## 3 Results  
Every material has its own refractive index. For temperatures below room temperature, the refractive indices of air, polyethylene terephthalate (PET), and saline (sodium chloride) are 1.000293 [23], 1.5750 [24], and 1.544 [25], respectively. IV chambers are primarily composed of PET according to the International Organization for Standardization. To quantify the loss rate, a comparative experiment was conducted, as shown in Figure 3. One of the two settings was executed without any saline drops. The procedures conducted are shown in Figure 5.  
Light from the laser passed from the (a) air to the chamber's PET (\(\eta_{1}\)); (b) PET to air in the chamber (\(\eta_{2}\)); (c) air in the chamber to the chamber's PET (\(\eta_{4}\)); (d) chamber's PET to air (\(\eta_{6}\)) and to the photoresistor. At each step, light diminishes according to the characteristics of the medium. The loss rate is calculated according to Equation (10), which is based on [PERSON]'s equations [26]. \(R_{0}\) represents the reflectance of light, and \(n_{1}\) and \(n_{2}\) are the refractive indices of each material. \[R_{0}=\left|\frac{n_{1}-n_{2}}{n_{1}+n_{2}}\right|^{2} \tag{10}\]  
The loss rate in the first experiment without saline was 14.68%. The other experiment was conducted with saline drops in the chamber. Light passed from the (a) air to the chamber's PET (\(\eta_{1}\)); (b) PET to air in the chamber (\(\eta_{2}\)); (c) air in the chamber to saline (\(\eta_{3}\)); (d) saline to air in the chamber (\(\eta_{4}\)); (e) air in the chamber to the chamber's PET (\(\eta_{5}\)); (f) the chamber's PET to air (\(\eta_{6}\)) and to the photoresistor. The loss rate in the experiment with saline was 22.30%, indicating a difference of 7.62% compared to the case without saline drops. All the values recorded in each step are listed in Table 1.  
Figure 4: Body design and actual application. Figure 6a illustrates the experimental system. As shown in the figure, the test between each sensor and the developed system was conducted 10 times for 20 min. In the fluid chamber, the stored time for drop velocity was 2 s, while the time elapsed between the laser and photoresistor was 12 s, as shown in Figure 6a. To draw a comparison between the proposed method and methods developed in previous studies, we considered a patient walking at a speed of 1.5 km/h to aid recovery. We considered three cases for all methods. In the first case, we presumed that the device is located near the patient's bed without any movement from the patient. In the second case, we presumed the patient to be walking on a slip-resistant pad, which causes horizontal motion. In the third case, we presume a shaking motion from left to right, which frequently occurs when moving about with monitoring devices. Figure 6b shows comparative outcomes of the first case. The ideal value of \(Gtt\) was 10 drip/min. The photoresistor yielded an average accuracy of 80%. Compared with the ideal \(Gtt\), the load cell yielded an average accuracy of 85%, and the proposed system yielded an accuracy of 88%. This system does not have any advantages over other sensors in static conditions. However, if movement is applied, i.e., in dynamic conditions, the accuracy of both sensors decreases considerably. Figure 6c,d depict the comparative experimental results of the second and third cases. If movement is in a horizontal direction, the photodiode cannot accurately detect the dripping fluid due to its physical characteristics. Most drips fall vertically toward the ground irrespective of whether the system is in motion or not. Because of this reason, single photosensors experience difficulties in detecting drips. Moreover, the accuracy decreases to 52%, which is rather poor. Furthermore, if movement is added in a vertical direction, the load cell bounces up and down, thereby yielding unreliable results, which disrupts the weighing process of the IV fluid and its accuracy. While the single-sensor experiments also yielded