主题：[讨论]微型扬声器、受话器仿真软件

Audio Transducers

The use of electromagnetic simulation software, with the benefit of end user command files, enables transducer engineers to balance the various design variables within a loudspeaker motor assembly, and to optimize the size and shape of its components. It may take as little as 10 minutes to see how changing a component’s geometry affects the magnetic performance of the whole, so it is relatively easy to investigate many different iterations and converge on an optimized design.

Static Field Analysis

A simple DC analysis of a motor assembly can be carried out using Opera-2d/st, taking into account the nonlinear material properties of the permanent magnets and low carbon annealed steel. The B field and flux lines can be studied and the flux leakage can be observed. The magnetic B field in the air gap is required to be as uniform as possible, but any non-uniformity is apparent as a variation of Bl(z) and b(z) = (Bl(z))²/R_e as the coil is moved between ±X_max, where l is the length of wire within the magnetic gap, and R_e is the DC resistance of the voice coil (W).

AC Analysis (Induced Currents)

When the coil is driven by a time varying current, eddy currents will be induced in the conducting parts of the motor assembly. This can have the effect of causing an additional variation on coil impedance with respect to displacement. This is due to the reaction field from the eddy currents. Modifications to the design (including copper and/or aluminum shorting rings) can help to overcome changes in inductance vs. position, L_e(z), and can be analyzed using Opera-2d/ac. To ensure correct predictions, the steel permeability is the DC value calculated in the DC analysis, including saturation effects.

Thermal Analysis (Temperature Rise)

The input current and the eddy current densities induced in the motor assembly will cause the operating temperature to rise. This can be analyzed using the thermal analysis software Opera-2d/th, where the voice coil and the eddy currents are the heat sources. Performing this coupled analysis leads to a prediction of the temperature distribution, ensuring the operating requirements are not exceeded.

Motion Analysis (Harmonic Distortions)

The DC and AC analyses can be used to predict instantaneous values of the DC and AC magnetic fields, or the eddy currents at a single frequency for a given coil position. A full dynamic response can also be performed by modeling the movement of the coil with an AC signal present using Opera-2d/lm. As the current is switched on, the forces accelerate the coil. The displacement is then dependent on the forces and the damping in the system.

2D or 3D Analysis?

In many instances it is possible to perform the complete analysis using a 2D axi-symmetric simulation software. If there are significant 3D effects however, it may be necessary to run a complete 3D analysis. The static and time varying analyses can be performed using Opera-3d/Tosca and Opera-3d/Elektra. The thermal design can then be performed using the Opera-3d/Tempo software, including steady state and transient temperature effects. The Opera-3d/Modeler allows simple model creation for all the Opera-3d modules.