In the present study, an analysis has been conducted on the reception sensitivity as a function of change in the number of piezoelectric element and contact surface for improvement of reception sensitivity of ultrasonic sensor for measurement of fuel amounts in the CNG tank. To reduce errors due to changes in outside temperatures, experiments were conducted under the condition of 25℃. For experimental conditions, a total of 405 experimental data sets could be obtained through the variables that included 6 types of transmission frequency value ranging from 60kHz to 80kHz by the unit of 5kHz, 6 types of pressure value inside aluminum tank ranging from 0bar to 5bar by the unit of 1bar, 3 types of shape of ultrasonic transmission /reception contact surface including Surface, Line, and Point, and 2 types of the number of piezoelectric elements inside the ultrasonic sensor.
To improve accuracy of experiments, an average value was used after measuring each experimental data 5 times. In the case of the ultrasonic sensor using a single piezoelectric element, the highest reception sensitivity values could be confirmed to be observed upon fixing the value of reception frequency value at 75kHz, even if the shape of contact surface was changed. According to the analysis results for reception sensitivity as a function of change in the shape of contact surface, an increase of the maximum reception sensitivity value by about 60% compared with Line-Line selected as the reference mode could be confirmed when the shape of contact surface of the transmission/reception ultrasonic sensor was changed to the Surface.
In the case of transmission/reception ultrasonic sensor produced with multiple piezoelectric elements, the highest reception sensitivity value could be confirmed to be obtained when the reception frequency value was at 80kHz due to the change in resonant frequency characteristics of the aluminum tank and the ultrasonic sensor. In the case of maximum reception sensitivity value, a reduction by about 50% compared with the reference model could be confirmed. In the case where only the transmission sensor produced with multiple piezoelectric elements, the highest reception sensitivity value was observed when the reception frequency value was fixed at 80kHz, and an increase by about 63% compared with the reference model could be confirmed in the case of the highest reception sensitivity value. Also, even when the number of piezoelectric elements and the shape of the contact surface of the transmission/reception ultrasonic sensor are changed, a tendency where the reception sensitivity value reduced with an increase of pressure value inside the aluminum tank could be confirmed. In addition, an improvement of resolution of the ultrasonic sensor as a result of an increase in pressure inside the aluminum tank could be observed as the maximum reception sensitivity value was increased. As a whole, the highest reception sensitivity value was displayed when the transmission sensor of surface shape produced with multiple piezoelectric elements and the surface-shaped reception sensor produced with a single piezoelectric element were used. An improvement in reception efficiency at the same voltage value could be confirmed as a result of change in contact surface shape of the ultrasonic sensor and change in the number of piezoelectric elements. Based on this, it is considered to provide help to the technical part upon future development of ultrasonic sensors for measurement of the CNG fuel amounts.