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A rechargeable AA battery supporting Qi wireless charging

Alexey A. Dmitriev, Egor D. Demeshko, Danil A. Chernomorov, Andrei A. Mineev, Oleg I. Burmistrov, Sergey S. Ermakov, Alina D. Rozenblit, Pavel S. Seregin, Nikita A. Olekhno

TL;DR

The paper addresses enabling Qi wireless charging for devices that rely on standard AA batteries by integrating a curved receiving coil with a Qi Baseline compliant load-modulation circuit, a rectifier, and DC-DC converters to deliver a 1.5 V output from a Li-ion cell. The approach combines numerical CST simulations of coil coupling around curved radii $\rho$ and experimental validation with a fully functional prototype, showing a power-transfer contract can be established at roughly $h=4$ mm and that charging at $h=2$ mm with $I_{cell}=100$ mA is feasible, with full charge achieved in about $95$ minutes. The work demonstrates the practicality of universal wireless charging for AA-type peripherals and outlines pathways toward higher power density and interoperability with broader standards such as Qi2 and room-scale systems.

Abstract

Wireless power transfer is one of the key drivers in modern consumer electronics, as it allows one to enhance the convenience and usability of many devices. However, in most cases, wireless charging is accessible only to devices with incorporated receivers or at least to gadgets with standard charging connectors, such as USB Type-C, that allow to attach an external receiver. We propose a rechargeable battery that has the size and output voltage of a standard AA battery but supports wireless power transfer from charging stations of the widely used Qi standard. The proposed design uses a series resonant circuit with a curved receiving coil, as well as load modulation using detuning capacitors switched by a microcontroller unit to implement a receiver compatible with the Qi Baseline protocol. It also utilizes a number of DC-DC converters to store energy in a Li-ion cell and convert it to the 1.5 V voltage level. Our design is supported by numerical simulations of magnetic field distributions and scattering parameters of the introduced battery coupled to a planar transmitting coil. The performance of the proposed battery has been studied experimentally, including measurements of the maximal distance between the battery and a charging station that allows wireless charging at various rotation angles and the charge curve. The developed battery design facilitates the addition of wireless charging functionality to a wide range of electronic devices in a universal way.

A rechargeable AA battery supporting Qi wireless charging

TL;DR

The paper addresses enabling Qi wireless charging for devices that rely on standard AA batteries by integrating a curved receiving coil with a Qi Baseline compliant load-modulation circuit, a rectifier, and DC-DC converters to deliver a 1.5 V output from a Li-ion cell. The approach combines numerical CST simulations of coil coupling around curved radii and experimental validation with a fully functional prototype, showing a power-transfer contract can be established at roughly mm and that charging at mm with mA is feasible, with full charge achieved in about minutes. The work demonstrates the practicality of universal wireless charging for AA-type peripherals and outlines pathways toward higher power density and interoperability with broader standards such as Qi2 and room-scale systems.

Abstract

Wireless power transfer is one of the key drivers in modern consumer electronics, as it allows one to enhance the convenience and usability of many devices. However, in most cases, wireless charging is accessible only to devices with incorporated receivers or at least to gadgets with standard charging connectors, such as USB Type-C, that allow to attach an external receiver. We propose a rechargeable battery that has the size and output voltage of a standard AA battery but supports wireless power transfer from charging stations of the widely used Qi standard. The proposed design uses a series resonant circuit with a curved receiving coil, as well as load modulation using detuning capacitors switched by a microcontroller unit to implement a receiver compatible with the Qi Baseline protocol. It also utilizes a number of DC-DC converters to store energy in a Li-ion cell and convert it to the 1.5 V voltage level. Our design is supported by numerical simulations of magnetic field distributions and scattering parameters of the introduced battery coupled to a planar transmitting coil. The performance of the proposed battery has been studied experimentally, including measurements of the maximal distance between the battery and a charging station that allows wireless charging at various rotation angles and the charge curve. The developed battery design facilitates the addition of wireless charging functionality to a wide range of electronic devices in a universal way.
Paper Structure (6 sections, 2 equations, 10 figures, 2 tables)

This paper contains 6 sections, 2 equations, 10 figures, 2 tables.

Table of Contents

  1. Introduction
  2. Structure of the battery
  3. Battery circuit implementation
  4. Numerical simulations of magnetic coupling between transmitting and receiving coils
  5. Experimental studies of the battery prototype
  6. Conclusion and Outlook

Figures (10)

  • Figure 1: Design of the proposed battery. The AA battery-sized module which includes a receiving coil (copper), a receiver circuit board (green), a converter circuit board (blue), a rechargeable battery (gray), and a plastic casing (white) is placed atop the transmitting coil of a Qi standard charge station.
  • Figure 2: Structure of the proposed battery.
  • Figure 3: Circuit implementation of the proposed battery.
  • Figure 4: Algorithm of the microcontroller unit (MCU) firmware enabling (when Power Good is assigned true) or disabling (when assigned false) the 5 V buck converter and driving the load modulation to send Control Error ($\mathtt{CE}$), End of Power Transfer ($\mathtt{EPT}$) and 8-bit Received Power ($\mathtt{RP8}$) Qi packets, accomplishing the voltage feedback and foreign object detection. The Signal Strength ($\mathtt{SIG}$), Identification ($\mathtt{ID}$) and Configuration ($\mathtt{CFG}$) packets are sent during the initialization procedure.
  • Figure 5: (a) Numerically calculated $S_{21}$-parameters for different values of curvature radius $\rho$ of the receiving coil: $\rho=\infty$ for a planar coil (blue), $\rho=49$ mm (red), $\rho=13$ mm (green), and $\rho=7$ mm corresponding to an AA battery (orange). (b)-(d) Magnetic field profiles in the (xy)-plane passing through the battery midpoint for the receiving coils with curvature radii (b) $\rho = \infty$, (c) $\rho = 13$ mm, and (d) $\rho = 7$ mm, respectively. (e) Frequency dependencies of $S_{21}$-parameters for different distances $h$ between a transmitting coil and a curved receiving coil ($\rho = 7$ mm). (f)-(h) Magnetic field profiles in the (xy)-plane for (f) $h=1$ mm, (g) $h=5$ mm, and (h) $h=10$ mm. (i) Frequency dependencies of $S_{21}$-parameters for different receiving coil rotation angles $\theta$; $\rho = 7$ mm. (j)-(l) Magnetic field profiles in the (xy)-plane for (j) $\theta=0^{\circ}$, (k) $\theta=90^{\circ}$, and (l) $\theta=180^{\circ}$.
  • ...and 5 more figures