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Page 8 of 11 Kim et al. Soft Sci 2024;4:12 https://dx.doi.org/10.20517/ss.2023.50

Figure 4. Examples of Coupled Mechanics in Haptic Systems. (A1-3) Haptic Interfaces across Large Areas of the skin optimized by the
[8]
investigation of deformation and wave propagation of the actuator using the combination of 3D-DIC and PTV . Copyright©2022,
Nature Publishing Group; (B1-3) Strain analyses of representative types of vibrotactile actuators on the phantom skin using 3D-DIC and
Triangular Cosserat Point Element method [28] . Copyright©2023, Elsevier. 3D: Three-dimensional; DIC: digital image correlation; PTV:
particle tracking velocimetry.

actuators use a direct current (DC) motor, typically rotating laterally, with an off-center mass connected to
the output shaft within a closed metal housing, whereas LRA and tactor actuators operate on alternating
current (AC) based on voice coils and magnets suspended on springs, typically vibrating vertically
[Figure 4B1]. Colored contours in Figure 4B2 and graphs in Figure 4B3 display strain distributions and
center line profiles induced by an ERM actuator and tactor at different depths of the skin phantom, h and
1
h , with various contact areas L/L , indicating their distinctive characteristics. The strain results induced by
2
0
the ERM actuator exhibit high magnitudes around the actuator’s border near the surface of the phantom
skin, with substantial in-plane components. In contrast, the peak strain induced by the tactor occurs at the
actuator’s center in-depth, oriented out of the plane of the skin. A combination of various types of
actuators, along with the studies of associated coupled mechanics, may be necessary to achieve robust and
sophisticated haptic sensations.

REMARKS AND FUTURE PERSPECTIVE
In conclusion, we have summarized the recent developments in computer vision methods and their
applications in skin-interfaced electronics. These methods are not limited to skin-interfaced electronics but
extend to other forms of soft or 3D electronics, including 3D passive microflying systems [29,30] ,