KEYWORDS: Thin films, Thin film solar cells, Crystals, Solar cells, Annealing, Solar energy, Scanning electron microscopy, Optical properties, Optics manufacturing, Copper
Solar cells can be produced using thin film based photovoltaic materials; these are highly efficient with respect to their optical properties and manufacturing cost. The prospective thin film solar cells are composed of Copper, Zinc, Tin, and Sulfide, or ‘CZTS’, this contains chemicals, which are both earth-abundant and non-toxic. The all-solution based process is investigated which is on a single-step electro-chemistry deposition that provides all constituents from the same electrolyte. This investigation was successful in our research group with a high degree of success and a photo-thermal energy driven sintering process that forms a CZTS material from the as-deposited chemicals was added. This enables the as-deposited chemicals to be covalently bonded and crystallized without using a costly vacuum process. In post-heat treatment, a homemade intense pulsed lighting (IPL) system was utilized for rapid thermal annealing. The successful deposition of the CZTS thin film was then evaluated and analyzed using cyclic voltammetry (CV), SEM/EDAX, and XRD. It has been concluded that photovoltaic thin film fabrication is truly comparable to the conventional deposition and annealing methods in terms of photovoltaic efficiency and cost-effectiveness.
The improvement of photovoltaic performance using micro- and nano-sized scale manufacturing is discussed in this paper. The development and design of small structures for photovoltaic applications are the most challenging aspects in enhancing light absorption efficiency. We demonstrate novel methods that allow for more efficient and successful manufacture and improvement of absorption properties using a nano-particle spraying method and generation of nano-islands by making a thin film and heat treatment of the thin film. In the nano-particle spraying method, a solution which can disperse particles uniformly is sought. The nano-particles are sprayed on a typical polycrystalline silicon solar cell with an air brush gun, and then an intense pulsed light is irradiated onto the surface to cause surface driven diffusion to the nano-particles and form the nano-islands. The whole process was performed under dry and ambient conditions. The secondary method, generation of nano-islands was achieved to improve the uniformity of scattered nanostructures. A deposition process, evaporation and sputtering under vacuum, is used to manufacture the metallic thin films with 10~30 nm thickness, and thermal treatment provides surface energy so that uniform nano-sized islands are generated. Both methods are verified through the improvement of light absorption and short circuit current density – an improvement of 14.8% and 17.1%, respectively. The simulated model verified the enhancement of light absorption under the range of the solar spectrum and the absorption profile into the photoactive layer.
Due to the complex nature of sandwich structures, damage detection in honeycomb sandwich structures inherently
imposes many challenges. In this study, leaky guided wave properties generated by piezoelectric wafer actuators/sensors
in honeycomb sandwich structures are first simulated by the finite element method. In the numerical model, the detailed
honeycomb core geometry is considered. Differential features due to presence of debonding are determined through an
appropriate damage index analysis of the signals at the normal and debonded conditions. The image of the debonding is
formed by using a probability analysis of the leaky guided wave at each frequency. The final image of the structure can
be fused from multi-frequency leaky guided waves. A new method for multi-debonding detection is proposed. Based on the analysis, information about the debondings in the honeycomb sandwich structures can be quantitatively characterized.
Wireless sensor networks (WSN) are proving to be a good fit where real time monitoring of multiple physical
parameters is required. In many applications such as structural health monitoring, patient data monitoring, traffic
accident monitoring and analysis, sensor networks may involve interface with conventional P2P systems and it is
challenging to handle heterogeneous network systems. Heterogeneous deployments will become increasingly
prevalent as it allows for systems to seamlessly integrate and interoperate especially when it comes to applications
involving monitoring of large infrastructures. Such networks may have wireless sensor network overlaid on a
conventional computer network to pick up data from one distant location and carry out the analysis after relaying it
over to another distant location.
This paper discusses monitoring of bridges using WSN. As a test bed, a heterogeneous network of WSN and
conventional P2P together with a combination of sensing devices (including vibration and strain) is to be used on a
bridge model. Issues related to condition assessment of the bridge for situations including faults, overloads, etc., as
well as analysis of network and system performance will be discussed. When conducted under controlled conditions,
this is an important step towards fine tuning the monitoring system for recommendation of permanent mounting of sensors and collecting data that can help in the development of new methods for inspection and evaluation of bridges. The proposed model, design, and issues therein will be discussed, along with its implementation and results.
