Papers by Mehmet Buğra Su
Journal of Computational and Theoretical Nanoscience, 2007
Page 1. Delivered by Ingenta to: ? IP : 93.91.26.12 Tue, 24 May 2011 19:18:37 RESEARCH AR TICLE .... more Page 1. Delivered by Ingenta to: ? IP : 93.91.26.12 Tue, 24 May 2011 19:18:37 RESEARCH AR TICLE ... 1546-198X/2007/4/494/010 doi:10.1166/jctn.2007.010 Page 2. Delivered by Ingenta to: ? IP : 93.91.26.12 Tue, 24 May 2011 19:18:37 RESEARCH AR TICLE Reda Taha et al. ...
Smart Structures and Systems, 2009
ABSTRACT Damage detection has been proven to be a challenging task in structural health monitorin... more ABSTRACT Damage detection has been proven to be a challenging task in structural health monitoring (SHM) due to the fact that damage cannot be measured. The difficulty associated with damage detection is related to electing a feature that is sensitive to damage occurrence and evolution. This difficulty increases as the damage size decreases limiting the ability to detect damage occurrence at the micron and submicron length scale. Damage detection at this length scale is of interest for sensitive structures such as aircrafts and nuclear facilities. In this paper a new photonic sensor based on photonic crystal (PhC) technology that can be synthesized at the nanoscale is introduced. PhCs are synthetic materials that are capable of controlling light propagation by creating a photonic bandgap where light is forbidden to propagate. The interesting feature of PhC is that its photonic signature is strongly tied to its microstructure periodicity. This study demonstrates that when a PhC sensor adhered to polymer substrate experiences micron or submicron damage, it will experience changes in its microstructural periodicity thereby creating a photonic signature that can be related to damage severity. This concept is validated here using a three-dimensional integrated numerical simulation.
2011 IEEE 24th International Conference on Micro Electro Mechanical Systems, 2011
This paper demonstrates silicon carbide phononic crystal cavities for RF and microwave micromecha... more This paper demonstrates silicon carbide phononic crystal cavities for RF and microwave micromechanical resonators. We demonstrate design, fabrication, and characterization of Silicon Carbide/air phononic crystals used as Bragg acoustic mirrors to confine energy in a lateral SiC cavity. Aluminum nitride transducers drive and sense SiC overtone cavities in the 2-3GHz range with fxQ products exceeding 3x10 13 in air. This
2010 IEEE International Ultrasonics Symposium, 2010
ABSTRACT
Nature Communications, 2015
Large reductions in the thermal conductivity of thin silicon membranes have been demonstrated in ... more Large reductions in the thermal conductivity of thin silicon membranes have been demonstrated in various porous structures. However, the role of coherent boundary scattering in such structures has become a matter of some debate. Here we report on the first experimental observation of coherent phonon boundary scattering at room temperature in 2D phononic crystals formed by the introduction of air holes in a silicon matrix with minimum feature sizes 4100 nm. To delaminate incoherent from coherent boundary scattering, phononic crystals with a fixed minimum feature size, differing only in unit cell geometry, were fabricated. A suspended island technique was used to measure the thermal conductivity. We introduce a hybrid thermal conductivity model that accounts for partially coherent and partially incoherent phonon boundary scattering. We observe excellent agreement between this model and experimental data, and the results suggest that significant room temperature coherent phonon boundary scattering occurs.
The Big Dam Bridge (BDB) levee on the Arkansas River at Little Rock, AR, and the Lollie Levee nea... more The Big Dam Bridge (BDB) levee on the Arkansas River at Little Rock, AR, and the Lollie Levee near Conway, AR, were surveyed with Ground Penetrating Radar (GPR) to assess their structural integrity. GSSI SIR-30 and SIR-3000 systems with multi-frequency (200, 400, and 900MHz) antennas were utilized. The purpose of this study was to detect cavities, continuous animal burrows, and any deformation in the levee body. GPR profiles exhibited many sub-surface anomalies at various depths. Several holes were dug to inspect the true nature of the shallower anomalies to “ground-truth” the reliability of the GPR data. Steven Soil Sensor was utilized to measure the dielectric constant near the surface of the levees. These values were used to calculate the precise depth of the anomalies that were detected by GPR. Connected empty cavities, continuous animal burrows, clay clasts, and metal objects were found at different depths having different sizes. The depths of the located features ranged betwee...
ECS Transactions, 2013
ABSTRACT
2007 IEEE Antennas and Propagation International Symposium, 2007
Page 1. Selective Enhancement of Mid-IR Quantum Dot Electroluminescent Emissions Using Defect Mod... more Page 1. Selective Enhancement of Mid-IR Quantum Dot Electroluminescent Emissions Using Defect Mode Photonic Crystal Cavities Mehmet F. Su*(1), Ihab F. El-Kady (1,2), Eric A. Shaner(2), and Christos G. Christodoulou(1 ...
