The effect of a metal shell on the launch efficiency of an asynchronous coil launcher (coil AC pulse linear motor) remains insufficiently understood in terms of the underlying mechanisms and principles. To address this gap

this study conducted extensive modelling simulations and calculations

varying the shell's conductivity

permeability

and dimensions. Through comparative analysis of these models

this paper identifies a unique ‘tick-shaped efficiency curve’ for the asynchronous coil launcher: the launch efficiency first decreases and then increases as the shell's electromagnetic parameters are enhanced. Enhancements that bolster the electromagnetic induction effect within the shell—such as increased conductivity

permeability and dimensions—are termed as the augmentation of electromagnetic parameters. This study delves into Lenz's law of electromagnetism to elucidate the observed phenomena

attributing them to the spatio-temporal force characteristics of the multi-peak and multi-valley armature of the transmitting device

and the resulting ‘tick-shaped efficiency curve’. A comprehensive summary of shell-related research in electromagnetic emission reveals that the driving current fundamentally dictates the shell's impact on launch efficiency. DC-driven launchers conform to the monotonic effect efficiency curve

whereas AC-driven launchers conform to the tick-shaped efficiency curve.