A portable audible-range acoustical approach for determining headspace vapour-phase properties

Measuring vapour-phase properties including pressure, density, concentration and molecular weight is an important step towards integrating mobile olfactory devices into smart societies for monitoring chemical processes. However, there are few portable and low-cost devices for realising dynamic headspace vapour-phase measurements, which work for various molecules. Herein, the concept of utilising audible-range sound waves, in the form of an acoustic resonator, is introduced for extracting vapour-phase properties. As different headspace molecules enter the acoustic resonator, the weight and number of molecules change, and molecular vibrations are perturbed, manifesting in modified local acoustic waves due to changing vapour density and specific heat ratio. Physical waves enable the accurate determination of vapour properties for different molecules, agreeing well with reference values. A minimum vapour pressure down to n-decane of 0.2 kPa is detectable using an audible-range acoustical approach, either by flowing N2 to force molecules into the headspace; or using a simple cap-based design, which securely fastens onto a vial without any external flow. Low-cost speaker and microphone technologies are an innovative physical approach for determining vapour characteristics, whilst simultaneously demonstrating the inherently complex dynamic fluid space over time. Audible-range acoustical techniques can easily integrate into sensor networks and may yield new alternatives in mobile olfactory technology, due to its physical nature and irrelevance to chemical affinity, which may be useful for portable devices in various applications.

Automated summary

Measuring vapour-phase properties is crucial for integrating mobile olfactory devices into smart societies. This study introduces the concept of utilizing audible-range sound waves to extract vapour-phase properties, showing accurate determination of different molecules' characteristics. Audible-range acoustical techniques can easily integrate into sensor networks, providing new alternatives for portable devices in various applications.