Coupled Resonators for Ultraprecise Sensing Applications: Fabrication using State-of-the-art Laser Micromachining

This thesis documents a first time demonstration of electromechanical transducer and/or sensor fabricated using Direct Laser Writing (DLW). A low-cost prototype has been fabricated via a rapid and high-tech laser micro-milling technique to achieve a parallel kerf-width (capacitive gaps) of about 60 micrometers (µm) into a piece of aluminum and a stainless steel each of 1 and 2 millimeters (mm) thickness respectively, thus leading to a high-aspect ratio (> 33) structure. A device is demonstrated to facilitate actuation via electrostatic means and sense a capacitive change across its electrode. Experiments have been performed with a structure made of aluminum. Emphasis is on the fabrication and associated issues. A strategic fabrication and measurement of an average kerf-width of about 60 micrometres is reported, which is advantageous to develop our application. A detailed study of width variation using laser cut is also given. Based on the in-depth literature survey, it is postulated that achieving simultaneously a kerf-width as small as 60 µm with metal parts up to 2 mm thickness is unprecedented (either in the industry or in academia). This important aspect is one of the highlights of this research. Results comprising analytical modeling, fabrication, and electrical characterization are presented. An applicability of a device as a 2 degree-of-freedom (DoF) resonating mode-localization sensor that employs a weak electrostatic coupling is demonstrated to offer vibration amplitude based sensitivity to a relative change in the stiffness. This sensor is able to resolve a minimum stiffness perturbation (normalized), of the order of 7.98×10-4. This magnitude is of the same order to that achievable in MEMS based coupled resonators. Based on our results, it is postulated that this navigating research opens up new possibilities to fabricate new devices and/or sensor based on alternative fabrication platform such as laser micromachining as reported here.
In parallel, a work in this thesis closely observes the state-of-the art for coupled resonators and thereby proposes realistic system level models in the context of our architecture fabricated using high-tech laser machining. Based on the representative system-level models developed in this thesis, theory estimate of maximum sensitivity to stiffness perturbation is found to be comparable to that achievable in MEMS for two degree of freedom (DoF) coupled resonating sensor. Developed models represents findings in open/closed loop implementation. A work on the most fundamental and crucial aspects such as sensitivity, resolution and noise floor of coupled resonators is reported.