7/27/2023 0 Comments Piezo electric load cellTwo additional buffer rods (one in the top plate and the other one in the bottom plate) are used to protect the film sensor from excessive mechanical impacts (see Fig. In the ridge-like loadcell, along the film length the distance between two successive rods on a plate is 1cm. The schematic of the fabricated loadcell for ridge-like structure is shown in Fig. Considering plain and ridge-like structures a total of eight loadcells are fabricated. In order to obtain ridge-like shape at the inner surfaces of the plates, plastic coated metal rod (length 2.5 cm, diameter 0.1 cm) are bonded using epoxy. In addition to plain sandwich structure, ridge-like structure is also fabricated. Four materials including hard and soft materials such as glass, glass-epoxy PCB, plexiglass, and plastic fiber are used to fabricate the plates of loadcells. All the plates are of rectangular shape of size 7×5 cm. The PVDF piezo film sensor (Model: SDT1-028K Make: Measurement Specialties, USA Capacitance: 2.6 nF) is sandwiched between two plates using small nut-bolt pair at the four corners of the plates. In this investigation, sandwich type loadcell is designed and fabricated. For example, when a small moving ball hits a fixed film sensor perpendicularly, a very small area of the film interacts with ball and this area of interaction of the film sensor is the active area of the impact event. On the other hand, the active area of a film sensor is the area of the film that effectively takes part during an impact event. 13,15–17 As far as output voltage is concerned, stretching the film in longitudinal direction is more effective than compressing film along its thickness. Another important factors that influence the conversion efficiency are direction of stretching (or compressing) and the active area of the film during mechanical impact. 1,2 Further examples can be given for the cases of impact energy detection, 5,10–14 in which sponge, rubber, aluminum, plexiglass, ionic polymer–metal composite materials etc. For example, special textile fiber is chosen for loadcell in biomedical applications. The design and material of the loadcell are chosen based on the nature of application of the sensor. Usually in practical application, a loadcell (or fixture) is designed and fabricated that holds the PVDF film sensor. Conceptually, in all these applications the PVDF film is considered as an active dynamic strain gauge. The application of PVDF film sensor includes a wide range of areas such as biomedical, 1,2 microforce detection, 3 irrigation, 4,5 ultrasonic sensing, 6 material quality detection, 7 dynamic stress detection, 8,9 mechanical impacts 5,10–14 etc. Apart from the energy harvesting, PVDF film is emerging as primary sensor in variety of applications due to its vast dynamic range, wide frequency coverage, high conversion efficiency, high elastic compliance, cost effectiveness etc. Piezoelectric PVDF film is active sensor and behaves like a dynamic strain gauge. The merits and demerits of the fabricated loadcells are discussed. Both the bandwidth and frequency range of the output signal is found to be independent and dependent of the loadcell materials for indirect and direct impact with the loadcell respectively. In case of loadcell made of glass plates, more than 100% increase in the output voltage is observed for ridge-like shape in comparison to its plain counterpart. The effectiveness of the ridge-like shape is confirmed statistically by conducting two factorial design of experiment in which shape and material of the loadcell are considered as the two factors with 2×4 matrix. It is shown that the active area is significantly increased due to the ridge-like shape given at the inner surfaces of the plates of sandwich type loadcell and as a result of which higher conversion efficiency is obtained. More is the active area of the film higher will be the output voltage. For a given film sensor, the output voltage produced due to mechanical impact is highly dependent on the direction of stretching (or compressing) and active area of the film sensor. Conversion efficiency of mechanical impact into electrical voltage remains ever increasing demand for piezoelectric PVDF film sensor.
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