## 5 Results
### Energy Harvesting--Powering Up Smart Sensor
For the performed tests, the Vout obtained from the best result in Figure 23 is illustrated in Figure 28.  
Because the energy-harvesting system was not able to generate sufficient voltage to power up the sensor, and there were only preliminary results for the MRE transducer regarding signal conditioning, the presented outcomes that measured strain inputs and sent them to the dashboard on a website  
Figure 26: Energy harvesting for Replica 3. The maximum generated voltage was 1.487 V.  
Figure 25: Energy harvesting for Replica 2. The maximum generated voltage was 1.621 V.  
were completed on the basis of a strain-gauge sensor with a Wheatstone bridge and a signal amplifier. Moreover, the executed tests for the dashboard considered a powered-up smart sensor with a regular laboratory power supply. For this experiment, a commercial rosette-array strain gauge arrangement SGD-6/350-RYT21 by Omega Engineering was employed (Figure 29). The strain gauge was used to measure the strain in the area subjected to deformation by the application of force. To successfully install the strain gauges, there was a preparation and installation process, and for this experiment, an installation kit for strain gauges was employed. It is outside the scope of this report to describe the materials and cementing process regarding the strain-gauge transducer. Due to the nature of strain gauges, signal conditioning is usually required to read the output signal and to send it to the CPU. To solve this problem, two circuits were implemented, a Wheatstone bridge and a signal amplifier with operational amplifiers. As part of the design effort, both circuits were simulated in the Proteus Design Suite to validate their functioning. A Wheatstone bridge circuit is typically employed to measure the difference in electrical resistance of a strain gauge when a force is applied on the surface where the strain gauge is located. This type of circuit needs a power supply to excite the circuit, and an output voltage signal that is proportional to the applied force is produced. For this research, just one strain gauge of the \(0^{\circ}/45^{\circ}/90^{\circ}\) three-element strain rosette was used to measure uniaxial stress. The utilized Wheatstone bridge configuration was the quarter-bridge three-wire array. This array with one strain gauge and three resistors with the same electrical resistance value (350 \(\Omega\) in this instance, cancels the thermal effects generated for the lead wires. The second circuit that constituted the signal-conditioning section was a differential amplifier to increase the voltage. The voltage signal coming from the Wheatstone bridge was in the order of  
Figure 27: Energy-harvesting tests for the implemented piezoelectric system. (**a**) Replica 1; (**b**) Replica 2; and (**c**) Replica 3.  
mV, and it had to be amplified to be read by the microcontroller. The employed operational amplifier was the LM741 integrated circuit powered with \(-5\) and \(5\) V to keep the amplified voltage within these limits. After the preliminary tests, the signal-conditioning circuits were placed and welded onto a perforated phenolic plate and inside a protective case designed using computer-aided-design (CAD) software. For more information on Wheatstone bridges and signal conditioning (amplification), refer to [1,2].