Optical sensors for high sensitivity motion detection
Teo, Adrian Jian Tong
Date of Issue2017-05-30
School of Mechanical and Aerospace Engineering
Temasek Labs @NTU
Optical methods providing fast detection, electromagnetic resilience and high sensitivity are discussed. In this thesis, two different optical device design concepts are discussed. One design concept employs the use of an optical gratings based accelerometer design concept that was developed for seismic motion detection purposes that provide miniaturization, high manufacturability, low costs and high sensitivity. Finite element simulations and theoretical modeling have been carried out for the optimization of design variables. Detailed in-house fabrication procedures of a double-sided deep reactive ion etching (DRIE) on a silicon-on-insulator (SOI) wafer for the MOEMS device are presented and discussed. Experimental results obtained show that the conceptual device successfully captured motion similar to commercial accelerometer with average sensitivity of 13.6 mV/G with highest recorded sensitivity of 44.1mV/G. This is the first MOEMS accelerometer developed using double-sided DRIE on SOI wafer for the application of seismic motion detection, being a breakthrough technology platform to open up options for lower cost MOEMS devices. The second design concept involves the development of a proof of concept for a wearable cuffless blood pressure sensor. Three different approaches have been simulated for this device, with the first one employing a curved PMMA waveguide. The other two approaches employ the use of a ball shaped side-fire optical tip as a waveguide for detection of deflections along the skin due to blood pressure. Experimental results have shown that the PMMA waveguide was able to detect pulse rates when only one device is used and pulse wave velocity readings with the addition of a separate pulse transducer. This is the first optical fiber device used for the development of a wearable blood pressure sensor, and also the first application of an optical ball shaped side-fire optical fiber tip in a biomedical device. The development of these two design concepts would open up avenues for optical devices in their respective fields. This would thus act as new platforms for optical motion sensing and optical wearables technology, bringing these fields closer to users in the long run.