Temperature-dependent Gilbert damping in Co2 FeAl thin films with different B2 ordering degrees

The temperature-dependent Gilbert damping in Co2FeAl thin film grown on a Pb(Mg1/3Nb2/3)O3-30%PbTiO3 substrate is investigated by the systematic measurement of physical property measurement system(PPMS) on a series of samples with different substrate temperatures. Varying the substrate temperatures from 350℃ to 500℃, the B2 ordering degrees of Co2FeAl thin films increase, which can lead the Gilbert damping to decrease, indicated by the field-sweep in-plane PPMS measurements. In addition, the measurement result of PPMS demonstrates that the Gilbert damping decreases first with measurement temperature decreasing down to about 150 K, then increases at a measurement temperature of ~ 50 K, and decreases again with the measurement temperature decreasing. There are two independent damping manners, namely bulk damping and surface damping, which contribute to the Gilbert damping. Moreover, the observed peak of Gilbert damping at ~ 50 K can be attributed to the spin re-orientation transition at the Co2FeAl surface, which is similar to the result of the effective magnetization as a function of measurement temperature. The result presents the evidence for further studying the Gilbert damping in Co2FeAl thin film.

Fall preventive gait trajectory planning of a lower limb rehabilitation exoskeleton based on capture point theory

We study the balance problem caused by forward leaning of the wearer's upper body during rehabilitation training with a lower limb rehabilitation exoskeleton. The instantaneous capture point is obtained by modeling the human-exoskeleton system and using the capture point theory. By comparing the stability region with instantaneous capture points of different gait phases, the balancing characteristics of different gait phases and changes to the equilibrium state in the gait process are analyzed. Based on a model of the human-exoskeleton system and the condition of balance of different phases, a trajectory correction strategy is pro-posed for the instability of the human-exoskeleton system caused by forward leaning of the wearer's upper body. Finally, the reliability of the trajectory correction strategy is verified by carrying out experiments on the Zhejiang University Lower Extremity Exoskeleton. The proposed trajectory correction strategy can respond to forward leaning of the upper body in a timely manner. Additionally, in the process of the center of gravity transferred from a double-support phase to a single-support phase, the ratio of gait cycle to zero moment point transfer is reduced correspondingly, and the gait stability is improved.