fig6

Figure 6. Facial skin-mounted strain sensors for SSIs. (A) Working principle of strain sensor-based SSIs. The left part of (A): Adapted from Ref. [119], under CC BY 4.0 license. Signals in the right part of (A): Adapted from Ref. [120], under CC BY 4.0 license; (B) SSIs enabled by resistive strain sensors for monitoring facial strain and DIC techniques for selecting sensing locations based on strain and displacement. Adapted with permission from Ref. [121], Copyright 2022, ACS; (C) SSIs enabled by biaxial resistive strain sensors for monitoring facial strain. Adapted from Ref. [120], under CC BY 4.0 license; (D) SSIs enabled by triboelectric sensors for monitoring facial movements. Adapted from Ref. [11], under CC BY 4.0 license. SSIs: Silent speech interfaces; DIC: digital image correlation.