Objective
The project aimed to explore the wireless power transfer capabilities via resonant inductive coupling. The specific goal was to measure the magnetic field strength emitted by a coil and convert this into an electrical relationship to understand how voltage and distance affect wireless power transfer efficiency. The principles of Wireless power transfer (WPT) date back to experiments by Nikola Tesla, with modern advancements highlighting resonant inductive coupling as a favored method for efficient wireless power transfer.
Theory
The experiment was grounded in Faraday’s Law of Electromagnetic Induction and also referenced the Biot-Savart Law and Ampère’s Law for analyzing the magnetic field created by the current-carrying coil. The induced EMF was calculated using the formula:
EMF = Magnetic Field × Rate of Change of B
Procedure
The setup included a coil with 100 turns connected to a 12V DC power source with a 100-ohm resistor in series. The coil’s area was 2 square inches, and a Samsung S22 Ultra phone equipped with an internal wireless charging coil was used for measurements. The phone was moved from 100 cm to 1 cm over the coil, and changes in magnetic field strength were recorded.
Calculation Method
Calculations included determining the current in the coil using Ohm’s Law, calculating the coil area, and estimating the maximum EMF induced based on the peak magnetic field strength.
Specifications of the Phone’s Wireless Charging Coil
| Specification | Value |
|---|---|
| Input Voltage | 12Vdc |
| Output Voltage | 5Vdc |
| Output Current (max) | 600mA |
| Transmitter Coil Inductance | 30uH |
| Transmit-receive distance | 1-20mm |
| Transmitter Dimensions | 17x12x4mm |
| Receiver Dimensions | 24x10x3mm |
| Coil Diameter | 38mm |
| Coil Height | 2mm |
Data and Results
| Distance (cm) | Magnetic Field (µT) | t (s) | Induced EMF (µV) |
|---|---|---|---|
| 100 | 30 | 5.0 | 360 |
| 90 | 35 | 4.5 | 420 |
| 80 | 40 | 4.0 | 480 |
| 70 | 45 | 3.5 | 540 |
| 60 | 50 | 3.0 | 600 |
| 50 | 55 | 2.5 | 660 |
| 40 | 60 | 2.0 | 720 |
| 30 | 65 | 1.5 | 780 |
| 20 | 70 | 1.0 | 840 |
| 10 | 80 | 0.5 | 960 |
| 5 | 85 | 0.25 | 1020 |
| 1 | 90 | 0.0 | 1080 |
The results demonstrate a clear trend: as the distance between the coils decreases, both the magnetic field strength and the induced EMF increase, which is indicative of the increased efficiency of wireless power transfer with closer proximity.
Error Analysis
Sources of error included ambient electromagnetic interference, alignment and positioning of the phone, calibration of the magnetometer, and variations in coil properties. Error mitigation strategies included implementing a shielded environment, utilizing standardized positioning mechanisms, regular calibration of measurement devices, and employing precision-made coils.
Conclusion
The experiment demonstrated the detection of magnetic fields at varying distances using a smartphone’s internal coil, but the induced voltages were below levels required for practical wireless charging, highlighting challenges in optimizing wireless power transfer systems.
References
- N. Tesla, “Art of transmitting electrical energy through the natural mediums,” US Patent 787412A, 1905.
- A. Sample, D. Meyer, and J. Smith, “Analysis experimental results and range adaptation of magnetically coupled resonators for wireless power transfer,” IEEE Transactions on Industrial Electronics, vol. 58, pp. 544–554, 2011.
- phyphox, “Physical phone experiments.”
- Shanjedul Hassan, “Wireless charging module specification.”