Tanju YILDIRIM1. Outline of Research2. Research Activities Fig. 1. Yildirim et al., Dual domain acoustic olfactory discriminator, 2023, Sens. Actuators A: PhysFig. 2. Yildirim et al., Audible sensing of low-ppm concentration gases, 2023, Sens. Actuators A: Phys.References1) T. Yildirim, M.-Q. Feng, T.A. Ngo, K. Shiba, K. Minami, G. Yoshikawa, Sens. Actuators A: Phys. 350, (2023) 1141022) T. Yildirim, M.-Q. Feng, K. Shiba, K. Minami, G. Yoshikawa, Sens. Actuators A: Phys. 370, (2024) 115215ICYS Annual Report 2023 In the last 40 years, minimal strides towards commercial olfactory systems have been made due to various limitations. Therefore, alternative thinking in olfactory sensing is required for the field to progress in a new direction. Re-purposing audio equipment for olfactory identification can give >20 kHz worth of data dimensionality using acoustic pressure waves, which can be measured in a fast and portable manner. Conventional olfactory sensors have difficulties in determining chemical constituents in gas mixtures and issues with the minimum limit of detection, overcoming these issues is the focus of my work. Previously, I demonstrated acoustic-olfaction and converted chemical data into audio data that can easily be read by a computer as shown in Figure 1 [1]. I found significant signal output changes from my device as different gases flow into a custom chamber design that uses standing wave resonances to maximise the signal output from my device. It is possible to use a standard computer audio jack to make measurements, reducing the cost of intended devices and simple integration with a computer is possible. Various physical parameters can be extracted from the system including density and speed of sound, which is linked to the vapour pressure and molecular weight. Overcoming issues associated to low data dimensionality, signal enhancement and separation requires inducing additional mechanisms in acoustic-olfaction. Additionally, gas mixtures in large acoustic fields experience losses due to thermoviscous properties of the internal mixture components, aiding in the separation of different components along a boundary wall. Acoustic-olfaction allows for great design flexibility for portable, low-cost gas sensing and separation.I demonstrated the detection of low-ppm (parts per million) molecules using an affordable and portable acoustic setup. This system operates by detecting changes in the acoustic properties that occur when low-ppm molecules are introduced near acoustic standing wave mode resonances. As illustrated in Fig. 2 [2], the presence of foreign molecules causes a distinct alteration in the acoustic behaviour of the resonator. Specifically, two distinct regions are formed: one above and one below the resonance frequency (fr), each showing a corresponding increase or decrease in the sound pressure level when compared to a resonator filled with nitrogen (N2), depending on gas properties.To capture these subtle changes, I developed high-resolution chirp signals, allowing for the accurate extraction of the frequency response function at low-ppm concentrations. These measurements align closely with theoretical predictions, confirming the validity of the approach. Moreover, the results demonstrated consistent and repeatable results over extended periods, highlighting the robustness of the technique. Such a successful demonstration emphasizes the potential for chemical Research Digest sensing applications using acoustic principles, particularly with the use of widely accessible and commercially available acoustic components. A practical solution for real-world detection of trace molecules is promising for a variety of fields including healthcare, agriculture and indoor air monitoring.I am furthering my designs to incorporate surface modifications, nonlinear intermodulation and thermoviscous acoustics for gas separation coupled with an existing nanomechanical sensor platform at NIMS.30Non-linear Thermoviscous Acoustics (TVA) Induced Multi-Component Gas Separation for Mobile Olfaction
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