On the Optimal Modes for Glucose Droplet Sensing Based on Multi-Modes

In this paper, we demonstrate the optimal multi-modes for glucose droplet (GD) sensing depending on sample (glucose droplet) positions in a half-wavelength (
$\lambda $
/2) microstrip resonator. Using two different GD positions, i.e., an edge and a center position, in the resonator, the resonant behavior of microwave multi-modes for GD sensing was investigated. GDs with three different concentrations, i.e., 0.1, 0.2, and 0.3 g/ml, were tested in the present experiment. With increasing GD concentration, the
${S}_{21}$
-level of the edge-positional GD gradually was declined at all resonant modes. For a center-positional GD, the frequency not only was deviated into the high-frequency region, but its
${S}_{21}$
-level also gradually was declined for the second and fourth modes. Based on the experimental results, the resonant behavior indicated the edge-(center-) positional GD had the resolution (~0.01/gmL
⁻¹
or ~0.05 dB/gmL
⁻¹
) at the second (second) and third (fourth) modes, respectively. Furthermore, we showed that the edge-positional GD sensing is more suitable when the resonator is associated with an active circuit system, and simultaneous sensing is also possible for different positions in multi-modes.