Microwave Sensing for Contactless Surface Measurement

Synopsis

The goal of this thesis is to develop a sensor capable of contactless, nondestructive measurements of lithium-ion battery (LiB) electrodes. The LiB electrodes consist of a metallic foil (current collector) coated in a conductive material; the application of the coating is performed in a reel-to-reel process, and the properties of the resulting coating, such as thickness and conductivity, are crucial to the battery performance. The purpose of the sensor is to enable online quality control during the manufacturing process.

We propose a sensor design based on a resonant microwave cavity, and present a prototype. We discuss two approaches to performing the required measurements: (1) using a vector network analyzer and (2) using an oscillator circuit, and present the results of performing the measurements with both.

The main challenge in operating such a sensor is the variation in the geometry of the microwave cavity induced by the vertical movement of the sample (LiB electrode). Small–amplitude high–frequency variations introduce vibration noise into the measurements, while large–amplitude variation result in mode-crossings. We discuss these problems in detail, and propose possible ways to mitigate them.

Finally, we present a systematic approach to analyzing microwave cavities under small deformation of the geometry, with particular focus on symmetry-breaking (and thus degeneracylifting) perturbations. Our approach uses a global change of variables and some differential geometry machinery to convert the the perturbation of the geometry to that of the equation coefficients, which can then be treated using standard perturbative techniques.

For Zoom link info, please contact Lindiwe Coyne at physgrad@sfu.ca.