# Free-hand gas identification based on transfer function ratios without gas flow control

## TL;DR

This paper introduces a novel gas identification method using transfer function ratios that allows for free-hand measurements without gas flow control, enabling portable and wearable gas sensing applications.

## Contribution

The study presents a new protocol for gas identification that works with arbitrary gas input patterns and integrates it with MEMS sensors and machine learning for high-accuracy detection.

## Key findings

- Achieved high accuracy in identifying solvents, spices, and herbs.
- Enabled gas identification without flow control units.
- Demonstrated potential for portable and wearable gas sensors.

## Abstract

Gas identification is one of the most important functions of gas sensor systems. To identify gas species from sensing signals, however, gas input patterns (e.g. the gas flow sequence) must be controlled or monitored precisely with additional instruments such as pumps or mass flow controllers; otherwise, effective signal features for analysis are difficult to be extracted. Toward a compact and easy-to-use gas sensor system that can identify gas species, it is necessary to overcome such restrictions on gas input patterns. Here we develop a novel gas identification protocol that is applicable to arbitrary gas input patterns without controlling or monitoring any gas flow. By combining the protocol with newly developed MEMS-based sensors (i.e. Membrane-type Surface stress Sensors (MSS)), we have realized the gas identification with the free-hand measurement, in which one can simply hold a small sensor chip near samples. From sensing signals obtained through the free-hand measurement, we have developed machine learning models that can identify not only solvent vapors but also odors of spices and herbs with high accuracies. Since no bulky gas flow control units are required, this protocol will expand the applicability of gas sensors to portable electronics and wearable devices, leading to practical artificial olfaction.

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Source: https://tomesphere.com/paper/1812.05193