What’s Maximum Energy Product / BHmax

The term Maximum Energy Product (BHmax) is a generally used, however usually misunderstood figure of advantage of magnets.  The BHmax is an Energy Density and it’s oftentimes used to indicate grade.  The grade convention is very used for Rare Earth magnets, (Neodymium Iron Boron Magnets and Samarium Cobalt Magnets).  For example, a grade 48 Neodymium Iron Boron magnet will usually have an advertised BHmax of 48 MGOe.  (The unit MGOe, Gauss•Oerstedx10^6, or Mega-Gauss•Oersted is used within the CGS (Centimeter-Gram-Second) unit system.  The Maximum Energy Product within the SI (Systeme International) unit system is Joules/m^3.)

This conference appears affordable, however it does have limitations as a result of it doesn’t enable for the prediction of magnetic efficiency.  Typically, a magnet with a better BHmax can be stronger than a magnet with a lower BHmax, however that also doesn’t enable us to foretell efficiency relative to magnetic discipline density or flux generation.

With a purpose to predict the performance of a magnet in a specific utility, different magnetic traits of the magnet materials and the bodily geometry of the magnet have to be identified.  Predicting efficiency just isn’t within the scope of this text, however the magnet geometry is pertinent to the Maximum Energy Product discussion.

Technical Explanation:

BHmax is a quantity unbiased magnetic attribute, which means a small and large magnet constructed from the same ND-48 Neodymium Iron Boron magnet alloy can have the same BHmax, although though they create vastly completely different magnetic fields or flux.  The Maximum Energy Product, or BHmax, is attained when the magnet is working on the highest Induction level (Gauss) and on the smallest quantity for a specific pole cross-section.  Bigger volumes of the magnet will produce bigger magnetic fields and extra flux, although the magnet will not be working at BHmax.

In relation to the BH Curve or Demagnetization Curve, the second quadrant of a magnet’s hysteresis curve, the Maximum Energy Product is the biggest rectangle that may be inscribed beneath the Regular Curve (see determine 1).  The rectangle’s vertex on the X axis (Area Power) is the working level Hd at BHmax, whereas the vertex on the Y axis (Magnetic Induction) is the working level Bd at BHmax.

Also, if the (H-B) data-points for the Regular Curve are identified, their product might be calculated after which plotted towards the Area Power, (X axis).  This plot will generate a parabola and the vertex of the parabola can be on the Maximum Energy Product for the actual grade within the items of MGOe, if B is in Gauss and H is in Oersteds (see determine 2).

Commercial magnet magnetic traits are marketed with tolerances.  The vary of the Residual Induction (Br) and the Coercive Force (Hc) change the place the working factors, Hd and Bd happen for the BHmax.  This is the reason there’s an efficient vary for the Maximum Energy Product.

For a magnet to function at its BHmax it will need to have a specific geometry.  This geometry is a generally used ratio in magnetic design and it’s the ratio of the Magnetic Size to the Diameter of the Magnet, L/D.  (For non-round magnets, the diameter of a circle with an equal space of the non-round pole is used.)  Since it is a ratio, there are an infinite variety of prospects of magnet geometries for any explicit magnet grade.

When a specific magnet is working at BHmax it may be mentioned to have the best effectivity relative to energy density.  Once more, when a magnet operates at BHmax it will not be producing a big sufficient magnetic discipline for a specific utility and due to this fact, a better quantity could also be required.  Most magnets utilized in functions should not designed to function at BHmax.

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