Experimental Investigation of Complex Permittivity & Determination of Ethanol Content in Gasoline Anagha Kunte and Savita Kulkarni Department of Electronics and Telecommunication, MAEER's Maharashtra Institute of Technology, Pune (India) Abstract - The proposed nondestructive method is used for the accurate detection of complex permittivity and adulteration in petroleum liquid. The microstrip straight resonator is used to record the resonant frequency shift and Quality factor change for different percentages of ethanol in gasoline. The instrument prototype with the necessary GPIB interface and the network analyzer is used for the efficient and accurate measurements of these parameters. The attempt has been made to present the characteristics study of lossy dielectric liquids like petrol and ethanol around the resonant frequency shift and Quality factor, Dielectric losses and dissipation factor. Index Term -- Complex Permittivity, Lorentzian fitting, Planar Resonator Sensor, Q Unloaded I. INTRODUCTION Standard gasoline is a dielectric liquid with about 30 different hydrocarbons. The dielectric constant of such liquids is a function of dielectric constant of its components. On this line the Powerful measurement technique such as Nuclear Magnetic Resonance and Gas Chromatography although very accurate however as far as the portability of the setup and slow pace parameter measurements is concerned the use of the proposed alternative method is suggested. In view of this the proposed setup in frequency domain can be used as inspection tool for detecting the ethanol content in Gasoline. As per the Indian oil and natural gas regulatory norms the Gasoline should have 5% ethanol content. Ethanol is a polar liquid, and its complex permittivity presents a Debye relaxation response. Transmission coefficient method is used to determine ethanol concentration in gasoline. The gasoline is being adulterated by adding a higher concentration of ethanol, or using hydrated ethanol, or adding solvents like naphtha, kerosene etc. In this paper the method deployed for the measurement of these adulterations is based on microstrip straight 1J2 resonator sensor. The typical resonators 1.5GHz, 1.8GHz, 2GHz, and 2.3 GHz has been designed with RT/Duroid 5880 substrate with a dielectric constant of 2.2 and a loss tangent 0.0009. The length of resonator varies in mm as designed frequency varies. Coupling gap is taken as 0.8mm and is critically coupled.3dB bandwidth varies approximately 60MHz and return loss of up to -60dB. [6] The dielectric constant of gasoline is expected to vary slightly in the RF range (up to 3 GHz); on the other hand the dielectric constant of ethanol varies drastically in the aforesaid range as ethanol is polar liquid. 978-1-4244-2690-4444/08/$25.00©2008 IEEE 171 II. MICROSTRIP RESONATOR SENSOR This method reports an accurate and fast complex permittivity measurement using a microstrip resonator. The resonant frequency and the quality factor Q of microstrip resonator are measured. The change in the effective permittivity [I] of the microstrip resonator is given by following first equation. 2 2 10 / Is = £ effs / £ effo (I) Where "fo" and "Eeffo" indicate resonant frequency and effective Permittivity without sample, while "fs" and "Eeffs" indicate resonant frequency and effective Permittivity with sample. /o=/(£eff') (2) L1Q = /( Eeff' ,Eeff") (3) Second and third equation shows functional dependence of frequency on permittivity, where Eeff* is the complex permittivity of the sample. Eeff' and E eff" indicate real and imaginary parts of the complex permittivity. Eeff' of the material under test (MUT) is determined with the help of spectral domain analysis . To verify Eeff' of complex permittivity fourth equation is used. £eff = QMUT.£'MUT+QSUB.£'SUB+l-qMUT -QSUB (4) In the quasi-static approximation, [2] the effective permittivity can be expressed as a linear combination of the permittivity of the air (E r = I), the substrate (E'SUB) and the MUT (E' MUT) as shown in equation fourth. qMUT (filling factor q of ethanol mixed with gasoline) and qSUB (filling factor of RT-Duroid) being the corresponding filling factors. They are obtained by calculating the fractions of the total energy stored in the three regions (MUT, Substrate and Air). MUT filling factor qMUT depends not only on the structure geometry but also on the MUT dielectric constant, while qSUB is independent of the MUT. Using real part of fourth equation effective permittivity is verified. A careful fabrication procedure for half wavelength straight resonator, one can make the input and output air gaps equal to each other, so that coupling coefficient kl from input side and k2 from output side proves equation kl =k2. For such symmetrical coupling [3][4] one can obtain fifth equation for unloaded Qu. Qu = QL (5) 1-S 21 ( /0) Authorized licensed use limited to: Maharashtra Institute of Technology. Downloaded on September 8, 2009 at 10:46 from IEEE Xplore. Restrictions apply.