An Ultrasonic Time-of-Flight Sensing System Based on Custom Hardware of Time to Digital Converter (TDC) for Measurement of Glucose Concentration

The proposed work presents a custom hardware implementation of pulse shrinking time to digital converter (PSTDC) on a field programmable gate array (FPGA) for the measurement of the time-of-flight (ToF) of an ultrasonic wave. The PSTDC is used here to measure a time interval between two events (START and STOP) and convert it into a corresponding digital output value. It improves the measurement accuracy by estimating the width of the pulse between the time intervals, which is dependent on the ToF of the signal. The proposed system was successfully implemented on FPGA to measure the ToF of an ultrasonic wave when propagated through the glucose (aqueous) solution. The experiments were conducted, and around 50 readings were taken for approximately 8 h at various concentrations of glucose (aq.) solution at room temperature ( <tex-math notation="LaTeX">27 ∘ C </tex-math> ). The experimental results show the correlation factor ( <tex-math notation="LaTeX">R^2 </tex-math> ) equal to 0.99997 between glucose concentration and corresponding velocity measurement. A relative standard deviation (RSD) of 0.01395, a standard deviation of 0.203, and a relative error within ±1.48% were obtained between the measured and actual value of glucose concentration which provides us the accuracy of around 98.52%. The obtained result shows that the proposed system can be useful in the design of an ultrasound system for precise measurement of the ToF of the signal. The proposed implementation processes the signal in the digital domain, thus avoiding signal conditioning front-end such as the analog-to-digital converter (ADC), digital-to-analog converter (DAC), and so on, offering the benefits of reliability, more comprehensive dynamic range of 192.6 dB, and higher precision.