Abstract Body

Recent research on microwave wireless power transmission has shown that the transmission efficiency of 60% can be achieved by using normal-conducting patch antenna arrays (88) at 28 cm with 1 dB of conductor loss at the antenna [1]. To reduce the conductor loss, it is effective to use a superconductor for the antenna materials. We recently proposed, designed, and fabricated an antenna using HTS bulk to improve the power handing capability of conventional superconducting antennas [2], but the transmission efficiency of the HTS bulk resonator was lower than the level reached in previous studies [1]. To improve the transmission efficiency, the antenna directivity must be improved, which might be possible by arraying or loading directors [3]. There are currently no reports of HTS bulk resonator antennas with directors.

In this paper, we evaluated the transmission efficiency of the HTS bulk resonator antenna with a director for wireless power transfer. For this propose, first, we designed the HTS bulk resonator antenna with a director using CST Microwave Studio. Fig. 1(a) shows the model of the HTS bulk resonator antenna, and (b) shows the model of the HTS bulk resonator antenna with the director and the expanded reflector area. Second, we fabricated the director on the basis of the simulated results. Finally, we measured the HTS bulk resonator with and without the director and reflector and evaluated the transmission efficiency. For preparing the HTS bulk antenna, the HTS bulk and fabricated PTFE to implant the HTS bulk and feed port were parceled by substrates made using c-sapphire plate. After that, the substrates and SMA connector were placed in the bottom of the Cu cavity, and the upper part of the Cu cavity was set to the bottom one. The director was fabricated by cutting FR-4 substrates into square shapes. The director was loaded by spacers made of the PTFE. The bottom of the Cu cavity was used by the reflector, and when expanding the reflector area, the square Cu plate was placed in the bottom of the Cu cavity. We carried out the measurements in an anechoic chamber. The antenna was cooled to about 48 K by using a pulse tube cryocooler.

Fig. 1(c) shows the dependence of the transmission efficiencies on the transmission distance measured using a vector network analyzer and a commercially available horn antenna as a receiver antenna. With the HTS bulk resonator antenna used as a transmission antenna, the transmission efficiency was 22.8% when the transmission distance was 0 cm, and with the HTS bulk resonator using the director and expanded reflector, it was 36.8%. These results indicate that the HTS bulk resonator with the director and expanded reflector is effective for improving the transmission efficiency.

References

[1] T. Tomura et al., IEEE Open Journal of Antennas and Propagation, Vol. 2, pp. 170-180, 2021.

[2] K. Ehara et al., Electronics and Communications in Japan, Vol. 82, pp. 55-69, 1999.

[3] S. Arao et al., Proceedings of the conference on Electronics mounting, Vol. 20, pp. 139-141, 2006.

Acknowledgment

Some of this work was performed in the clean room at Yamagata University.

Figure 1. (a) Simulation model of HTS bulk resonator antenna. (b) Simulation model of HTS bulk resonator antenna with the director and expanded reflector. (c) Comparison of transmission efficiency with and without director and reflector.

Keywords: Antenna, HTS, Wireless Power Transfer