Permanent magnets & maximum force

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Discussion Overview

The discussion revolves around the theoretical maximum force that permanent magnets can exert, particularly in relation to their mass and distance from the object being influenced. Participants explore the complexities of calculating this force, including the need for specific material properties and geometric considerations.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant questions how to calculate the theoretical maximum force of permanent magnets per kilogram at a certain distance.
  • Another participant notes the difficulty of such calculations without microscopic details and suggests that a hysteresis curve could provide some insights, although it would still be geometry dependent.
  • A participant expresses the belief that there is an upper limit to the strength of permanent magnets per unit mass and indicates an intention to find supporting information.
  • One participant references theoretical analyses indicating that Inductrack systems can levitate significant weights, suggesting that these forces are close to the theoretical maximum for permanent magnets, while also citing actual test results that align with these predictions.

Areas of Agreement / Disagreement

Participants do not reach a consensus on the maximum force of permanent magnets, with some expressing uncertainty about the existence of an upper limit and others providing specific examples of levitation forces achieved in practice.

Contextual Notes

The discussion highlights the dependence on material properties and geometric configurations for accurate calculations, as well as the potential limitations of theoretical models when applied to real-world systems.

Thrice
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What's the theoretical maximum force? At a certain distance & per kg, i guess. How would you go about calculating this?
 
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Very difficult to calculate without some microscopic details of the system.

If you had a hysteresis curve for the material you could calculate the field strength nearby the magnet roughly, but it'd still be geometry dependent and probably not that accuracte to the real system.
 
But is there an upper limit for all materials? I was under the impression there's a limit to how strong (per unit mass or something) permanent magnets can get. I'll try track down the link.
 
Last edited:
Theoretical analyses show that, if required by the application, Inductrack systems can be designed to levitate more than 40 metric tons per square meter of Halbach array, with up to 50-to-1 ratio of levitated weight of a train car to magnet weight. These levitation forces are close to the theoretical maximum that can be exerted by permanent magnets. Actual values achieved in a test run at GA are about 30 metric tons per square meter, in close agreement with the theoretically predicted levitation force for the configuration that was tested.
Source: http://www.llnl.gov/str/November03/Post.html
 
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