December 9, 2023

Sensors used to monitor extreme environments need to provide reliable measurements at high temperatures and harsh conditions. Now, researchers have developed a piezoelectric sensor that works at the temperature of erupting mafic lava, the hottest type of lava on Earth.

Aerospace, energy, transportation and defense – all are extreme environments that pose challenges when developing sensors to monitor physical and mechanical parameters such as pressure, force, strain and acceleration.

To operate in these environments, sensors must be able to withstand very high temperatures and harsh conditions. For example, aircraft turbines generate temperatures between 167 °F (75 °C) and 932 °F (500 °C). Nuclear reactors operate between 572 °F (300 °C) and 1,832 °F (1,000 °C). Temperatures in pipelines used in the petrochemical industry range from near arctic cold to scorching desert heat.

Researchers at the University of Houston have developed a piezoelectric sensor that can withstand these types of extreme conditions while remaining sensitive and reliable.

“Highly sensitive, reliable and durable sensors that can withstand such extreme environments are necessary for the efficiency, maintenance and integrity of these applications,” said Jae-Hyun Ryou, corresponding author of the study.

Piezoelectricity is the accumulation of electric charges in solid materials when they are placed under mechanical stress. Piezoelectric sensors measure changes in pressure, acceleration or strain by converting them into electrical charges.

The research team has developed a gallium nitride (GaN) piezoelectric pressure sensor designed for use in extreme environments. However, they found that the sensor’s sensitivity decreased at temperatures above 662 °F (350 °C). Although GaN is a wide-bandgap semiconductor, the researchers hypothesized that the drop in sensitivity was due to an insufficiently wide bandgap. The bandgap is the minimum energy required to excite electrons and create conductivity. So the researchers created a new sensor using aluminum nitride (AlN).

The researchers compared the performance of AlN and GaN sensors by placing them in a tube furnace and increasing the heat in 100-degree increments from 212 °F (100 °C) to 1,652 °F (900 °C). Use pressure-regulated nitrogen to assess their pressure-sensing capabilities.

Compared to GaN sensors, AlN sensors were found to have wider band gaps and can operate at higher temperatures, while still providing fast, stable and reliable measurements. In fact, it operates at temperatures as high as 1,652 °F (900 °C), the temperature of erupting mafic volcanic lavas—the hottest type of lava on Earth.

“This hypothesis was supported by operating the sensor at approximately 1,000 °C (1,832 °F), which is the highest operating temperature among piezoelectric sensors,” said Nam-In Kim, lead author of the study.

Due to the physical properties of AlN, it not only can withstand high temperature, but also has high radiation resistance, resistance to organic solvents, sea water, ultraviolet rays and weak acids and bases.

Now that the researchers have demonstrated the robustness of their AlN piezoelectric sensor in the lab, they plan to test it in a real-world environment.

“Our plan is to use the sensor in several harsh situations,” Ryou said. “For example, neutron exposure and hydrogen storage are performed in nuclear power plants for testing at high pressures. Due to its stable material properties, AlN sensors can operate in the atmosphere and very high pressure ranges exposed to neutrons.”

But the researchers have set their sights on applications beyond heavy industry. They foresee integrating their sensors into wearable devices for health monitoring or for precise sensing of soft robots.

The study was published in the journal Advanced Functional Materials.

source: university of houston