Design and fabrication of a metal core PVDF fiber for an air flow sensor

Abstract

To track prey or avoid predators, many arthropods can detect variations in airflow and pressure gradients using an array of very thin and sensitive filiform hairs. In this study, metal core piezoelectric poly(vinylidene fluoride) (PVDF) fibers were prepared to mimic such hair sensors. The flexibility of the fibers was very good, which was helpful for overcoming the typical brittleness of piezoelectric ceramic fibers. At the same time, the diameter of the fibers was very small (down to 50 μm in diameter). In order to mimic the insects' hairs to the maximum extent, which was expected to greatly improve the sensitivity of such PVDF fiber-based sensors, a feasible process to prepare and extract electrodes on the surface of the fibers had to be developed. Compared with stainless steel filament-core fibers, the molybdenum filament-core PVDF fibers were easy to stretch. The molybdenum filament was then covered by a cylindrical PVDF layer with a diameter of 400 μm. One half of the longitudinal surface of the fibers was spray-coated with a conductive silver adhesive. The metal core was then used as one electrode, and the conductive silver adhesive was used as the other electrode. After polarization, a single metal-core PVDF fiber could be used as an airflow sensor. The surface structure and the sections of the PVDF fiber were analyzed by scanning electron microscopy. The results of the mechanical stretching tests showed that the metal core greatly enhanced the mechanical properties of the PVDF fibers. X-ray diffraction revealed that the greater the stretching ratio, the higher the α-to-βphase conversion rate during the preparation of the PVDF fibers. A single metal-core PVDF fiber was used as a bionic airflow sensor, and a mechanical model of this sensor was derived. The airflow sensing capability of the PVDF fiber was experimentally confirmed in a miniature wind tunnel. The results showed that a cantilevered metal-core PVDF fiber is capable of detecting the range and direction of the surrounding airflow variations. The experimental results also verified the theoretical model.

Effects of in-situ poling and process parameters on fused filament fabrication printed PVDF sheet mechanical and electrical properties

“…Similar to the efforts of [13], a post-deposition electrical poling was required to align the dipoles. Single layer samples could be post poled, though the area of poling was quite small.…”

“…By applying a voltage to the hot end of a 3D printer, Lee"s group was able to acquire individual piezoelectric PVDF extradite fibers that generated charge when flexed. In addition, Bian, et al, created a PVDF covered metal molybdenum fiber, electrically poled the structure, and then used the fiber as an air flow sensor [13]. Voltage responses for Bian"s 10 mm long 0.4 mm diameter fibers were in the 100"s of µV range for air flow rates of 0 to 18 m s -1 .…”

Piezoelectric Microstructured Fibers via Drawing of Multimaterial Preforms

“…Using a similar method, Bian et al . demonstrated a metal-core piezoelectric fiber that had a PVDF sheath and a molybdenum filament core 21 . Recently, Martins et al .…”

Piezoelectric microstructured fibers via drawing of multimaterial preforms

“…For example, Lund et al reported the melt-spinning of a PVDF-yarn with a conductive carbon black/polypropylene (CB/PP) core 20 . Using a similar method, Bian et al demonstrated a metal-core piezoelectric fiber that had a PVDF sheath and a molybdenum filament core 21 .…”

“…More importantly, the piezoelectric fiber retained its performance even after three days' cyclic bend-release tests. Compared to other piezoelectric fibers [20][21][22][23]28 , the fibers presented in this work feature a swiss roll structure of the piezoelectric layer, which considerably increases the active surface area and reduces the layer thickness, this resulting in considerably higher voltages and currents (and consequently electric powers) that can be generated by such fibers. Large-area piezoelectric textiles could be fabricated by incorporating the drawn fibers into woven fabrics, thanks to their excellent mechanical properties (as they are made only of plastics), and the use of low-cost, high volume fabrication techniques (fiber drawing).…”