# Non-Invasive Glucose Measurement Technique Based on Time-of-Flight
## 4 Results
### Measurements Performed  
The performance of the sensor was determined by multiple measurements of the produced samples. A buffer solution of physiological saline was used, to which different amounts of D-glucose (Sigma Aldrich G8270-1 KG, St. Louis, MO, USA) were added. The quantity added was adjusted so as to create multiple solutions with glucose concentrations that initially covered the range of human normal blood glucose levels (70 mg/dL-140 mg/dL) [17]. Additional samples were created to cover values up to an upper limit of 500 mg/dL.  
A cuvette holder was designed and 3D printed to prevent position changes during measurement and to attempt and preserve the cuvette placement while different samples were placed on the sensor (Figure 7).  
To verify that the sensor's measurements were not affected by the sample container used, full measurements were acquired using just an empty container. The results showed that the sensor did not register significant signal change with or without the sample holder, that could not be attributed to ambient and system noise.  
After initial verification of the sensor operation, the full samples were measured using the sensor developed. The initial results were not as expected and indicated that the samples did not have the expected glucose concentration. This led to their recreation and verification using laboratory instruments. The samples were then relabeled based on the measured glucose concentration. The final measurements are shown in Figures 8 and 9.  
The results shown in the previous figures are the raw sensor values for each pixel of the sensor (an array of 80 \(\times\) 60 pixels). This sensor value is proportional to the phase difference of the received signal vs the emitted (reference) signal. An increased value for a sensor pixel represents an increased distance traveled by the light pulses emitted by the LED.  
Figure 7: A 3D rendering of the designed sample holder.  
To correlate the measured values with the real glucose values, the moving average window was increased to 4000 samples. The result of plotting the mean value of data received versus the concentration is shown in Figures 10-12. Error bars were added using the values from multiple measurements performed on each sample (with the exception of Figure 12). Error bars were added only on sensor measurements--glucose concentration of samples was verified with existing certified sensors. An initial linear fit was attempted--the polynomial degree was chosen so as to arrive to an \(R^{2}>0.95\). Thus, a first degree polynomial was chosen for both the amplitude data and the phase data. The factors of those as well as the \(R^{2}\) values are shown in the relevant figures.  
Additionally, the measured amplitude signal of the pure saline sample was used along with the amplitude signals of the rest of the samples to create scaling factors. These were applied to the phase measurements and the results are shown in Figure 12.  
Figure 8: Averaged sensor output (phase of received signal) versus sensor pixel for different glucose concentrations in the sample.  
Figure 9: Averaged sensor output (amplitude of received signal) versus sensor pixel for different glucose concentrations in the sample.  
Figure 11: Averaged sensor output (amplitude channel) for different glucose concentrations.  
Figure 10: Averaged sensor output (phase channel) for different glucose concentrations.