# Study on Molybdenum-Rhenium Alloy Ultrasonic Resonance Temperature Sensor
## 1 Introduction  
There is significant demand for innovative approaches to high-temperature measurement within aerospace [1], liquid metal [2], and metallurgy fields, among others. The precise monitoring of internal temperature fields is critically important in such applications. Traditional thermocouple [3] and radiation [4] temperature measurement methods have limitations in high-temperature, high-pressure, and strong oxidation environments. Tungsten-rhenium thermocouples are easy to oxidatize above 1700 \({}^{\circ}\)C, affecting the accuracy of temperature measurement; platinum-rhodium thermocouples are oxidation-resistant, but the price of the material is high; radiation temperature measurement is susceptible to dust, emissivity, and measurement distance, and other factors interfere with the accuracy of the temperature measurement, meaning that it is difficult to meet the testing needs using traditional temperature-measurement methods. The ultrasonic temperature measurement [5; 6] has gradually become the focus of attention in the industrial field due to its advantages of good stability in high-temperature environments, oxidation resistance, and a large temperature-measurement range. Compared to conventional thermocouple and radiation thermometry methods, ultrasonic temperature sensing has increasingly gained attention in the industrial sector due to its superior stability, rapid response, and broad material compatibility, particularly under high-temperature conditions. Thermocouples are vulnerable to oxidation at high temperatures, which reduces measurement accuracy and increases material costs. Although radiation thermometry provides a rapid response, it is mainly suited to surface temperature measurements; its accuracy in assessing internal temperatures is limited, and it is highly susceptible to variations in emissivity [7] and environmental conditions. Ultrasonic resonance temperature measurement is based on acoustic-wave transmission frequency for measurement, which is characterized by a small size, high resolution, frequency output, and less interference from environmental factors. In recent years, ultrasonic temperature measurement has made significant progress at home and abroad. In 1994, for instance, [PERSON] [8] conducted research on ultrasonic temperature-measurement technology at Tsinghua University, demonstrating that, with a fixed propagation distance, temperature can be measured by observing the propagation time of ultrasonic pulses through a guide rod and molten aluminum using a pulse emission-reception method. The next year, [PERSON] introduced an ultrasonic resonance temperature-measurement method for measuring liquid metal temperatures based on resonance frequencies. However, signal attenuation and undue echo noise posed challenges in terms of accuracy. In 2019, [PERSON] et al. achieved high sensitivity by optimizing coil designs, using spiral and folding coils to simulate and receive ultrasonic signals, in experiments at Zhejiang University. Combined with numerical simulation and coil-optimization design, the structural parameters of the transducer [9; 10] were determined and the transducer was prepared with a thickness measurement error of less than 0.1 mm. In 2024, [PERSON] [11] and his team from the University of Utah developed a three-section nickel-chromium 625 cylindrical waveguide for placement in the combustion zone of a boiler. They successfully measured internal temperature distributions in real time by continuously collecting acoustic data and analyzing echo characteristics, effectively addressing the temperature-monitoring challenges of equipment operating in extreme environments over extended periods. By integrating the magnetostrictive effect with a resonant sensor, the resonant sensing element can be coupled with the magnetostrictive transducer to design an optimized ultrasonic-guided-wave resonant temperature sensor. A high-voltage pulse signal excites the longitudinal mode [12] of the ultrasonic-guided wave, causing a sound wave to propagate within the sensor.