Carol Livermore

Impact-driven, frequency up-converting coupled vibration energy harvesting device for low frequency operation

This paper presents experiments and models of an energy harvesting device in which a low frequency resonator impacts a high frequency energy harvesting resonator, resulting in energy harvesting predominantly at the systems coupled vibration frequency. Analysis shows that a reduced mechanical damping ratio during coupled vibration enables increased electrical power generation as compared with conventional technology. Experiments demonstrate that the efficiency of electrical power transfer is significantly improved with the coupled vibration approach. An average power output of 0.43 mW is achieved under 0.4g acceleration at 8.2 Hz, corresponding to a power density of 25.5 µW cm − 3. The measured power and power density at the resonant frequency are respectively 4.8 times and 13 times the measured peak values for a conventional harvester created from a low frequency beam alone.

Scalable, MEMS-enabled, vibrational tactile actuators for high resolution tactile displays

The design, fabrication, and characterization of a new type of tactile display for people with blindness or low vision is reported. Each tactile element comprises a piezoelectric extensional actuator that vibrates in plane, with a microfabricated scissor mechanism to convert the in-plane actuations into robust, higher-amplitude, out-of-plane (vertical) vibrations that are sensed with the finger pads. When the tactile elements are formed into a 2D array, information can be conveyed to the user by varying the pattern of vibrations in space and time. Analytical models and finite element analysis were used to design individual tactile elements, which were implemented with PZT actuators and both SU-8 and 3D-printed scissor amplifiers. The measured displacements of these 3 mm × 10 mm, MEMS-enabled tactile elements exceed 10 µm, in agreement with models, with measured forces exceeding 45 mN. The performance of the MEMS-enabled tactile elements is compared with the performance of larger, fully-macroscale tactile elements to demonstrate the scale dependence of the devices. The creation of a 28-element prototype is also reported, and the qualitative user experience with the individual tactile elements and displays is described.

A high-power MEMS electric induction motor

An electric induction micromotor with a 4-mm-diameter rotor was designed and built for high-power operation. Operated at partial actuating voltage, the motor has demonstrated an air gap power in excess of 20 mW and torque of 3.5 /spl mu/Nm at speeds in excess of 55 000 rpm. Operation at higher power and speed was limited by bearing stability at higher rotational speeds. The device builds on an earlier micromotor demonstrated by Frechette et al. The high power of the present motor is enabled by its low-loss, high-voltage electric stator, which also offers improved efficiency. The development of this electromechanical device is an important enabling step not only for watt-scale micromotors, but also for the development of microelectric generators. This paper presents the motors design, the fabrication process that was created to meet its stringent design requirements, and its performance to date.

An electric induction micromotor

This paper presents the analysis, design, fabrication, and testing of a planar electric induction micromotor. The micromotor is a 6-phase motor with 131 pole pairs distributed on a stator having a 4 mm outer diameter. The axial air gap is 3 /spl mu/m. With a 90 V stator excitation, applied at a 300-kHz slip frequency, the motor produces a torque of 2 /spl mu/N/spl middot/m. Special attention is paid to the limitations that microfabrication places on the design of the motor.

Compact passively self-tuning energy harvesting for rotating applications

This paper presents a compact, passive, self-tuning energy harvester for rotating applications. The harvester rotates in the vertical plane and is comprised of two beams: a relatively rigid piezoelectric generating beam and a narrow, flexible driving beam with a tip mass mounted at the end. The mass impacts the generating beam repeatedly under the influence of gravity to drive generation. Centrifugal force from the rotation modifies the resonant frequency of the flexible driving beam and the frequency response of the harvester. An analytical model that captures the harvester systems resonant frequency as a function of rotational speed is used to guide the detailed design. With an optimized design, the resonant frequency of the harvester substantially matches the frequency of the rotation over a wide frequency range from 4 to 16.2 Hz. A prototype of the passive self-tuning energy harvester using a lead zirconate titanate generating beam achieved a power density of 30.8 µW cm−3 and a more than 11 Hz bandwidth, which is much larger than the 0.8 Hz bandwidth calculated semi-empirically for a similar but untuned harvester. Passive tuning was also demonstrated using the more robust and reliable but less efficient polymer polyvinylidene fluoride for the generating beam.

A pivot-hinged, multilayer SU-8 micro motion amplifier assembled by a self-aligned approach

The design, fabrication, and characterization of an out-of-plane micro tactile actuator that employs pivot hinges fabricated by a multilayer self-aligned approach to deliver exceptional high force and large displacement are demonstrated. The device includes a piezoelectric extensional actuator that vibrates in plane and a micro-fabricated motion amplifier to convert the in-plane vibrations to larger out-of-plane vibrations. These advances are enabled by a self-aligned assembly process that eliminates the need to fabricate re-entrant SU-8 multilayers. For pivot-hinged actuators with 10 mm2 and 2 mm2 areas, maximum displacements of 9.8 μm and 5.5 μm respectively and maximum forces of 9.6 mN and 5.9 mN respectively are reported.

