Woonbong Hwang

Hybrid Energy Cell for Degradation of Methyl Orange by Self-Powered Electrocatalytic Oxidation

In general, methyl orange (MO) can be degraded by an electrocatalytic oxidation process driven by a power source due to the generation of superoxidative hydroxyl radical on the anode. Here, we report a hybrid energy cell that is used for a self-powered electrocatalytic process for the degradation of MO without using an external power source. The hybrid energy cell can simultaneously or individually harvest mechanical and thermal energies. The mechanical energy was harvested by the triboelectric nanogenerator (TENG) fabricated at the top by using a flexible polydimethysiloxane (PDMS) nanowire array with diameters of about 200 nm. A pyroelectric nanogenerator (PENG) was fabricated below the TENG to harvest thermal energy. The power output of the device can be directly used for electrodegradation of MO, demonstrating a self-powered electrocatalytic oxidation process.

Effect of debonding on natural frequencies and frequency response functions of honeycomb sandwich beams

The natural frequencies of honeycomb sandwich beams having debonding or delamination embedded between the face-layer laminates and the honeycomb core are studied herein. A theoretical analysis of the effect of the extent of debonding on the flexural stiffness and on the natural frequency is compared with experimental observations. In this analysis the free vibration of the delaminated sandwich beams is studied using the split sandwich beam model, and the equations of motion are set up for the undelaminated region of the sandwich beam and the delaminated region of the laminated beams. Finally, changes in the peaks and valleys of the frequency response functions (FRFs) due to delamination are examined. By using the modal parameter identification method [H.Y. Kim, W. Hwang, Compos. Struct., 2001 (in press)], the extent of delamination of the sandwich beams can be identified in terms of the natural frequencies and damping ratios of the debonded beams. Vibration testing was conducted on honeycomb sandwich beams with carbon/epoxy laminated composite faces and Nomex-aramid honeycomb core. Agreement between the predictions of the model and experimental results is good.

Robust superhydrophilic/hydrophobic surface based on self-aggregated Al2O3 nanowires by single-step anodization and self-assembly method.

Superhydrophilic and superhydrophobic surfaces were studied with an eye to industrial applications and use as research tools. Conventional methods involve complex and time-consuming processes and cannot feasibly produce large-area three-dimensional surfaces. Here, we report robust and large-area alumina nanowire structures with superhydrophobic or superhydrophilic properties, generated by an inexpensive single-step anodization process that can routinely create arbitrary three-dimensional shapes. This process is expected to open up diverse applications.

Vibration Control of a Laminated Plate with Piezoelectric Sensor/Actuator: Finite Element Formulation and Modal Analysis

The combined effects of passive and active control on the vibration control of a com posite laminated plate with piezoelectric sensors/actuators are investigated. Finite element formula tion and modal analysis are presented. Classical laminated plate theory with the induced strain ac tuation and Hamiltons principle are used to formulate the equation of motion of the system. The total charge developed on the sensor layer is calculated from the direct piezoelectric equation. The equa tions of motion and the total charge are discretized with 4-node, 12-degree of freedom quadrilateral plate bending elements. The stiffness and damping property changes of composite structures by varying the layer angles are used as a passive control method. Piezoelectric sensors/actuators with negative velocity feedback control are used as an active control method. By numerical simulation, the effects of stiffness and damping property changes of composite structures and the effects of sen sor/actuator division on the response of the structure and the performance of the vibration control are investigated. Since active control and passive control affect each other, the active control and the passive control should be considered simultaneously in designing the efficient adaptive structures.

Optimum placement of piezoelectric sensor/actuator for vibration control of laminated beams

The optimum placement of a collocated piezoelectric sensor/actuator is investigated numerically and verified experimentally for vibration control of laminated composite beams. The finite element method is used for the analysis of dynamic characteristics of the laminated composite beams with the piezoceramic sensor/actuator. The damping and the stiffness of the adhesive layer and the piezoceramics are taken into account in the process of finite element modeling. Tailoring that varies the stiffness and the damping properties of the composite material is used. The stacking sequence of the laminated composite beam is [θ 4 /0 2 /90 2 ] s , where θ = 0, 15, 30, 45, 60, 75, and 90 deg. The sensor/actuator attached to a structure changes the mass, the damping, and the stiffness of the entire structure. Thus, interaction between sensor/actuator and structure is very important in the vibration control of a flexible structure. Modal damping (2ζω) is chosen as a more appropriate performance index, because it is directly related to the settling time of the vibration. The structural damping index (SDI) is defined from the modal damping. Weights for each vibrational mode are taken into account in the SDI calculation. The optimum location of the sensor/actuator is determined as the point where the SDI is maximum. Numerical simulation and experimental results show that the SDI depends on outer-layer fiber orientations of the host structure, the location, and the size of the sensor/actuator.

