With the seeming unprecedented number of biomagnet options available these days, I’ve been trying to find ways to view their differences. No ideas I express are particularly original, however, the idea of using geometry itself as a lens to understand the intricacies of potential applications is something, I feel, makes it easier to discuss–not mention find the right tool, for the right application.
Disagree? See something I missed? Better at animating? Feel free to jump in.
Preface
@Az_F gives us three use cases for biomagnets in his ebook and research: lifting, sensing, and sensors.
Lifting doesn’t warrant further explanation but, as you’ll see, geometries have a strong influence.
Sensing is complicated. As it is typically used, it refers to the ability to feel electric current flow through wires. Other potential abilities related to having a magnet in communication with your nervous system are:
- determine magnetic polarity
- detect ferrous/magnetic materials
- detect electromagnetic fields (think solenoid testing)
- distinguish between magnetic material and magnetic fields
Beyond that, we have what Az_F calls “sensors.” What he’s getting at is the ability to interact with devices such as hall effect sensors and reed switches. There are few off the shelf products that exploit these but there are a great many fascinating possibilities. I feel we could do use a better term for this family of properties, so I will use, “device interaction.” Got something better? Throw it down.
One thing I see absent, is the discussion of haptics. For those not aware, Az_F did research into the haptic potential of biomagnets. You’ll note in his research, his premise is, “if the magnet is good at sensing, it’s good for haptics.” In particular, he focuses on the field strength to mass ratio we are referring to as reactive potential. As you work through this document, I suspect you will see that the matter is more intriguing than that simplification.
Overview
| Geometry | Effective Mono-Pole | Field Response | Polarity Distinction |
|---|---|---|---|
| Disc | Yes | Oscillatory | Absolute |
| Cylinder, Axial | No | Torsional | Absolute |
| Cylinder, Diametric | Rotation | Pull Bias | No |
| Spheres | Rotation | Pull Bias | No |
| Bar, Axial | No | Torsional | Absolute |
| Bar, Diametric | Yes | Oscillatory | Absolute |
Details
Discs
Polarization Oscillatory Response
In a typical installation, you end up with one pole permanently unusable. If you know the polarity facing out, you can determine the polarity of magnetic fields absolutely by feeling or even seeing the difference between a push and a pull. This also means for the purpose of haptics, we get a deterministic response as the reaction is always either a push or pull when exposed to a field of a given polarity. One notable weakness is the inability to sense the difference between magnetic material and magnetic fields due to access to only one pole.
Best for: Sensing (when reactive potential is high). Lifting (when reactive potential is low). Strong secondary sensing.
Cylinders
Let’s examine axial and diametric properties as a means of exploring how these impact various applications.
Axial
Polarization Torsional Response
Equal access to both poles means that if you know which poles are oriented what direction, you can determine polarity absolutely. This has the further benefit of allowing you to utilize polarity specific devices such as bipolar hall sensors and latching reed switches. Another unique feature of axial cylinders is that applying a field of a given polarity across it’s long axis pushes and pulls at either end simultaneously making push and pull into the dermis simultaneously. Yet another perk of access to two poles simultaneously is the ability to feel how each pole reacts–consistent pull for magnetic material, push-pull for magnetic fields.
Best for: Efficient haptics. Device interaction. Ideal secondary sensing.
Diametric
Polarization Pull Bias
One of the key benefits of diametric cylinders is their ability to rotate to orient their poles optimally–ultimately, whatever pole is opposite the field’s polarity will face it. This means that you can theoretically determine whether two fields in your immediate vicinity are the same polarity (since it’s unlikely the magnet will rotate immediately after leaving the field) but due to the rotation, you’ll never be able to determine polarity. The rotation also makes the field response quirky. Ultimately, it will always pull but there could be a brief push as the magnet rotates. Given Az_F essentially uses waveforms to render haptic feedback, this behavior is of interesting note as it should effectively clip the lower half of the waveform.
Best for: Lifting. Strong secondary sensing.
Spheres
Polarization Pull Bias
Spheres are interesting. Is it axial or diametric? With every surface equal distance from the center it just isn’t a relevant question. Given an appropriately smooth encapsulation, the magnet should quietly orient itself into the optimum alignment. It comes at the cost of a very small patch of effectively peak field strength, however, as the radius rapidly increases distance from the skin. I’m very curious to see what folks get into with these.
Best for: ? ?
Bars
There are subtle and not so subtle differences between bars and cylinders. Note: I do not have pictures of a finished bar magnet so I am reusing others. If there is demand, we’re happy to offer them 
Axial
Polarization Torsional Response
The only chief differences between these and an axial cylinder is the lack of radius. This gives a peak field strength over a great area (as the radius falls away from the surface of the skin).
Best for: Efficient haptics. Device interaction. Ideal secondary sensing.
Diametric
Polarization Oscillatory Response
The lack of rotational ability gives this some of the more beneficial properties of a disc via it’s mono-pole nature giving it some useful sensing properties alongside its lifting prowess.
Best for: Liftng. Strong secondary sensing.
A Quick Note
This is, by no means, intended to be a perfect or absolute system of classification. One notable issue is the tendency of smaller disc magnets to flip in vivo. I’m told, that at least initially but sometimes every time, it is a painful experience. While the temptation is strong to classify those capable of flipping as their own thing due to the instability that property infers on certain other properties, tldr, the Ship of Theseus exists in insufferable defiance of classification.The point at which a magnet is flipping and not just tearing the pocket loose and flopping about becomes hard if not impossible to determine when a strong enough field is applied given that it tends to hurt. Beyond that, the elasticity of our tissues is annoyingly variable. As is our willingness to endure post-install playing–which also doubtlessly influences long term stability.