The FastHenry alternative with a real UI.
FastHenry is the classic free inductance extractor from MIT. AirInduct Sim answers the same L and M question for wireless power coils without writing a single segment by hand.
Last reviewed: October 2026
What FastHenry does well
FastHenry, developed at MIT, computes the frequency-dependent resistance and inductance matrix of 3D conductor structures. Conductors are split into filaments so skin and proximity effects come out naturally, and a multipole-accelerated solver keeps large problems fast. It is free, scriptable and well validated, and FastFieldSolvers ships a Windows build with the FastModel GUI.
Where AirInduct Sim is faster for WPT coils
- No netlist: pick a topology, enter dimensions in mm, and get L, M and k.
- Gap and lateral misalignment sweeps in seconds, with plots.
- 3D field maps, which FastHenry does not produce.
- A genetic optimizer, PDF report, and KiCad, DXF and SPICE export.
- An AI Copilot that drives the app and runs the real solver, and an MCP server for your own agents.
It is free to start: the free plan covers the Helmholtz topology with 3 simulations a month, and AirInduct Pro unlocks every topology, the AI Copilot and unlimited runs (see pricing).
FastHenry vs AirInduct Sim at a glance
An inductance extractor and a WPT coil simulator, compared.
| Criterion | AirInduct Sim | FastHenry |
|---|---|---|
| Solver method | Closed-form Biot–Savart field + Neumann mutual inductance, no mesh | Partial-inductance extraction on conductor segments split into filaments, multipole-accelerated |
| Input | Topology presets and plain-English inputs in mm | Text input file of nodes and segments (FastModel GUI in some distributions) |
| Outputs | L, M, k, 3D field plots, link efficiency, PDF report | Frequency-dependent impedance matrix (R and L) between ports |
| Skin and proximity effect | Not modelled | Yes, through filament discretisation |
| Field maps | 3D B and H fields | No |
| Platforms | Browser, iOS and Android | Command line on Linux and macOS; Windows build with GUI from FastFieldSolvers |
| Price | Free plan + Pro subscription | Free |
| AI assistance | AI Copilot that drives the app and runs the real solver; MCP server for agents | None |
Competitor details are taken from public vendor pages and documentation, last reviewed October 2026. Product names are trademarks of their respective owners and are used only to identify them. AirInduct is not affiliated with, endorsed by or sponsored by any of these vendors.
Which should I use?
Use FastHenry when you need AC resistance from skin and proximity effect, or inductance of arbitrary conductor layouts in a scripted flow. Use AirInduct Sim when you want L, M and k for wireless power coils, with sweeps and field plots, without writing the geometry by hand. The two agree on air-core inductance, so each is a good check on the other.
Compare with other tools
See all 20 AirInduct Sim alternatives and comparisons →Skip the netlist. Get L, M and k now.
Frequently asked questions
Can FastHenry calculate mutual inductance between two coils?
Yes. Describe both coils as conductor segments, define a port on each, and FastHenry returns the impedance matrix whose off-diagonal term gives M. It handles 3D geometry, including offsets.
Why use AirInduct Sim if FastHenry is free?
Speed of setup. FastHenry needs every turn written as nodes and segments in a text file. AirInduct Sim builds the coils from a preset and a few dimensions, sweeps gap and offset, and plots the field, in a browser.
Which is more accurate?
For air-core coils at low frequency both converge to the same L and M. FastHenry adds frequency-dependent resistance from skin and proximity effect, which AirInduct Sim does not model.