Progress in Resonance Method Testing
The resonance testing method is primarily developed to address the limitation of the impedance testing method in real-time sensing of parasitic capacitance changes when evaluating the stability of antenna substrates. By integrating a capacitor into the near-field test antenna, the resonance point is tuned to around 13.56MHz. When the substrate under test is placed on the surface of the test antenna, resonance occurs near the operating point. A network analyzer is connected to the coupling coil to record the resonance point and determine its offset status, thereby assessing the substrate's stability.
Compared with the impedance testing method, which only reflects changes in antenna inductance, the resonance testing method not only manifests the parasitic capacitance variations caused by the integration of the substrate but also forms a resonant network between the near-field antenna and its matching circuit, enabling the evaluation of the antenna substrate's quality. Therefore, the resonance testing method is a comprehensive approach that can reflect changes in both inductance and capacitance parameters.
Test results indicate that the resonance frequency of the test antenna exhibits a linear offset with variations in the substrate's permeability, and such changes in permeability can be intuitively detected through variations in the S11 parameter of the coupling antenna. Additionally, the peak difference between resonance points is approximately 50Hz, which falls within the control range for center frequency offset in industrial production, representing a relatively high stability standard.
