Information about vibrating objects can be obtained by vibration measurements. Piezoelectric sensors made by piezoelectric ceramics, quartz, or organic piezoelectric materials, e. g. polyvinylidene fluoride (PVDF) have been adopted by many researchers to measure vibrations. Among these piezoelectric materials, PVDF has attracted much attention for its excellent properties such as outstanding chemical resistance, high thermal stability, low permitivities, low acoustic impedances, flexibility and membrane forming properties. In this paper, PVDF is introduced in brief. In addition, this paper briefly reviews the use of PVDF films as sensors for vibration measurement in the areas of portable medical detections, structural health monitoring, mechanical equipment vibration measurements and other applications. Meanwhile, some cases which have good low-frequency performances or novel features in structures will be especially introduced to provide helpful experiences for future applications. In the end, a spiral-shaped PVDF cantilever and a double-clamped PVDF beam of two piezoelectric energy harvesters are mentioned to provide ideas for reducing the resonant frequencies and enhancing the output signals of PVDF vibration sensors respectively. The idea of how to enhance the output signals of PVDF sensors for low frequency vibration measurements may be helpful to the development of geophone.

Flexible tactile sensors have promising applications at the field of intelligent robotics. However, manufacturing flexible tactile sensors with excellent stability and high sensitivity remain a great challenge. In the present work, polyvinylidene fluoride (PVDF)-based nanofibers are prepared by electrospinning loaded with Fe ₃ O ₄ nanoparticles (NPs). X-ray diffraction (XRD) and attenuated total reflection fourier transform infrared spectroscope (ATR-FTIR) results indicate that the addition of Fe ₃ O ₄ NPs promotes the generation of β-phase in PVDF polymer, which greatly improves piezoelectric properties of composite nanofibers. Simultaneously, a flexible piezoelectric tactile sensor with cilia-inspired structures (PTSCS) based on PVDF/Fe ₃ O ₄ nanofibers is proposed, which consists of the substrate with cilia structures, Ag electrodes, composite nanofiber membrane and nanofiber protective layer. The PTSCS demonstrates a higher output voltage compared to sensors with bump and planar structures, which also exhibits high robustness, with a stable output after 30000 cycles of vibration testing. More importantly, the PTSCS demonstrates superior performance in recognizing surface texture and temperature of objects. The flexible PTSCS has potential use in areas such as intelligent soft robotics and material recognition.

Poly(vinylidene fluoride) (PVDF) has been a kind of particularly attractive piezoelectric materials for its excellent piezoelectric property. Due to its light weight, impedance characteristic is very similar to water, and good mechanical flexibility, PVDF piezoelectric film is very suitable for the field of hydrophones. Although the piezoelectric ceramic hydrophone has been widely used, but due to the disadvantage of high inherent frequency and fragile characteristics of the piezoelectric ceramics slice, the development of the piezoelectric hydrophone is limited. The application of PVDF piezoelectric film has solved many problems encountered in the use of piezoelectric ceramics. In this article, the classification of hydrophone is briefly introduced at first, and then the current status of hydrophone research is involved. And then, by analyzing the electrical equivalent model of the PVDF piezoelectric sensitive unit, the signal conditioning circuit of the PVDF piezoelectric hydrophone is summarized as well. After that, the current status of PVDF hydrophone research is discussed. Finally, a summary of all the work listed in this article is given and an outlook of PVDF hydrophone is proposed.

Based on the tactile mechanism of human fingertips, a bionic tactile sensor fabricated from polyvinylidene fluoride piezoelectric film is proposed, which can identify the surface softness, viscoelasticity, thermal conductivity, and texture roughness of the object. The tactile sensor is mounted on the fingertip of the bionic manipulator, which obtains the surface features by touching and sliding the object. The time-domain features of the output signal are used for preliminarily discriminating the softness, viscoelasticity, and heat conduction of the object. Finally, based on the Back Propagation and the Particle Swarm Optimization-Back Propagation neural network algorithm, the recognition experiment of texture roughness is carried out using the PSO algorithm to improve the BP neural network so that the optimized BP algorithm has a higher convergence accuracy. The results show that the PSO-BP algorithm achieved the highest accuracy of 98% for identifying samples with different roughnesses and the average recognition achieved an accuracy of 94%. The bionic piezoelectric tactile sensor proposed in this paper has a good application development prospect in recognizing the surface features of objects and intelligent robots.

Real-time monitoring of seismic information is important, a wide variety of geophones have emerged to achieve this goal. According to the principle of transforming seismic signals, the geophones can be classified into electromagnetic geophones, piezoelectric geophones, electrochemical geophones, fiber optic geophones and so on. Among them, piezoelectric geophones have been widely used in seismic detection. In this article, the piezoelectric material is briefly introduced at first, and then the piezoelectric seismic detector with piezoelectric ceramic and polyvinylidene fluoride as a sensitive material is involved. After analyzing the electrical equivalent model of the piezoelectric sensitive unit, the signal conditioning circuit of the piezoelectric geophone is summarized as well. After that, the promotion of MEMS technology to piezoelectric geophones is discussed. Finally, a summary of all the work listed in this article is given and an outlook of combining MEMS and PVDF to improve the performance of geophones is proposed.