Development of a Carbon Nanotube-Based Electromechanical Resonator: Device Modeling

We present an electromechanical analysis of a novel double-sided driven carbon nanotube-based electromechanical resonator. The device comprises a cantilevered carbon nanotube actuated by two parallel-plate electrodes. Close-form analytical solutions capable of predicting the steady-state resonation of the device and its resonant pull-in conditions are derived using an energy-based method. Our close-form formulas clearly reveal the complex relationship among the device geometry, the driving voltages, and the device’s electromechanical dynamics. Our theoretical modeling shows that the stable steady-state spanning range of the resonating cantilever substantially exceeds the previously reported quasi-static pull-in limit for single-sided driven cantilevered nanotube-based NEMS, while the resonant pull-in voltage is only a small fraction of the quasi-static pull-in voltage. The unique behaviors of this novel device are expected to significantly enhance the applications of electromechanical resonators in the fields of signal processing, mass and force sensing, and chemical and molecule detection.

Further Development and Preliminary Testing of the α-Prototype of an Ultra-Micro Gas Turbine for Portable Power Generation

The ever increasing development of portable electronics leads to a higher demand for compact and reliable power sources. Significant resources are being presently dedicated to the study of micro machined turbines, because of their remarkable power density that suggests that the generation of about 100–300 W with a total device weight of few hundreds grams and a fuel mass flow rate of few grams per second may be feasible in the short range. In this paper a possible configuration of such a nano-GT set is considered, which was defined on the basis of previous thermo-fluid dynamic analysis: the results of a preliminary design study, including some cold-run tests, are reported in this paper. The layout of the device was finalized on the basis of both a CFD and a FEM analysis that identified the “optimal” blade shape, shaft size and rotors arrangements under the point of view of the energy efficiency and of thermo-mechanical material stresses, Some of the problems deriving by the physical construction and preliminary testing of the prototype are analyzed and discussed.

Fabrication, Characterization and Microsensing of Whispering-Gallery Mode Micro-Coupling Systems

An optical micro-coupling system of whispering-gallery mode usually consists of a resonator (e.g. a sphere) and a coupler (e.g. a taper). In this report, silica microspheres of 50–500 μm in diameter are fabricated by hydrogen flame fusing of an end of a single mode fiber or fiber taper. Fiber tapers are fabricated by the method of heating and pulling that meets an adiabatic condition. Taper’s waist diameter can routinely be made less than 1 μm and almost zero transmission loss in a taper is achieved which allows an effective and phase-matched coupling for a wide range sizes of microspheres. Both resonators and couplers’ surface microstructure and shapes are examined by scanning electronic microscopy. Three regimes of coupling are achieved, enabling a good flexibility to control Q value and coupling efficiency of a micro-coupling system. Whispering gallery mode shift is used to demonstrate a novel temperature micro-sensor. Its sensitivity determined from actual experimental results agrees well with the theoretical value. A concept of using the photon’s cavity ring down (CRD) in the microsphere to make a novel high-sensitivity trace gas micro-sensor is proposed. The CRD time constant when ammonia is chosen as the analyte gas is predicted using the simulated absorption lines.

MEMS Pressure Sensor Array for Aeroacoustic Analysis of the Turbulent Boundary Layer

The design, fabrication, and characterization of a surface micromachined, front-vented, 64 channel (8×8), capacitively sensed pressure sensor array is described. The array was fabricated using the MEMSCAP PolyMUMPs® process, a three layer polysilicon surface micromachining process. An acoustic lumped element circuit model was used to design the system. The results of our computations for the design, including mechanical components, environmental loading, fluid damping, and other acoustic elements are detailed. Theory predicts single element sensitivity of 1 mV/Pa at the gain stage output in the 400–40,000 Hz band. A laser Doppler velocimetry (LDV) system has been used to map the spatial motion of the elements in response to electrostatic excitation. A strong resonance appears at 480 kHz for electrostatic excitation, in good agreement with mathematical models. Static stiffness measured electrostatically using an interferometer is 0.1 nm/V2, similar to the expected stiffness. Preliminary acoustic sensitivity studies show single element acoustic sensitivity (as a function of frequency) increasing from 0.01 mV/Pa at 200 Hz to 0.16 mV/Pa at 2 kHz. A more in depth analysis of acoustic sensitivity is ongoing.

