TWO-FREQUENCY CONTINUOUS WAVE ULTRASONIC SYSTEM FOR TEMPERATURE MEASUREMENT IN AN INFANT INCUBATOR

Abstract

In this paper, we develop a new ultrasonic measurement method based on the speed of sound to measure the temperature. The average temperature of the air between the pair of ultrasonic T/R transducers is positively associated with the speed of sound. The method presented here is based upon the comparative phase shifts generated by two continuous ultrasonic waves with different but closely spaced frequencies. In the infant incubator, two low cost 40 kHz ultrasonic transducers are set face to face and used to transmit and receive ultrasound. Two frequencies are transmitted serially, each generating its own phase shift. Comparison of the phase shifts allows a highly accurate evaluation of the ultrasonic velocity when the distance between the transmitter and receiver is fixed. Ultrasonic velocity measurement system can provide a quick and precise monitoring of the temperature in an infant incubator. A single-chip microcomputer-based two-frequency continuous wave generator and phase detector was designed to record and compute the phase shift information and the resulting temperature, which is then sent to PC. The PC is used for calibrating the system and recording or controlling the temperature in an infant incubator. Experimentally, the accuracy of temperature measurement was found to be within ±0.02 °C when the distance between the transmitter and receiver is 1 m. The main advantages of this ultrasonic temperature measurement system are high resolution, low cost, and ease of implementation.