78 J. N. Satme et al. Fig . 8. 3 FEA modal simulation results indicating the first three mode shapes of the bench top experimental beam Fig . 8. 4 Power consumption of the various modules onboard the sensor package For the wireless system, the latency of triggering between two deployed packages is presented along with an experimental modal analysis test to measure the first three mode shapes of a beam. With longer deployment periods in mind, a standalone power subsystem is used. A lithium polymer battery was chosen as it has desirable power density per footprint, optimal for areal deployment applications where the payload is a significant concern. Solid-state voltage regulators and a power conditioning circuit are also added to step down voltage and deliver it to the various subsystems onboard. An experiment is constructed to measure each module’s power consumption. As indicated in Fig. 8.4, the Teensy 4.0 microcontroller has the highest steady-state power consumption at 0.52 W. For extended deployment (. >10 hours), a strict power-saving mode can be deployed where the microcontroller along with non-vital modules is turned off, when not in use, further preserving power. Temperature dependencies were observed in this phase as lithium polymer’s charge output can degrade in low temperatures causing voltage drops. This problem was partially rectified by adding conditioning capacitors to the package to compensate for the temperature-related voltage swings. furthermore, increasing the number of cells in the battery can ensure the voltage regulators receive adequate voltage regardless of temperature. As for battery life, the capacity of the battery chosen for this work was a 1500 mAh 2-cell lithium polymer, and this was chosen for medium-length deployment (. <10 hours). An experiment is constructed to measure the possible deployment period before the battery voltage gets critical. A safety system with an alarm is added during this stage to prevent the battery from over draining which can decrease the lifespan and cause deformation to the battery itself. The experiment was run at a constant room temperature to construct a linear model of the power system. Temperature variations can introduce high nonlinearities in the battery’s state of charge making it challenging to model. In this case, only the voltage of the battery was observed as an indicator of the discharge rate. As shown in Fig. 8.5, the experiment ran for over 8.3 hours with the voltage
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