Evaluation of an ultrasonic propagation speed measurement system in the temperature range from 20°C to 45°C

The aim of this work is the evaluation of a device for the ultrasonic propagation speed measurement in biological tissues as well as its possible error sources during signal acquisition process. The proposed measurement system basically consists of an immersion transceiver, which was excited by a home-made pulser. The transducer radiates the interrogated material and a needles arrangement inserted in it. This arrangement generates a well defined echo pair. These echoes combine with the echoes generated in the characterized medium after they have been amplified. In the case of the measurement of the temperature dependence of ultrasonic propagation speed, the measurement system must be submerged inside a thermostatic bath which is capable of regulating the temperature within a 0.1°C resolution. The measurement of the distance between the needles that work as reflectors, and the vibrations caused by the hydraulic pump could generate artifacts in the acquired ultrasonic signals. These variations would induce error in the ultrasonic propagation speed measurements. A method to measure the distance between the reflector needles is proposed, and an evaluation of the effects of the vibrations as well as the advantages of using a fixed distance between the reflector needles is presented. The obtained results show that the thermostatic bath operation has effect on the ultrasonic signals; however, it could be neglected due to its minimal contribution in the propagation speed measurement. It is also proved that the needles arrangement is a good option to measure the propagation speed showing values near to the reported in degasified bidistilled water.