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A magnet assembly includes a back iron and an array of magnets. The back iron is in the form of a plate having opposed surfaces. The magnets are arranged along one of the surfaces, with the other surface being dimensioned and configured according to the magnetic field distribution associated with t

A magnet assembly includes a back iron and an array of magnets. The back iron is in the form of a plate having opposed surfaces. The magnets are arranged along one of the surfaces, with the other surface being dimensioned and configured according to the magnetic field distribution associated with the magnets. The back iron geometry provides for reduced mass, reduced leakage flux, and high flux densities to improve performance of a linear motor that employs such a magnet assembly. Additionally, the back iron can be a magnetically conductive annular ring, such as is employed in a rotary motor. Moreover, the magnets can be arranged in a manner that generates a Halbach array to increase force output in a desired direction while canceling stray magnetic fields in other directions. Similar reduced-mass designs can be employed in conjunction with a back iron of a fixed cross-section and magnets of variable thicknesses, variable lengths, and/or variable widths. In a case where the arrangement is employed in a platen and forcer system, plates on both the platen and forcer may be scalloped to reduce mass.

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What is claimed is: 1. A magnet assembly for a motor comprising: a magnetically conductive annular ring with a uniformly varied cross-sectional dimension; and a plurality of magnets associated with the magnetically conductive annular ring, the magnets are disposed in a spaced apart relationship on

What is claimed is: 1. A magnet assembly for a motor comprising: a magnetically conductive annular ring with a uniformly varied cross-sectional dimension; and a plurality of magnets associated with the magnetically conductive annular ring, the magnets are disposed in a spaced apart relationship on a side of the annular ring, the annular ring has a smaller cross-sectional width in locations where the magnets are disposed, relative to a cross-sectional width in locations where magnets are not disposed, such that the magnets are recessed into the annular ring. 2. The assembly of claim 1, the plurality of magnets is oriented to generate a Halbach array. 3. The assembly of claim 1, the annular ring comprises a core of optimized non-oriented electrical steel. 4. The assembly of claim 1, the assembly is integral to a rotary motor. 5. The assembly of claim 1, the uniformly varied cross-sectional dimension comprises peaks and valleys that are generally sinusoidal in shape and that conform to the magnetic flux distribution. 6. The assembly of claim 1, the uniformly varied cross-sectional dimension comprises peaks and valleys that are square in shape for ease of manufacturing. 7. The assembly of claim 1, the uniformly varied cross-sectional dimension comprises peaks and valleys that are triangular in shape for ease of manufacturing. 8. A magnet assembly for a motor comprising: a magnetically conductive metal backing with a varied cross-sectional thickness that forms a series of peaks and valleys; and a plurality of magnets associated with the magnetically conductive metal backing wherein the valleys occur in regions aligned with centers of individual magnets in the plurality of magnets. 9. The magnet assembly of claim 8, the metal backing is an iron plate in a platen-and-forcer motor arrangement. 10. The magnet assembly of claim 8, the plurality of magnets is arranged to generate a Halbach array. 11. The magnet assembly of claim 10, employed in a platen-and-forcer device in a semiconductor fabrication system. 12. The magnet assembly of claim 11, the Halbach array cancels a magnetic field in a region above the platen and forcer. 13. The magnet assembly of claim 8, the peaks and valleys are generally sinusoidal in shape and conform to the magnetic flux distribution. 14. The magnet assembly of claim 8, the peaks and valleys are square in shape for ease of manufacturing. 15. The magnet assembly of claim 8, the peaks and valleys are triangular in shape for ease of manufacturing. 16. The magnet assembly of claim 8, further comprising notches in the metal backing that retain the magnets in position. 17. The magnet assembly of claim 8, wherein the metal comprises no notches in order to minimize weight of the magnet assembly.