The paper describes two different approaches to ultrasonicmeasurements of temperature in aqueous solutions. The first approach\r\nuses two narrowband ultrasonic transducers and support electronics that form an oscillating sensor which output frequency is\r\nrelated to the measured temperature. This low-cost sensor demonstrated sensitivity of about 40Hz/K at the distance of 190mm\r\nand the operating frequency of about 25 kHz. The second approach utilised pulse-echo mode at the centre frequency of 20 MHz.\r\nThe reflector featured a cavity that was filled with deionised water. The ultrasound propagation delay in the cavity was related\r\nto the temperature in the solution. The experiments were conducted for deionised water, and solutions of sodium persulfate,\r\nsodium chloride, and acetic acid with concentrations up to 0.5 M. In the experiments (conducted within the temperature range\r\nfrom 15 to 30?C), we observed increases in the ultrasound velocity for increased temperatures and concentrations as was expected.\r\nMeasurement results were compared with literature data for pure and seawater. It was concluded that ultrasonic measurements\r\nof temperature were conducted with the resolution well below 0.1K for both methods. Advantages of ultrasonic temperature\r\nmeasurements over conventional thermometers were discussed.
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