seminar on fibers

T. Venkateswara Rao
Seminar
On
Detection of Adulteration of Edible Oils
Using Optical Fibers

1.Introduction

The development of an intensity modulated fiber optic Evanescent Wave sensor for the detection of the amounts of adulteration of oils like pure ground nut oil and coconut oil is presented. Technology advancement has taken place in the recent years in the fabrication and use of optical fibers as a sensing element.

Optical fiber sensors act as transducers that encode information, which describes non optical external perturbation onto an optical fiber.

The INTENSITY based Optical fiber sensors are the most basic type of sensors which can be realized with ease. Groundnut oil in A.P, and Coconut oil in Kerala and the southern parts if Karnataka and Tamilnadu are widely used as edible oils. These oils very much prone to adulteration due to many reasons.

The use of Optical fiber sensors for detection of contamination in the above oils is present work using optical fibers. The most commonly used adulterants are cheap oils like paraffin, palm oil etc. It is very important to check the purity of the above mentioned edible oils.
Present Work
In the Evanescent wave, the external plastic jacket and cladding are removed the mid point along the length of the fiber. The sensing region in the sensor used is a multimode fiber 220/230 μm with a laser diode and power meter, which are operated at 820nm and 850nm.

The present sensor used comes under the class of Intensity (amplitude) modulated sensors.

On the basis of the techniques used to modulate the signal, sensors can be classified as:
Intensity (amplitude) modulated sensors
Phase modulated sensors
(interferometric sensors)

Evanescent Evanescent Sensor :
Evanescent Wave:
Because of the TIR of the light wave at a boundary, some energy of the light wave in the core of the fiber actually penetrate into the cladding for a very short distance and then escapes from the core and immediately comes back. This thin penetration of light energy into the cladding is called as Evanescent Wave. In order to use the Evanescent Wave as a sensor, the cladding is removed. Now, because of removal of cladding light, leaks out. Here to avoid the leakage, we use some oils like groundnut oils& coconut oils whose refractive indices are approximately nearer to that of cladding. The disadvantage is that light will leaks out without cladding.
We can design a sensor where energy is absorbed from the evanescent wave in the presence of Oils. This being versatile portable and reliable sensor.

With development of modulated fiber optic evanescent wave sensor, it is possible to detect the amounts of adulteration in impure oil.
When light is injected into an optical fiber, a fraction of the radiation extends a small distance from the guiding region into the liquid medium of lower refractive index that surrounds the core.
This is an evanescent field and the evanescent energy may interact with the guiding medium and attenuate the energy , because refractive index changes the absorption of scattering.
From the equation it is evident that the power coupled into the fiber after the sensing region decreases linearly with increase in .
This result is exploited to construct a fiber optic refractive index based sensor to the adulterance present in edible oils.
3.Experimental arrangement

The experimental arrangement shown in fig consists a laser diode as a source, a 200/230 m plastic optical fiber and a power meter.
The sensing region is slowly placed in a bent mould.
Oil mixtures of different ratios is introduced in to the sensing region.
The light is injected from a laser diode into the core of the plastic fiber at one end.
The output power is measured from the second end of the plastic fiber using an optical power meter.
The core material is PMA (Polymethyle metha crylate)
The cladding is a thin layer of fluorinated polymer

Block diagram of experimental setup
Laser diode
Splicing
Samples for Investigations
Different concentrations of impure oil – Paraffin oil or Palm oil
The refractive index of these samples are determined by Abbey’s refractometer
4. Results & discussion
A plot of normalized optical power output as a function of ,of different volumes of adulterant in pure oil.
5.Conclusion
Evanescent wave sensing system using plastic optical fibers is developed for detection of adulterants present in edible oils.
The sensor exploits the Evanescent field attenuation by modulating the refractive index.
The observed sensitivity is linear and the detection limit is in the range 1-2% by volume of impurity present in pure oils.
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