Session B42: SPS Undergraduate Research I

Interferometric studies of a piano soundboard

Electronic speckle pattern interferometry has been used to study the deflection shapes of a piano soundboard. During the experiments the soundboard remained attached to the piano, providing, to our knowledge, the first optical examination of soundboard movement \textit{in situ}. The lowest modes have been studied in detail, and the interferograms have been compared to predictions of a simple model that assumes the soundboard is well approximated by an isotropic plate clamped at the edges. Analysis indicates that this model is insufficient to explain the deflection shapes associated with the resonances of the soundboard. It is shown that a finite element model results in more accurate predictions of the mode shapes, and provides insight into the parameters that are important in determining the final sound of the instrument.   

Acoustical study of the Nigerian slit log gong.

The acoustically important resonances of a Nigerian slit gong consist of two significant mechanical resonances and a Helmholtz acoustical resonance. Beating in the acoustical signal from the struck gong suggests that energy is cyclically transferred between the acoustical and mechanical resonators, as is known to happen in similar idiophones. However, we have determined that in the slit log gong there is no significant two-way exchange of energy. Rather, the beating occurs as a result of interference between the frequencies associated with the mechanical and acoustic resonances. The relationship between these resonances has an impact on the tuning and sound quality of the gong.   

Visualizing the sound field of an acoustic fire extinguisher

Our objective is to study the effects of acoustics on flames for the purpose of encouraging new research that will provide a different approach to reducing and extinguishing a combustion reaction. Through experiment, we have already demonstrated that it is possible to extinguish fire with sound. Our apparatus uses 12'' subwoofer speakers in order to generate the necessary acoustic field. By placing dry ice at the bottom of the apparatus, this field becomes visible. We give visual data of how various sound patterns affect the flame and combustion reaction and provide qualitative explanations of the physical phenomena responsible for the effects.   

Construction and Investigation of three HTSC diamagnetic devices

NVCC physics students plan to build and investigate the operation of three devices based on the interaction of permanent magnets and high termpature superconductors. Those devices are: A magnetic flywheel; A Meissner Effect Heat Engine: a wheel rimmed with superconductors which spontaneously spins in the presence of a magnetic field; A superconducting pendulum: Another thermodynamic engine---the pendulum transitions between superconducting and insulating states, gaining kinetic energy each time.   

Construction of an apparatus to characterize the early evolution of ultracold neutral plasma

A magneto-optical trap was constructed for the purpose of charting early atomic recombination rates in an ultracold neutral plasma, which is created by photo-ionizing laser cooled rubidium atoms. Planned experiments will focus primarily on the first 100 nanoseconds of plasma evolution, during which a ramped electric field will be applied to Rydberg atoms that recombine from the plasma components. The ramped field will ionize loosely-bound states, liberating electrons at times that are correlated with binding energy. An electron beam comprised of a series of electrostatic lenses enables the transport of these electrons from the MOT region to a multi-channel plate electron detector (MCP). We devised a system to raster the beam across the MCP to prevent detector saturation and the loss of signal due to electron multiplier recovery times. We will also discuss other apparatus features that allow flexible electric and magnetic field configurations.   

Mode shapes of the American five-string banjo

Experimental studies of the mode shapes of the American five string banjo have revealed the importance of properly tuning the membrane that comprises the head of the instrument. Electronic speckle pattern interferometry has been used to visualize the deflection shapes of the banjo head at several frequencies. Although the off-center placement of the bridge results in asymmetric forces on the head, the mode shapes of a properly tuned banjo head appear symmetric. The implication is that the preferred sound results only when asymmetric pressure is applied to the rim of the membrane to compensates for the off-center placement of the bridge.   

Electrical Characterization of Organic Conducting Polymers

As Moore's Law drives the silicon semiconductor industry to its limits, organic conducting polymers have been explored on a small scale as a possible solution to the breakdown of silicon. Here, the electrical properties of two organic polymers were measured using nanopore and micron-sized devices. In this electrical characterization, polypyrrole was found to exhibit hopping conduction, and both polypyrrole and polyaniline yield nonlinear I-V curves and degradation after sweeps of high voltage. Consequently, these organic polymers and possibly others may have only limited applications in the future semiconductor industry.   

Contact Potential Difference Measurements of Self Assembled Monolayers

In this work, the metal work function and its evolution with systematic chemical changes were studied using an Atomic Force Microscope. A technique, Scanning Kelvin Probe Microscopy, was used to measure the metal work function of various surface dipoles. This metal-molecule interface is also known as a Helmholtz double layer. We expect that this work will lead to a fundamental way of understanding and rationalizing the electrical characteristics of select metal-molecule-metal systems.   

Nonlinear Optical Properties of CdSe Quantum Dots

Detailed research into the nonlinear optical properties of several quantum dot samples is conducted. Data from the research is being used to investigate applications for the quantum dots. Possible applications may include quantum encryption for more secure forms of communication, lithography techniques for improved capabilities of writing computer chips, and the generation of entangled photons through the use of a four-wave mixing process. Other applications may also include more efficient and cheaper photovoltaic cells. Evident Technologies has provided several different samples of quantum dots, each with distinct nonlinear properties. Using z-scan techniques, absorptive and refractive information are extracted for each of the samples. The absorptive natures are observed by scanning the dot sample through varying intensities and measuring their transmission values with an open aperture. Comparing these values with the same process, but utilizing a closed aperture, allows extraction of values of n$_{2}$, the nonlinear refractive index.   

Bond Angles in the Crystalline Silicon/Silicon Nitride Interface

Silicon nitride deposited on a silicon substrate has major applications in both dielectric layers in microelectronics and as antireflection and passivation coatings in photovoltaic applications. Molecular dynamic simulations are performed to investigate the influence of temperature and rate of externally applied strain on the structural and mechanical properties of the silicon/silicon nitride interface. Bond-angles between various atom types in the system are used to find and understand more about the mechanisms leading to the failure of the crystal. Ideally in crystalline silicon nitride, bond angles of 109.5\r{ } occur when a silicon atom is at the vertex and 120\r{ } angles occur when a nitrogen atom is at the vertex. The comparison of the calculated angles to the ideal values give information on the mechanisms of failure in silicon/silicon nitride system.