What Is an Electromagnetic Actuator?

Magnetic actuators can be divided into Lorentz force types and bipolar types. Magnetic actuators are driven by magnetic field forces generated by electromagnetic or permanent magnets. There are many forms of magnetic actuators: magnets can be divided into permanent magnets and electromagnetics. ^[1]

Magnetic actuators are driven by magnetic field forces generated by electromagnetic or permanent magnets. According to the source of magnetic force, magnetic actuators can be divided into Lorentz force type and bipolar type. The type of Lorentz force is that the current inside the actuator generates Lorentz force to the external output power under the action of an external magnetic field (generally a fixed magnetic field). Generally, it is not necessary to integrate a magnetic thin film material in a microactuator, which is relatively easy to manufacture; bipolar The sub-actuator is the force generated by the magnetic material inside the actuator under an externally changing electric field, and it is necessary to manufacture a magnetic material. According to the displacement direction of the actuator, magnetic actuators can be divided into gap type and area type, as shown in Figure 1. The displacement direction of the gap type actuator is perpendicular to the gap, and the overlapping area does not change during the operation. The spacing changes. The movement direction of the area type magnetic actuator is perpendicular to the pitch direction. The pitch does not change during the operation, and the overlap area changes. In macro magnetic actuators, because the magnetic resistance of the magnetic circuit gap is much larger than the magnetic resistance of the magnetic core itself, the magnetic field energy is almost concentrated at the gap. In micro-actuators, the magnetic core reluctance is equivalent to or even greater than the gap reluctance, so the magnetic field can be distributed over the entire core and gap. When the magnetic field energy of the magnetic core and the magnetic field energy of the gap are equal, the magnetic actuator can output the maximum energy and driving force.

According to some important principles of magnetic execution, magnetic fields can be used to generate forces, moments or microstructure displacements: a driving magnetic field can act on a locust element, such as a current-carrying wire, an inductor, a magnetic material, or a magnetostrictive material.

The formula for calculating the magnetic interaction between the current-carrying wire and the magnetized magnetic material is discussed here.

The Lorentz force actuator uses the interaction of a current-carrying conductor and an external magnetic fieldthe Lorentz force on the moving charge with the most q charge is:

its

Is the velocity of the charge, and the magnitude of the force is:

Where is the angle between the speed and the magnetic field ( <180 °), and the direction of the force can be determined by a simple mnemonic method. Extend your right hand. The direction of the thumb points to the direction of positive charge movement. The other four fingers point to the direction of the magnetic field. The palm faces the direction of the force. The direction of the force is perpendicular to the direction of the charge movement and the direction of the magnetic field.

Magnetic actuators work through the interaction of permanent magnets and external DC magnetic fields. A typical example is the familiar compass (Figure 2). The permanent magnet used in the compass is a hard ferromagnetic material. If the internal and external magnetic lines of force are parallel, no force or moment will be applied to the compass. When the internal magnetization direction is not parallel to the local magnetic line of force, the compass will receive a moment (called magnetic force) Moment) effect. This torque causes the pointer to rotate until the internal magnetic field lines are parallel to the external magnetic field lines and stop: the principle of this interaction can be extended to microsensors and actuators. In fact, artificially bonded or integrated permanent magnet micromagnetic actuators have been developed. ^[2]

Micromagnetic actuators can be classified according to the type of magnet and the microstructure it contains.

The source of the magnetic field can be a permanent magnet, an integrated electromagnetic coil (with or without a magnetic core), or an external solenoid. Multiple sources of magnetic fields can be used in a mixed manner.

The microstructure that generates the force on the chip can be one of the following: a permanent magnet (hard magnet), a soft magnet, or an integrated electromagnetic coil (with or without a magnetic core).

Magnetic motor

The first example is a planar variable reluctance micromotor with a fully integrated stator and coil (Figure 3). The stator is made of an integrated electromagnet, while the rotor is made of a soft magnetic material. The motor has two sets of magnetic poles, one on the stator (it is usually wound with an excitation coil), and the other on the rotor.

image 3

When the phase coil is excited, the rotor poles close to the excited stator electrode will attract the stator poles (Figure 8-12a and Figure 8-12b). As the stator rotates, the stator poles will be aligned with the rotor poles. Turn off the current that excites the phase coil, and the next phase starts to excite and make it move continuously. In this design, the electrodes of all phases are arranged in pairs of opposite polarity, so that the path between adjacent plates is short: the stator coils arranged in one or more groups are sequentially excited to generate continuous rotor rotation. .

The rotor is 40 m thick and 500 m in diameter. It is assembled on a chip containing the stator or manufactured in an integrated manner by electroplating. When 500mA is applied to each stator, a rotation of 12 ° is generated (each incremental stroke). A three-phase 200mA current pulse is applied to the stator, and the speed and direction of the rotor are adjusted by the current frequency and phase switching sequence provided by the power supply. It can be observed that the continuous rotation speed of the rotor is as high as 500 rpm. The motor torque can be calculated at 500mA drive current is 3. 3nN · m-bow-folded magnetic core wire.

Use a ring-bent integrated induction element to generate magnetic flux in the motor. The multilayer core "wraps" around a flat curved wire (Figure 4 (c)). This structure can be considered as the result of exchanging the roles of wires and cores in traditional inductors (Figure 4 (d)). The manufacturing process starts with an oxidized silicon wafer (Figure 4). A 200 nm-thick titanium film is deposited as a plating seed (step b). Polyimide was spin-coated on the wafer to build an electroplating mold for the bottom layer of the magnetic core: a thick polyimide layer with a cured thickness of 12 m was obtained with four coats (step c). Cover the polyimide with an aluminum metal film, then apply photoresist and lithographically pattern. The photoresist is used as a mask for etching aluminum (in wet etching) and then as a mask for etching polyimide (in oxygen plasma) (step d). Inconel is grown at the window of the polyimide layer by electroplating and fills the window (step f).

Figure 4 (2 photos)

Spin-coat another polyimide layer to isolate the bottom core (step g). A 7 m thick metal layer (aluminum or copper) is deposited on top of the polyimide insulating layer and patterned (step i). Spin more polyimide on the patterned metal to flatten the wafer and isolate the bent conductors (step j). The polyimide layer was patterned using the same method as before (step k). Open the through hole all the way to the bottom core and electroplating to create the top core (step 1). ^[2]