TABLE II. Comparison Between Different Types of Stretchable and Electrically Conductive Sensors.

Reference	Type of sensor	Hysteresis	Detection of only bending	Sensor position	Evaluation metrics(Static test)	Evaluation metrics (Dynamic test)
Mengüç et al. [17]	Resistive			Hip, knee, and ankle	Electrical hysteresis percentages (and linearity ratios) of 7.8% (0.77 linearity), 3.9% (0.91), and 4.3% (0.92) for the hip, knee, and ankle (mechanical loading and unloading)	RMSE < 5° (Walking at 0.89 m/s for 60 s) RMSE < 15° (Running at 2.7 m/s for 60 s)
Oubre et al. [30]	Resistive (potentiometer)			Knee		RMSE = 5.0 ± 1.0° MAE = 3.9 ±0.8° (Walking at three different self-selected speeds)
Wood et al. [28]	Resistive			Knee		The average RMSE = 7.6° (Knee flexion-extension movements and walking)
Tognetti et al. [13]	Resistive (Double-layer)		✓	Knee	Maximum standard deviation = 5100 Ω, corresponding to an angular error of 5.3° (quasi-static flexion test in the 0–90° range)	Maximum error = 5.0° (Knee flexion-extension movements)
Nakamoto et al. [26]	Capacitive	✓		Knee and ankle	R2 = 0.9993 (stretching test in the 30–70 mm range)	Mean error = 4.4 ± 3.6° (knee flexion-extension movements)
Li et al. [27]	Capacitive	✓		Ankle	R2 = 0.9991 (bending test in the 0–90° range)	RMSE < 3.0° (Horizontal and descending walking for 90 s) RMSE < 5.0° (Ascending walking for 90 s)
Totaro et al. [24]	Capacitive (Shielding)	✓		Knee and ankle	Linear behavior in the entire range (tensile test)	RMSE < 4.0° (Ten knee flexion/extension in the 0–90° range)
This work	Capacitive (Double-layer and shielding)	✓	✓	Knee	RMSE = 3.1° (bending test in the 0–130° range) RMSE = 2.9 ± 0.2° (robotic arm bending test in the 20–120° range at 16 rpm) RMSE = 3.0 ± 0.1° (robotic arm bending test in the 20–120° range at 32 rpm) RMSE = 3.5 ± 0.2° (robotic arm bending test in the 20–120° range at 48 rpm)	RMSE < 7.0° (Cycling experiment for 10 min)