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 2e2/h (where e is the electron charge and h is Planck's constant), the measured conductance peaks of the double dot exhibit pronounced changes in agreement with many-body theory.
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.
This paper presents experiments and models of a passive self-tuning energy harvester for rotational vibration applications. Tensile stress due to centrifugal force in a radially oriented piezoelectric cantilever beam passively tunes the resonant frequency so that the harvester remains at or near its resonant frequency. Because centrifugal force is proportional to the square of driving frequency, the resonant frequency of an optimized harvester can track and match the driving frequency over a wide frequency range. An analytical model is presented to explain the harvester’s operation, advantages, and design parameter selection. A prototype demonstrated significantly improved performance compared with an untuned harvester.
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.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.