Planar microwave sensor for detection and discrimination of aqueous organic and inorganic solutions

Visualization of microwave near-field distribution in sodium chloride and glucose aqueous solutions by a thermo-elastic optical indicator microscope

“…The highly sensitive and stable sensing of electrolytes and biological solutions containing organic molecules has drawn widespread attention in recent years 1 – 9 . Using microwave measurement techniques, for example, extensive research has been done to develop non-contact and non-invasive monitoring of glucose concentration in blood and biological liquids in medicine 10 – 15 .…”

“…Sensitive single-target sensors with the ability to detect these compounds can reflect health status 25 . Among these compounds, for example, sensing NaCl concentrations in an aqueous solution can provide critical information regarding the water–salt balance in human tissues, hydration levels, and other health diagnoses 1 , 26 , 27 . Therefore, the design and fabrication of highly accurate and practice sensors is one of the challenging tasks in modern science.…”

Real-Time Water Quality Monitoring with Chemical Sensors

“…Amirian et al [ 56 ] simulated the feasibility of distinguishing between pure liquid materials, such as ethanol, ammonia, benzene and pentene using a novel sensor design and mathematical approach, reaching higher sensitivity and noise reduction. Harnsoongnoen et al [ 57 ] demonstrated the discrimination of organic and inorganic materials using planar sensors and principal component analysis (PCA). Magnitude spectra at 2.3–2.6 GHz were able to measure specific concentrations of sucrose, glucose, NaCl and CaCl 2 citric acid between others, generating linear and nonlinear prediction models, correlating the transmission coefficient (S 21 ) and R 2 .…”

“…Especially at 0.91–1.00 GHz (peak 2) the f-EM sensor shows an improvement for Cu detection with an improvement in sensitivity, higher Q-factor and low LoD compared with an uncoated (UNC) sensor, shown in bold in Table 1 [ 74 ].The sensor was able to detect Cu concentration with a limit of detection (LoD) of 0.036, just above the environmental quality standards for freshwater (28–34 µg/L) Responses for Cu and Zn were then compared by analysing microwave spectral responses using a Lorentzian peak fitting function and investigating multi-peaks (peaks 0–6) and multi-peaks’ parameters (peak center, xc, FWHM, w, area, A, and height, H, of the peaks) for specific discrimination between these two similar toxic metals [ 74 ]. It is useful to compare additional parameters for determining the selectivity, as it was demonstrated by Harnsoongnoen et al [ 57 ], to distinguish between sugars and salts. However, more work is required for reaching higher discrimination between similar contaminants.…”

“…( a ): magnitudes of the transmission coefficient (S21) between 2.3 and 2.6 GHz; ( b ): amplitude of S21 at the resonance frequency. Reproduced with permission from [ 57 ] © Elsevier.…”