We experimentally demonstrated full-duplex light-emitting diode (LED)-to-LED visible light communication (VLC) using LEDs as the transmitter and receiver. Firstly, we investigated the performance dependency on the wavelengths of the LED transmitter and receiver by measuring the rise time and signal-to-noise ratio (SNR). Through the investigation, we were able to choose the optimal LED color set for LED-to-LED VLC using Shannon’s channel capacity law. The bit error rate (BER) results of full-duplex and half-duplex LED-to-LED VLC systems with the optimal LED sets are shown to compare the performance. Furthermore, we discuss major distortions and signal losses in the full-duplex LED-to-LED VLC system.
We experimentally demonstrate an underwater optical wireless power transfer (OWPT) using a laser diode (LD) as a power transmitter. We investigate the characteristics of a solar cell and a photodiode (PD) as a power receiver. We optimize the LD, the PD, and the solar cell to achieve the maximum transfer efficiency. The maximum transfer efficiency of the back-to-back OWPT is measured as 4.3% with the PD receiver. Subsequently, we demonstrate the OWPT in tap and sea water. Our result shows an attenuation of 3 dB/m in sea water. OCIS codes: 010.3310, 010.
Optical wireless communication (OWC) is one of the promising candidates for beyond fifth-generation communication (B5G). Depending on the type of transmitters, receivers, and information carriers applied in the system, OWC can be categorized into visible light communication, light fidelity, free-space optical communication, optical camera communication, etc. In addition to these OWC subcategories, this paper proposes light-emitting diode (LED)-to-LED communication as another subcategory of OWC technique. Furthermore, we show an experimental demonstration of the multiple-input multiple-output (MIMO) LED-to-LED communication system using red, green, and blue colored LEDs. We believe that LED-to-LED communication is an effective solution to resolve the communication burden arising from massive connectivity in B5G internet of things. Along with the measurement results of the transmitter LED, receiver LED, and the channel properties, it is shown that the MIMO LED-to-LED system is able to successfully recover the transmitted signal with low inter-channel interferences due to the receiver LED’s unique characteristics. Finally, the bit error rate (BER) performance of the MIMO LED-to-LED system is shown in comparison with the BER performance of the single-input single-output (SISO) LED-to-LED system. We successfully implemented the 3 × 3 MIMO LED-to-LED communication system using RGB colors at a data rate of 30.62 kbps over a 10 cm transmission distance along with direct current biased optical orthogonal frequency division multiplexing (DCO-OFDM) modulation and zero-forcing (ZF) equalizer.
The boron neutron capture therapy (BNCT) system developed by the Korea Institute of Radiological and Medical Sciences is a compact neutron source that can be installed at medical institutes. The target energy was accelerated to a maximum of 2.4 MeV–20 mA by introducing a gas stripping device that converts negative hydrogen ions into positive ions. By using the tandem-type accelerator in this way, a high-voltage DC power supply was designed with 1.2 MV–45 mA as the maximum capability. The design was improved to reduce the number of stages of a Cockcroft–Walton voltage multiplier. Hence, the ripple risk of the DC flat top resulting from unwanted stray capacitance was lowered. The overall height and volume of the Cockcroft–Walton voltage multiplier were reduced to less than half those of the existing design method, making miniaturization possible. After such advanced design and manufacturing, performance tests were performed at 750 kV–45 mA under 23 stages of the Cockcroft–Walton voltage multiplier, which is the highest level that can perform at its maximum under in-air conditions. It demonstrated stable performance under in-air conditions without breakdown for 2 h, even at 620 kV–35 mA. To reach the final target of 1.2 MV–45 mA, the groundwork is laid for achieving experimental performance while satisfying the optimal requirements in SF6 gas.
To build a proton beam accelerator that can be applied to a boron neutron capture therapy system based on an electrostatic accelerator, a high-voltage direct-current (DC) power supply system equivalent to the generation of neutrons should be provided. The symmetrical Cockcroft–Walton voltage multiplier method is suitable for stable acceleration of the proton beam in the tandem electrostatic accelerator in this system. Before the second step-up with the Cockcroft–Walton circuit, the design of the inverter is prioritized by preponderantly considering the first voltage and resonance frequency. Moreover, the optimized stacking number is determined with consideration of the ripple voltage, voltage drop, average output voltage, and fundamental harmonics, and a design is performed to set related parameter values to be stable in the flat-top region of the voltage. A high-voltage DC power supply system of 1.2 MV/45 mA is needed for a stable terminal energy of 2.4 MeV/20 mA. Such a design can be optimized by securing reliable data using a simulation tool on the basis of theoretical calculations. This will become a formidable touchstone in manufacturing technology based on acquiring practical know-how for setting up a tandem electrostatic accelerator-based boron neutron capture therapy system in the future.
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