As we’ve been pushing forward into Magnetlandia, we’ve been gathering data and it has been quite the fascinating ride. I’m going to address some common questions and assumptions by breaking things down considering the properties of both magnetic cores and their encapsulations.
Have a question, find a mistake, or think of something else worth looking into? Let me know!
Field Strength Decline Over Distance In Action
Our process allowed me to take readings of the cores of the m0422a before encapsulation. What I found was that on the thin side (~.5mm), field strength had dropped just under 50%–3180G → 1600G. See diagram below to visualize this as the m0422a data was used to generate these curves.
Titanium Gets Weird
It has been argued that the thickness of titanium encapsulation should be kept thin to minimize field strength loss. This is not backed up by my experiences. What I found when comparing cores (and the m31) of approximately the same size as the Titan’s is that field strength does not seem to appreciably diminish until after the encapsulation. This is explained by Ti’s paramagnetic properties. Given the current Ti offerings are geared towards sensing, this brings us back to focusing on a ratio of field strength and mass. But, it does suggest that Ti magnets will outperform their resin counterparts in lifting.
The SmCo offerings boast a thinner encapsulation that, it has been said, is a more equitable trade compared to the Titan’s thicker shell in terms of field strength. Obviously, Ti is heavy. But at 4.5 g/cm^3, it is a far cry lighter then the massive density that a high strength magnetic core requires. NdFeB comes in at a weighty ~7.6 g/cm^3. SmCo at ~8.5 g/cm^3. In short, the thinner Ti shell of a SmCo magnet actually hurts its field strength to mass ratio since Ti is much lighter. This is easily observed by noting that the Titan weighs ~80% of what the 4825 does and packs in more field strength. However, SmCo’s higher Curie Point is still an amazing feature.
| Name | Diameter (mm) | Thickness (mm) | Volume (mm^3) | Mass (g) | Field Strength (G) |
|---|---|---|---|---|---|
| Titan | 4.5 | 2.3 | 178.13 | .23 | 2900 |
| 4825 | 4.8 | 2.5 | 180.96 | .29 | 2600 |
Ti v. Resin
Unlike Ti, resin encapsulated magnets do lose field strength across their thickness in addition to adding mass. However, resin’'s weight is less than 1/3 of Ti giving the m0422a a much higher reactive potential than the Titan which itself outperforms the far more dense 4825 albeit by a less dramatic margin. Ti is obviously much more durable than resin. We’re not going to test a Ti encapsulated magnet to failure. It will survive plenty your meat won’t.
Will resin implants survive forces that break metacarpals? Initial testing maxed our force meter @ 500. The material starts to deform around 160N but it just gets denser. I was able to make one of the five fail dramatically by essentially maxing out the scale, using different spots. On the third attempt to max the scale, it failed ~250N. I tried to repeat this by maxing another on opposite sides. It cracked but didn’t separate like the other. While it’s hard to get good numbers on metacarpal breakage, mostly because of the insane variability of it all compared to the consistent density of femurs, 500N seems to be what is considered the upper limit.
N52 v. N55
As I compared the m31 to the m0422a I immediately noticed something weird: the encapsulated m0422a weighed about the same as the m31. The TiN coating is thin–less than a micrometer. N55 cores–at least the ones we have sourced–weigh less than their n52 counterparts. That makes the extra field strength count for even more in terms of reactive potential.
| Name | Core | Mass | Field Strength | Grade |
|---|---|---|---|---|
| N55 core | 3x1mm | .05g | 3180 | N55 |
| m31 | 3x1mm | .07g | 2870 | N52 |
