Actuators and Transducers are a well established use of electromagnetic fields, that are growing in importance due to the replacement of hydraulic systems by electromechanical devices. Their motion can be linear or rotary.
Actuator
Apply electrical power to a device => Causes motion
Transducer
Apply mechanical force to device creating movement => Causes electrical output
Actuator model
Applications:
- Accelerometer
- Galvanometer
- Load Cell
- Pressure Sensor
- Strain Gauge
- Loudspeaker
- Microphone
- Hydrophone
- Transponder
B shown on Actuator in open position
Movement in the system
There are two possibilities for movement in the system:
Moving coil
– Loudspeakers and microphones
– Coil sited in background DC magnetic field. Inject current in coil => Lorentz force. Move coil => Induces voltage in coil (Faraday’s law).
Moving armature
– More heavy duty
– Actuator. Current in coil => Armature moves to position of lowest reluctance. Return spring when current is removed
– Transducer. DC field => Flux linking coil changes when armature moves
Effect of magnetic saturation when closed
Simulation
Opera offers several levels of simulation for designing your actuator or transducer:
Basic characterization
– Non-linear material effects
– Force v or flux linkage v position
Dynamic simulations
– Mechanical coupling
– Circuits
– Eddy currents
– Advanced material models
displacement for anhysteretic vs hysteretic model for valve
Advanced material models
All ferromagnetic materials exhibit hysteresis in some degree. Frequently, it is a reasonable assumption that hysteresis can be ignored and that the nonlinear behaviour of a material can be characterized simply by its anhysteretic curve, because the hysteresis loop is narrow. However, with the
increasing use of power electronics in many applications hysteresis is becoming more important. Continual switching of operating point on the magnetic characteristic results in repeated traversal of minor loops. Consequently, it is becoming particularly important to obtain an assessment of the losses due to hysteresis when rapid switching is occurring. Opera includes the ability to model hysteretic materials under transient conditions using a B(H) trajectory-following algorithm. The user needs to supply data for only the major hysteresis loop. The algorithm uses a reconstruction technique to determine minor loops and turning points of the trajectory and to erase turning points when the magnetization of a material exceeds the previous excursion. The algorithm also correctly transfers to the saturated material curve beyond the end of the user data, in the same way as for anhysteretic materials in Opera. It calculates energy lost due to hysteresis, leading to losses. The performance depends on previous history:
– Additional losses
– “Latching” forces
Multiphysics
temperature rise in winding decreases electrical conductivity by 25%
Opera supports multiphysics simulations. The electromagnetic analysis can be automatically coupled to thermal and mechanical stress analyses. Thermal aspects can be important in an actuator; particularly the effect of temperature on winding resistance. In this case it is weakly coupled since electromagnetic and thermal time-constants differ by orders of magnitude.