A MEMS Singlet Oxygen Generator—Part II: Experimental Exploration of the Performance Space

This paper reports the quantitative experimental exploration of the performance space of a microfabricated singlet oxygen generator (muSOG). SOGs are multiphase reactors that mix H2O2, KOH, and Cl2 to produce singlet delta oxygen, or O2 (a). A scaled-down SOG is being developed as the pump source for a microfabricated chemical oxygen-iodine laser system because scaling down a SOG yields improved performance compared to the macroscaled versions. The performance of the muSOG was characterized using O2 (a) yield, chlorine utilization, power in the flow, molar flow rate per unit of reactor volume, and steady-state operation as metrics. The performance of the muSOG is measured through a series of optical diagnostics and mass spectrometry. The test rig, which enables the monitoring of temperatures, pressures, and the molar flow rate of O2 (a), is described in detail. Infrared spectra and mass spectrometry confirm the steady-state operation of the device. Experimental results reveal O2 (a) concentrations in excess of 1017 cm-3, O2 (a) yield at the chip outlet approaching 80%, and molar flow rates of 02(a) per unit of reactor volume exceeding 600 times 10-4 mol/L/s.

Generating electric power with a MEMS electroquasistatic induction turbine-generator

This paper presents a microfabricated electroquasistatic (EQS) induction turbine-generator that has generated net electric power. A maximum power output of 192 /spl mu/W was achieved under driven excitation. We believe that this is the first report of electric power generation by an EQS induction machine of any scale found in the open literature. This paper also presents self-excited operation in which the induction generator self-resonates and generates power without the use of any external drive electronics. The generator comprises five silicon layers, fusion bonded together at 700/spl deg/C. The stator is a platinum electrode structure formed on a thick (20 /spl mu/m) recessed oxide island. The rotor is a thin film of lightly doped polysilicon also residing on an oxide island, (10 /spl mu/m) thick. This paper also presents a generalized state-space model for an EQS induction machine that takes into account the machine and its external electronics and parasitics. This model correlates well with measured performance and was used to find the optimal drive conditions for all driven experiments.

Characterizing the failure processes that limit the storage of energy in carbon nanotube springs under tension

We report measurements of the mechanical properties and energy storage capabilities of carbon nanotube (CNT) springs under tensile loading, including correlated measurements of their cyclic loading and electrical resistance behavior. Tests are conducted on fibers of multi-walled CNTs fabricated from 6 mm tall forests. The highest measured strength and stiffness of the fibers are 2 N tex−1 and 70 N tex−1 respectively. The highest recorded energy density is approximately 7 kJ kg−1 or 500 kJ m−3, more than an order of magnitude higher than the gravimetric energy density of steel springs, and half the volumetric energy density of steel springs. The resistance and stress responses of the fibers during loading to failure and cyclic loading demonstrate that disorder at the nanoscale affects the bulk response. CNT springs show limited effects of fatigue under 75 tensile cyclic loading cycles. Improving the structural quality of the CNTs and the organization of the fibers offers potential to significantly increase the energy storage capacity of the springs.

Design of a MEMS-based microchemical oxygen-iodine laser (/spl mu/COIL) system

A design of a microelectromechanical systems (MEMS)-based microscale chemical-oxygen iodine laser (/spl mu/COIL) system is presented. A mathematical model of the /spl mu/COIL system, based upon existing macroscale models of the COIL system and related microscale technologies, is formulated and used to predict system performance. The new /spl mu/COIL concept is comprised of an array of cocurrent gas- and liquid-flow singlet-oxygen generators, which supply a supersonic slit nozzle for Iodine dissociation and excitation, a segment of a macroscale optical cavity, and a /spl mu/-scale pressure-recovery system to maintain low-pressure operation. Reactor, nozzle, optical cavity, and pressure recovery system models are developed individually and integrated into a model of the overall system. The resulting model of the /spl mu/COIL system is employed to determine the optimal reagent throughputs, reactor dimensions, and operating pressures to maximize output energy density, defined as the output power divided by the total system and reagent weight for a 100 s operating time. Detailed simulation results corresponding to an optimal energy density of 24.6 kJ/kg are presented, in conjunction with energy density values obtained over the entire parameter space studied. Consideration is given to the design of a realizable, integrated /spl mu/COIL system, for minimum (7.1 kW) and high-power (/spl sim/100 kW) systems. Results of the study suggest that the /spl mu/COIL system could be a superior alternative to existing COIL devices, via reduced system volume and weight and improved reliability and safety.