A fully printed sensor with optical readout for real-time flow monitoring

In recent years, there has been a growing interest in the development of flexible thermal flow sensing devices due to their wide-ranging applications. In this study, we present the fabrication of a screen-printed optical flow sensor on a 125 μm PET substrate in a three-layer configuration. The device comprises electrodes made from a commercial Ag ink, a heating area using a commercial carbon ink, and a thermochromic layer employing a commercial ink with a standard activation temperature of 31°C. We designed a specialized experimental setup to evaluate the performance of the optical flow sensor under static and dynamic conditions. To analyze the device's thermal response and performance across various flow conditions, we utilized a combination of electrical measurements and IR-optical imaging techniques. The all-printed device operates on the basis of a thermodynamic cycle frequency, which activates the thermochromic ink, causing it to blink at a frequency related to the flow passing over the sensor. The results of our preliminary testing are highly promising, as the sensor successfully demonstrated a clear relationship between flow and optical duty cycle. This innovative device offers a contactless, low-cost, easy-to-use flow detection method and holds significant potential for various practical applications.