202504291345

• Source: [[ @potyrailo2020 Extraordinary performance of semiconducting metal oxide gas sensors using dielectric excitation ]]
• Tags: #gas-sensor #detection #MOX

In order to overcome the Limitations of chemiresistive gas sensors , instead of measuring the resistance, the authors propose to measure the impedance of the sensitive layer.

It is important to keep in mind that there's a fenomenological power-law rule regarding the resistivity of the sensing layer:

$$R=R_0(1+K_{\text{gas}}[\text{gas}]{)}^{-\beta }$$ Where $K_{\text{gas}}$ is the sensitivity to a specific gas, while $\beta$ depends on different factors, such as: 1. The nature of the measured gas 2. The type of sensing material, including the grain size, grain surface-to-volume ratio, types of dopants 3. The geometry and material of the electrodes of the sensing element.

Using the following circuit diagram for the sensing measurement (IC: intergranular contacts, EC: electrode/particle contacts)

We can define (not sure where this is coming from):

$$Z^{\prime }=\frac{R}{1+(2\pi fCR{)}^2}$$ $$Z^{″}=\frac{-R^{2}C2\pi f}{1+(2\pi fCR{)}^2}$$ The entire observation of the paper is that while resistance alone has a non-linear behaviour and saturates at relatively low concentrations of gas, $Z^{″}$ shows a linear behavior in a wide range of parameters.

Interesting to remember: - The sensor used was TGS 2611 - ASIC: AD5933, ADuCM355