Abstract
Background: Ethanol is an important fuel for the automotive industry in different countries and an alternative to fossil non-renewable fuels. However, it is usual the malpractice of ethanol adulteration in many countries The illegal adulteration of ethanol fuel results in reduced engine lifetime and increases the production of toxic gases. The conventional ethanol analyses require expensive laboratory methodologies and equipment. This paper proposes a microwave sensor to analyze the complex permittivity of ethanol fuel by applying the cavity perturbation technique.
Methods: The sensor is a microstrip patch antenna coated with Single-Walled Carbon Nanotubes (SWCNTs). The SWCNTs deposited over the microstrip antenna allows characterizing the sample vapor-phase due to the change of the effective permittivity. When the ethanol-water vapor is injected, part of the Material Under Test (MUT) is adsorbed by the SWCNTs, increasing the charge transfer and changing the resonant frequency and Q factor. After the injection, the vapor is desorbed, returning to the initial values of frequency and Q factor of the device. Results: The sensor presented a repetitive response, with no evidence of poisoning or drift. The measurements allowed to determine a relation between the resonant frequency for each fraction of ethanol-water sample and the real part of the complex permittivity. The same procedure was used with Q factor, which is related to the imaginary part of the complex permittivity. The sensor showed good sensitivity to detect small fractions of ethanol and water based on the complex permittivity of the mixtures. Conclusion: The sensor was able to discriminate small fractions of ethanol-water with a fast response and good sensitivity. The proposed methodology allows in situ and real-time analysis of the ethanol fuel, towards the development of a compact, integrable, and portable electronic system. Therefore, the proposed microwave sensor presents consistent results related to the qualification of ethanol fuel, making it a promising tool for developing material characterization sensors and devices.Keywords: Microwave sensors, fuel qualification, carbon nanotubes, cavity perturbation methods, permittivity measurements, gas sensors.
Graphical Abstract
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