A fluid mechanics-based approach seems to hold the key to a new electronic nose design, claimed to provide consistent accuracy when measuring volatile organic compounds (VOCs).
The health consequences of explosure to many VOCs makes it important to maximise their detection. They are often found in paints, pharmaceuticals, and refrigerants, among other common products, but they can also act as markers of explosives, insect infestation, food spoilage, and disease.
The new approach introduces a fluid mechanics-based chamber design for an electronic nose (e-nose) that consistently detects VOCs at low concentrations. The strategy, which includes using a shuntlike device to control the behavior of fluid flow is described as a step forward in e-nose technology.
Methods for detecting VOCs face many challenges in terms of selectivity, sensitivity, reproducibility, and stability. E-noses, inspired by the olfactory system, can overcome some of these barriers by combining arrays of chemical sensors with pattern recognition techniques to recognize odours.
However, many e-noses generate different signals in response to VOCs at the same concentration when the sensor is located in different parts of the “nose” chamber.
“To counteract this problem, the fluidic behavior of the gas flow needs to be well controlled,” said author Weiwei Wu. “This ensures a uniform fluidic field and concentration of VOCs in the chamber and avoids generating any fake sensing characteristics.”
The starting e-nose design featured a vertical chamber that looks much like a showerhead. This promotes vertical flow as gas spreads through holes at the bottom of the device and around to evenly distributed sensors.
Using fluid mechanics simulations, the team optimized the volume, symmetry, hole location, and sensor location of their e-nose chamber. They added a shuntlike device to promote the flow of gas through the device and shorten response time.
Based on their simulation results, the researchers fabricated a Teflon chamber and measured the sensing performance of their e-nose. They compared two chambers, one with the shunt and one without. The chamber with the shunt device consistently performed around 1.3 times better at sensing an example VOC.
In the future, the authors plan to focus on minimizing the chamber and improving the structure further to decrease response and recovery time.
“E-nose research is a highly interdisciplinary field,” said Wu. “Chemists, physicists, biologists, electronics engineers, and data scientists need to work together to solve issues including effective sensing that considers the fundamental mechanisms of absorption/desorption, algorithms that achieve precise recognition of VOCs more quickly and with lower energy consumption, and how new technologies, such as memristors, should be involved.”
• The article “Controlling fluidic behavior for ultrasensitive volatile sensing” appeared in Applied Physics Reviews in May. It is authored by Tianqing Liu et al.
