Hyun Bum Kim

Hybrid Surface Acoustic Wave- Electrohydrodynamic Atomization (SAW-EHDA) For the Development of Functional Thin Films

Conventional surface acoustic wave - electrostatic deposition (SAW-ED) technology is struggling to compete with other thin film fabrication technologies because of its limitation in atomizing high density solutions or solutions with strong inter-particle bonding that requires very high frequency (100 MHz) and power. In this study, a hybrid surface acoustic wave - electrohydrodynamic atomization (SAW-EHDA) system has been introduced to overcome this problem by integrating EHDA with SAW to achieve the deposition of different types of conductive inks at lower frequency (19.8 MHZ) and power. Three materials, Poly [2-methoxy-5-(2-ethylhexyloxy)-1, 4-phenylenevinylene] (MEH-PPV), Zinc Oxide (ZnO), and Poly(3, 4-ethylenedioxythiophene):Polystyrene Sulfonate (PEDOT:PSS) have been successfully deposited as thin films through the hybrid SAW-EHDA. The films showed good morphological, chemical, electrical, and optical characteristics. To further evaluate the characteristics of deposited films, a humidity sensor was fabricated with active layer of PEDOT:PSS deposited using the SAW-EHDA system. The response of sensor was outstanding and much better when compared to similar sensors fabricated using other manufacturing techniques. The results of the device and the films’ characteristics suggest that the hybrid SAW-EHDA technology has high potential to efficiently produce wide variety of thin films and thus predict its promising future in certain areas of printed electronics.

All-printed highly sensitive 2D MoS 2 based multi-reagent immunosensor for smartphone based point-of-care diagnosis

Immunosensors are used to detect the presence of certain bio-reagents mostly targeted at the diagnosis of a condition or a disease. Here, a general purpose electrical immunosensor has been fabricated for the quantitative detection of multiple bio-reagents through the formation of an antibody-antigen pair. The sensors were fabricated using all printing approaches. 2D transition metal dichalcogenide (TMDC) MoS2 thin film was deposited using Electrohydrodynamic atomization (EHDA) on top of an interdigitated transducer (IDT) electrode fabricated by reverse offset printing. The sensors were then treated with three different types of antibodies that were immobilized by physisorption into the highly porous multi-layered structure of MoS2 active layer. BSA was used as blocking agent to prevent non-specific absorption (NSA). The sensors were then employed for the targeted detection of the specific antigens including prostate specific antigen (PSA), mouse immunoglobulin-G (IgG), and nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB). IgG was then selected to test the sensors for point of care (POC) diagnosis through a specially designed electronic readout system for sensors and interfacing it with a smartphone using Bluetooth connection. The sensors showed promising performance in terms of stability, specificity, repeatability, sensitivity, limit of detection (LoD), and range of detection (RoD).

Liquid assisted exfoliation of 2D hBN flakes and their dispersion in PEO to fabricate highly specific and stable linear humidity sensors

A highly specific and sensitive linear humidity sensor has been fabricated using a dispersion of 2D hexagonal boron nitride (hBN) flakes in polyethylene oxide (PEO). Bulk hBN powder was exfoliated via liquid-assisted mechanical exfoliation to achieve few-layered 2D nano-flakes with thicknesses in the range of 3–4 nm. PEO was used as the polymer matrix to disperse the hBN flakes evenly throughout the suspension. An interdigitated transducer (IDT) electrode pair fabricated via reverse off-set printing using silver nanoparticles ink (AgNPs) on a piezoelectric LiNbO3 substrate serves as the transducing portion of the sensor. Electrohydrodynamic atomization was used to spray a uniform thin film of the active composite material onto the sensor electrodes. All the fabrication methods used are compatible with printed electronics approaches and are suitable for mass production. The sensors show excellent stability for up to 40 days of testing. The sensitivity of the near-linear sensors was ∼24 kΩ/%RH, which is better than most of the previously reported studies. The sensors showed response and recovery times of 2.6 s and 2.8 s, respectively. The selectivity of the sensors was tested by exposing the sensors to O2, N2, and CH4 gases in addition to humidity and the results showed no effect of the other gases on the sensors output. The fabricated sensors based on the 2D hBN/polymer composite can be employed in high-end target specific applications requiring accurate and high performance humidity sensors.

Defect Monitoring of a Wind Turbine Blade Surface by using Surface Wave Damping

These days much efforts are being dedicated to wind power as a potential source of renewable energy. To maintain effective and uniform generation of energy, defect preservation of turbine blade is essential because it directly takes effects on the efficiency of power generation. For the effective maintenance, early measurements of blade defects are very important. However, current technologies such as ultrasonic waves and thermal imaging inspection methods are not suitable because of long inspection time and non-real time inspection. To supplement the problems, the study introduced a method for real time defect monitoring of a blade surface based on surface wave technology. We examined the effect of various parameters such as micro-cracks and peelings on the propagation of surface wave.