Overview

This project implements a fully analog wireless power system capable of delivering 5-10 W across a 5-10 cm air gap, while maintaining a stable regulated DC output at the receiver.

The system is designed to tolerate large coupling variations caused by distance changes and misalignment, prioritizing predictable behavior and robustness over optimization.

Motivation

Wireless power links are often sensitive to geometry, tuning, and load conditions, leading to instability or unreliable output when operating outside narrow design points.

This project explores a pragmatic approach to wireless power delivery in which link variability is treated as a given, and stability is achieved through local regulation rather than active coordination or digital control.

Problem Definition & Constraints

• No firmware or digital control
• No transmitter-receiver control communication
• Tolerance to receiver motion and coil misalignment
• Stable output voltage despite coupling variation
• Must power real hardware reliably, not test loads

Architectural Approach

The receiver is the focus of this project. Given an existing transmitter that generates a strong, alternating magnetic field as the energy source (see Architecture Overview for the topology), the receiver treats the wireless link as a variable power source and applies regulation locally.

This approach confines voltage regulation to the receiver side, avoids global instability, and removes the need for coordination logic or feedback across the air gap.

Architecture Overview

Transmitter

The transmitter is a push-pull self-resonant oscillator based on a Royer topology, with a minor modification I made to the inductor connection (a star-to-triangle change). I originally built this transmitter as part of my final high-school project. The Royer topology is well-documented and is not my design; the inductor variant is a small adaptation. The schematic and component values are visible in the project images. Specifications:

• Self-resonant oscillator (Royer-derived)
• Air-core inductive transmitter
• Operating frequency: ~1-2 MHz (self-adjusting)

Receiver

• Tuned LC pickup stage
• Series inductance for current smoothing
• Full-wave rectification
• RF filtering
• Classical DC-DC regulation stage for stable output

Specific component values of the receiver, matching strategies, and layout details are intentionally not fully disclosed.

Power Delivery Results

• Delivered up to ~7.5 W reliably at ~10 cm
• Powered multiple real loads simultaneously
• Output voltage remained stable under:
  • receiver movement
  • small coil misalignment
  • lack of fine tuning
• Excess input voltage at close distances absorbed cleanly by the regulation stage
• No adaptive loops, calibration, or firmware required

Real-World Performance

• Operated under vibration and motion
• No observed EMI issues within tested conditions
• No thermal issues within the validated power range

Technical Trade-Offs

• Power rises rapidly at very close distances - overvoltage risk
• No explicit input clamping; regulation stage absorbs excess energy
• Link efficiency not measured
• Potential EMI concerns at higher power levels
• No thermal protection - ~10 W is a practical upper bound

Future Work

• Add explicit input clamping
• Improve receiver shielding
• Measure efficiency vs. distance
• Explore higher-power variants (15-20 W)
• Add thermal monitoring or throttling

Key Takeaways

• Wireless power links are best treated as variable sources
• Local regulation significantly improves robustness
• Self-resonant analog systems perform well under constrained conditions
• Predictability often matters more than theoretical efficiency

What This Project Demonstrates

• Receiver-side engineering of an analog wireless power link, including regulation under variable coupling
• Robust handling of loosely coupled power links
• Pragmatic trade-offs guided by measured behavior
• Preference for simplicity where it improves reliability