Sugar and Salt Concentration Detection in Water Employing ENZ Metamaterial Microwave Sensor

A design of high sensitivity Vivaldi antenna is introduced for detecting the low sugar and salt concentrations in water. The reason for selecting the Vivaldi antenna configuration is to provide two desired features; ultra-wideband and a high directivity so the surrounding clutter effect can be minimized. The prospective antenna embraces the ultra-wideband from 4 to 11 GHz. Two techniques are exploited to improve the antenna detectability; epsilon-near-zero (ENZ) metamaterial and antenna aperture amending. The ENZ metamaterial is very sensitive to the permittivity of the substrate, so any loading effect can easily alter the electric field distribution and hence affect the antenna phase properties. The aperture amending is used to improve substrate-air matching. An equivalent circuit model is scrutinized for further emphasis of the ENZ metamaterial operation, showing good agreement with EM simulation results. In terms of phase variation, the designed antenna is employed to sense sugar and salt in water. The amount of sugar and salt affects the material characteristics of the solution and, as a result, the reflected phases. Practical observations reveal that when the sugar and salt contents in the liquid increase, the phase falls. At 5 GHz the difference between the highest and lowest sugar concentrations is about 3 degrees in the sugar case and 5 degrees in the salt case, but at 8 GHz, the phase difference is about 30o in the sugar case and about 50 degrees in the salt case. The sensitivity can be increased by operating at a higher frequency since the proposed antenna can detect very low levels (1%) of salt and sugar concentrations. The time-domain analysis is discussed, revealing low distortion of received pulses.