Sodium chloride sensing by using a near-field microwave microprobe

Abstract

The authors observed the NaCl concentration of solutions using a near-field microwave microprobe (NFMM). Instead of the usual technique, they take advantage of the noncontact evaluation capabilities of a NFMM. A NFMM with a high Q dielectric resonator allows observation of small variations of the permittivity due to changes in the NaCl concentration. By measuring the reflection coefficient S11, they could observe the concentration of NaCl. The measured signal-to-noise was about 53dB and the minimum detectible signal was about 0.005dB∕(mg∕ml). In order to determine the probe selectivity, they measured a mixture solution of NaCl and glucose.

Glucose aqueous solution sensing by a near-field microwave microprobe

“…The Q factor of glucose solution increased as the temperature increased due to the real and imaginary part of the relative permittivity of glucose decreasing. Note that, as the temperature of the glucose solution increased, the imaginary part of relative permittivity ε of glucose decreases more rapidly than that of real part ε , hence Q factor increased [21].…”

“…was S 11 / c = 0.005 dB/(mg ml) at the lower concentration regime. Note that, we could determine the concentrations of glucose (or NaCl) in solution through the separate measurement of the loss tangent tan ı and the reflection coefficient S 11 [21].…”

Noncontact characterization of glucose by a waveguide microwave probe

“…The sensitivity of the microwave reflection coefficient vs. the NaCl concentration was DS 11 / Dc = 0.0034 dB/(mg/ml). Note that, we could determine the concentrations of glucose (or NaCl) in solution through the separate measurement of the loss tangent tan d and the reflection coefficient S 11 [16].…”

“…Techniques with high sensitivity and efficiency for the detection of glucose concentration using a noninvasive technology are therefore of importance in biosensor construction. In order to better characterize the concentration of glucose concentration, we take advantage of the noninvasive evaluation capabilities of near-field interaction techniques using a microwave waveguide resonator biosensor [13][14][15][16][17]. An important ability of the microwave waveguide resonator biosensor is a new physical approach to noninvasive characterization of glucose aqueous solutions.…”

Microwave sensor for accurate measurements of water solution concentrations

“…In order to get maximum sensitivity of the microwave sensor, aqueous solution must be positioned near maximum of electric field. From this point of view, the sensors based on different resonator's configurations are preferable in comparison with the sensors where liquid interacts with a near-field microwave microprobe [2,3].…”