All-fiber piezoelectric-friction composite nanogenerator for wearable human body posture monitoring

Fabrics have become a very popular device base material for interdisciplinary research in materials science and electronics due to their good stretchability, flexibility and wearing comfort. In recent years, smart fabrics have become the cornerstone of the device's leap from “wearable” to “wearable”. With the rapid development of smart fabrics, the research of fabric-based wearable nano-generators has received more and more attention. The related research work has made great progress, but the fabric-based wearable nano-generator still has the disadvantages of being difficult to balance the functionality, wear comfort and high-performance output, which restricts its application in a wider range of fields. .

Summary of results

Recently, Professor Zhang Qinghong from the Donghua University, Professor Zhang Xiaosheng from the University of Electronic Science and Technology, and Professor Juergen Brugger from the Federal Institute of Technology in Lausanne, Switzerland (co-author) jointly proposed a fabric-based wearable friction-piezoelectric composite nanogenerator. (Tribo-piezoelectric nanogenerators, TPNG) not only have excellent output performance, but also enable self-energy detection for human movements. The related research results are titled "All-fiber hybrid piezoelectric-enhanced triboelectric nanogenerator for wearable gesture monitoring" and published in Nano Energy, an important journal in the field of nanoscience and technology. Doctoral student Guo Yinben is the first author of the paper. The work on the conductive fabric substrate by electrospinning method to prepare silk fibroin nanofibers and polyvinylidene fluoride (PVDF) nanofibers constitute the poles of TPNG, the fiber membrane has good gas permeability, greatly increasing the wearability of the device. Comfort. Thanks to the excellent piezoelectric properties of polyvinylidene fluoride, the authors optimized the relationship between triboelectric and piezoelectric properties through in-depth theoretical analysis of the working mechanism of the device to obtain mutually enhanced output performance. In addition, the TPNG has two operating modes (separate mode and integrated mode) and is tested for output performance. In split mode, the highest output voltage, current, and power of TPNG are 500 V, 12 μA, and 0.31 mW/cm2, respectively. In the integrated mode, TPNG can be worn on the body, output different electrical signals to different actions of the human body, and achieve the purpose of human motion recognition. In addition, the authors connected the device to a micro cantilever-based MEMS switch circuit to design a self-powered human fall alarm system. When the wearer falls, the alarm system immediately alerts the pre-set receiving mobile phone to get timely assistance. Therefore, this smart fabric device has important application prospects in the field of self-powered wearable human health monitoring.

Graphic guide

Figure 1: Schematic diagram of TPNG structure and its working principle

(a) Schematic diagram of all-fiber TPNG;

(b, c) Electron micrographs of silk fibroin and PVDF nanofibers;

(d) Schematic diagram of the working principle of TPNG.

Figure 2: Interaction between triboelectric effect and piezoelectric effect

(a, b) when the piezoelectric current is in the same direction as the friction current, the outputs are mutually enhanced;

(c, d) When the piezoelectric current is reversed from the friction current, the outputs weaken each other.

Figure 3: Actual output voltage of TPNG and its finite element analysis

(a, b) finite element simulation of the TPNG output voltage of a PVDF film with different polarization directions;

(c) the output voltages are mutually enhanced;

(d) The output voltages weaken each other.

Figure 4: Effect of different spinning conditions on device output

(a, b) XRD patterns and corresponding output voltages of PVDF nanofibers prepared by applying different voltages in electrospinning;

(c,d) Thickness values ​​and corresponding output voltages of PVDF nanofibers electrospun at different times.

Figure 5: TPNG output performance and its self-powered detection of bending

(a) TPNG output voltage;

(b, c) output voltage, current, and power of the device under different matching loads;

(d) the output voltage when the TPNG is bent at different angles;

(e) When the TPNG is attached to the elbow, the elbow bends the output voltage at different angles;

(f) TPNG is used to collect the energy of the human hand and drive the test chart of the LCD.

Figure 6: TPNG-based self-powered fall remote alarm system

(a) Schematic diagram of a remote fall alarm microsystem based on TPNG and microcantilever;

(b) Real-time operational test chart of the self-powered fall remote alarm system;

(c-e) TPNG collects test charts of the daily energy of the human body such as swing, sliding and impact.

summary

In this work, high specific surface area silk fibroin and PVDF nanofibers were prepared on a conductive substrate by electrospinning. Through the theoretical research and simulation of triboelectric and piezoelectric working principle, a piezoelectric-triboelectric hybrid nanogenerator with high output performance is prepared. Its maximum output voltage, current and power are 500 V, 12 μA and 0.31 mW/cm2, respectively. In addition, the flexibility and tailorability of TPNG allows it to be designed as a key part of a microsystem that is easy to integrate into apparel. The self-powered micro-system not only recognizes different types of movements of the human body and collects energy, but also can send remote alarms in real time when the human body accidentally falls, so that the wearer can get timely assistance, and has a good application in the field of wearable health monitoring. potential.