Fig. 5. Control experiment of silent word recognition using EMG.

a–c Schematics (top) and photographs (bottom) of three epidermal sEMG electrodes with different electrode dimensions. The exposed contact areas of small-sized (a), medium-sized (b), and large-sized (c) electrodes are ~0.1, ~5.5, and ~22.3 mm², respectively. Other than the exposed contact area is encapsulated with a polyimide layer. Inset in (a, bottom): magnified optical image of small-sized electrode; scale bars, 1 mm (a, b) and 1.5 mm (c). d–f Raw EMG signals of three sEMG electrodes while the subjects clench their jaw tightly with electrodes attached to the buccinators. Insets: magnified views of noise part. g Confusion matrix of the result of silent 100 words recognition using our small-sized EMG sensor (four channels with eight electrodes on buccinators, levator anguli oris, depressor anguli oris, and anterior belly of digastric) with the recognition rate of 42.60%. A total of 100 datasets are acquired, 46 of which are from Subject A and 54 are from Subject B. h, t-SNE of the total 100-word classification.