  Citation: Dala, A.; Arslan, T. In Situ Sensor for the Detection of Oil Spill in Seawater Using Microwave Techniques. Micromachines 2022, 13, 536. https://doi.org/10.3390/ mi13040536 Academic Editors: Shizhi Qian and Teng Zhou Received: 6 March 2022 Accepted: 25 March 2022 Published: 29 March 2022 Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affil- iations. Copyright: © 2022 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/). micromachines Article In Situ Sensor for the Detection of Oil Spill in Seawater Using Microwave Techniques Aliyu Dala * and Tughrul Arslan Integrated Micro & Nano Systems, University of Edinburgh, Edinburgh EH8 9AB, UK; t.arslan@ed.ac.uk * Correspondence: a.dala@ed.ac.uk; Tel.: +44-745-104-0888 Abstract: Nearly 30% of oil drilled globally is done offshore. Oil spillage offshore has far-reaching consequences on the environment, aquatic lives, and livelihoods as it was evident in the Deepwater Horizon and Bonga oil spills. A novel microwave in situ oil spill sensor was developed in this work. The device is comprised of two polydimethylsiloxane (PDMS)-encapsulated ultra-wideband underwater microwave trefoil antennas enclosed in a Faraday cage with one serving as the receiving antenna and the other as the transmitting antenna. Heavy aromatic-naphthenic Azeri crude oil was used as an inclusion in the seawater host medium. Substantial changes in the measured reflection (S11) and transmission (S21) coefficients were observed as the medium was adulterated with crude oil starting from 200 MHz to around 2500 MHz. The changes in the dielectric properties of the media resulted in changes in both the S11 and S21 signifying and detecting an occurrence of the oil spillage. Thus, by employing radio frequencies, oil spillage was detected using the in situ monitoring device in seawater. Keywords: microwave; underwater antenna; PDMS; crude oil; sweater; Faraday cage; radio fre- quency; reflection coefficient; transmission coefficient 1. Introduction Humans have been using crude oil in one form or another for thousands of years. From the ancient Egyptians that used it to mummify their dead to the Babylonians that waterproofed their boats with it [1]. However, the real potential of crude oil was unleashed in the mid-19th century. The modern history of the world is entwined with that of oil. The Industrial revolution, the invention of the automobile, and the world wars were all powered by oil. It has been able to uplift countries from squalor to prosperity in an instance. We live in an oil world; we are surrounded by it. Oil is presently used to power our industries, automobiles, aviation, homes, and offices. The derivatives of crude oil have permeated every sphere of our lives. From some of the plastics we use to some synthetic rubber, cosmetics, chemicals, and lubricants, the importance of crude oil cannot be overemphasised [2]. Oil has an edge over other energy sources in that it is concentrated and could be easily transported over long distances. Sometimes, during these transportations, accidents do occur. For example, the largest accidental oil spill in US history, BP’s Deepwater Horizon oil spill [3]. Oil spilled into the Gulf of Mexico from April to September 2010. This resulted in the loss of lives of 11 workers with 134 million gallons of oil spilled resulting in about 2100 km of the U.S. Gulf Coast covered in oil. British Petroleum (BP) was forced to pay $65 billion as settlement. The incident was as a result of the failure of the blowout preventer (BOP) [4], which was connected to the riser for oil drilling from the well. The BOP was supposed to seal the oil well to prevent the spillage when the rig exploded but it failed to do so. Around a year later, a similar incident occurred off the coast in the Gulf of Guinea. The Bonga oil spill is one of the largest in Africa involving Shell Nigeria Exploration and Micromachines 2022, 13, 536. https://doi.org/10.3390/mi13040536 https://www.mdpi.com/journal/micromachines