For the maintenance of mechanical system integrity and human safety in extreme environments, sensors are required to measure and monitor various variables under challenging circumstances in several crucial industries, including aerospace, energy, transportation, and defence.
Environments in several critical industries – aerospace, energy, transportation, and defence require sensors to measure and monitor numerous factors under harsh conditions to ensure human safety and the integrity of mechanical systems.
In the petrochemical industry, for example, pipeline pressures must be monitored in climates ranging from hot desert heat to near arctic cold. Various nuclear reactors operate at 300-1000 degrees Celsius, while deep geothermal wells hold temperatures up to 600 degrees Celsius.
Researchers at the University of Houston created a new piezoelectric sensor that has been confirmed to perform in temperatures as high as 900 degrees Celsius (1,650 degrees Fahrenheit), the temperature at which mafic volcanic lava erupts.
“Highly sensitive, reliable, and durable sensors that can tolerate such extreme environments are necessary for the efficiency, maintenance, and integrity of these applications,” said Jae-Hyun Ryou, associate professor of mechanical engineering at University of Houston.
The UH research team previously developed III-N piezoelectric pressure sensor using single-crystalline Gallium Nitride, or GaN, thin films for harsh-environment applications. However, the sensitivity of the sensor decreases at temperatures higher than 350 degrees Celsius, which is higher than those of conventional transducers made of lead zirconate titanate (PZT), but only marginally.
The team assumed that a narrow bandgap caused the drop in sensitivity – the minimal energy required to excite an electron and give electrical conductivity. To put their hypothesis to the test, they created a sensor out of aluminum nitride or AlN.
“The hypothesis was proven by the sensor operating at about 1000 degrees Celsius, which is the highest operation temperature among the piezoelectric sensors.” said Nam-In Kim, the first author of the article and a post-doctoral student working with the Ryou group.
While both AlN and GaN have unique and exceptional features that make them acceptable for use in sensors for extreme environments, the researchers were ecstatic to discover that AlN had a bigger bandgap and a wider temperature range. However, the researchers needed help synthesizing and manufacturing the high-quality, flexible thin film AlN.
The team had to overcome technical difficulties in synthesizing and manufacturing high-quality, flexible thin film AlN.
“I have always been interested in making devices using different materials, and I love characterizing various materials. Working in the Ryou group, especially on piezoelectric devices and III-N materials, I could use the knowledge I learned in my studies.” said Kim, who earned his Ph.D. in materials science and engineering from UH in 2022.
His award-winning dissertation was on flexible piezoelectric sensors for personal health care and extreme environments.
He added, “It was very interesting to see the process leading to the actual results, and we solved the technical challenges during the development and demonstration of the sensor.”
They have successfully demonstrated the potential of the high-temperature piezoelectric sensors with AlN, which can operate in neutron-exposed atmospheres and at high-pressure ranges.
Ryou said, “Our plan is to use the sensor in several harsh scenarios. For example, in nuclear plants for neutron exposure and hydrogen storage to test under high pressure, AlN sensors can operate in neutron-exposed atmospheres and at very high-pressure ranges thanks to its stable material properties.”
The sensor’s flexibility provides additional benefits that will make it suitable for future applications, such as wearable sensors in personal health care monitoring goods and use in precise-sensing soft robotics.
The researchers hope that their sensor will become commercially feasible at some point in the future.
Kim said, “It’s hard to put a specific date on when that might be, but I think it’s our job as engineers to make it happen as soon as possible.”