Xiaoliang Chen

Self-powered flexible pressure sensors with vertically well-aligned piezoelectric nanowire arrays for monitoring vital signs

Human vital signs such as the heartbeat and respiration are important physiological parameters for public health care. Precisely monitoring these very minute and complex time-dependent signals in a simple, low-cost way is still a challenge. This study shows a novel fabrication of vertically well-aligned piezoelectric nanowire arrays with preferential polarization orientation as highly sensitive self-powered sensors for monitoring vital signs. The process realizes in situ poling of the P(VDF-TrFE) nanowires within the nanopores of the anodized aluminium oxide (AAO) template to yield a preferential alignment of both nanowires and the polymer chains required for superior sensitivity in one step. The resulting self-powered flexible sensor shows high sensitivity, good stability and strong power-generating performance. Under bending conditions, the device exhibits a maximum voltage of ∼4.8 V and a current density of ∼0.11 μA cm−2. The fabricated self-powered sensor shows a linear relationship of output voltage versus compressive force with a high sensitivity, and the piezoelectric voltage of the P(VDF-TrFE) nanowire array is enhanced 9 times that of conventional spin-coated bulk films. Furthermore, the highly sensitive vertically well-aligned nanowire array can be applied as a self-powered sensor for detecting some tiny human activities including breath, heartbeat pulse, and finger movements, which may possibly serve for medical diagnostics as sensors, robotics and smart electronic devices.

High‐Performance Piezoelectric Nanogenerators with Imprinted P(VDF‐TrFE)/BaTiO3 Nanocomposite Micropillars for Self‐Powered Flexible Sensors

Piezoelectric nanogenerators with large output, high sensitivity, and good flexibility have attracted extensive interest in wearable electronics and personal healthcare. In this paper, the authors propose a high-performance flexible piezoelectric nanogenerator based on piezoelectrically enhanced nanocomposite micropillar array of polyvinylidene fluoride-trifluoroethylene (P(VDF-TrFE))/barium titanate (BaTiO3 ) for energy harvesting and highly sensitive self-powered sensing. By a reliable and scalable nanoimprinting process, the piezoelectrically enhanced vertically aligned P(VDF-TrFE)/BaTiO3 nanocomposite micropillar arrays are fabricated. The piezoelectric device exhibits enhanced voltage of 13.2 V and a current density of 0.33 µA cm-2 , which an enhancement by a factor of 7.3 relatives to the pristine P(VDF-TrFE) bulk film. The mechanisms of high performance are mainly attributed to the enhanced piezoelectricity of the P(VDF-TrFE)/BaTiO3 nanocomposite materials and the improved mechanical flexibility of the micropillar array. Under mechanical impact, stable electricity is stably generated from the nanogenerator and used to drive various electronic devices to work continuously, implying its significance in the field of consumer electronic devices. Furthermore, it can be applied as self-powered flexible sensor work in a noncontact mode for detecting air pressure and wearable sensors for detecting some human vital signs including different modes of breath and heartbeat pulse, which shows its potential applications in flexible electronics and medical sciences.

A Flexible Piezoelectric-Pyroelectric Hybrid Nanogenerator Based on P(VDF-TrFE) Nanowire Array

The piezoelectric and pyroelectric effects are well known and have been widely used for energy harvesting and self-powered sensing systems. This paper presents a high performance piezoelectric-pyroelectric hybrid nanogenerator based on P(VDF-TrFE) nanowire array that is capable of simultaneously harvesting mechanical and thermal energies. The nanowire array was synthesized by nanoimprinting P(VDF-TrFE) polymer into anodic aluminum oxide (AAO). The ferroelectric β crystalline phase of the aligned P(VDF-TrFE) nanowires has been demonstrated by Fourier transform infrared spectrum and X-ray diffraction measurements. Under periodic mechanical bending, electric signals are repeatedly generated from the hybrid nanogenerator and the measured piezoelectric output reach 4.0 V/65 nA. The cyclic bending-releasing process and impacts of strain rate on the electrical outputs are thoroughly characterized and analyzed. Besides, upon exposure of heat-cool condition with a temperature range of 8 K around room temperature, pyroelectric output up to 3.2 V/52 nA was obtained. There is a linear relationship between the output and the temperature difference across the device. Because the fast response time of 90 ms and high detected sensitivity of 0.8 K, the hybrid nanogenerator can also use as a self-powered temperature sensor. Finally, the piezoelectric and pyroelectric output voltages were successfully integrated together to obtain an enhanced output. These results demonstrate the great potential of the flexible hybrid nanogenerator for self-powered electronic devices.

