Research Unveils Ultralow-Power E-Nose for Real-Time Gas ID

Abstract 1

This study presents a novel, ultralow-power single-sensor-based electronic nose (e-nose) system for real-time gas identification, distinguishing itself from conventional sensor-array-based e-nose systems, whose power consumption and cost increase with the number of sensors. Our system employs a single metal oxide semiconductor (MOS) sensor built on a suspended 1D nanoheater, driven by duty cycling─characterized by repeated pulsed power inputs. The sensor's ultrafast thermal response, enabled by its small size, effectively decouples the effects of temperature and surface charge exchange on the MOS nanomaterial's conductivity ….

Abstract 2

The demand for power-efficient micro-and nanodevices is increasing rapidly. In this regard, electrothermal nanowire-based heaters are promising solutions for the ultralow-power devices required in IoT applications. Herein, a method is demonstrated for producing a 1D nanoheater by selectively coating a suspended pyrolyzed carbon nanowire backbone with a thin Au resistive heater layer and utilizing it in a portable gas sensor system. This sophisticated nanostructure is developed without complex nanofabrication and nanoscale alignment processes, owing to the suspended architecture and built-in shadow mask ….

An ultra-small electronic nose (e-nose) that operates on ultralow power has been developed, opening up possibilities for applications in various fields, such as air quality monitoring, health diagnostics, food safety, and environmental protection.

Professor Heungjoo Shin in the Department of Mechanical Engineering and Professor Jae Joon Kim in the Department of Electrical Engineering at UNIST have successfully implemented an e-nose capable of accurately measuring both the type and concentration of gases by integrating nanotechnology and deep learning.

Figure 1. Schematic of a suspended 1D nanoheater built on a carbon nanowire backbone. Enlarged section view of the built-in shadow mask consisting of SiO2 eaves and undercut structures (red dashed lines) which break the electrical connection (the Au line) along the substrate.

The newly developed e-nose utilizes a nano-sized heater-based semiconductor gas sensor. Unlike conventional sensors that consume significant power due to high operating temperatures, this sensor operates with less than 200 microwatts, making it ideal for mobile and IoT devices. Furthermore, it boasts high productivity as it leverages semiconductor manufacturing processes.

Figure 2. Scanning electron microscopy (SEM) images of the suspended nanoheater and built-in shadow mask structure.

The high power consumption associated with existing electronic noses has been mitigated through the miniaturization of sensors, complemented by the introduction of duty cycling technology. This technology reduces power consumption by an additional 90% by periodically supplying and cutting off power to the heater.

Figure 3. Schematic image, describing the overview of ultralow-power single-sensor-based e-nose system powered by duty cycling and deep learning for real-time gas identification.

The nanoheater can reach temperatures of 250 °C and cool down to room temperature within one-hundred-thousandth of a second, enabling effective gas measurement even within short duty cycles.

Figure 4. Real-time prediction of gas type and concentration for five gases [air, (a) SO2, (b) CO, (c) H2, (d) NO2] using dual-response signals (time window = 30 s, duty cycle = 10%, duty frequency = 1 Hz).

The research team has enhanced the existing e-nose design, which traditionally required multiple sensors, to operate with a single sensor. Gas desorption from the surface of semiconductors occurs more slowly than the operational speed of the nanoheaters. Consequently, during duty cycling, gas reactions continue even during brief cooling periods of the heater. This allows different signals to be collected both during operation and interruptions of the heater. By analyzing these dual signals in real time using a convolutional neural network (CNN), the system can accurately identify various gas types and concentrations.

Professor Shin stated, "The limitations of existing electronic noses can be addressed with a single sensor," adding, "This technology can be readily applied to mobile and IoT devices that necessitate miniaturization."

Professor Kim elaborated, "The ability to create a micro-gas measuring device that operates on low power opens avenues for diverse applications, including real-time wireless monitoring systems."

The findings were published Small and ACS Sensors, respectively. The findings related to the nanometer-based gas sensor were published in September 2022, while those concerning the e-nose technology were published in June 2024, each as a featured cover paper. This research received support from the National Research Foundation of Korea (NRF), the Ministry of Trade, Industry, and Energy (MOTIE), and the Ministry of Science and ICT (MSIT).

Journal Reference

1. Taejung KimYonggi KimWootaek Cho, et al., "Ultralow-Power Single-Sensor-Based E-Nose System Powered by Duty Cycling and Deep Learning for Real-Time Gas IdentificationArticle link copied!," ACS Nano, (2024).

2. Taejung Kim, Wootaek Cho, Beomsang Kim, et al., "Batch Nanofabrication of Suspended Single 1D Nanoheaters for Ultralow-Power Metal Oxide Semiconductor-Based Gas Sensors," Small, (2024).