# Towards Environmentally Friendly Accelerometers Based on Bacterial Cellulose
## 4 Results and Discussion
### The Investigation on the Mechanoelectrical Transduction Nature  
This section explores the mechanoelectrical transduction nature of the BC-based composite. BC-based compounds, impregnated with ILs and covered with conducting layers, have been reported to have electromechanical transduction capabilities because of piezoionic properties, i.e., because of the migration of charged species. According to such properties, the BC-based composite investigated in this paper should be classified as an ionic-electroactive polymer (IEAP).  
* IEAPs are characterized by both electromechanical and mechanoelectrical transduction properties.
* An inversion of polarity between the mechanical signal and the electrical one is observed when the two transduction phenomena are investigated.
* The sign of the charges accumulated at each electrode depends on the nature of the prevailing mobile charges.  
In a previous work [40], some of the authors gave indirect experimental evidence of the piezoionic nature of the involved transduction phenomenon. However, in that contribution, no investigation was performed on the nature of the mobile charges. Here, experimental evidence will be given compatible with the hypothesis that mobile charges  
Figure 11: The output voltage of the accelerometer as a function of the applied acceleration. The reported curves refer to different amplitudes of the applied input.  
Figure 12: The output of the accelerometer as a function of an acceleration input, with a peak-to-peak amplitude equal to about 20 m/s\({}^{2}\). The graph includes some periods of the input source and outlines the presence of low-frequency fluctuations.  
are cations. Suppose that we are in the presence of mobile cations; the schemes in Figure 13 show the cations' redistribution. Up-deflections and positive charges at the top electrodes are assumed as positive.  
As it can be noted, the same tip deflection implies a voltage signal of opposite polarities for the sensing and actuating working modes. Moreover, when the tip of the sensor is deflected in the up direction, positive charges accumulate at the bottom face.  
Experiments on the BC-based compound, both as a sensor and as an actuator, have been performed by modifying the experimental setup shown in Figure 8 (see Figure 14). More specifically, low-frequency signals were applied by using the modified setup, which includes a fork-shaped hinge for forcing the composite tip motion.  
A comparison of the signals obtained when sensing and as actuating working modes (polarities are as indicated in the schematic) is shown in Figure 15a,b, respectively.  
Figure 14: A picture of the setup used to investigate the mechanoelectrical transduction nature.  
Figure 13: Schematic of the BC transduction mechanism in presence of cations.  
Results evince that there is a change in phase between the sensing and acting signals. Moreover, a motion of the anchor in the down direction produced an accumulation of positive charges at the bottom electrode. Such results are compatible with the hypothesis that the redistribution of positive charges is involved in the transduction phenomenon.  
Finally, while sensing signals are in phase opposition, a small phase lag was observed for the actuation signals. The existence of such a phase lag for the case of the actuation needs further investigation.