrical Engineering (Institute of Laser and Plasma) from Bagdad University in 2001 and he Ph.D. degree in laser Engineering from Technology University/Iraq-Bagdad in 2009. She joined to the Laser and Optoelectronic center in Ministry of Science and Technology in 2009, and carried out research in laser a design system and laser application .In 2010 she formed fiber communication section and began program in optical fiber sensor. She has numerous publication in the areas of fiber laser, laser system design and fiber sensor technology.

Nahla. A. Aljaber

was born in Bagdad, Iraq in 1969,she received B.S degree in Physics Science from Technology University, in1992, M.S degree in Laser Application in Physics Science (Institute of Laser and Plasma )in 2003. She joined to the Laser and Optoelectronic center in Ministry of Science and Technology in 2009, and carried out research in laser a design system and laser application .In 2010 she formed fiber communication section and began program in optical fiber sensor.

Dr. Shehab A. Kadhim

was born in Bagdad ,Iraq in 1961, he received Ph.D. Degree in applied physics/laser from technology Univ., Iraq, 1998. He is a head of fiber optics and laser communication department /M.O.S.T/Iraq.

Jamal F. Hammodi

was born in Bagdad, Iraq in 1965, he received B.Sc. Degree in Chemistry from Mustinsry Univ., Iraq, 1989.He is Sci./ Researcher., Directorate of Materials Science .He is Good experience in Chemical & Mechanical Properties Analysis. Good experience in bioceramics processing .Good experience in Phases & Microstructures evaluations. Good experience in corrosion by electrochemical for materials science. Good experience in preparation elements nano particlesIhave a patent issued by the Central Agency for measuring and quality control number 3477 in 2 \ 12 \ 2012 " Preparation of Brass Alloy (Cu-Zn) of Enhanced mechanical Properties by Using Glow discharge plasma Technique.

Abeer H. Khalid

was born in Bagdad, Iraq in 1975. She received B.S degree in Physics Science from Bagdad University in 1997. She joined the Laser and Optoelectronic Center in Ministry of Science and Technology in 2009, and carried out research in Spectroscopy system and laser application. In 2010 she formed fiber communication section and began program in optical fiber sensor.

Suad M. Alj

was born in Bagdad, Iraq in 1969. She received B.S degree in Physics Science from Technology University, in 1992. She joined the Laser and Optoelectronic Center in Ministry of Science and Technology in 2009, and carried out research in laser a design system and laser application. In 2010 she formed fiber communication section and began program in optical fiber sensor.

Afrah. S. Mhdi