Statics and Dynamics of Electrothermal Micromirrors
This event is part of the PhD Final Oral Exams.
Examining Committee: David Bishop, Thomas D.C. Little, Shyamsunder Erramilli, Robert Carey, David Campbell
Adaptive and smart systems are growing in popularity as we shift toward personalization as a culture. With progressive demands on energy eﬃciency, it is increasingly important to focus on the utilization of energy in a novel way. This thesis investigates a microelectromechanical system (MEMS) mirror with the express intent to provide ﬂexibility in solid state lighting (SSL). By coupling the micromirror to an optical source, the reﬂected light may be reshaped and directed so as to optimize the overall illumination proﬁle. In addition, the light may be redirected in order to provide improved signal strength in visible light communications (VLC) with negligible impact on energy demands.
With ﬂexibility and full analog control in mind, the design of a fully integrated tip-tilt-piston micromirror with an additional variable focus degree of freedom is outlined. Electrothermal actuators are used to both steer the light and tune the focal length. A detailed discussion of the underlying physics behind composite beams and thermal actuators is addressed. This leads directly into an overview of the two main mirror components, namely the segmented mirror and the deﬂection actuators.
An in-depth characterization of the dynamics of the mirror is discussed including the linearity of the thermal response. Frequency domain analysis of such a system provides insight into tunable mechanical properties such as the resonant frequency and quality factor. The degenerate resonant modes can be separated signiﬁcantly. It is shown that the frequency response may be tuned by straining speciﬁc actuators and that it follows a predictable pattern. As a result, the system can be scanned at increasingly large angles. In other words, coupled mechanical modes allow variable damping and ampliﬁcation. A means to determine the level of coupling is examined and the mode shape variations are tracked as a function of the tuning parameters.
Finally, the applications of such a device are explored and tested. Such applications include signal-to-noise ratio (SNR) enhancements in VLC of up to 40 dB and color tunable steerable lights using laser diodes. A brief discussion of the implications of dynamic illumination and tunable systems is juxtaposed with demonstrated integration of an electrothermal micromirror and an all digital driver.