- Does magnetic variation have effect on the oscillator’s frequency as it does for a magnetic pendulum ?
No magnets are used only to transmit energy through the magnetic field. Magnetic variation would affect the amplitude of the oscillators but not its frequency. Frequency is only depending on the oscillator’s characteristics such as the shape, and elasticity coefficient.
-How stable is the magnetism over the years?
Thanks to recent materials such as neodymium magnets, demagnetization over time or under external “daily” magnetic fields is insignificant. In a normal magnetic environment with temperature bellow 80°C (176°F) the magnets manufacturer is announcing 5% of loss over a century. De Bethune is taking a 25% safety margin in terms of magnetic variation that should cover 500 years of demagnetization.
- What is the impact of temperature variation on magnets ?
Magnetic field of permanent magnets is indeed changing with temperature. Variation is low and reversible as long as you stay bellow maximum working temperature and bellow Curie temperature where magnetization would disappear. Today, magnets used by De Bethune specification is 100°C (212°F) maximum working temperature, 300°C (572°F) Curie temperature and magnetic variation of -0.1% per °C above 20°C (68°F). A temperature of 70°C would lower magnetic field by 5% which is still in the tolerance threshold.
- Does magnetic field associated to the magnets affect the rest of the mechanism?
The magnets that are used today are among the smallest available on the market. The magnetic field has a very short range and the effects on the rest of the mechanism are insignificant, even considering long term usage.
- Wouldn’t a strong magnetic field damage the magnets?
Yes, if very strong. But we could consider as well that any other watch would be severely damaged under the same circumstances. Nevertheless, for specific conditions we could still protect the mechanism with some kind of Faraday shield using mu metal.