48 research outputs found
Efficient electrothermal actuation of multiple modes of high-frequency nanoelectromechanical resonators
The authors observed resonances from multiple vibrational modes of individual silicon-carbide-based nanomechanical resonators, covering a broad frequency range from several megahertz to over a gigahertz. The devices are actuated thermoelastically in vacuum at room temperature using localized Joule heating in a device-integrated metal loop. Their motion is detected piezoresistively using signal downmixing in a similarly integrated metal piezoresistor. The frequencies and amplitudes of the observed resonant peaks are in good agreement with the results from theoretical modeling and finite-element simulations
Tuning nonlinearity, dynamic range, and frequency of nanomechanical resonators
We explore an electrostatic mechanism for tuning the nonlinearity of nanomechanical resonators and increasing their dynamic range for sensor applications. We also demonstrate tuning the resonant frequency of resonators both upward and downward. A theoretical model is developed that qualitatively explains the experimental results and serves as a simple guide for design of tunable nanomechanical devices
Large-Scale Integration of Nanoelectromechanical Systems for Gas Sensing Applications
We have developed arrays of nanomechanical systems (NEMS) by large-scale integration, comprising thousands of individual nanoresonators with densities of up to 6 million NEMS per square centimeter. The individual NEMS devices are electrically coupled using a combined series-parallel configuration that is extremely robust with respect to lithographical defects and mechanical or electrostatic-discharge damage. Given the large number of connected nanoresonators, the arrays are able to handle extremely high input powers (>1 W per array, corresponding to <1 mW per nanoresonator) without excessive heating or deterioration of resonance response. We demonstrate the utility of integrated NEMS arrays as high-performance chemical vapor sensors, detecting a part-per-billion concentration of a chemical warfare simulant within only a 2 s exposure period
Efficient electrothermal actuation of multiple modes of high-frequency nanoelectromechanical resonators
Numerical and Experimental Study on the Addition of Surface Roughness to Micro-Propellers
Micro aerial vehicles are making a large impact in applications such as
search-and-rescue, package delivery, and recreation. Unfortunately, these
diminutive drones are currently constrained to carrying small payloads, in
large part because they use propellers optimized for larger aircraft and
inviscid flow regimes. Fully realizing the potential of emerging microflyers
requires next-generation propellers that are specifically designed for
low-Reynolds number conditions and that include new features advantageous in
highly viscous flows. One aspect that has received limited attention in the
literature is the addition of roughness to propeller blades as a method of
reducing drag and increasing thrust. To investigate this possibility, we used
large eddy simulation to conduct a numerical investigation of smooth and rough
propellers. Our results indicate that roughness produces a 2% increase in
thrust and a 5% decrease in power relative to a baseline smooth propeller
operating at the same Reynolds number of Rec = 6500, held constant by
rotational speed. We corroborated our numerical findings using
thrust-stand-based experiments of 3D-printed propellers identical to those of
the numerical simulations. Our study confirms that surface roughness is an
additional parameter within the design space for micro-propellers that will
lead to unprecedented drone efficiencies and payloads.Comment: 23 Pages, 9 Figure
Entanglement transfer between bipartite systems
The problem of a controlled transfer of an entanglement initially encoded
into two two-level atoms that are successively sent through two single-mode
cavities is investigated. The atoms and the cavity modes form a four qubit
system and we demonstrate under which conditions the initial entanglement
encoded into the atoms can be completely transferred to other pairs of qubits.
We find that in the case of a nonzero detuning between the atomic transition
frequencies and the cavity mode frequencies, no complete transfer of the
initial entanglement is possible to any of the other pairs of qubits. In the
case of exact resonance and equal coupling strengths of the atoms to the cavity
modes, an initial maximally entangled state of the atoms can be completely
transferred to the cavity modes. The complete transfer of the entanglement is
restricted to the cavity modes only with the transfer to the other pairs being
limited to up to 50%. We have found that the complete transfer of an initial
entanglement to other pairs of qubits may take place if the initial state is
not the maximally entangled state and the atoms couple to the cavity modes with
unequal strengths. Depending on the ratio between the coupling strengths, the
optimal entanglement can be created between the atoms and one of the cavity
modes.Comment: 3 figures. Oral talk presented in CEWQO 18, Madrid 201
Entanglement in Coupled Harmonic Oscillators via Unitary Transformation
We develop an approach to study the entanglement in two coupled harmonic
oscillators. We start by introducing an unitary transformation to end up with
the solutions of the energy spectrum. These are used to construct the
corresponding coherent states through the standard way. To evaluate the degree
of the entanglement between the obtained states, we calculate the purity
function in terms of the coherent and number states, separately. The result is
yielded to two parameters dependance of the purity, which can be controlled
easily. Interesting results are derived by fixing the mixing angle of such
transformation as \pi/2. We compare our results with already published work and
point out the relevance of these findings to a systematic formulation of the
entanglement effect in two coupled harmonic oscillators.Comment: 19 pages, 6 figures, clarification and reference added, misprints
corrected. Version published in JSTA