Surface Acoustic Wave Tactile Display

eveloping realistic tactile displays for virtual reality has been challenging. Tangible displays are increasingly important interfaces not only for augmenting the reality of computer graphics but also for conveying graphical information to persons with visual impairments. Researchers have used various actuators for displays such as miniature loud speakers , 1 a pin array, 2 pneumatic actuators, 3 and ultrasonic vibrators. 4 Researchers have also proposed methods based on the processing properties of human tactile information. Humans feel tactile sensations via mechanoreceptive units that are classified into four cat-egories—rapidly adapting I and II (RAI and RAII) and slowly adapting I and II (SAI and SAII), whose end organs are Meissner corpuscles, Pacinian corpuscles, Merkel cell-neurite complexes, and Ruffini endings , respectively. 5 Shinoda developed a tactile display that stimulates each mechanoreceptor selectively, using the human skin's elastic transfer property. 6 However, because the researchers didn't clarify the parameters that characterize roughness, rigidity, and material quality, they weren't able to show a principle for systematic control of tactile sensations by the previously mentioned devices. This resulted in using ad-hoc stimulation in the displays for creating particular sensations. Furthermore, the researchers didn't consider the mechanisms for the mechanoreceptors' motion. Clarifying the receptors' mechanical properties lets us obtain a more effective method for stimulating the processing system of human tactile sensation. Thus, in this article, we first analyze which skin deformations the RA-type mechanoreceptors detect. Based on the result of the analysis, we clarify a flow of tactile information from the objects' parameters to the receptors' deformation, which leads to a proposal for the surface acoustic wave (SAW) tactile display. In this section, we analyze the properties of mechanoreceptors and skin from the viewpoint of skin deformation to which the mechanoreceptors are sensitive. This analysis suggests the principle of the SAW tac-tile display. Meissner corpuscles, which have a relatively low characteristic frequency of about 40 Hz, are localized in the papillary dermis with a height of around 150 µm and a diameter of 40 to 70 µm. A structural feature is their coiled axons 7 on which Ca 2+ ion channels exist. 8 Guharay et al. 9 showed that a probability of general mechanosensitive ion channels being open depends on the energy of deformation expressed as U = K/2 ⋅ (∆A/A) 2 ⋅ A, where K is the channel's elastic modulus and A is the channel's size. Thus, we must analyze the axon surface's …