Failure Mechanisms of Balanced Armature Receivers under Drop and Shock Loading Conditions

Failure Mechanisms of Balanced Armature Receivers under Drop and Shock Loading Conditions

Haayen, Bas (TU Delft Mechanical, Maritime and Materials Engineering)

Delft University of Technology

Biomedical Engineering

2023-09-15

Balanced armature receivers are electroacoustic transducers that are mostly integrated in hearing aids or pro audio products. The balanced armature receiver is a key component for hearing aids as it converts the processed electrical signal into sound waves. Failure of the balanced armature receiver are problematic for the end user. The receivers are tested under shock loading conditions. But in order to understand the failure mechanisms that arise, it is important to gain insight in the mechanical response of the structure. A combination of Finite Element Analysis, experiments and measurements will help understanding the failure mechanisms in more depth what will lead to creating more robustness which has value for the end used.
It is important to understand how mechanical shock loads affect the receiver. The performance is measured as sound pressure output and Total Harmonic Distortion (THD) before and after shocking the receiver at different acceleration levels. To properly study the impact analysis of the receiver and building virtual prototypes it is essential to have a controlled shock environment suitable for repeatability. A half sine pulse is derived from the measurement results of the impact test set-up. The explicit finite element software, Ansys LS-Dyna, is used to model the shock wave during impact. In parallel, different experiments and measurements are performed to gain confidence in the FE models. One of the major challenges in measuring impact responses in this study is the size and the closed casing of the receiver. It is possible to test difference components separately to gain confidence. The armature is tested separately for its eigenfrequencies and mode shapes. The deformation of the membrane is measured before and after shock via an optical profiler.

The results of the FE models indicate that two components, the armature and membrane, are
the most prone to damage. To highlight the critical regions, a high input acceleration of 19000 [g] is applied in the FE model. The von Mises stress in the hinges of the membrane exceed the yield criteria, which leads to plastic strain which results in a permanent deformation of approximately 25 𝜇m in the hinge. The armature experience high stresses beyond the yield criteria in the hinge region and around the drive pin. The result of these plastic deformations lead to an increase in the total harmonic distortion.

The virtual prototype with a 50 𝜇m thicker membrane resulted in a more robust response. The internal
energy, energy stored due to deformation, and plastic strain in the hinges has decreased. The improved robustness does decrease the sound pressure output. Adding shock plates between the permanent magnets and the armature resulted in a decrease of internal energy. The maximum contact force between the armature against the magnets went down with almost 20%. Changing the material of the shock plates to Rubber Nitrile provided more improvement of the robustness of the balanced armature receiver.

Finite Element Analysis
Balanced Armature Receivers
Drop and Shock Loading Conditions
failure mechanisms

http://resolver.tudelft.nl/uuid:56acd186-75a8-4109-a56d-ba411433c297

2024-09-16

Student theses

master thesis

© 2023 Bas Haayen