Smart Structures and Materials 2006: Smart Electronics, MEMS, BioMEMS, and Nanotechnology, 2006
Photonic crystals (PC) are artificially fabricated crystals with a periodicity in the dielectric ... more Photonic crystals (PC) are artificially fabricated crystals with a periodicity in the dielectric function. These crystals have the novel ability to mold and control light in three dimensions by opening a frequency region (bandgap) in which light is forbidden to propagate. We demonstrate using a simulation model that a photonic crystal sensor attached to a composite substrate will experience a
Advanced Sensor Technologies for Nondestructive Evaluation and Structural Health Monitoring II, 2006
Photonic bandgap materials (PBM) are synthetic materials that artificially manufactured at the na... more Photonic bandgap materials (PBM) are synthetic materials that artificially manufactured at the nano-scale to control light propagation. These crystals have the ability to control light propagation in three dimensions by opening a frequency gap in which light is forbidden to propagate. When light is reflected by a nano photonic (NP) crystal a spectral signature that is directly related to its
Volume 13: Sound, Vibration and Design, 2010
A two-dimensional phononic crystal (PnC) that can operate in the GHz range is created in a freest... more A two-dimensional phononic crystal (PnC) that can operate in the GHz range is created in a freestanding silicon substrate using NanoFIBrication (using a focused ion beam (FIB) to fabricate nanostructures). First, a simple cubic 6.75 × 6.75 μm array of vias with 150 nm spacing is generated. After patterning the vias, they are backfilled with void-free tungsten scatterers. Each via has a diameter of 48 nm. Numerical calculations predict this 2D PnC will generate a band gap near 22 GHz. A protective layer of chromium on top of the thin (100 nm) silicon membrane confines the surface damage to the chromium, which can be removed at a later time. Inspection of the underside of the membrane shows the vias flaring out at the exit, which we are dubbing the ‘trumpet effect’. The trumpet effect is explained by modeling the lateral damage in a freestanding membrane.
Volume 7: Fluids and Heat Transfer, Parts A, B, C, and D, 2012
Thin films composed of dielectric materials are attracting growing interest in the solid state ph... more Thin films composed of dielectric materials are attracting growing interest in the solid state physics and nanoscale heat transfer communities. This is primarily due to their unique thermal and electronic properties and their extensive use as components in optoelectronic, and potentially in thermoelectric, devices. In this paper, an elaborate study is presented on silicon thin films ranging from a few nanometers in thickness to very thick bulk-like thicknesses. Full lattice dynamics calculations are performed incorporating the entire film cross section and the relaxation of the free surfaces. The phonon properties emerging from these calculations are then incorporated into Holland-Callaway models to predict the thermal conductivity and other phonon transport properties. A rigorous curve fitting process to a limited set of available experimental data is carried out to obtain the scattering lifetimes. Our results demonstrate the importance of proper consideration of the full thin-film dispersion description and provide insights into the relationship between thermal conductivity, film thickness and temperature.Copyright © 2012 by ASME
2009 IEEE International Ultrasonics Symposium, 2009
Recently phononic crystal slabs operating in the very high frequency (VHF) range have been report... more Recently phononic crystal slabs operating in the very high frequency (VHF) range have been reported and have gained interest for RF signal processing. This paper reports phononic crystal slabs and devices operating in the commonly used GSM-850 and GSM-900 cellular phone bands, representing nearly an order of magnitude increase in operating frequency compared to the state-of-the-art. Phononic crystals centered at 943 MHz are formed by arranging 1.4 µm diameter W rods in a square lattice with a pitch of 2.5 µm inside a 1.85 µm thick suspended SiO 2 membrane. The resulting phononic crystal has a bandgap width of 416 MHz or 44% and a maximum bandgap depth of 35 dB. Waveguide devices formed by placing defects in the phononic lattice have also been realized with propagation frequencies of 780 and 1060 MHz.
ABSTRACT With the application of microfabrication techniques, phononic crystals have been transfo... more ABSTRACT With the application of microfabrication techniques, phononic crystals have been transformed over the past decade: from hand assembled millimeter-to-meter scale crystals consisting of metal balls in water or epoxy, to precisely machined crystals with sub-micron features operating at frequencies in excess of 1 GHz. This paper reviews the contributions of Sandia National Laboratories to micro and nano scale phononic crystal devices including: the integration of piezoelectric transducers, the choice of phononic crystal materials, phononic crystal design, and the application of phononic crystals to radio frequency and thermal management applications.
Abstract It has been observed experimentally that solid-solid PnCs have larger bandgaps for a wi... more Abstract It has been observed experimentally that solid-solid PnCs have larger bandgaps for a wide range of hole radii and slab thicknesses than their solid-air counterparts. Here, we theoretically investigate the optimal hole radius and thickness parameters for full bandgap formation ( ...
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Papers by Mehmet Buğra Su