[Paper Review] Beamforming for Magnetic Induction based Wireless Power Transfer Systems with Multiple Receivers

S. Kisseleff, I. F. Akyildiz+1 more|arXiv (Cornell University)|Aug 11, 2015

Wireless Power Transfer Systems4 citations

TL;DR

This paper proposes an iterative beamforming algorithm for magnetic induction-based wireless power transfer (WPT) systems with a 3D transmitter coil and multiple single-coil receivers. By jointly optimizing transmit signal magnitude and phase while accounting for mutual coupling and reflected power, the method achieves up to 96% power efficiency, significantly outperforming baseline schemes like closest-neighbor or eigenvalue-based beamforming, especially under strong coupling conditions.

ABSTRACT

Magnetic induction (MI) based communication and power transfer systems have gained an increased attention in the recent years. Typical applications for these systems lie in the area of wireless charging, near-field communication, and wireless sensor networks. For an optimal system performance, the power efficiency needs to be maximized. Typically, this optimization refers to the impedance matching and tracking of the split-frequencies. However, an important role of magnitude and phase of the input signal has been mostly overlooked. Especially for the wireless power transfer systems with multiple transmitter coils, the optimization of the transmit signals can dramatically improve the power efficiency. In this work, we propose an iterative algorithm for the optimization of the transmit signals for a transmitter with three orthogonal coils and multiple single coil receivers. The proposed scheme significantly outperforms the traditional baseline algorithms in terms of power efficiency.

Motivation & Objective

• To address the suboptimal power efficiency in multi-receiver magnetic induction wireless power transfer (MI-WPT) systems due to ignored signal phase and amplitude optimization.
• To develop a beamforming solution that accounts for mutual coupling between multiple receivers and the transmitter, which traditional methods overlook.
• To enable priority-aware power allocation, allowing preferential power delivery to specific receivers based on system requirements.
• To maximize WPT efficiency by jointly optimizing transmit signal parameters while considering the non-convex nature of transmit power constraints.
• To demonstrate significant efficiency gains over baseline algorithms like closest-neighbor and maximum eigenvalue beamforming in realistic multi-receiver scenarios.

Proposed method

• Uses a 3D transmitter with three orthogonally deployed coils to enable directional magnetic field control via beamforming.
• Models the system using resonant LC circuits for each coil, with individual load resistors at receivers to minimize reflection.
• Derives the transmit power metric as a function of beamforming coefficients, including mutual inductance and coupling effects.
• Proposes an iterative algorithm that optimizes beamforming vectors to maximize WPT efficiency under power constraints, accounting for all coil couplings.
• Introduces a priority-aware optimization framework that scales receive power based on user-defined priorities, enabling targeted energy delivery.
• Employs a suboptimal but computationally feasible approach by reducing problem dimensionality through assumptions on coupling and signal structure.

Experimental results

Research questions

• RQ1 How does joint optimization of transmit signal magnitude and phase improve WPT efficiency in multi-receiver MI systems compared to conventional methods?
• RQ2 To what extent do mutual couplings between multiple receivers and the transmitter affect transmit power and efficiency, and how can they be modeled and mitigated?
• RQ3 Can a beamforming algorithm that accounts for reflected power and coupling effects outperform baseline schemes like closest-neighbor or eigenvalue-based beamforming?
• RQ4 How does the inclusion of priority-based power allocation affect the overall system efficiency and beam pattern directivity?
• RQ5 What is the maximum achievable power efficiency in a multi-receiver MI-WPT system when using the proposed beamforming algorithm?

Key findings

• The proposed beamforming algorithm achieves up to 96% power efficiency in multi-receiver WPT systems, even with more than three receivers, demonstrating minimal power loss of only 4%.
• For strong coupling conditions (F > 1), the proposed method shows a steeper efficiency increase compared to baseline methods, yielding up to 37% higher average efficiency.
• The algorithm outperforms both the closest-neighbor and maximum eigenvalue-based beamforming approaches, particularly in high-coupling regimes where coupling effects are significant.
• Priority-aware optimization enables targeted power delivery: increasing the priority factor from 1:1 to 2:1 significantly boosts receive power at the preferred receiver, even surpassing the closest-neighbor method.
• The beam pattern becomes increasingly directional with increasing beamforming factor F, concentrating energy toward preferred receivers and minimizing loss in non-priority directions.
• The iterative algorithm converges to a locally optimal solution, effectively balancing transmit power, coupling, and phase alignment to maximize system efficiency.