# Rapid and Cost-Effective Fabrication and Performance Evaluation of Force-Sensing Resistor Sensors
## 3 Results
### Load Test of the FSR Sensor
During testing, it was observed that the output voltage exhibited significant noise. The first test data was averaged and analyzed to check the change in output voltage according to the load, as shown in Figure 8. When Velostat was pressurized, the output voltage changed according to the load at each pressurizing step, though there was an unstable response when depressurizing (Figure 8a). The resistance value of the 4B pencil lead FSR sensing surface was measured to be approximately 37 k\(\Omega\), so a fixed resistance of 100 \(\Omega\) was used for voltage measurement based on the voltage divider principle. In Figure 8b, there is a slight change in output voltage as pressurization begins and both sides of the sensing surface come into contact, but no change in output is confirmed for continuous pressurization. This indicates that the 4B FSR sensor lacks piezoelectric characteristics typical of general FSR sensors. For the TE piezoelectricity sheet, while it exhibited piezoelectric properties, it showed an increase in voltage rather than a decrease in resistance in response to pressing force due to piezoelectricity. This material was selected to observe the difference between piezoresistive and piezoelectric properties and is not suitable as an FSR sensor. The resistance value of the 9B FSR sensing surface was measured to be approximately 13 k\(\Omega\), so a fixed resistance of 100 \(\Omega\) was used for voltage measurement based on the voltage divider principle (Figure 8c). Figure 7: Load cell load and Interlink FSR\(-\)402 output voltage. The load is the force applied to an area of 10 mm \(\times\) 10 mm, which is equivalent to pressure. The measurement interval is 1000 ms (one data point per second). Figure 8: FSR sensor average output voltage for continuous pressurizing and depressurizing loads. (**a**) Velostat, (**b**) 4B, and (**c**) 9B. The load is the force applied to an area of 10 mm \(\times\) 10 mm, which is equivalent to pressure. The measurement interval is 1000 ms (one data point per second). Figure 9 illustrates the voltage output characteristics of the FSR sensor made by mixing a specific amount of silicone sealant with 9B pencil lead powder. As shown in Table 3, the resistance value of this FSR sensing surface was measured to be approximately 0.8 M\(\Omega\), significantly higher than the other selected materials, so a fixed resistance of 1 k\(\Omega\) was used for voltage measurement based on the voltage divider principle. Unlike the voltage output of the FSR sensor using only 9B powder in Figure 8c, it was confirmed that the output voltage was clearly responsive as the pressurized load increased, and the changes at the pressurization end were distinctly visible. When applying a load using the load cell as in Figure 7, a graph similar to Figure 10 was obtained. The difference in the number of data points represents the number of data collected per second, so the difference in the x-axis can be disregarded. Figure 10a shows the output of the mixture of 9B pencil lead and silicone sealant for continuous pressurization and decompression load voltage (1 st cycle). It can be clearly seen that the output voltage increases as pressurization starts and the load increases. During the 30 s pressurization maintenance period, the voltage value was not uniform, showing an initial slope. Figure 10b,c display the output voltage for continuous compression load of Interlink FSR-402 and Flexiforce A201-1, commercial products tested under the same conditions. The results exhibit a similar trend. Figure 9: 9B & Silicone Sealant Mixed for continuous pressurizing and decompressing loads output voltage. The load is the force applied to an area of 10 mm \(\times\) 10 mm, which is equivalent to pressure. The measurement interval is 1000 ms (one data point per second).