Mechanism Models of the External Ear Shape-Structure Factors

A comprehensive ergonomic and anthropometric investigation is presented into the morphological characteristics, deformation behavior, and wear comfort mechanisms of the external ear, encompassing both the auricle and the external acoustic meatus (EAM). To address the limitations of conventional static measurements, deformation ratio is introduced as a normalized metric for quantifying tissue deformation under compressive and expansive loads induced by ear-worn and in-ear devices. Through controlled deformation experiments combined with comfort perception scaling, deformation-comfort models are established to identify comfort thresholds and perceptual limits for key auricular and EAM parameters. Analysis of data from a large, demographically stratified adult population indicates that deformation ratios of major auricular dimensions are not significantly influenced by sex, age group, or laterality, supporting the use of pooled predictive models. For the EAM, where direct measurement of cross-sectional circumference and area is restricted by anatomical accessibility, rapid estimation methods based on elliptical approximation and regression fitting are proposed and validated with high accuracy. In addition, persistent and phasic age-growth models are developed to describe lifespan-related changes in auricular and canal dimensions. By integrating morphology, deformation mechanics, comfort perception, and age-related growth patterns, this chapter provides a quantitative foundation for the ergonomic design, evaluation, and long-term adaptation of ear-related wearable devices.