Fabrication and Characterization of Nano-Structuring Polymeric Surfaces for MEMS Applications

Using external stimuli to control surface properties, such as surface topology or wettability, has been of great interest. This paper presents the fabrication, mechanism, and analysis of an active method that modulates surface nano-topology and wettability of polymeric films. The polymeric film possesses the unique property of electrical potential-induced wettability conversion: when its doping level is electrically altered, the interstitial ions are incorporated or released, causing the polymer network to stretch and thereby changing its surface morphology.

Simultaneous Water Droplet Formation and Sorting Using an Electric Field

The droplet-based microfluidic technology has a potent high throughput platform for biomedical research and applications [1]. Recently, Link et al. showed that an electric field can be very useful to control water droplet in carrier oil [2]. In this research, simultaneous droplet formation and sorting has been demonstrated using an electric field, allowing very precise droplet sorting to different outlets depending on the electrical actuation.

Thermal Transport From Gold Nanorod to Solvent, an Investigation of Ligand Effects by Ultrafast Laser Spectroscopy

To facilitate analysis of nanoscale heat transfer in nanoparticle systems the thermal properties of ligand layers must be understood. To this end, we use an optical pump-probe technique to study the thermal transport across ligands on gold nanorods and into the solvent. We find that varying properties of the ligand can have large impacts on the thermal decay of a nanorod after exposure to a laser pulse. By raising the concentration of free CTAB from 1 mM and 10 mM in solutions, the CTAB layer’s effective thermal interface conductance increases three fold. The transition occurs near the CTAB critical micelle concentration. Similar results are found for other ligand layers.

Electromechanical Coupling of PZT Nanofibers

This paper presented the results of electromechanical characterization of PZT nanofibers through applied mechanical strain and forced vibration. PZT nanofibers were fabricated by electrospinning process. Titanium film with ZrO2 layer was used to collect the nanofibers and also used as the substrates of the test coupons for the bending tests. Mechanical strain was applied to the test coupons through three-point-bending using Dynamic Mechanical Analyzer (DMA). The largest output voltage was 170mV under 0.5% applied strain. Silicon substrate with trenches was also used to collect the PZT nanofibers for the forced vibration tests. The output voltage from 150Hz sinusoid vibration source was also measured. The peaks of the output voltage were 64.9mV and −95.9mV, respectively. These tests have demonstrated the piezoelectric response of PZT nanofibers. Further tests are to be conducted to precisely determine the piezoelectric constants of PZT nanofibers.

A Technique for Interface Thermal Resistance Measurements Between a Nanoelectrode and a Substrate Using the 3ω Method

Developing a fundamental understanding regarding energy flow across nanoscale interfaces is critical in realizing viable nanoelectronics device systems and efficient low-dimensional thermoelectric devices. This work presents investigations of the interface thermal resistance (ITR) in a nanoelectrode-on-substrate system using the DC heating as well as the 3ω method.

Heat Transfer Spectroscopy and “Heat Transfer-Distance” Curves

Thermal radiative transfer between objects as well as near-field forces such as van der Waals or Casimir forces have their origins in the fluctuations of the electrodynamic field. Near-field radiative transfer between two objects can be enhanced by a few order of magnitude compared to the far-field radiative transfer that can be described by Planck’s theory of blackbody radiation and Kirchoff’s laws. Despite this common origin, experimental techniques of measuring near-field forces (using the surface force apparatus and the atomic force microscope) are more sophisticated than techniques of measuring near-field radiative transfer. In this work, we present an ultra-sensitive experimental technique of measuring near-field using a bi-material atomic force microscope cantilever as the thermal sensor. Just as measurements of near-field forces results in a “force distance curve”, measurement of near-field radiative transfer results in a “heat transfer-distance” curve. Results from the measurement of near-field radiative transfer will be presented.