6. Final performance of optimized sensor and signal processing

Improvements to the sensor (polishing) and signal processing have enabled us to reduce the minimum pressure measured with the reference sensor using a water coupling on a tube incorporating a retaining spring. With this sensor operating at 3.5 MHz and 8 MHz, and with signal processing that studies the first and second echoes, it is now possible to measure an underwater pressure close to 20 bar (figure 9 ) for any mixture of helium and xenon.