Reconfiguring room-scale magnetoquasistatic wireless power transfer with hierarchical resonators

Abstract

Magnetoquasistatic wireless power transfer can deliver substantial power to mobile devices over near-field links. Room-scale implementations, such as quasistatic cavity resonators, extend this capability over large enclosed volumes, but their efficiency drops sharply for centimeter-scale or misoriented receivers because the magnetic field is spatially broad and weakly coupled to small coils. Here, we introduce hierarchical resonators that act as selectively activated relays within a room-scale quasistatic cavity resonator, capturing the ambient magnetic field and re-emitting it to concentrate flux at a target receiver. This architecture reconfigures the wireless power environment on demand and enables localized energy delivery to miniature devices. Experimentally, the hierarchical link improves power transfer efficiency by more than two orders of magnitude relative to direct room-scale transfer and delivers up to 500 mW of DC power to a 15 mm receiver. We further demonstrate selective multi-relay operation and field reorientation for furniture-embedded charging scenarios. These results establish a scalable route to reconfigurable wireless power delivery for miniature and batteryless devices in room-scale environments.

Figures (5)

• Figure 1: Concept of hierarchical resonators for wireless power transfer.a Illustration of a representative deployment scenario. The room-scale transmitter generates a wide-area magnetic field, while objects in the interior can embed relay modules that form hierarchical links and selectively focus the magnetic field. b, c Illustration of the field-focusing effect, in which intermediate relay resonators selectively concentrate and redirect magnetic flux from the room-scale transmitter to miniature receivers. d Schematic representation of the hierarchical coupling architecture. Because direct coupling between the transmitter and the tiny receivers ($k_{\rm TX,RX}$) is very weak, hierarchical links can be used to enhance power transfer efficiency. e Relationship between the $kQ$-product and power transfer efficiency. The plot illustrates representative operating points for standard ($\sim100~\mathrm{mm}$) receivers and tiny ($\sim10~\mathrm{mm}$) or orientation-misaligned receivers. In the extremely weak-coupling regime, the efficiency scales approximately as $d_{\rm RX}^4$, where $d_{\rm RX}$ is the characteristic dimension of the receiver. f Three-dimensional model of the cavity resonator used in this study. The transmitter uses conductive sheets with integrated lumped capacitors to generate a magnetic field while confining electric fields. g Top-down view of the baseline magnetic field distribution, showing a homogeneous field pattern. h, i Reconfigured field distributions with Relay 1 and Relay 2 activated, respectively. The localized amplification of the magnetic field near the relay modules illustrates the ability to selectively direct power within large spaces.
• Figure 2: Experimental setup for efficiency measurements.a Photograph of the room-scale quasistatic cavity resonator used in this study Sasatani2021. b Interior view of the furnished cavity, showing the drive coil and a representative relay--receiver measurement arrangement. c Detailed view of the relay module and miniature receiver, together with the local coordinate system used to define receiver position relative to the relay. d Power transfer efficiency as a function of the distance between the relay and receiver for two vertical offsets ($z^\prime=0$ and $z^\prime=\qty{50}{mm}$), compared with the baseline direct-transfer case. e Power transfer efficiency as a function of the transmitter--relay $kQ$-product, showing a substantial improvement of the hierarchical relay link over baseline direct transfer.
• Figure 3: Multi-relay reconfigurability.a Schematic of a room-scale transmitter supporting two hierarchical links, from Relay 1 to RX1 and from Relay 2 to RX2. b--d Measured power transfer efficiency of RX1 and RX2 for the four relay states (OFF, OFF), (OFF, ON), (ON, OFF), and (ON, ON) under different transmitter--relay $kQ$ configurations. The results show how simultaneous relay activation redistributes power between the two links depending on their relative coupling strengths.
• Figure 4: Rectified power performance and overall efficiency.a Circuit schematic of the miniature receiver, including the resonant coil ($L_{\rm RX}$), tuning capacitors, and a full-wave bridge rectifier. b Measured output power and overall DC-to-DC efficiency as functions of input power. The system delivers up to $\qty{500}{mW}$ of rectified output power while maintaining an overall efficiency of approximately $5\%$.
• Figure 5: Demonstrations and usage scenarios of hierarchical resonators.a Localized power delivery to a batteryless microcontroller unit (MCU) with an LED indicator. b Charging a Li-Po battery in water, illustrating the weak interaction of magnetic fields with dielectric environments. c A field-bending relay module embedded in a wooden shelf, designed to capture the horizontal room field and re-emit it as a vertically reoriented field. d, e Smartphone charging demonstration showing the transition from no charging with the relay OFF (d) to active charging with the relay ON (e) through field reconfiguration.