Portable Fungi Growth Detection of Botrytis Cinerea Enabled by Swept Frequency GHz Ultrasonic Imaging

This paper demonstrates the detection of Botrytis Cinerea using a CMOS-integrated GHz ultrasonic imager. This work expands on the previous work on detecting pathogen growth by introducing new ultrasonic characterization methods of fungal colonies through magnitude, phase, and frequency sweep analysis. A spore solution is created from dishes of Botrytis fungal culture and placed on the ultrasonic imager for 24-48 hours to sporulate and grow under three primary conditions: exposure to only air, with periodically added water, and with a food source to promote growth. Through visual analysis of the return signal magnitude and phase images and using a frame-to-frame visual comparison method, one can determine that growth occurs primarily in the first 12 hours. The addition of Potato Dextrose Agar (PDA) has significantly increased the growth rate and visibility of Botrytis. Frequency sweeps are conducted over a 300 MHz bandwidth centered at 1.85 GHz with 200 kHz steps. The effect of fungal growth on the frequency response is measured as a change in the amplitude of the I and Q components of the reflections as a function of frequency. A shift in frequencies and change in the amplitude is observed in pixel frequency sweeps where Botrytis appears to have developed compared to pixels where no growth was seen optically. The methods developed here facilitate further study in categorizing and differentiating Botrytis growth from other fungal and bacterial growths to create an on-farm diagnostic tool for Botrytis Cinerea.