Ick-Jae Yoon

Ferroelectric nanoparticle-embedded sponge structure triboelectric generators

We report high-performance triboelectric nanogenerators (TENGs) employing ferroelectric nanoparticles (NPs) embedded in a sponge structure. The ferroelectric BaTiO3 NPs inside the sponge structure play an important role in increasing surface charge density by polarized spontaneous dipoles, enabling the packaging of TENGs even with a minimal separation gap. Since the friction surfaces are encapsulated in the packaged device structure, it suffers negligible performance degradation even at a high relative humidity of 80%. The TENGs also demonstrated excellent mechanical durability due to the elasticity and flexibility of the sponge structure. Consequently, the TENGs can reliably harvest energy even under harsh conditions. The approach introduced here is a simple, effective, and reliable way to fabricate compact and packaged TENGs for potential applications in wearable energy-harvesting devices.

An electrically small, 3D printed folded spherical meander antenna

An electrically small, 3D printed folded spherical meander (FSM) monopole antenna is presented. It is observed from the simulated results that the designed antenna at the electrical size ka of 0.4 resonates at 750 MHz with the radiation efficiency of 96 %, while approaching the lower physical bound for a radiation quality factor. The frame of the designed antenna is built using a selective laser sintering method and is currently under process of painting with a silver paste. The measured antenna parameters will be reported at the conference.

A 3D printed low profile magnetic dipole antenna

An electrically small, low profile magnetic dipole antenna is presented. The proposed antenna is composed of multiple small twisted loops connected in parallel. The simulated radiation efficiency is 87 % at the resonant frequency of 222.5 MHz. The corresponding electrical size ka is 0.276 with the height of 0.0016λ. The prototype is built using a selective laser sintering technology and silver paste painting. The measured result is discussed.

Electrically small, copper strip made folded spherical helix antennas realized by 3D printing technology

The radiation characteristics of electrically small, copper strip made folded spherical helix antennas are studied. It is found that the electrical size of a volumetric wire helix antenna can be further miniaturized when thin and wide copper strips replace the thick wires. It is shown that the proposed antenna designs can approach the lower physical bound for a radiation quality factor Q with electrical size ka less than 0.2. A prototype of the copper strip made folded spherical helix antenna with ka of 0.21 is fabricated using 3D printing and silver painting processes and verified experimentally.

Wireless power transfer in the radiating near-field region

Many works on near-field wireless power transfer (WPT) have been carried out in the coupled-mode resonance region. In this region, very high power transfer efficiency (PTE) above 80% can be attained. However, such a region is very short when measured in terms of wavelength and it is rather difficult to design antennas that extend the distance over which such coupled mode phenomenon can be maintained. Furthermore, optimal impedance matching is distance-dependent and challenging to implement in practice.