Wireless charging is a transformer with a very large air gap, which means very loose coupling, and the whole design problem is recovering the performance that loose coupling throws away. This project builds a series-series resonant link: a half-bridge inverter drives a transmitter coil tuned to resonance, a receiver coil tuned to the same frequency feeds a rectifier and a load, and the measurements that matter are how efficiency varies with gap, with lateral misalignment and with detuning. The result is a working charger and, more usefully, a set of curves showing exactly where the technology stops being practical.
Not just the parts. Teams budget from a component list, then run out in week six on wire, connectors and the driver board they destroyed. These are the lines that catch them.
| Line | Cost |
|---|---|
Components and materials From the bill of materials | Rs 3,100 to Rs 8,810 |
Spares and replacements 15 % — you will destroy something | Rs 465 to Rs 1,322 |
Consumables and hardware Wire, connectors, headers, screws, heatshrink | Rs 372 to Rs 1,057 |
PCB fabrication | Rs 350 to Rs 900 |
Report, printing and binding Two or three bound copies, plots and the plagiarism check | Rs 400 to Rs 1,200 |
| Total | Rs 4,687 to Rs 13,289 |
| Each, split 3 ways | Rs 1,562 to Rs 4,430 |
Indicative bands last checked in August 2026 — a guide, not a quotation. Prices move and vary by seller, and anything you can borrow from the lab comes straight off the total. The 4.3 week figure assumes 10 person-weeks of work shared between 3; students past 4 add coordination rather than output, so the estimate stops improving there.
The same chain in words
The half bridge drives the transmitter coil with a square wave at the resonant frequency. At resonance the coil's inductive reactance and the series capacitor's capacitive reactance cancel, so the driver sees a low impedance and a large current flows in the coil.
That current produces an alternating magnetic field. A fraction of it links the receiver coil — that fraction is the coupling coefficient, and across a real air gap it is small.
The receiver is tuned to the same frequency, so the small induced voltage drives a large circulating current in the receiver's own resonant loop. This is why resonance matters: it magnifies a weak coupling into a useful power transfer.
The receiver output is rectified and smoothed to charge the load.
Efficiency is measured as DC output power over DC input power, across a range of gaps and lateral offsets.
This is the chapter that separates an engineering project from an assembly job. Every value below carries the formula that produced it and the assumptions it rests on — check them against your own ratings before you use them, because your motor is not this motor.
C = 1 / (4 x pi^2 x f^2 x L)
4 x pi squared is 39.478; 39.478 x 1e10 x 25e-6 = 9.87e6, so C = 101 nF. Use a low-loss film capacitor rated for the circulating current, not a ceramic — the current in the resonant loop is far larger than the current drawn from the supply.
Q = 2 x pi x f x L / R
2 x pi x 1e5 x 25e-6 = 15.71, divided by 0.3 gives Q = 52. AC resistance is what counts here, not DC: skin and proximity effects at 100 kHz make a solid conductor much worse than its DC value suggests.
FOM = k x sqrt(Q1 x Q2)
0.3 x 52.4 = 15.7. This single number, not the coils or the frequency separately, is what determines the best efficiency the link can achieve.
eta max = FOM^2 / (1 + sqrt(1 + FOM^2))^2
247 / (1 + 15.75) squared = 0.88. Halve the coupling to k = 0.15 and the figure of merit halves, and the ceiling drops sharply — which is exactly the curve this project sets out to measure.
Skin depth = sqrt(rho / (pi x f x mu))
Current at 100 kHz flows in roughly the outer fifth of a millimetre of the conductor, so the middle of a thick wire carries almost nothing while adding cost and weight. Litz wire splits the conductor into many insulated strands so the whole cross-section is used.
| Item | Qty | Unit cost |
|---|---|---|
Microcontroller or driver IC Arduino Nano for control, or a fixed 100 kHz oscillator | 1 | Rs 250 to Rs 500 |
Gate driver IR2110 half bridge driver with bootstrap components | 1 | Rs 90 to Rs 260 |
Power MOSFETs IRF540N or similar, fast switching | 2 | Rs 30 to Rs 90 |
Litz wire 100 strand, for both coils | 1 | Rs 400 to Rs 1,200 |
Ferrite plates Backing plates for both coils, to shape the field | 2 | Rs 200 to Rs 600 |
Resonant capacitors Polypropylene film, 100 nF, 630 V, low loss | 4 | Rs 45 to Rs 140 |
Rectifier Schottky bridge, fast recovery, 100 V | 1 | Rs 60 to Rs 200 |
Smoothing capacitor 470 uF low ESR electrolytic with film bypass | 1 | Rs 50 to Rs 160 |
Load bank Wirewound power resistors, assorted values, 10 W | 1 | Rs 200 to Rs 550 |
Measurement Two INA219 modules, or a bench meter on each side | 2 | Rs 180 to Rs 400 |
Coil formers and jig 3D printed or acrylic formers with a calibrated gap slide | 1 | Rs 350 to Rs 1,000 |
Bench supply or SMPS 24 V, 3 A adjustable | 1 | Rs 700 to Rs 2,200 |
Specifications are written as ratings rather than brands, so any equivalent part works. Where a line says to borrow from the lab, do — it is usually the largest number on the page, and the total drops to Rs 4,687 at the low end without them.
