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In this study, the post-embedded piezoceramic transducers are used to perform structural health monitoring (SHM) and detect crack damage on the reinforced concrete (RC) column. The piezoceramic transducers are utilized as actuators and sensors, respectively. To investigate the use of the piezoceramic transducer in detecting crack damage in RC columns, SHM tests are performed on three full-size RC column specimens with various failure modes under cyclic loading. The sensors are installed at two depth ranges (40–50 and 70–80 mm) beneath the surface of the column to investigate the effect of the sensor depth on the damage index. In this study, the energy and amplitude-based damage indexes are developed. Both approaches follow the same trend under various drift ratios of the specimen. However, the value of energy-based damage index is much higher than the amplitude index for all peak drift ratio of the specimen. From different depth range of piezoceramic transducers, this study recommends a depth of 80 mm as optimal for post-embedded piezoceramic transducers, since it receive more stable signals in various frequencies. In the proposed health monitoring approach using piezoceramic transducers, the equation to predict the maximum residual crack width and damage index smart aggregates are developed. The normalized damage index equation which in this study is referred as 'crack damage index' is introduced and used to calculate the limiting value for each damage level. The suggested value of the crack damage index for each damage level is also provided. The energy, strength and stiffness reduction factors for each damage level, which correlate with the crack damage index, are also presented. These results demonstrate that the proposed post-embedded piezoceramic transducers has the potential to be used as a tool for SHM on an RC column.

Cyclical wet clean in DI-O 3 /SC1/DHF and low temperature bake in HCl/H 2 are presented as effective surface treatments for selective SiGe epitaxial deposition used to fabricate embedded SiGe pMOSFETs. The presented methods are most effective for device structures under limited chemical and thermal budgets.

Direct growth of metamorphic structure of high quality InP layers on GaAs substrates by metalorganic vapor phase epitaxy is presented. The quality of the top InP layer is strongly affected by the growth temperatures, group III and V partial pressure ratios and peripheral environment parameters control. A growth window that has successfully suppressed the numerous dislocations and rough surface as a result of the large lattice mismatch between InP and GaAs is obtained. Only 400 nm thick InP buffer layer compared with that of previous reports of 2 µm thick is qualified to obtain low dislocations and defects, high crystal quality, and uniform and specular surface morphologies. The material quality measured by photoluminescence is even better than that of InP substrates. In addition, the 2.8 nm surface roughness is lower than that of previous reports of 11.1 nm.

A new method to directly grow InxGa1-xAs strained layers, instead of using graded buffer layers, on misoriented GaAs (1 0 0) substrates by 10° towards (1 1 1)A while maintaining low interface dislocations, high crystal quality, and uniform and mirror like surfaces of the layers grown by metalorganic chemical vapor deposition (MOCVD) is presented. The large lattice defects existing between InxGa1-xAs and GaAs layers which lead to numerous interface dislocations and rough surface areas have been suppressed successfully by accurate control of growth temperature, growth rates, and the group III and V partial pressures with the V/III ratio of at least 91. The surface roughness is less than 1 nm as measured by atomic force microscopy (AFM). Lower interface dislocations can be observed by transmission electron microscopy (TEM). High crystal quality compared with that in previous studies is measured by an X-ray diffractometer (XRD). The mirror like surface is characterized by optical microscopy.

Wind turbines are a cost-effective alternative energy source; however, their blades are susceptible to damage. Therefore, damage detection of wind turbine blades is of great importance for condition monitoring of wind turbines. Many vibration-based structural damage detection techniques have been proposed in the last two decades. The local flexibility method, which can determine local stiffness variations of beam-like structures by using measured modal parameters, is one of the most promising vibration-based approaches. The local flexibility method does not require a finite element model of the structure. A few structural modal parameters identified from the ambient vibration signals both before and after damage are required for this method. In this study, we propose a damage detection approach for rotating wind turbine blades using the local flexibility method based on the dynamic macro-strain signals measured by long-gauge fiber Bragg grating (FBG)-based sensors. A small wind turbine structure was constructed and excited using a shaking table to generate vibration signals. The structure was designed to have natural frequencies as close as possible to those of a typical 1.5 MW wind turbine in real scale. The optical fiber signal of the rotating blades was transmitted to the data acquisition system through a rotary joint fixed inside the hollow shaft of the wind turbine. Reversible damage was simulated by aluminum plates attached to some sections of the wind turbine blades. The damaged locations of the rotating blades were successfully detected using the proposed approach, with the extent of damage somewhat over-estimated. Nevertheless, although the specimen of wind turbine blades cannot represent a real one, the results still manifest that FBG-based macro-strain measurement has potential to be employed to obtain the modal parameters of the rotating wind turbines and then locations of wind turbine segments with a change of rigidity can be estimated effectively by utilizing these identified parameters.

Structural health monitoring of concrete structures under seismic loads has always attracted a lot of attention in the earthquake engineering community. In this paper, two tests of structural health monitoring of concrete columns using piezoceramic-based sensors are presented. The first test was a shake table test of a reinforced concrete (RC) column. A piezoceramic-based device, called a 'smart aggregate', was pre-embedded and adopted for the structural health monitoring of the concrete column under earthquake excitations. The second test of this study was the in situ health monitoring of RC piers of Niu-Dou Bridge in Taiwan, under seismic loading. RC piers instrumented with the post-embedded piezoceramic-based sensors were tested using reversed cyclic loading. During the shake table test and the in situ reversed cyclic loading test, one sensor was used as an actuator to generate propagating waves, and the other sensors were used to detect the waves. By analyzing the wave response, the existence of cracks can be detected and the severity can be estimated. The experimental results demonstrate the sensitivity and the effectiveness of the piezoceramic-based approach in the structural health monitoring of large-scale concrete structures under earthquake loading.

Highly selective wet etching of GaAs on Al0.2Ga0.8As can be realized using citric buffer (citric acid/H2O2/H2O) solutions. The selectivity can be up to 256, which is distinct from the previous non-selectivity inference, due to consulting the role of H2O2 in this etching system. The etch stop mechanism is demonstrated by X-ray photoelectron spectroscopy (XPS) and indicates the formation of dense oxide Al2O3 on Al0.2Ga0.8As to stop etching. The applications to pseudomorphic high electron mobility transistors (PHEMT) gate recess processes, no obvious drain current decrease can be perceived even after 8 min overetching. The etched surface is very smooth with the roughness of only 1.97 Å. The devices also show excellent etched uniformity with a small threshold voltage deviation of 28 mV and good electrical performance, which is useful to the heterostructure device fabrications.