Carol Livermore

Bio: Carol Livermore is an academic researcher from Northeastern University. The author has contributed to research in topics: Quantum dot & Coulomb blockade. The author has an hindex of 20, co-authored 76 publications receiving 1641 citations. Previous affiliations of Carol Livermore include Harvard University & Massachusetts Institute of Technology.

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

Abstract: 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 system's 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.

The Coulomb Blockade in Coupled Quantum Dots

Abstract: Individual quantum dots are often referred to as “artificial atoms.” Two tunnel-coupled quantum dots can be considered an “artificial molecule.” Low-temperature measurements were made on a series double quantum dot with adjustable interdot tunnel conductance that was fabricated in a gallium arsenide-aluminum gallium arsenide heterostructure. The Coulomb blockade was used to determine the ground-state charge configuration within the “molecule” as a function of the total charge on the double dot and the interdot polarization induced by electrostatic gates. As the tunnel conductance between the two dots is increased from near zero to 2 e 2 / h (where e is the electron charge and h is Planck9s constant), the measured conductance peaks of the double dot exhibit pronounced changes in agreement with many-body theory.

Compact passively self-tuning energy harvesting for rotating applications

Abstract: 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 system's 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.

Measuring interactions between tunnel-coupled quantum dots

Abstract: We report low-temperature tunneling measurements through double and triple quantum dots with adjustable interdot tunnel conductance, fabricated in a GaAs/${\mathrm{Al}}_{\mathit{x}}$${\mathrm{Ga}}_{1\mathrm{\ensuremath{-}}\mathit{x}}$As heterostructure. As interdot tunnel conductance is increased, Coulomb blockade conductance peaks split into two peaks for double dots and three for triple dots. The splitting approaches zero for weak tunneling and saturates as the dots merge for strong tunneling. Coupled double and triple dots with different gate capacitance show quasiperiodic beating and peak suppression for weak interdot tunneling. Analysis of the data in terms of tunneling and classical charging theories shows that quantum charge fluctuations due to interdot tunneling dominate dot interactions when interdot tunnel conductance approaches 2${\mathit{e}}^{2}$/h. \textcopyright{} 1996 The American Physical Society.

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

Abstract: 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

Multiphase Electric Machines for Variable-Speed Applications

Abstract: Although the concept of variable-speed drives, based on utilization of multiphase machines, dates back to the late 1960s, it was not until the mid- to late 1990s that multiphase drives became serious contenders for various applications. These include electric ship propulsion, locomotive traction, electric and hybrid electric vehicles, ldquomore-electricrdquo aircraft, and high-power industrial applications. As a consequence, there has been a substantial increase in the interest for such drive systems worldwide, resulting in a huge volume of work published during the last ten years. An attempt is made in this paper to provide a brief review of the current state of the art in the area. After addressing the reasons for potential use of multiphase rather than three-phase drives and the available approaches to multiphase machine designs, various control schemes are surveyed. This is followed by a discussion of the multiphase voltage source inverter control. Various possibilities for the use of additional degrees of freedom that exist in multiphase machines are further elaborated. Finally, multiphase machine applications in electric energy generation are addressed.

Electron transport through double quantum dots

Abstract: Electron transport experiments on two lateral quantum dots coupled in series are reviewed. An introduction to the charge stability diagram is given in terms of the electrochemical potentials of both dots. Resonant tunneling experiments show that the double dot geometry allows for an accurate determination of the intrinsic lifetime of discrete energy states in quantum dots. The evolution of discrete energy levels in magnetic field is studied. The resolution allows one to resolve avoided crossings in the spectrum of a quantum dot. With microwave spectroscopy it is possible to probe the transition from ionic bonding (for weak interdot tunnel coupling) to covalent bonding (for strong interdot tunnel coupling) in a double dot artificial molecule. This review is motivated by the relevance of double quantum dot studies for realizing solid state quantum bits.

Single-electron devices and their applications

Abstract: The goal of this paper is to review in brief the basic physics of single-election devices, as well as their-current and prospective applications. These devices based on the controllable transfer of single electrons between small conducting "islands", have already enabled several important scientific experiments. Several other applications of analog single-election devices in unique scientific instrumentation and metrology seem quite feasible. On the other hand, the prospect of silicon transistors being replaced by single-electron devices in integrated digital circuits faces tough challenges and remains uncertain. Nevertheless, even if this replacement does not happen, single electronics will continue to play an important role by shedding light on the fundamental size limitations of new electronic devices. Moreover, recent research in this field has generated some by-product ideas which may revolutionize random-access-memory and digital-data-storage technologies.

A review of the recent research on vibration energy harvesting via bistable systems

Abstract: The investigation of the conversion of vibrational energy into electrical power has become a major field of research. In recent years, bistable energy harvesting devices have attracted significant attention due to some of their unique features. Through a snap-through action, bistable systems transition from one stable state to the other, which could cause large amplitude motion and dramatically increase power generation. Due to their nonlinear characteristics, such devices may be effective across a broad-frequency bandwidth. Consequently, a rapid engagement of research has been undertaken to understand bistable electromechanical dynamics and to utilize the insight for the development of improved designs. This paper reviews, consolidates, and reports on the major efforts and findings documented in the literature. A common analytical framework for bistable electromechanical dynamics is presented, the principal results are provided, the wide variety of bistable energy harvesters are described, and some remaining challenges and proposed solutions are summarized.