None of these blocks you — they are learnable inside a semester. Each one you do not have costs a couple of weeks, so count them into your plan.
Anything marked required is a blocker, not a difficulty. Arrange the access before you commit to the project, not after.
Use these when your guide says the scope is too small, or when you want something in the results chapter that nobody else in your batch will have.
The structure below is what a project report is marked against, with the mistake that costs marks in each chapter. There is no template to download and there will not be one: the writing is your work, and a site that did it for you would be helping you cheat rather than helping you pass.
A mini project report runs to about 40 to 50 pages, and the literature survey is usually brief. Guides expect one clear objective, met and measured. A final year report is normally 60 to 90 pages with a substantial literature survey, and many departments expect a paper submission alongside it.
The full report guide — front matter, conventions and page countsOne paragraph covering what the problem is, what you built, and what the result was. Written last, even though it appears first.
Loses marks: Describing the problem and the method but never stating a result. If there is no number in your abstract, it is not finished.
Why the problem matters, the context it sits in, and a clear statement of the objectives your project set out to meet.
Loses marks: Objectives written so vaguely that nobody can tell at the end whether they were met. Write objectives you can tick off in the conclusion.
What has already been done, what each approach achieved, and the specific gap your work addresses.
Loses marks: A list of paper summaries with no comparison and no gap. The survey exists to justify your design choice, so end it by saying what you chose and why.
The system as a whole: the block diagram, what each block does, and the signal or power path between them.
Loses marks: A block diagram copied from a datasheet or another report. Draw yours to match what you actually built, including the parts that are inconvenient.
Every component value and rating, with the formula, the assumptions and the arithmetic that produced it. This is the chapter that distinguishes an engineering project from an assembly job.
Loses marks: Component values with no justification. If a resistor is 10 kOhm, the report must say why it is not 1 kOhm.
The circuit as built, the PCB or wiring, the flowchart, and the parts of the code that carry the actual logic.
Loses marks: Twenty pages of pasted source listing. Include the flowchart and the few functions that matter, and put the full listing in an appendix.
What you measured, in tables and graphs, compared against what you predicted in the design chapter — including where they disagreed.
Loses marks: Photographs of the working model presented as results. A photograph is evidence that it exists, not evidence that it works. Results are measurements.
Whether each objective was met, what the measured performance was, and what the honest next step would be.
Loses marks: Future scope written as a wish list of unrelated features. It should follow from a limitation you actually hit.
Every source in a consistent style, plus datasheets, full code listings and the complete bill of materials.
Loses marks: Citing a blog or a video where a datasheet or a standard exists. Cite the primary source for anything you relied on.
The demonstration is half the assessment. These are the questions this project invites, and the answers are written the way you would give them out loud.
Because the coupling across an air gap is very weak, so the voltage induced in the receiver is small and the leakage inductance dominates. Tuning both sides to resonance cancels the reactance of that leakage inductance, so a small induced voltage can drive a large current in the receiver loop. Without resonance almost all the energy stays in the field and returns to the source instead of reaching the load.
It is the fraction of the flux produced by one coil that links the other, between zero and one. It falls rapidly with the gap between the coils, falls with lateral misalignment, and improves with larger coil diameter relative to the gap and with ferrite backing that shapes the field. A conventional transformer has a coupling coefficient near one; a wireless charger might have 0.2 to 0.4.
Because what matters is how much energy the link transfers per cycle compared with how much it loses per cycle. Coupling sets the transfer and quality factor sets the loss, so the product, expressed as the figure of merit k times the root of Q1 Q2, is what fixes the best efficiency achievable. Low coupling can be compensated by high Q coils, which is exactly how these systems are made to work at all.
Because at a hundred kilohertz the skin effect confines current to about the outer two tenths of a millimetre of the conductor, and the proximity effect between adjacent turns makes it worse. Litz wire divides the conductor into many individually insulated strands that are transposed along their length, so all the copper carries current and the AC resistance stays close to the DC value, which keeps the quality factor high.
The reactances no longer cancel at the driving frequency, so the circulating current drops, the transferred power falls and the driver sees a reactive load it was not designed for. In loosely coupled systems this is very sensitive; a few percent of detuning can halve the delivered power, which is why practical systems track the resonant frequency instead of assuming it.
Normally taken as a B.E. mini project (5th/6th sem) or B.E. final year project (7th/8th sem) project. If yours is a different course, the extensions above scope it up and the simpler half of the design scopes it down — the arithmetic does not change. Back to all projects.