Wireless Leaf Temperature Sensors


TL;DR: Wireless and batteryless: Spyros developed a plant moisture sensor using standard FM radio waves to power itself and to transfer data by backscattering!

These days everybody knows that water is the most essential resource for life as we know it. That’s why for example scientists are looking for water on planets as a possible hint for extraterrestrial life. Being stuck (for now) on this planet with decreasing fresh water resources, we should think about an efficient way to use it!

Agriculture consumes most of the world’s freshwater (70%!). One of the main causes of wasteful and unsustainable water use (listed by the WWF) which leads to such a high water consumption are wasteful field application methods. To establish more efficient irrigation methods it is important to know the moisture level of the plant as precisely as possible. But unfortunately we can’t just ask the plant. And if we could how would we collect all this information within a field of thousands of plants? But there are some people working on a solution for this.

Spyros and his colleagues developed a novel wireless leaf temperature sensor to measure the moisture level of plants using ambient backscattering over analog modulated (FM) signals (Wikipedia: use of existing radio frequency signals to transmit data without battery or power grid connection).

Detecting the temperature difference between the leaves and the air is a well proven monitoring practice to control water stress and is already used in the field. That’s why the currently developed proof-of-concept set-up consists out of a novel tag for leaf and air temperature measurements using ambient backscattering. The tag reflects ambient RF signals from nearby FM stations to communicate with a low cost RTL-SDR reader. Additionally, matched filtering following reception of the backscattered signal envelope, optimized the correct receive symbol probability. The sensing tag topology consists of a microcontroller for processing, a sensor board for the plant sensing and a RF front-end consisting of a commercial switch and an antenna for the communication. This basically means that they developed a plant moisture sensor using standart FM radio waves to power itself and to transfer data by backscattering!

This is work in progress and the laboratory set-up has to established in the field next. But these first results are promising and we are really excited to follow the progress!

If you want to read more about this project you can have a look at the respective paper or at Spyros website.

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