Soil liquefaction in Northeast Arkansas (NEA) is expected to result in substantial damage during seismic events. Insitu
shear wave velocity (Vs) profile of the subsurface, to a depth of at least 30-meters (according to the International
Building Code or IBC), is necessary for determining the "Site Class", which is subsequently used in the structural
analysis of buildings, and can be used as a screening tool to evaluate the depth and thickness of potentially
liquefiable soil layers. Shear wave velocity profiles at 3 sites in Craighead County, AR were determined utilizing
simplified equipment by means of a non-invasive technique. The results indicated good agreement with previous
work performed by other researchers. These profiles were used to evaluate the liquefaction resistance at these sites
using the simplified procedure by Seed and Idriss (Vs approach). The liquefaction resistance was also evaluated
using the Standard Penetration Test (SPT approach) results from the geotechnical investigations that were conducted
by others. The equipment and procedure should allow governmental agencies and engineering professional to
determine the shear wave velocity profiles of the upper soil zones at relatively low cost. These profiles can aid different agencies in mapping areas of interest and assessing seismic hazard potential during planning future development or evaluating current facilities.
Concrete structures have been used widely in civil infrastructural systems especially in bridges. Due to the complex
nature of its microstructure, nondestructive testing (NDT) of concrete inherently imposes many challenges, which can
cause severe limitations to both the resolution and sensitivity of the observed signals. In this study, surface wave
propagation in concrete is examined and simulated by using a surface bonded active piezoelectric actuators/sensors
system experimentally and numerically, especially at high frequency. First, different experimental tests are conducted to
evaluate effects of the loading frequency upon the resulting surface wave propagation. Secondly, the numerical results
are compared with experimental data. The very good agreement shows the great feasibility and potential of surface wave
signals by using piezoelectric actuators/sensors to locate and characteristics of surface damages.
Vibration-based damage detection has grown over the past decade with considerable attention paid towards
monitoring of civil structures and machines. Much of the focus has been based on comparison of system properties
'before' and 'after' damage, with the premise that the system can be treated as linear in both states. This work uses
a novel method for analyzing vibration signatures, aimed at monitoring structures and machines for incipient
damage. This non-destructive method is based on a new technique, Empirical Mode Decomposition (EMD) and
Hilbert-Huang Transform (HHT) for non-stationary and non-linear time series analysis. The technique essentially
allows the decomposition of the time-domain signals into intrinsic oscillatory modes, providing a time-frequency
distribution. Results from analysis of vibration signatures from anti-friction bearings will be presented. The data
was obtained from experiments conducted on a lab test set-up specifically designed for this study. Analysis based
on the time-frequency plots and Hilbert-Huang spectrum illustrate that this new approach may allow for the
development of a reliable damage detection methodology for antifriction bearings.
Over the past few years, actuators have been characterized and analyzed under several different boundary conditions. One of these conditions is loading, which plays a critical part in any application where the actuator is used in a structure. This study concentrated on comparing the displacement under load for different types of actuators of the same length and width, but having different layer compositions. The same load and excitation frequency was used at different voltages. Eleven different groups of devices were tested with metal thickness ratios (MTR - ratio of metal thickness to the total thickness) varying between 0.3 and 0.44. The metals used were stainless steel and brass. The results indicated that the devices with an MTR between 0.31 and 0.37 were able to lift a load of 76 grams. All the devices with this MTR had a ceramic thickness of 0.38mm and stainless steel or brass backing. It was also observed that the positive and negative peak displacements were equal for most devices except for the devices with a metal to PZT thickness ratio of 1 showing a negative peak displacement more than 65% higher than positive peak displacement. This may be due to differences in location of the neutral axis, distribution of pre-stresses, and deformations of the devices under load. It was found that the maximum displacement per applied voltage per mm of ceramic thickness was produced by the devices, which had an MTR of 0.33 to 0.37, with no top, and with a ceramic thickness of 0.38mm.
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