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How Construction Affects Solenoid Force

How Construction Affects Solenoid Force

Solenoid force is greatly affected by how the solenoid – particularly in regard to the pole piece – is constructed.

Solenoid Force and Pole Geometry

The image below shows 4 different polepiece configurations for a solenoid. As the displacement increases moving from left to right, the magnetic reluctance (resistance to magnetic flux flow) is kept similar by making the polepiece angle smaller from flat to 30 degrees. The overall magnetic flux is similar in each case.

Solenoid Force Pole Piece Geometry Examples

Solenoid Force Magnetic Flux chart

The force developed by a solenoid is proportional to the vector quantity of magnetic flux flowing between the polepieces in the direction of the axis

For a flat polepiece device, almost all of the flux developed is aligned with the axis, force at short displacement is high, however as stroke increases, the airgap and reluctance increases, and overall flux and force decrease rapidly

For a shallow polepiece the flux flows at an angle to the axis, more flux flows in an extended position, but due to this angle the resulting force is less. The force developed is roughly proportional to the sine of this angle.

Push Pull Solenoids are designed to supply very high force at a short stroke.

Push-Pull-Solenoid-874 .GIFConstruction Considerations on Solenoid Force and Speed

From force and efficiency considerations, it is generally desirable to design geometry such that the gap between fixed base and moving plunger polepieces is located approximately in the centre of the solenoid coil, however there might be other considerations which make it advantageous to move the airgap.

For solenoid applications with very high speed requirement, it may be advantageous to make the plunger as short as possible to reduce moving mass and facilitate rapid acceleration.

For applications subject to high mechanical forces, a longer plunger may provide greater bonding / fixation length to achieve a stronger connection between plunger and shaft.


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