Development of a Lorentz force drive system for a torsional paddle microresonator using Focused Ion Beam machining

Chitsaz Charandabi, Sahand (2014). Development of a Lorentz force drive system for a torsional paddle microresonator using Focused Ion Beam machining. University of Birmingham. Ph.D.

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This thesis focuses on the concept, design, fabrication and characterisation of a torsional micro paddle resonator. The ultimate intention is to use the device for rapid detection of anthrax bacteria. A comprehensive research was carried out to review the state of the art in MEMS based mass sensing. Various driving and detection strategies were investigated and discussed. Based on evidence from literature, a novel approach was adopted to realise a device with improved functionality and overcome currently existing drawbacks. The working principle of the proposed device is based on electromagnetic actuation and monitoring of the shift in resonance frequency of a micro paddle. The design of the paddle was optimised using theoretical and finite element methods. Dual beam Focused Ion Beam (FIB) machining techniques were used to fabricate the prototype devices. The chosen substrate is a LPCVD 200 nm thick silicon nitride membrane. Prior to milling the substrate, the sputtering rate of silicon nitride was validated experimentally to ensure machining stability. Different actuating pattern designs were fabricated to generate torque including micro spiral coil, micro dual loop, and single conductive track on the micro paddle. The geometry was finalised for a defined working condition of 1 MHz resonance frequency. Important fabrication parameters were discussed and damage prevention issues were investigated. The sensitivity to the added mass was experimentally characterised and found to be 2.35 fg/Hz. To characterise the asymmetrical paddle resonator, piezoelectric excitation was applied to the device and a laser Doppler vibrometer was used to record the resonant frequency. Resonant frequencies of 0.841 and 0.818 MHz were detected by testing the device in an air medium and a quality factor of about 300 was calculated by applying a Lorentzian curve fit to collected data.

Type of Work: Thesis (Doctorates > Ph.D.)
Award Type: Doctorates > Ph.D.
College/Faculty: Colleges (2008 onwards) > College of Engineering & Physical Sciences
School or Department: School of Engineering, Department of Mechanical Engineering
Funders: None/not applicable
Subjects: T Technology > TJ Mechanical engineering and machinery


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