Lab Electrospinning System| Curvilinear Slit Electrodes and Orientated PAN-PVDFNanofibers: Synergistic Broadband and AcoustoelectricEnhancement for Multi-Mode Power Generation, SpeechRecognition, and Voice Recording
Views: 1973
Author: Nanofiberlabs
Publish Time: 2025-06-26
Origin: Bio-inspired acoustic-electric device
Inspired by the hypersensitive vibration sensing mechanism of the "slit sensilla" on scorpions' feet, Professor Lin Tong's team from the School of Textile Science and Engineering, Tianjin Polytechnic University, has proposed for the first time internationally an innovative design of a nanofiber multimodal acoustoelectric conversion device based on a bionic curved slit structure. This work achieves a breakthrough in the synergistic enhancement of three energy conversion mechanisms by bionically constructing a cross-scale coupling system of gradient curvature slit electrodes and highly oriented PAN-PVDF nanofiber membranes (Figure 1): (1) Piezoelectric dipole reconstruction triggered by periodic dislocation stretching of fibers induced by slit vibration; (2) Endogenous triboelectric self-enhancement effect; (3) Acousto-mechanical-electrical multi-physical field matching of oriented fibers, which significantly improves the broadband response and electrical output of the device (Figures 2 and 3). This acoustoelectric device supports multimodal acoustic energy generation and exhibits high-fidelity recording capability in voice recording (with a signal-to-noise ratio of 66.8 dB). Combined with a convolutional neural network (CNN), it achieves a 96% speech recognition accuracy (Figure 4). This research overcomes the technical bottlenecks of narrow frequency band and weak output of nanofiber acoustoelectric devices, providing a transformative solution for wearable acoustic sensors, passive IoT front-ends, and intelligent human-computer interaction systems.
The work was published in Advanced Functional Materials under the title "Curvilinear Slit Electrodes and Orientated PAN–PVDF Nanofibers: Synergistic Broadband and Acoustoelectric Enhancement for Multi-Mode Power Generation, Speech Recognition, and Voice Recording". Doctoral student Ma Xiangda and Dr. Jiang Peng from the School of Textile Science and Engineering are the co-first authors of the article, Professor Wang Hongxia and Professor Lin Tong are the corresponding authors, and Tianjin Polytechnic University is the sole corresponding unit. The research is supported by the National Natural Science Foundation of China.
Figure 1. Preparation and material characterization of bionic acoustoelectric device with curved slits and oriented nanofibers
The authors prepared highly oriented PAN-PVDF nanofibers (with diameters between 660–683 nm) using electrospinning technology and assembled them with electrodes of curved slit structure into an acoustoelectric device. TEM+EDS revealed the inhomogeneous distribution of the two polymer materials inside and on the surface of the fibers. PAN is enriched inside the fibers to form mutually isolated "island" phases, while PVDF forms an approximately continuous "sea" phase. Both components are exposed on the surface of the fibers, showing a phase-separated state. XRD and FTIR tests showed that the β-phase content of PVDF reaches 84%, and the zigzag configuration content of PAN reaches 76%.
Figure 2. Electrical output performance analysis of PAN-PVDF acoustoelectric device
The PAN-PVDF acoustoelectric device adopts a curved slit structure design, where the two ends of the oriented nanofibers are fixed, while the fibers inside the slits are suspended and exposed to the air. The vibration frequency of these nanofibers is determined by their angle relative to the electrodes, and the natural frequency is inversely proportional to the length of the fibers inside the slits. When the angle α is 90° and 0°, the exposed length of the fibers is shorter than that when α = 45°, thus showing a higher natural frequency. Practical tests confirmed that when the angle is 90°, the response performance of the device is the best, thus realizing the optimization of dynamic response through geometric parameters.
Experimental tests found that the PAN-PVDF device exhibits a stable response in the wide frequency acoustic spectrum range of 100–1300 Hz. Under the excitation of a sound source at 115 dB and 360 Hz, the open-circuit voltage of the device (with a working area of 12 cm²) reaches 87.85 V, the short-circuit current is 15.64 μA, and the power density is as high as 384 mW/m². The output performance is 4–5 times that of single-component PAN and PVDF nanofiber devices, and its comprehensive performance is better than all previously reported nanofiber acoustoelectric devices.
Figure 3. Electrical output enhancement mechanism of PAN-PVDF acoustoelectric device.
Finite element simulation results show that under the action of sound waves, four obvious asymmetric amplitude peaks and valleys are formed in the electrode regions on both sides of the slit. The vibration frequency (Fr) and average stress (σ) in the slit region increase proportionally with the increase of the slit period and amplitude. When the slit size increases, stronger vibration irregularity and asymmetry are generated, thereby increasing the vibration displacement. However, when the amplitude exceeds 5 mm, the growth trends of Fr and σ tend to be flat and eventually saturated. The curved slit structure can induce asymmetric vibration behavior, thereby increasing the mechanical stress on the nanofibers and improving the piezoelectric conversion efficiency. The electromechanical synergistic effect between this special electrode structure and the PAN-PVDF composite material enhances the working bandwidth and electrical output capability of the device. The excellent piezoelectric properties of PAN and PVDF and the endogenous triboelectric effect between the nanofiber interfaces caused by phase separation further increase the acoustoelectric output of the device.With its wide frequency response characteristic of 100–1300 Hz, the PAN-PVDF acoustoelectric device accurately covers the core frequency band of human voice (80–1200 Hz) and the characteristic spectrum of environmental sound, becoming the underlying hardware platform of intelligent acoustic sensing systems.
Figure 4. Application demonstration of PAN-PVDF acoustoelectric device in self-powering, voice recording, and speech recognition
The authors applied the PAN-PVDF acoustoelectric device to power generation, sound recording, and speech recognition. The alternating current generated by the device is converted into direct current through a bridge rectifier circuit. Under the sound excitation of 115 dB and 360 Hz, the device with a working area of 3×4 cm² can output rectified DC pulses up to 87.85 V, which has sufficient energy density to directly drive low-power electronic devices (including electronic thermometers, calculators, and electronic watches) and charge energy storage capacitors at the same time.
The audio signals recorded by the PAN-PVDF device are very similar in waveform and form to those recorded by commercial microphones. The SNR calculation result of the PAN-PVDF device is 66.8 dB, indicating that it has high-quality acoustic signal recording capability with low background noise, which is especially suitable for scenarios where weak signals are submerged by environmental noise.
To evaluate the capability of the PAN-PVDF acoustoelectric device in speech recognition, the authors built a machine learning (ML)-based classification platform. The voice signals collected by the device are processed through a convolutional neural network (CNN) architecture, achieving a 96% recognition accuracy, which verifies its effectiveness in real voice command systems.
High-fidelity acoustic signal capture and rapid response significantly improve the accuracy of human-computer interaction, the real-time performance of environmental perception, and the resolution of dynamic sound fields. It has a wide range of application spaces in scenarios such as high-precision speech recognition, abnormal sound diagnosis of industrial equipment, and barrier-free interaction, and is expected to provide universal acoustic solutions for industrial Internet of Things, intelligent terminals, and digital medical care.
By bionically mimicking the "slit sensilla" of scorpions and combining nanofiber materials with high piezoelectric performance, this research achieves excellent results in both acoustoelectric conversion efficiency and response bandwidth. The excellent acoustoelectric performance makes the PAN-PVDF curved slit acoustoelectric device expected to play a key role in the next generation of human-computer interaction, Internet of Things, and intelligent acoustic sensing fields, providing new design ideas for the development of nanofiber acoustic sensors.
DOI Link: https://doi.org/10.1002/adfm.202509283
