Maintaining mechanical system integrity and human safety in extreme environments requires sensors to measure and monitor various variables under challenging conditions in several critical industries, including aerospace, energy, transportation and defense.

Environments in a variety of critical industries – aerospace, energy, transportation and defense 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 pressure must be controlled in climates ranging from hot desert heat to near arctic cold. Several nuclear reactors operate at 300-1000 degrees Celsius, while deep geothermal wells maintain temperatures of up to 600 degrees Celsius.

Researchers at the University of Houston created a new piezoelectric sensor that has been confirmed to perform at temperatures up to 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, an associate professor of mechanical engineering at the University of Houston.

The UH research team previously developed a III-N piezoelectric pressure sensor using single-crystalline Gallium Nitride, or GaN, thin films for applications in harsh environments. However, the sensitivity of the sensor decreases at temperatures above 350 degrees Celsius, which is higher than that of conventional lead zirconate titanate (PZT) transducers, but only marginally.

The team hypothesized that a narrow bandgap was to blame for the decrease in sensitivity – the minimum energy required to excite an electron and give it electrical conductivity. To test their hypothesis, they created a sensor from aluminum nitride, or AlN.

“The hypothesis was proven by the sensor operating at about 1000 degrees Celsius, which is the highest operating temperature among piezoelectric sensors.” said Nam-In Kim, the paper’s first author and a postgraduate student working with the Ryou group.

While both AlN and GaN have unique and exceptional characteristics that make them acceptable for use in sensors for extreme environments, the researchers were thrilled to discover that AlN had a wider bandgap and wider temperature range. However, the researchers needed help synthesizing and manufacturing the high-performance, flexible thin film AlN.

The team had to overcome technical difficulties in synthesizing and producing high-performance, flexible thin-film AlN.

“I’ve always been interested in making devices with different materials, and I like characterizing different materials. Working in the Ryou group, especially on piezoelectric devices and III-N materials, allowed me to use the knowledge I learned during my studies.” said Kim, who completed his Ph.D. in materials science and engineering from UH in 2022.

His award-winning thesis was on flexible piezoelectric sensors for personal healthcare and extreme environments.

He added, “It was very interesting to see how the process led 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 AlN piezoelectric sensors, which can operate in neutron-exposed atmospheres and at high pressure ranges.

Ryou said, “Our plan is to use the sensor in various difficult scenarios. For example, in nuclear power plants for neutron exposure and hydrogen storage to test under high pressure, AlN sensors can operate in neutron-containing atmospheres and at very high pressure ranges due to the stable material properties.”

The sensor’s flexibility offers additional benefits that make it suitable for future applications, such as wearable sensors in personal healthcare monitoring products and use in precise, sensitive soft robotics.

The researchers hope that their sensor will become commercially viable in the future.

kim said, “It’s hard to put a specific date on when that might be, but I think our job as engineers is to make it happen as soon as possible.”

Magazine reference:

  1. Nam-In Kim, Mina Moradnia, et al. Piezoelectric Sensors Operating at Very High Temperatures and Extreme Environments Made of Flexible Ultrawide-Bandgap Single-Crystalline AlN Thin Films. Advanced functional materials. DOI: 10.1002/adfm.202370056