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Generators

The general principle behind a permanent magnet generator is to induce a voltage in specifically wound wires via a changing magnetic field.  When this voltage is applied to a load power is produced.  So called “off-the-shelf” generators often lack the power or form-factor desired for customer specific applications.

There are two primary configurations of custom designed permanent magnet generators:

  • Externally driven rotor
  • Internally driven rotor

Alignment magnets are used to provide uniform fields across a substrate.  These fields are used to coerce magnetically permeable materials into a preferred orientation.  Alignment may occur either in process, or as a post process operation as is the case with annealing magnets.

Dexter has designed and built alignment magnets as small as 10 lbs and as large as 10,000 lbs.  During the design, magnetic circuits of a specified topology are configured to precisely control the magnetic field shape, magnitude, and uniformity of the device.   These output characteristics are all critical to the final performance of the product being processed.

To verify final performance, Dexter serializes and magnetically maps each device by making use of its 3D field mapping system.

Dexter_Alignment_Permanent      
               Alignment Magnet - Permanent

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                                                                          Dexter_Alignment_Electromagnet
                                                                                       Alignment Magnet - Electromagnet

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Annealing

Some products require post process orientation of grains in order to achieve full functionality.  These post processes usually occur at elevated temperatures to allow granular motion.  By exposing the product to a magnetic field while at elevated temperatures, the grains are free to align themselves with the magnetic flux lines.   Keeping the product exposed to the magnetic field during the cooling cycle pins the domains in a preferred orientation.   These types of magnets are typically external to the annealing oven, but can be placed within them utilizing proper material selections.  These magnets can either be permanent, electromagnet, or superconducting depending on the field requirements and degree of adjustability required.  Dexter’s expertise is in permanent and electro-magnets.  Applications requiring superconducting versions are not supported.  As such, fields in these devices are typically limited to 1 Tesla.

When used external to annealing ovens, thermal exposure must also be considered as significant heat can be transmitted from the oven to the magnet.  Proper insulation or spacing of the magnet is recommended.

Electoplating

Frequently, Permalloy films are electroplated onto a wafer during the manufacturing process of read/write heads.  Alignment of the Permalloy grains is critical to proper functionality of the final product.  By exposing the wafer to a magnetic field while in the plating bath, the grains are free to align themselves with the magnetic flux lines.   When removed from the plating bath, the film characteristics are pinned in a preferred direction of orientation  

These types of magnets are installed external to the plating bath.  These magnets can either be permanent or electromagnet depending on the field requirements and degree of adjustability required.  Fields in these devices are typically limited to 1 Tesla.

As a result of the plating environment, these magnets can be exposed to corrosive elements.  Proper plating and shielding of the magnets is critical to longevity of performance.

Sputtering

In process grain alignment of sputtered films can be critical to final performance of a product.  During the thin film deposition process, magnetically permeable materials are deposited onto a substrate.   If the sputtered atoms are exposed to a magnetically biased field during deposition, grain growth preferentially aligns with the magnetic flux lines.   Upon solidification, the film characteristics are pinned in a preferred direction of orientation.  

These types of magnets can be found either external to, or within sputter deposition system.  These magnets can either be permanent or electromagnet depending on the field requirements and degree of adjustability required.  Fields in these devices are typically limited to .1 Tesla.

As a result of the sputtering process, magnets located within the vacuum chamber typically require hermetic sealing to guarantee compatibility.  Electromagnets found within the vacuum chamber typically require active cooling to assure thermal control over Ohmic losses that are occurring in the convection free environment.

When working with our engineering group, you might be asked:

1.  What power output is required?

2.  What is the required voltage output? (AC/DC and Quantity)

3.  What is the maximum acceptable diameter?

4.  What is the maximum acceptable length?

5.  What is the maximum ambient temperature?

6.  What is the maximum ambient pressure?

7.  What is the desired configuration of your generator? Internal or external rotor?

8.  What is the operating rpm range of the generator?

9.  Will there be shock and vibration during operation?

10. What is the desired “life” of the generator?

  • Neodymium Iron Boron can be used for “low” temperature rotor applications.
  • Samarium Cobalt can be used for “high” temperature rotor applications.
  • In most applications, a ferrous material will be used for the base of the rotor.
  • The stator portion will be composed of magnet steel laminations which will be welded into a stack.
  • The lamination stack is commonly wound with copper wire.
  • In most applications, the rotor and stator are encapsulated with a thin sleeve of nonmagnetic metal.
  • The magnets of the rotor assembly are adhered to the base of the rotor.
  • The stator assembly is often “potted” with an epoxy which is application specific.

The design process for custom generators is very expensive and very timely.  Once all of the design criteria have been established, an initial stator laminate geometry, copper wire diameter and number of windings can be analyzed for power output through the use of Finite Element software.  This analysis will give an estimate of the diameter and length of the finished generator.  If the size constraints meet the customer’s requirements, a prototype can be manufactured.  If the size constraints do not meet customer requirements, diameter and length can be changed by increasing one of the variables to decrease the other. 

The manufacturing process begins with parallel paths for the rotor and stator assemblies.  The stator assembly is initiated with the purchase of a laminate stack.  Once received, the laminate stack is sent out to be wound with copper wire.  The rotor assembly process can begin when the magnets are completed.  The magnets are then adhered to the base.

Once the aforementioned steps have taken place, the custom generator may be tested internally to verify voltage output.  If the voltage output meets specification, the finishing manufacturing operations will be completed.  The steps involve epoxy filling of the stator assembly and laser-welding the nonmagnetic protective shields into place on both assemblies.

We will perform testing of prototypes as requested to meet customer specifications.  Some fixturing charges may apply.

Turnaround of the first prototype can range from 12 to 20 weeks.  Turnaround for production quantities of custom generators will very based on tooling and material lead times.