Passive ultrasonic temperature measurement through a metal wall

Abstract

Various industrial requirements often prevent traditional contact thermometry; for instance, in high-temperature environments, the proper functioning of electronics is compromised. Furthermore, if the measurement environment needs to be hermetic, we cannot adopt the conventional wired measurement techniques. In this study, we report on a novel, robust, and passive method of measuring temperature through the walls of a hermetic metal container exploiting ultrasonic waves with a zero-reflection matching. We designed a preliminary ultrasonic system across an aluminium wall mimicking a sealed metal container. The setup consists of a piezoelectric disc transducer coupled to the wall on one side, and a passive sensor element made from brass coaxially coupled to the other side of the wall. We modelled the transducer as a receiver and experimentally verified the zero-reflection loads to suppress unwanted echoes. The passive sensor element does not require any active electronics inside of the hermetic container and can, therefore, be placed in a harsh environment, whereas the sensible readout electronics stay outside in a safe zone.