Radio Frequency Detection and Characterization of Water-Ethanol Solution through Spiral-Coupled Passive Micro-Resonator Sensor

Abstract

We present a microfabricated spiral-coupled passive resonator sensor realized through integrated passive device (IPD) technology for the sensitive detection and characterization of water-ethanol solutions. In order to validate the performance of the proposed device, we explicitly measured and analyzed the radio frequency (RF) characteristics of various water-ethanol solution compositions. The measured results showed a drift in the resonance frequency from 1.16 GHz for deionized (DI) water to 1.68 GHz for the solution containing 50% ethanol, whereas the rejection level given by the reflection coefficient decreased from −29.74 dB to −14.81 dB. The obtained limit of detection was 3.82% volume composition of ethanol in solution. The derived loaded capacitance was 21.76 pF for DI water, which gradually decreased to 8.70 pF for the 50% ethanol solution, and the corresponding relative permittivity of the solution decreased from 80.14 to 47.79. The dissipation factor increased with the concentration of ethanol in the solution. We demonstrated the reproducibility of the proposed sensor through iterative measures of the samples and the study of surface morphology. Successive measurement of different samples had no overlapping and had very minimum bias between RF characteristics for each measured sample. The surface profile for bare sensors was retained after the sample test, resulting a root mean square (RMS) value of 11.416 nm as compared to 10.902 nm for the bare test. The proposed sensor was shown to be a viable alternative to existing sensors for highly sensitive water-ethanol concentration detection.

Near-Infrared Silicon Photonic Crystals with High-Order Photonic Bandgaps for High-Sensitivity Chemical Analysis of Water–Ethanol Mixtures

“…In order to overcome the limitations of the methods described above, recent research has focused on developing highly sensitive approaches for the in situ and real-time analysis of water content in organic solvents. Among the different approaches, electrical (e.g., capacitors, , resonators , ) and optical (e.g., fluorescent/colorimetric, ,, photonic/plasmonic , ) methods have been successfully reported. Among these, optical methods either exploit specific chemical reactions with water to enhances fluorescence and color changes or monitor refractive index changes ,, of the water–alcohol mixture using highly sensitive optical transducers, , with the advantages of higher sensitivity, lower detection limit, larger range, and improved portability with respect to electrical approaches.…”

A High-Sensitivity Microfluidic Sensor Based on a Substrate Integrated Waveguide Re-Entrant Cavity for Complex Permittivity Measurement of Liquids

“…Except for dielectric properties measurement, it is also meaningful to realize the quantification of a given binary liquid mixture [ 38 , 39 ]. Taking the acetone/water mixtures as an example, Figure 16 plots the volume fraction of water as a function of resonance frequency.…”

Design of a Highly Sensitive Sensor for Measuring Liquid Permittivity With Flexible Substrate

“…Among them, resonant cavity method has become the main method to measure the dielectric constant of liquid for its high sensitivity, high precision, and low cost. The method of measuring the permittivity of liquid by microwave method can be divided into plane type [9,10], container type [11,12], and intrusive type [13,14]. In recent years, many studies on the measurement of liquid dielectric constant have been reported.…”

“…In recent years, many studies on the measurement of liquid dielectric constant have been reported. A helical coupled passive resonator is proposed by Koirala et al [9], which uses a micropipette to drop the measured liquid onto the sensor surface. The planar liquid dielectric sensor needs to accurately control the volume of the liquid.…”