Magnesium aluminum spinel for ultrasonic temperature sensing based on guided waves

Sensors are crucial for measuring combustion temperatures in aerospace and aviation engine testing. However, current sensors have poor oxidation resistance, low impact resistance, limited lifespan, and inadequate temperature measurement accuracy, often resulting in unsatisfactory testing outcomes. New sensor designs are urgently needed to address these issues. We propose a new sensor with advanced materials and technologies, based on the principle of ultrasonic guided wave temperature measurement with magnesium aluminum spinel (MgAl₂O₄) and magnesium-doped aluminum oxide crystals as ultrasonic waveguides. The design parameters of this sensor's sensitive elements were meticulously crafted. Finite element method simulations were then conducted to assess the impact of groove depth on ultrasonic propagation characteristics. Ultrasonic temperature sensors with spinel and magnesium-doped aluminum oxide were fabricated via the laser heated pedestal growth method. These sensors were calibrated in an oxidative environment, demonstrating a temperature sensitivity of 0.48 m/s·℃ and a repeatability of 95% across a range from 20 ℃ to 1600 ℃. By comparison among the three materials at a constant temperature, the sound velocity of sapphire was the fastest, followed by magnesia-doped alumina, while magnesia-alumina spinel was slowest. Thus, magnesia-alumina spinel can be considered an effective acoustic waveguide material for facile signal acquisition and high-temperature resolution. The proposed sensor design shows promise for applications in environments prone to oxidative erosion and high temperatures, offering an innovative solution for reliable temperature measurement within the harsh environments of aerospace and aviation engines.