Feel like monitoring an erupting volcano? There’s a sensor for that

Sensors used to monitor extreme environments need to provide reliable measurements despite 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 a challenge when developing sensors to monitor physical and mechanical parameters like pressure, force, strain, and acceleration.

To operate in these environments, sensors must be able to withstand very high temperatures and harsh conditions. Aerospace turbomachinery, for example, generates temperatures between 167 °F (75 °C) and 932 °F (500 °C). Nuclear reactors operate at between 572 °F (300 °C) and 1,832 °F (1,000 °C). And temperatures in the pipelines used by the petrochemical industry vary from near-arctic cold to searing desert heat.

Researchers from the University of Houston have developed a piezoelectric sensor that can tolerate these types of extremes while remaining sensitive and reliable.

“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, corresponding author of the study.

Piezoelectricity is the electrical charge that accumulates in solid materials when they’re placed under mechanical stress. Piezoelectric sensors measure changes in pressure, acceleration, or strain by converting them into an electrical charge.

The research team had already developed a gallium nitride (GaN) piezoelectric pressure sensor designed for use in extreme environments. However, they found that the sensor’s sensitivity fell at temperatures higher than 662 °F (350 °C). Although GaN is a wide-bandgap semiconductor, the researchers hypothesized that the decrease in sensitivity was due to the bandgap not being wide enough. Bandgap is the minimum energy needed to excite an electron and produce electrical conductivity. So, the researchers created a new sensor using aluminum nitride (AlN).

The researchers compared the performance of the 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). Pressure-regulated nitrogen gas was used to evaluate their pressure-sensing capabilities.

Compared to the GaN sensor, the AlN sensor was found to have had a wider bandgap and could operate at higher temperatures while still providing fast, stable, and reliable measurements. In fact, it worked in temperatures up to 1,652 °F (900 °C), the temperature of erupting mafic volcano lava – the hottest type of lava on Earth.

“The hypothesis was proven by the sensor operating at about 1,000 °C [1,832 °F], which is the highest operation temperature amongst the piezoelectric sensors,” said Nam-In Kim, the study’s lead author.

Because of AlN’s physical properties, it can not only withstand high temperatures but also has high radiation resistance and is resistant to organic solvents, seawater, ultraviolet light, and weak acids and alkalis.

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

“Our plan is to use the sensor in several harsh scenarios,” Ryou said. “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.”

But the researchers have their eyes on applications other than heavy industry. They foresee incorporating their sensor into wearable devices used for health monitoring or used in precise-sensing soft robotics.

The study was published in the journal Advanced Functional Materials.

Source: University of Houston

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