Numerical modelling and optimization of an electronic system embedded in multi-layered viscoelastic materials under shock loads

Presented here is the use and optimization of mutli-layer viscoelastic buffer materials to protect embedded electronic systems from high mechanical forces such as impacts. The test vehicle was a solid sports ball, Figure 1. The embedded system was first encapsulated using standard epoxy encapsulant, then further encapsulated with two different buffer materials (a soft and a hard rubber) before the entire system was embedded in the ball. The ball (from the Irish game of hurling) has an original polyurethane/cork core encased in a leather outer skin and is 70 mm. in diameter and weighs 110g. The multi-layer buffering system reduces the imposed stress on the epoxy-encapsulated embedded system, so that the stress transmitted to the electronics is significantly reduced. From this point of view, the stress experienced at the embedded system edge was taken as the objective function to be minimized within the overall constraint that the modified ball must closely retain its original size, weight and “bounce” i.e. its Coefficient of Restitution (CoR). This is a specific example of the more general embedded systems problem of embedding, say, a system such as a wireless sensor node in a material or structure without significantly changing the material or structure mechanical properties and reliability. A numerical model, using ANSYS 11.0, was developed and used in a simulation-based designed experiment of eight runs. The element SOLID92 was used to model the plastic and electronic structures. The optimized multilayered structure reduced the stress on the embedded system by 50% in comparison to the original un-buffered structure and reduced stress by 25% in comparison to the non-optimized buffer system. The optimized structure was within 90% of the original one for weight and 85 % for CoR. This work has defined a design methodology for buffer layers that significantly increase the protection of embedded electronic systems from high mechanical forces without major impact on the host object mechanical properties. The methodology is particularly applicable to the mechanical design of smart objects and structures.