# Ultrasonic Technique for Density Measurement of Liquids in Extreme Conditions

## TL;DR

A new ultrasonic method for measuring liquid density in extreme conditions is developed, offering high accuracy and reliability even at high temperatures and pressures.

## Contribution

A novel ultrasonic technique with a quarter wavelength matching layer and a new calibration algorithm for density measurement in extreme environments is introduced.

## Key findings

- The proposed ultrasonic technique is invariant to temperature changes and suitable for extreme conditions.
- The use of a quarter wavelength acoustic matching layer significantly increases measurement sensitivity.
- The method achieves an expanded measurement uncertainty of Uρ = 7.4 × 10−3 g/cm3 (1%).

## Abstract

An ultrasonic technique, invariant to temperature changes, for a density measurement of different liquids under in situ extreme conditions is presented. The influence of geometry and material parameters of the measurement system (transducer, waveguide, matching layer) on measurement accuracy and reliability is analyzed theoretically along with experimental results. The proposed method is based on measurement of the amplitude of the ultrasonic wave, reflected from the interface of the solid/liquid medium under investigation. In order to enhance sensitivity, the use of a quarter wavelength acoustic matching layer is proposed. Therefore, the sensitivity of the measurement system increases significantly. Density measurements quite often must be performed in extreme conditions at high temperature (up to 220 °C) and high pressure. In this case, metal waveguides between piezoelectric transducer and the measured liquid are used in order to protect the conventional transducer from the influence of high temperature and to avoid depolarization. The presented ultrasonic density measurement technique is suitable for density measurement in different materials, including liquids and polymer melts in extreme conditions. A new calibration algorithm was proposed. The metrological evaluation of the measurement method was performed. The expanded measurement uncertainty Uρ = 7.4 × 10−3 g/cm3 (1%).