Highly sensitive DS-CSRR based microwave sensor for permittivity measurement of liquids
Akash Buragohain, Gouree Shankar Das, Yatish Beria, Partha Protim Kalita, Abu Tahir Talat Mostako
Abstract
Abstract In this work, a low-cost double split complementary split ring resonator (CSRR) microwave sensor has been designed and fabricated on an FR4 substrate for permittivity characterization of liquids. This modified CSRR structure is proposed to make use of the benefits of the dielectric resonator technique compared to other types of microwave methods. The resonator structure comprises two slits in each of the rings normal to each other while maintaining one slit in each ring along the feed line for maximum excitation of the resonator. The resonator with substrate dimensions of <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mn>20</mml:mn> <mml:mrow> <mml:mtext>mm</mml:mtext> </mml:mrow> <mml:mo>×</mml:mo> <mml:mn>30</mml:mn> <mml:mrow> <mml:mtext>mm</mml:mtext> </mml:mrow> </mml:math> acts like an inductance-capacitance-resistance (LCR) circuit and operates at <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mn>2.501</mml:mn> <mml:mrow> <mml:mtext>GHz</mml:mtext> </mml:mrow> </mml:math> of the industrial scientific and medical band. Eleven different liquid samples (each with <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mn>150</mml:mn> <mml:mi>μ</mml:mi> <mml:mi>l</mml:mi> </mml:math> of volume) covering a wide permittivity range of <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mn>1</mml:mn> <mml:mo>−</mml:mo> <mml:mn>111</mml:mn> </mml:math> have been used to measure the transmission coefficient <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mfenced close=")" open="("> <mml:mrow> <mml:mrow> <mml:msub> <mml:mi>S</mml:mi> <mml:mrow> <mml:mn>21</mml:mn> </mml:mrow> </mml:msub> </mml:mrow> </mml:mrow> </mml:mfenced> </mml:math> using vector network analyzer. In comparison with many recently reported works, the sensitivity of the sensor is found to be higher with average and normalized sensitivity of <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mn>35.07</mml:mn> <mml:mrow> <mml:mtext>MHz/unit</mml:mtext> </mml:mrow> </mml:math> permittivity and <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mn>1.4</mml:mn> <mml:mi mathvariant="normal">%</mml:mi> </mml:math> respectively. Fit equations are developed for both real and imaginary parts of permittivity, and using the fit equations the permittivity of three unknown samples are determined with less than <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mn>3.7</mml:mn> <mml:mi mathvariant="normal">%</mml:mi> </mml:math> error. The sensor adopts a unique orientation of the slits to enhance the E -field intensity for better interaction of the samples with the sensor. A compact form factor, low production cost, future integration possibilities, and high sensitivity are the distinct highlights of the sensor. The sensor promises to be a potential candidate for situations that demands low-cost and highly accurate measurements and may be a good alternative to commercial sensors for dielectric characterization, concentration analysis, and impurity measurement of liquids.