Comparison between (a) the intracoil and (b) the extracoil detection methods.
Comparison between sensor signals measured outside and inside a solenoid coil.
Equivalent electric circuit for an ME sensor inductively coupled with an electromagnetic coil.
Definition of signal amplitude, Δ|S11 |.
(a) Illustration of the coil's geometry and axes of orientation for the modeling; and (b) normalized magnitude of magnetic field on the YZ plane at X = 0.
Calculation model for the magnetic flux change: (a) ME sensor subjected to the time-varying magnetic field; and (b) the sensor modeled as a magnetic dipole.
Summary of the relationships among S11 parameter, load impendence, mutual inductance, and magnetic flux.
Normalized S11 signals of a 1 mm-long ME sensor measured with coils of different working length.
Comparison between normalized Δ|S11 | experimental data and the calculated result of normalized magnetic flux change.
Using a surface-scanning coil detector positioned above a watermelon surface, the resonant frequency changes for ME biosensors (measurement and control sensors) exposed to S. typhimurium at different concentrations were recorded as a function of exposure time.
SEM images of measurement and control sensors' surfaces after exposure to different bacteria concentrations: (a) measurement sensor exposed to 1.5 × 106 CFU/mm2, (b) measurement sensor exposed to 1.5 × 104 CFU/mm2, (c) measurement sensor exposed to 1.5 × 102 CFU/mm2, and (d) the control sensor exposed to 1.5 × 106 CFU/mm2 (Measurement bar: 5 μm; environmental humidity: 95% RH).
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