(Im not saying powerful magnets are not very valuable, but requirements for them can be overrated)

[1] https://forums.tesla.com/de_AT/forum/forums/no-rare-earth-me...

[2] https://www.mathworks.com/help/physmod/sps/powersys/ug/wind-...

>electromagnetism/induction is somewhat more complex to manage but potentially more powerful and efficient.

Quibble- at certain RPM ranges an induction motor can be more efficient than a PM motor of equal cost, but in general a PM motor will always be smaller and more efficient than an induction motor if built to the same quality. For most applications, the cost of the motor is very minor.

Wind turbines are an exception because the converter is cheaper than the motor at that scale. Tesla uses induction motors for several reasons but the primary one is probably cost. The cost is actually more in materials handling and assembly than the magnets themselves, since magnets will always find a way to fuck up your life eventually. PM motors also have much more demanding requirements of controllers and more cogging, but in general they can only be as good as a PM motor at high speed and low load.

PM motors have very large advantages over induction. They have half the iron laminations of an induction motor, so they have half the hysteresis losses. On an overall basis there is no way for an induction motor to make that up. Even at high RPMs I've only seen indications (papers/FEMM sims) that induction motors can roughly match PM motors, not surpass them.

A purely (doubly fed) superconductive motor would probably resemble a PM motor more than an inductive motor, but I'm not 100% sure. It would be for the same reduction in hysteresis losses. An air-core motor would also be possible, but that would result in 30 Tesla fields swinging around wildly, which would be a Bad thing.

You could probably get good gains with metal glass laminations, if you were gonna make a hilariously expensive motor. It's got very low core loss and extremely high permeability, which lets you shrink the motor and have a higher ratio of copper/iron, lowering winding resistance.

Still, electrical machines are so efficient it's kind of just not worth it. The friction in the bearings and the viscosity of air are significant factors in a motor's efficiency.

"In Vestas, rare earth elements are used in the magnets found in the towers of all new models of Vestas turbines" - Vestas[1]

[1]https://www.vestas.com/en/about/sustainability#!material-use

It is a little daunting to see that ladder going up into the dizzying heights and see that it is held in place by the same technology that keeps the kids' art stuck on the fridge.

Here's their patent on it: https://www.google.com/patents/US8567131

Anyone have more insight on this?

This uses permanent magnets arranged in a Halbach Array for levitation.

This method of levitating a pod is incredibly efficient and gets more efficient at higher speeds (in a vacuum). You can actually exceed typical rail efficiency (rolling resistance of 1:1000, i.e. an effective coefficient of friction of 0.001 or a lift-to-drag ratio of 1000) at 300m/s since levitation power remains basically constant above a certain speed (as opposed to increasing linearly in the case of friction or rolling-resistance). And because you're in a vacuum, you're far exceeding what could be possible in a non-hyperloop/vactrain design: https://www.google.com/patents/US20100064929

Especially at such big pipe diameters as required.

You can use cheap materials like modified concrete to patch a hole in an underwater tunnel, not so in a vacuum tube - that needs something much better and more expensive.

I assume the metric here would be something like cubic-yards-per-mile-per-day or something like that.

Hey! Are you basing this statement on your own experience of your personal/business hardware? Because spinning rust has never been more heavily used, for bulk on/near-line storage.

Judging by the list of alumni from Prof. Wang's group, HDD manufacturers have a strong demand for advanced applications of magnets, plus a tiny fraction from biomedical techs.

[0]: http://www.nanospin.umn.edu/people-0

[0] for some definition of obsolete.

There's still a lot of active research going into magnetic tape storage, I find it very difficult to believe research into hard drive storage is going to slow any time soon.

Not sure if serious or not. Just because SSD's are popular, does not mean HDD's are unused.

[1]http://www.physics.org/article-questions.asp?id=54 [2]https://en.wikipedia.org/wiki/Loudspeaker#History

I want lighter guitar amps that don't cost an arm and a leg, dammit! :)

Inverter-based power supplies are sufficiently light that a guitar amp should only be the weight of the wood and the speakers.

And, the speakers have to be a certain size to move the correct amount of air--so the copper coil is probably the limiting weight. It's remarkable how much air you have to actually move to get decent sound volume.

Ceramic 4.4lbs 50W http://celestion.com/product/20/rocket_50/

Neodymium 3.7lbs 60W http://celestion.com/product/14/g12_century_vintage/

And, yes, you will find that the values are all over the map in terms of weight. There are some much less powerful speakers that are quite a bit heavier.

Some others: electric bikes, electric skateboards, power tools, blow dryers, iPad cases.

If I recall correctly, one of the earlier iPhones was basically held together w rare earth magnets, with the screen module magnetically stuck into the case. Can't find info to verify this though, so take it w a grain of salt.

Basically, the stronger the fixed magnetic field, the more you can see and do.

Thanks anyway for the heads up. Very nice