A closer
Look.

From a winding to linear motion: the solenoid actuator

A helical coil surrounds a sliding steel plunger. The open assembly reveals the coil former, return frame and spring so the magnetic and mechanical parts can be inspected separately.

Inside the assembly

Copper turns wrap a dark insulating tube between teal flanges. A steel return frame joins the ends behind the winding. The plunger extends through one end beside an exposed return spring; the fixed pole lies at the other end. This is a single static position.

Scientific explanation

Current in a solenoid creates an axial magnetic field. For a long air-core winding, the central field is approximately proportional to turns per unit length and current. An iron-core actuator changes that field through its material and air-gap geometry. The air-core relation is a starting point, not a prediction of this actuator’s force.

B

Approximate central field of a long air-core solenoid (T)

μ₀

Permeability of free space (H/m)

N, l, I

Turns, winding length (m) and current (A)

The equation assumes a long air-core coil away from its ends. Iron saturation, leakage, spring loading and the moving air gap require a separate actuator model.

Explore the model

1. Follow the winding around the insulating former.
2. Identify the fixed pole and the projecting plunger.
3. Compare the spring and return frame with the winding’s electrical terminals.

From geometry to engineering

Predicting travel and pull force needs a magnetic circuit or field solution, material data, spring stiffness, friction and a thermal duty cycle.