Designing best-in-class impact-tolerant cellular phones and other portable products

In this paper, we detail our use of analysis and high-speed video photography in making Lucent Technologies cellular phones be best-in-class in impact tolerance, a much desired attribute. We show that the thin-walled clamshell case construction currently favored due to its size and weight advantages may not provide sufficient rigidity to withstand impact-induced loads, which can cause the housing to separate or open up when dropped. We present a simple method for increasing case rigidity — castellation of the housing interface to prevent slipping of the case halves — that can substantially improve a cell phone's drop tolerance. Implementation of variations of this technique in existing cell phone designs allows the phones to surpass their drop survivability requirements. In addition, we show that the traditional construction method for cell phone battery packs could lead to fracturing of the battery housing in a drop due to the multiple impacts that result. We describe a simple remedy — immobilization of the battery cells within the housing — that dramatically improves the battery pack's drop performance.