Evaluation of the Surface Properties of Hair with Acoustic Emission Analysis.

OBJECTIVE The tactile sensation of hair is an important consumer-perceivable attribute. There are limited instrumental options to measure the haptic properties of hair. In this study, we introduce a novel technique using the acoustic emissions produced when skin comes in contact with dry hair in a stroking motion. METHODS Using a free-field microphone with a frequency response of 8-12,500 Hz, we recorded acoustic emission data of the interaction of skin with hair. Data was captured with Electroacoustics Toolbox software and analyzed with Matlab. Acoustic emission profiles were generated allowing us to monitor the acoustic response at distinct frequencies. RESULTS Various experiments were conducted to develop this novel technique as a suitable measure to monitor the surface properties of hair. Increasing the normal force and velocity of the interaction led to an increase in acoustic emissions. We also examined the acoustic profile of hair that underwent chemical treatment. For example, bleached hair produced a much higher magnitude acoustic response than the corresponding virgin hair. On the other hand, hair conditioner systems mitigated the acoustic response. Finally, investigations of textured hair revealed that the three-dimensional structure of the hair fiber assembly and its ability to return to its original state when perturbed produce the most dominant acoustic response for this type of hair. CONCLUSION We introduce a cutting-edge method to reproducibly evaluate the surface properties of hair. Different types of hair geometry produce unique acoustic profiles as do hair types that experience harsh damaging treatments. This is also a very practical and efficient way to evaluate the degree of protection or conditioning of the fiber.