2.5 Applications of IEAR

2.5.1 Robotic fin

We first design a robotic fin (89.2 g) composed of two Double Bellows and a PVC sheet to verify our IEAR mechanism for applications in soft robotics (Figure 4a-f, Supplementary Note 5, and Movie S6). In an underwater experiment, the robotic fin swings and drags the PVC sheet to produce propulsion force, which fluctuates with different magnitudes and periods in real-time (Figure 4c). Experimental results show that, compared with DIDO for the full range of \(p_{high}\) , IEAR has a markedly higher swinging frequency and average propulsion force (Figure 4d, e), and the energy consumption with IEAR is significantly reduced (Figure 4f). For instance, when \(p_{high}\)  =75 kPa, the swinging frequency, average propulsion force and energy consumption with DIDO are 0.41 ± 0.00 Hz, 0.19 ± 0.01 N, and 9.29 ± 0.08 mWh·cycle-1, respectively. In contrast, the corresponding actuation performance with IEAR is 0.76 ± 0.01 Hz (85.4%↑), 0.32 ± 0.01 N (68.4%↑), and 4.77 ± 0.04 mWh·cycle-1 (48.7%↓). These results mean the robotic fin can produce higher swimming velocity with energy-efficient IEAR when actuating underwater vehicles \cite{Yin.2016}. Moreover, we observe an extra beneficial effect of IEAR that the supplied air pressure \(p_{tank}\)  is improved, and the system power is reduced simultaneously, which performs conducive factors in high-speed and high-efficiency actuation (Figure S8a-c).