Extremely high horsepower-to-liter ratios for naturally aspirated cars like the Honda S2000, Ferrari 458 Speciale, or, more recently, the Aston Martin Valkyrie, are inspiring works of engineering art.

If you want a strong magnet, the obvious answer is to buy one. However, for a variety of reasons, you might want to combine several smaller magnets. There are a few ways to do this, but the Halbach ...