Investigation of the role of template features on the electrically induced structure formation (EISF) for a faithful duplication

Electrically induced structure formation, as a physical approach to fabricate micro/nanostructures, has attracted much attention because of the simple process, low‐cost, high‐efficiency, and wide applications on electronics, microfluidics, and so forth. Hitherto, the influence of some process parameters, such as voltage, air gap, film thickness, polymer properties, on the polymeric behavior, and the structure formation has been explored, neglecting the effects of the template features, which affect the polymer deformation. Especially for the conductive protrusions directly contacting the polymer, the phenomenon of electric breakdown may occur, leading to a failure of structure formation. The limitation of the research on the template features triggers the necessity to study its influence for a faithful deformation. In this paper, three types of patterned template are studied based on the electric field at the air‐polymer interface, consisting of completely conductive template, partially conductive template, and dielectric template. Comprehensive consideration of the electric intensity for a sufficient driving pressure and the leaky current for preventing damaging the polymer, some guiding opinions on the template material and geometry can be provided to design the patterned template for the electrically induced structure formation process with a purpose for a faithful structure.

A Stretchable and Transparent Nanocomposite Nanogenerator for Self-Powered Physiological Monitoring

Smart sensing electronic devices with good transparency, high stretchability, and self-powered sensing characteristics are essential in wearable health monitoring systems. This paper innovatively proposes a stretchable nanocomposite nanogenerator with good transparency that can be conformally attached to the human body to harvest biomechanical energy and monitor physiological signals. The work reports an innovative device that uses sprayed silver nanowires as transparent electrodes and sandwiches a nanocomposite of piezoelectric BaTiO3 and polydimethylsiloxane as the sensing layer, which exhibits good transparency and mechanical transformability with stretchable, foldable, and twistable properties. The highly flexible nanogenerator affords a good input-output linearity under the vertical force and the sensing ability to detect lateral stretching deformation up to 60% strain under piezoelectric mechanisms. Furthermore, the proposed device can effectively harvest touch energies from the human body as a single-electrode triboelectric nanogenerator. Under periodic contact and separation, a maximum output voltage of 105 V, a current density of 6.5 μA/cm2, and a power density of 102 μW/cm2 can be achieved, exhibiting a good power generation performance. Owing to the high conformability and excellent sensitivity of the nanogenerator, it can also act as a self-powered wearable sensor attached to different parts of the human body for real-time monitoring of the human physiological signals such as eye blinking, pronunciation, arm movement, and radial artery pulse. The designed nanocomposite nanogenerator shows great potential for use in self-powered e-skins and healthcare monitoring systems.

Nanowire-based flexible P(VDF-TrFE) nanogenerator for simultaneously harvesting mechanical and thermal energies

This paper presents a high performance flexible nanogenerator based on P(VDF-TrFE) nanowire array that is capable of simultaneously harvesting mechanical and thermal energies. The nanowire array was synthesized by template-wetting P(VDF-TrFE) polymer into anodic aluminum oxide. The oriented β crystalline phase of the aligned P(VDF-TrFE) nanowires formed from nanoconfinement in AAO template nanoporous has been demonstrated by Fourier transform infrared (FT-IR) spectrum and X-ray diffraction (XRD) measurements. Under periodic mechanical bending, electric signals are repeatedly generated from the hybrid device and the measured output voltages reach 5.6V. Besides, upon exposure heat-cool condition with a temperature range of 7 K around room temperature, pyroelectric output up to 3.0V/50nA was observed and used to directly drive a LCD screen. Finally, the piezoelectric and pyroelectric output voltages were successfully integrated together under application of mechanical tapping and thermal irradiation at the same time. These results demonstrate the great potential of the flexible hybrid nanogenerator for self-powered electronic devices.