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Understanding the depolarization of ferroelectric materials caused by external stimuli is critical for maintaining the aligned polarization states. Although thermal depolarization in poled materials is well established, the mechanisms of electric field-induced depolarization remain largely unexplored. In this study, we investigate the electrical depoling behavior of [001]-oriented rhombohedral Pb(Mg1/3Nb2/3)O3-PbTiO3 (PMN-PT) single crystals poled using direct current poling (DCP) and alternating current poling (ACP). We reveal that the ACP sample exhibits a lower reverse coercive field than the DCP specimen. We compare the effects of bipolar and unipolar electric fields applied in the reverse poling direction, analyzing the changes in permittivity and piezoelectric resonance. Piezoresponse force microscopy is employed to characterize domain configurations in poled and electrically depoled samples. Our findings suggest that property degradation may arise from the nucleation and growth of domains oriented opposite to the initial arrangement. 

Functional electrical stimulation (FES) is a vital method in neurorehabilitation used to reanimate paralyzed muscles, enhance the size and strength of atrophied muscles, and reduce spasticity. FES often leads to increased muscle fatigue, necessitating careful monitoring of the patient’s response. Ultrasound (US) imaging has been utilized to provide valuable insights into FES-induced fatigue by assessing changes in muscle thickness, stiffness, and strain. Current commercial FES electrodes lack sufficient US transparency, hindering the observation of muscle activity beneath the skin where the electrodes are placed. US-compatible electrodes are essential for accurate imaging and optimal FES performance, especially given the spatial constraints of conventional US probes and the need to monitor muscle areas directly beneath the electrodes. This study introduces specially designed body-conforming US-compatible FES (US-FES) electrodes constructed with a silver nanowire/polydimethylsiloxane (AgNW/PDMS) composite. We compared the performance of our body-conforming US-FES electrode with a commercial hydrogel electrode. The findings revealed that our US-FES electrode exhibited comparable conductivity and performance to the commercial one. Furthermore, US compatibility was investigated through phantom and in vivo tests, showing significant compatibility even during FES, unlike the commercial electrode. The results indicated that US-FES electrodes hold significant promise for the real-time monitoring of muscle activity during FES in clinical rehabilitative applications.