3D Cell Printing of Functional Skeletal Muscle Constructs Using Skeletal Muscle-Derived Bioink

Engineered skeletal muscle tissues that mimic the structure and function of native muscle have been considered as an alternative strategy for the treatment of various muscular diseases and injuries. Here, it is demonstrated that 3D cell-printing of decellularized skeletal muscle extracellular matrix (mdECM)-based bioink facilitates the fabrication of functional skeletal muscle constructs. The cellular alignment and the shape of the tissue constructs are controlled by 3D cell-printing technology. mdECM bioink provides the 3D cell-printed muscle constructs with a myogenic environment that supports high viability and contractility as well as myotube formation, differentiation, and maturation. More interestingly, the preservation of agrin is confirmed in the mdECM, and significant increases in the formation of acetylcholine receptor clusters are exhibited in the 3D cell-printed muscle constructs. In conclusion, mdECM bioink and 3D cell-printing technology facilitate the mimicking of both the structural and functional properties of native muscle and hold great promise for producing clinically relevant engineered muscle for the treatment of muscular injuries.

Multilayer Effects on Microstrip Antennas for Their Integration With Mechanical Structures

The effect of multilayer geometry on microstrip antennas is investigated for the design of antenna-integrated mechanical structure. Changes in the gain of antenna due to the geometry have been determined using a transmission line analogy. Design of high-gain antenna in bandwidth is proposed away from structural resonance. Experiments are done on microstrip antennas covered by superstrates in order to verify high-gain conditions theoretically derived herein. The off-resonant conditions that use practical materials of moderate thickness make it possible to design the antenna-integrated mechanical structure with the perfect integration of high mechanical and electrical performances

Energy harvesting model of moving water inside a tubular system and its application of a stick-type compact triboelectric nanogenerator

As the first invention to efficiently harvest electricity from ambient mechanical energy by using contact electrification, the triboelectric nanogenerator has elicited worldwide attention because of its cost-effectiveness and sustainability. This study exploits a superhydrophobic nanostructured aluminum tube to estimate electrical output for solid-water contact electrification inside a tubular system. The linearly proportional relationship of short-circuit current and open-circuit voltage to the detaching speed of water was determined by using a theoretical energy harvesting model and experimentation. A pioneering stick-type solid-water interacting triboelectric nanogenerator, called a SWING stick, was developed to harvest mechanical energy through solid-water contact electrification generated when the device is shaken by hand. The electrical output generated by various kinds of water from the environment was also measured to demonstrate the concept of the SWING stick as a compact triboelectric nanogenerator. Several SWING sticks were connected to show the feasibility of the device as a portable and compact source of direct power. The developed energy harvesting model and the SWING stick can provide a guideline for the design parameters to attain a desired electrical output; therefore, this study can significantly increase the applicability of a water-driven triboelectric nanogenerator.

Microstrip Antenna for SAR Application with Composite Sandwich Construction: Surface-antenna-structure Demonstration

A 5.3 GHz microstrip antenna for use in synthetic aperture radar (SAR) systems was developed with a composite sandwich construction, using composite laminates, Nomex honeycomb and aluminum alloy. This is the surface-antenna-structure (SAS) for application to load-bearing structural surfaces. The design concept originated from a composite sandwich structure and a multi-layer microstrip antenna. Design, fabrication and validation of structural/electrical performances were all demonstrated. To verify the structural rigidity, flexural behavior was observed under the three-point bending test and was compared with two kinds of composite sandwich beams consisting of CFRP–GFRP skins and Nomex honeycomb core. Electrical measurements of the fabricated antenna array were in good agreement with design requirements, and a comparative study found that SAS has good mechanical characteristics. The SAS concept can be extended to give a useful guide to manufacturers of structural body panels as well as antenna designers, promising innovative future communication technology.

Toward robust nanogenerators using aluminum substrate.

Nanogenerators (NG) have been developed to harvest mechanical energy from environmental sources such as vibration, human motion, or movement of automobiles. We demonstrate a robust and large-area NG based on a cost-effective Al substrate with the capability to be easily integrated in series and parallel for high-output performance. The output voltage and current density of the three-dimensionally integrated NG device reaches up to 3 V and 195 nA under human walking conditions.