# Towards Environmentally Friendly Accelerometers Based on Bacterial Cellulose
## 4 Results and Discussion
### Mechanoelectrical Transduction  
The mechanoelectrical transduction properties of BC-IL-based devices were investigated by an experimental setup, realized by measure. The setup used to characterize the inertial motion sensor as an accelerometer is seen in Figure 8. It consists of:  
* A TIRA GmbH S503 shaker to impose a base motion of the sensor mounted in the cantilever configuration;
* A Keysight 33220A signal generator, required for driving the shaker;
* A digital oscilloscope (Agilent Infiniuism MSO9064A), which is used both for a visual inspection of the relevant signals and their acquisition;
* Two Baumer 12U6460/S35A laser sensors. These are used to measure the displacements at the anchor and at the sensor tip, respectively;
* An accelerometer (model PCB333B40-SN51174) is mounted to the shaker moving plate and works as the reference. A preliminary investigation in terms of impulse response has been accomplished, and a comparison to the estimation obtained by the model presented in Section 3 has been done. Figure 9 shows the tip displacement and the output voltage of the BC composite, considering the parameters defined in Table 1. The values of the elastic constant estimated, as obtained by Equation (2) and by experiments, have been compared. A difference between the values of the model and experiments of about 8% has been estimated. Furthermore, an investigation was performed for determining the resonant frequency of the sensor [23]. Then, sinusoidal signals at the resonant frequency of the system were applied at the sensor's fixed end by using the shaker. The amplitude of the applied signal was used to control the acceleration applied to the device. Figure 10 shows the results of the sensor characterization. The figure reports the estimated mean values and the corresponding uncertainty, considering acceleration values ranging in the interval 3 m/s\({}^{2}\) to 7.5 m/s\({}^{2}\). The least mean-square algorithm was used to regress data and estimate the corresponding linear characteristic curve. This is reported with a solid line in Figure 10. The two dashed lines represent the uncertainty band. A sensitivity of 2.1 \(\times\) 10\({}^{-5}\) V/m/s\({}^{2}\) has been estimated. The noise level resulted in about 0.1 \(\times\) 10\({}^{-4}\) V, corresponding to a resolution of about 0.47 m/s\({}^{2}\). Figure 8: Experimental setup for the characterization of the BC-IL-based accelerometer (-34.4 mm long and -10.6 mm wide). The inset shows a view of the accelerometer, mounted in the cantilever configuration. The transduction performance of the compound was further investigated to outline the presence of nonlinearities. The input-output signals at the resonance frequency were considered for this aim. Moreover, to filter out any high-frequency noise effect, a pre-filtering was performed on both signals by using a digital low pass filter for both signals, with a cut-off frequency equal to 35 Hz. Such a value was chosen to maintain the relevant signal while removing the power line contribution. Signals of different amplitude values were imposed on the system. The input-output plots for four values of the acceleration are shown in Figure 11. A perusal of the figure shows that the increase of the input acceleration does not produce a proportional change in the output voltage, which gives evidence of system nonlinearity, so that results reported in Figure 10 can be considered as a form of linearization of the system behavior in the considered range. The presence of low-frequency fluctuations in the output signal (an example of the input-output curve for some nominally identical periods is given in Figure 12) did not allow for a deeper investigation of the system nonlinearity. Figure 10: Characterization diagram of the conceived sensor. The solid line indicates the characteristic line. The dotted lines indicate the corresponding uncertainty. Figure 9: Impulse response: output voltage and tip displacement (both experimentally estimated) as a function of time.