Piezoelectric Behaviour in Biodegradable Carrageenan and Iron (III) Oxide Based Sensor

Abstract

This paper is dedicated to the research of phenomena noticed during tests of biodegradable carrageenan-based force and pressure sensors. Peculiar voltage characteristics were noticed during the impact tests. Therefore, the sensors' responses to impact were researched more thoroughly, defining time-dependent sensor output signals from calibrated energy impact. The research was performed using experimental methods when a free-falling steel ball impacted the sensor material to create relatively definable impact energy. The sensor's output signal, which is analogue voltage, was registered using an oscilloscope and transmitted to the PC for further analysis. The obtained results showed a very interesting outcome, where the sensor, which was intended to be piezoresistive, demonstrated a combination of behaviour typical for galvanic cells and piezoelectric material. It provides a stable DC output that is sensitive to the applied statical pressure, and in case of a sudden impact, like a hit, it demonstrates piezoelectric behaviour with some particular effects, which are described in the paper as proton transfer in the sensor-sensitive material. Such phenomena and sensor design are a matter of further development and research.

Keywords: dynamic properties; force sensor; k-carrageenan; piezoelectricity; proton transfer.

Figure 1

Visual representation of experiment: 1—oscilloscope as voltage registering device; 2—connecting wires; 3—electrodes; 4—CG film with Fe₂O₃; 5—plastic tube of selected height: 0.15 m, 0.3 m, 0.6 m, 0.9 m; 6—stainless steel ball: 0.007 kg; 7—lamination.

Figure 2

Visual representation of carrageenan film prepared for applied force measurements. (a) carrageenan/ iron oxide film cross-section before experiment: 1—ruler; 2—carrageenan/iron oxide film. (b) Mounting of sample for the applied force experiment: 1—carrageenan film; 2—lamination by parafilm; 3—aluminium electrodes 10 × 25 × 1 mm; 4—connectors of the oscilloscope; 5—guiding tube for falling ball; 6—Hantek DSO 6082BE digital oscilloscope.

Figure 3

Voltage of the sensor output from mechanical impact. Impact generated by a 10 mm, 7.04 g steel ball from 0.15 m height.

Figure 4

Measured potential dependence on time, when the distance of the falling ball was 0.3 m from the surface. Measurement of applied force on CG film.

Figure 5

Measured potential dependence on time, when the distance of the falling ball was 0.6 m. Measurement of applied force on CG film.

Figure 6

Measured potential dependence on time in comparing of applied distance of falling ball, results of first hit experiment.

Figure 7

SEM micrograph of CG film with iron (III) oxide particles. Size = 1280 × 1100; (a) DPI = 182.65; Conditions: V_acc = 15.0 kV; Mag- = ×400; Pixel size = 347.66 (left). (b) Mag- = ×1000; DPI = 182.65; Pixel size = 139.06 (right).

Figure 8

Visual representation of charge transfer in carrageenan film generated by applied force. (a) Visual representation of carrageenan film with iron (III) oxide particles; (b) charge generation in prepared film, the release of charge-carrying particles due to force; (c) visual representation of experiment scheme of film under short time mechanical load.