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A Guide to Magnetic Linear Couplers

Tube Style Magnetic Linear Coupler

Tube Style Magnetic Linear Coupler

In this third Tech Talk article in a five-part series about Magnetic Torque and Magnetic Linear Couplers, we take a closer look at Magnetic Linear Couplers.  Similar to a Magnetic Torque Coupler, a Magnetic Linear Coupler relies on the magnetic interaction between two coupler halves.  As in the Torque Coupler, usually one half is the driver, and the other half is the follower.  Linear Couplers are often simpler to design and to construct when compared to Torque Couplers because the movement is linear and non-rotational.

A Linear Coupler can be as simple as two magnets or more complex as to be comprised of engineered arrays containing multiple magnets of various configurations.  The operational gap between the coupler’s halves, the required coupling force, and the operating environment are the prime design variables.

There are many variations of Linear Couplers. The fundamental similarity is that the coupler’s “halves” are “linked” through a gap.  One “half” can propagate the other “half” without contact.  All of the common and unique designs for Linear Couplers try to minimize cost, increase performance, and make use of the application specific geometry.

One common style of Linear Couplers is simple magnets on a backing-plate.  The magnets are sized based on the gap and desired force to be transferred.  (As previously discussed, the larger the gap, the less magnetic flux linking will occur, and this results in a lower coupler force.)  The simplest design uses two magnets alternating NORTH – SOUTH.  The backing-plate connects the non-working faces of the magnets and increases the effective field in the gap, and therefore, the coupling force.

The magnet’s cross-sectional area, the magnetic length, the spacing between the magnets, the backing-plate alloy, and the backing-plate thickness are all variables in the design and need to be optimized for the needs of the particular application.

The two magnets per “coupler half” system can be expanded to three or more magnets per half to add additional coupling force.  The constraint is the available space and cost.

The second most common Linear Coupler style uses “steel poles” as the working areas and is used extensively in “round” applications, especially when pipes are employed.

True Radially Magnetized Ring

Ideally “radially” orientated magnets would be used for this geometry, but this orientation is very challenging to produce, is very expensive, and has limits on the OR and IR of the magnets.  More information about radially oriented magnets and other magnetizing options can be found here: Neodymium Magnetizing Options

To circumvent this limitation, axially-orientated magnets are used in conjunction with steel poles. This facilitates 360° coupling.  The magnets are “sandwiched” by the steel poles, and the magnet-steel pole pattern alternates to the required axial length.  The axial length of the coupler halves is the primary driver for the coupling force.

Similar to a Torque Coupler, this style of Linear Coupler has Inner and Outer array halves; however, there is no rotational coupling capacity.

We know that design, utility, and external variables are inextricably connected in many applications. Magnetic Linear Couplers are no different.  Please contact Dura Magnetics for design and selection.

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Did You Know?

Alnico is frequently specified but improperly used for sensor applications. See our Magnetic Sensors Page to ensure you are designing your sensor triggering application correctly.

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