Quasistatic Cavity Resonance for Ubiquitous Wireless Power Transfer

<div><p>Wireless power delivery has the potential to seamlessly power our electrical devices as easily as data is transmitted through the air. However, existing solutions are limited to near contact distances and do not provide the geometric freedom to enable automatic and un-aided charging. We introduce quasistatic cavity resonance (QSCR), which can enable purpose-built structures, such as cabinets, rooms, and warehouses, to generate quasistatic magnetic fields that safely deliver kilowatts of power to mobile receivers contained nearly anywhere within. A theoretical model of a quasistatic cavity resonator is derived, and field distributions along with power transfer efficiency are validated against measured results. An experimental demonstration shows that a 54 m³ QSCR room can deliver power to small coil receivers in nearly any position with 40% to 95% efficiency. Finally, a detailed safety analysis shows that up to 1900 watts can be transmitted to a coil receiver enabling safe and ubiquitous wireless power.</p></div

Measured and theoretical results.

<p>Measured, simulated, and analytically computed magnetic fields, (a), and electric fields, (b), when 15 W is transferred to a receiver at 50% efficiency. (c) Analytically computed WPT efficiency, <i>G</i>_<i>max</i> between the QSCR room and the receiver of <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0169045#pone.0169045.g003" target="_blank">Fig 3c</a>. The blue dotted line shows where the data in panel (d) is taken. (d) Line-slice plot of <i>G</i>_<i>max</i> vs. distance from center of wireless power room.</p

SAR simulation.

<p>(a) Setup of SAR simulation in finite element software. (b) Horizontal slices of local SAR values when the pole carries a 140 A current.</p

Top view of the QSCR.

<p>Locations and polarity of image currents due to the conducting walls (dotted circles). Solid circle in the center is the real pole current, and the black square is the QSCR outline from above.</p

Photographs of the experimental setup.

<p>(a) Image of the QSCR wireless power room as viewed from the outside (b) Close up image of the central copper pole and discrete capacitors inserted across the gap. (c) Photo of the multi-turn, square receiver coil used to measure WPT efficiency.</p

Safe input power thresholds.

<p>Maximum permissible power levels (green region) as a function of transfer efficiency. Red line shows where SAR limit is exceeded when the human body model is 46 cm away from the central pole, and the black line is the action level or where the E-field magnitude exceeds 614 V/m at 46 cm away from the pole.</p

AlterWear: Battery-free wearable displays for opportunistic interactions

As the landscape of wearable devices continues to expand, power remains a major issue for adoption, usability, and miniaturization. Users are faced with an increasing number of personal devices to manage, charge, and care for. In this work, we argue that power constraints limit the design space of wearable devices. We present AlterWear: an architecture for new wearable devices that implement a batteryless design using electromagnetic induction via NFC and bistable e-ink displays. Although these displays are active only when in proximity to an NFC-enabled device, this unique combination of hardware enables both quick, dynamic and long-term interactions with persistent visual displays. We demonstrate new wearables enabled through AlterWear with dynamic, fashion-forward, and expressive displays across several form factors, and evaluate them in a user study. By forgoing the need for onboard power, AlterWear expands the ecosystem of functional and fashionable wearable technologies