An Integrated Self-Powered Real-Time Pedometer System with Ultrafast Response and High Accuracy

Synthesis of shape-tunable PbZrTiO3 nanocrystals with lattice variations for piezoelectric energy harvesting and human motion detection

PbZr0.7Ti0.3O3 cubes with tunable sizes and cuboids have been hydrothermally synthesized. PbZrTiO3 cubes with three different Zr : Ti atomic percentages were also prepared. Analysis of synchrotron X-ray diffraction (XRD) patterns reveals the presence of two lattice components for these samples. Fast Fourier Transform (FFT) processing of high-resolution transmission electron microscopy (HR-TEM) images shows discernible lattice spot differences between the inner bulk and surface layer region for a PbZr0.7Ti0.3O3 cube, while a cuboid has distinct lattice spot deviations. The lattice variations yield different dielectric constant numbers for these two samples, despite being bound by the same crystal faces. The PbZrTiO3 crystals give size- and composition-dependent band gaps. Cuboids show notably larger piezoelectric and ferroelectric responses than cubes. Piezoelectric nanogenerators (PENGs) containing 30 wt% cuboids produce the highest open-circuit voltage of 20.36 V and short-circuit current of 2300 nA. The PENGs harvest energy through bending/releasing cycles to power devices and show photothermal pyroelectric activity. Moreover, a single 30 wt% cuboid PENG device integrated into a shoe insole can deliver an impressive 96.8% accuracy for human motion detection using a machine learning approach. This work illustrates that considerable lattice variation through crystal shape control is effective in enhancing material properties.

Capacitive Pressure Sensor Combining Dual Dielectric Layers with Integrated Composite Electrode for Wearable Healthcare Monitoring

Foot activity can reflect numerous physiological abnormalities in the human body, making gait a valuable metric in health monitoring. Research on flexible sensors for gait monitoring has focused on high sensitivity, wide working range, fast response, and low detection limit, but challenges remain in areas such as elasticity, antibacterial activity, user-friendliness, and long-term stability. In this study, we have developed a novel capacitive pressure sensor that offers an ultralow detection limit of 1 Pa, wide detection ranges from 1 Pa to 2 MPa, a high sensitivity of 0.091 kPa-1, a fast response time of 71 ms, and exceptional stability over 6000 cycles. This sensor not only has the ability of accurately discriminating mechanical stimuli but also meets the requirements of elasticity, antibacterial activity, wearable comfort, and long-term stability for gait monitoring. The fabrication method of a dual dielectric layer and integrated composite electrode is simple, cost-effective, stable, and amenable to mass production. Thereinto, the introduction of a dual dielectric layer, based on an optimized electrospinning network and micropillar array, has significantly improved the sensitivity, detection range, elasticity, and antibacterial performance of the sensor. The integrated flexible electrodes are made by template method using composite materials of carbon nanotubes (CNTs), two-dimensional titanium carbide Ti3C2Tx (MXene), and polydimethylsiloxane (PDMS), offering synergistic advantages in terms of conductivity, stability, sensitivity, and practicality. Additionally, we designed a smart insole that integrates the as-prepared sensors with a miniature instrument as a wearable platform for gait monitoring and disease warning. The developed sensor and wearable platform offer a cutting-edge solution for monitoring human activity and detecting diseases in a noninvasive manner, paving the way for future wearable devices and personalized healthcare technologies.

Laminated Triboelectric Nanogenerator for Enhanced Self-Powered Pressure-Sensing Performance by Charge Regulation

Triboelectric sensors provide an effective approach to solving the power supply problem for distributed sensing nodes. However, the poor stability and repeatability of the output signal limit its further development due to structural deficiencies and intrinsic working mechanisms. This work proposes a contact-separation mode laminated triboelectric nanogenerator (L-TENG) by introducing multifunctional layers to regulate triboelectric charges. A liquid metal Galinstan and PDMS mixture with a dense microstructure array is fabricated as the dielectric layer. Liquid squalene is filled in the space between two triboelectric layers to eliminate the influence of moisture in the air. A Cu shield film is sputtered on the surface to screen the electrostatic interference and enhance the repeatability. Owing to the effective design, the sensitivity of the L-TENG could reach 6.66 kPa^-1 in the low-pressure region and 0.79 kPa^-1 in the high-pressure region with a wide detection range from 8 Pa to 71.85 kPa. In addition, it also illustrates fast response and recovery times of 30 and 10 ms, respectively, and great stability in a humid environment. Finally, the L-TENG has been successfully demonstrated to monitor various physical activities in humans such as swallowing, finger bending, and so forth. This work has important scientific significance in opening up a new strategy for the structure optimization and performance improvement of triboelectric sensors.