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In resonant inductive coupling wireless power transfer systems, a repeater resonator is crucial in expanding the charging area, enabling efficient power supply to receivers, such as small Internet of Things (IoT) devices sparsely distributed in a wide area. However, the repeater current is highly susceptible to deviations in resonance frequency due to manufacturing tolerance and aging, as well as to the magnetic coupling between the transmitter and repeater coils, potentially leading to insufficient amplitude. Consequently, the magnetic field generated by the repeater decreases and the receiver may be difficult to obtain sufficient power from the transmitter via the repeater. To address this problem, this paper proposes a wireless power transfer system with active reactance compensators incorporated in the repeater and the transmitter. The proposed system can equivalently adjust the resonant frequencies of the transmitter and repeater to stably maximize the repeater coil current regardless of the variations in the resonant frequency and the magnetic coupling intensity. Experiments successfully verify that the proposed system can provide a more stable and larger repeater current and output power than the conventional system against the variations in the magnetic field intensity and the resonant frequency of the repeater, validating the feasibility of the proposed system for practical utilization of the repeater in expanding the charging area.

Natural activities such as mountain climbing are activities that require a good communication system, whether it is for the purposes of knowing the position or communication to fellow climbers in a small or large group. Cases of missing climbers often occur in the mountains, so communication in search in mountainous areas becomes one of the difficult things when searching. The purpose of designing LoRa RFM95 repeaters with a frequency of 915 MHz based on ESP32 is to improve the range and stability of communication in LoRa networks. International scale research on LoRa performance testing implies that the LoRa coverage distance is strongly influenced by the conditions of the tested area. Therefore, a repeater is needed for LoRa RFM95 to increase the range distance which refers to the System Development Life Cycle (SDLC) method. The results of tests conducted for transmitters and receivers can communicate as far as 80 meters with line of sight (LoS) conditions and 60meters with non-line of sight (NLOS) conditions. The results of trials conducted by repeaters can extend communication range as far as 60 meters with line of sight conditions and 40 meters with non-line of sight (NLOS) conditions. [ABSTRACT FROM AUTHOR]