Richard Waters

Fabrication and Analysis of a MEMS NIR Fabry–Pérot Interferometer

We report the design and fabrication of a tunable MEMS Fabry-Pérot étalon for use in microscale spectroscopic applications. The reflective elements of the interferometer are dielectric mirror stacks optimized for 1500-nm light and the tunability arises via capacitive attraction of a translatable mirror on a spring. The mirror reflectivity was measured to be 97.3%, corresponding to a calculated finesse of 115, while the measured linewidth and FSR are 70 cm-1 and 334 cm-1, respectively, corresponding to a measured finesse of 5.

Development of a MEMS-based Raman spectrometer

This paper discusses the development of a Raman spectrometer incorporated into a MEMS device for use in environmental monitoring against chemical and biological agents. The current design incorporates a 1525 nm laser diode as an optical pump source, and a tunable Fabry-Pérot interferometer as the wavelength selection element.

Optimization of kinetic energy harvester for low amplitude vibration

This paper presents the steps involved in optimizing the design of an electromagnetic kinetic energy harvester (KEH). The KEH device is conceptually a highly non-linear device. There are numerous dependent variables involved in the design of a KEH which are reliant upon the specific environmental conditions in which the KEH will be deployed. Furthermore, the non-linear nature of the device leads to an iterative design process. The environment that the KEH is deployed into also dictates the overall design and power per volume achieved by the device.

Development of kinetic energy harvesting systems for vehicle applications

This work demonstrates the implementation of a functional kinetic energy harvester designed to power wireless sensor electronics used in vehicular applications. The design, fabrication, and experimental characterization of a complete electrodynamic (magnetic) energy harvesting system capable of delivering in excess of 10 mW from 100 milli-gs of acceleration is presented. Unlike previous energy harvesting research, which typically focuses on individual components for proof-of-concept testing, the system implemented for this work includes the integration of a low-frequency transducer, power electronics circuitry, and a rechargeable storage element, all of which are required for a functional system. The design trade-offs, which result from the integration of these system components are examined and design rules for maximizing efficiency are given. Finally, field testing is presented, which demonstrates the ability of the system to operate over a range of different vehicle speeds.

Simulation of a MEMS Coriolis gyroscope with closed-loop control for arbitrary inertial force, angular rate, and quadrature inputs

A closed-loop control system for a MEMS gyroscope is proposed which greatly restricts the mechanical freedom of the sense mass while accurately measuring the total external force acting upon the sense mass. This is realized by an algorithm which uses the previous three sense mass position measurements to generate a position-, velocity-, and acceleration-dependant feedback force on the sense mass. The feedback force is equal and opposite to the average total external force the sense mass was subject to during the previous three position samples. As the feedback sampling rate increases, so too does the control loops ability to both spatially confine the sense mass and determine the total external force acting on the sense mass. For a 1.05 MHz feedback sampling rate, we achieve a measurement of the external force with less than 5 parts per million error, and constrain the sense mass to displacements of less than 10nm.

Design and analysis of a novel electro-optical MEMS gyroscope for navigation applications

A novel gyroscope design is presented that has potential to reach navigation-grade performance, i.e. bias instability < 0.01 °/hr and Angle Random Walk (ARW) < 0.001 °/√hr. The design is based on the incorporation of an optical transduction mechanism used to decouple drive and sense signals, a dual crystalline silicon spring fabrication approach along with a large drive mass and small sense mass to enhance Coriolis displacement.

Powering of wireless sensors through the exclusive use of kinetic energy

This paper demonstrates the powering of wireless sensor nodes with the exclusive use of a novel kinetic energy harvester (KEH). This KEH is designed to operate under low accelerations which are practical to find in a typical environment where a sensor would be deployed. Four different sensor types were powered with accelerations ranging between 17–300mg.

Window calibration for harmonic analysis of Raman spectra

In this paper, a method for calibrating a Raman spectrum within a measured wavelength window is presented. In support of a novel method for Raman analysis based on a FFT, the main peak needs to remain in the same position within the window in order to produce a repeatable transformation. This calibration uses multi-modal switching to efficiently and accurately tune the starting wavelength value. Upon completion of the calibration the main spectrum peak is in the center of the window. The results of the performed simulations show the calibration centering and stabilizing the main peak in less than 15 Raman spectra measurements within ±10 µs from the true center, with a sampling rate of 100 kHz.

Proposed digital, auto ranging, self calibrating inertial sensor

A novel means of measuring inertial force is proposed which converts the spatial displacement measurement of a conventional mass-on-a-spring accelerometer to a time interval measurement by harmonically oscillating the mass-on-a-spring and creating digital triggering events when the mass passes known displacement points. By curve fitting the measured time intervals into the sinusoidal nature of the harmonic oscillator, it is possible to measure acceleration without the need of adjustable parameters (such as bias and scale factor) derived by calibration. Being a function of the accuracy of the time interval measurement, the device sensitivity varies with resonant frequency, clock resolution, and oscillation amplitude. The resonant frequency of the harmonic oscillation and the oscillation amplitude can be adjusted in real time to optimize performance for a specific dynamic range.

Harmonic analysis with a MEMS-based Raman spectrometer

This paper discusses the incorporation of a novel method of signal processing with a MEMS Raman-based chemical/biological sensor. The method utilizes an absolute sum-difference calculation performed on the FFT of a periodic Raman signal that will be obtained from the MEMS sensor. The result of the sum-difference calculation is used in a threshold determination of the presence of an analyte of interest.