That in the future plants will be able to “talk” to us, broadcasting their water state or signaling s.o.s. in the presence of “unwelcome” parasitic guests is not an extract from a futuristic science fiction novel nor does it border on the insane. The fundamental notion that plants are inherently inexpensive, sustainable sensors for monitoring environmental factors such as soil quality and air pollution has been inquired into for quite a while now by academic institutions all over the world.
Most of these fascinating “Internet-of-Vegetables” researches have made heavy use of the typical Marconi radio transmitter. A Marconi radio e.g. a Bluetooth or ZigBee transmitter, consists of a sensor that has a capacitor, which is inserted inside the soil and transmits to your cell phone how wet the soil is using a simple capacitive soil moisture sensor. This system establishes a “unique” relationship between the plant and the farmer. The latter gets to know the plant’s needs, singles out emerging problems in prompt time, discerns alarmingly high humidity or low temperatures and waters the plant at the exact right time. Consequently, irrigation requirements slacken off by 20 to 30 per cent and farmers get their hands on a much more advanced knowledge of their plant’ s state, not to mention that consumers eat greener.
Structurally, a typical Marconi radio transmitter has a microcontroller or processor, and some signal conditioning animals, basically a filter, a mixer, an oscillator and a power amplifier. “That amounts to complexity and energy and monetary costs,” says Dr. Aggelos Bletsas , Professor of School of Electronic and Computer Engineering of the Technical University of Crete (TUC). “ If you want to network 10000 plants, it will cost tens to hundreds of dollars per plant, and will take about 60 milliWatts per plant for ranges of 100 meters to 1 kilometer . You can’t go lower than that.”
The research team Dr. Bletsas leads has fabricated a groundbreaking way to yield Marconi-type benefits sans the energy and financial burdens attached to a conventional Marconi transmitter.
“We got rid of all these little annoying animals,” says Dr. Bletsas. “Instead, we opted for one radio for each plant that has one antenna, one transistor that acts as a switch, and one low-cost microcontroller.”
“You illuminate the antenna with a carrier and that antenna reflects back that wave. The plant can modulate information by a very smart switching of this antenna. All you need is a switch. You have used that, you have seen that. Think about the alarm that sets off when a lady steps out of your favorite store without having removed a simple RFID tag. This device is based on the principles of the very same RFID technology or Radio Frequency Identification technology,” says Dr. Bletsas.
Traditional RFID technology covers a limited range of a few meters, however. Technical University of Crete is currently laying the groundwork for the creation of scatter radio of the order of tens to hundreds of meters. How?
“In typical RFID applications, the reader has also the illuminator of the initial wave. We separated these two. The carrier reader is a different device from the reader of the scatter information. You illuminate the tag with a carrier, the tag modulates information using this trick with the switch, and the reader demodulates the data the plant sends, extracting the information the user wants using smart signaling process – we worked hard on intelligent, software-defined signal processing at the reader, highlighting the differences with conventional Marconi-type signals, as well as efficient modulation and powering at the tag – the latter is so simple in terms of hardware and power consumption that could be powered by various means, including solar energy or super capacitors or other means that need no battery replacement” says Dr. Bletsas.
“This is bistatic scatter radio architecture. Our idea is based on backscatter communication, that is communication by means of signal reflection, rather than active signal transmission. With backscatter communication and appropriate design, the RF front-end of each sensor can be simplified to a single transistor, reducing complexity and cost by at least one-order-of magnitude, compared to conventional (i.e. Marconi-type) radios. Current RFID systems target short-range, large bit-rate applications but our research team leverages the idea of backscatter communication for long-range, low bit-rate and large number of simultaneously operating low-complexity sensors,” says the Professor.
And all these at the cost of a couple of euros.
The next big challenge is to treat plants as sensors themselves. “Plants are very intelligent sensors,” affirms Dr. Bletsas. “Instead of monitoring external parameters why not plug electrodes at the plant stem and convert that electric potential (EP) voltage to periodic signal that has a fundamental frequency proportional to that EP signal and transmit it with the same principle?”
By monitoring the electric potential the user can decipher not only whether there is rain in the air or soil but also whether the plant itself has been watered or not. Solar irradiance and electric potential signal are fully correlated. “By monitoring electric potential signal I can find out what time of the day this signal appeared. So I can find out the clock of the plant, “says Dr. Bletsas.
Clearly, the Internet of Vegetables offers a new window into decrypting plant mechanisms of communication previously unfathomed. In this optimistic context, TUC is ready to break new barriers for the way plants “network” with their kind and humans.
“Our main goal was to create systems enabling a large communication range of 150 meters. We have done it”.
“Then, a sensor and radio that cost less than a euro. We are at about 5 euros in quantities of ten now but the ultimate aim is not far. If we scale production up to quantities of 10000 or 100000 it may go down.”
“We want completely battery less sensors. We are close“.
A fascinating spectrum of projects on the Internet of Things (IoT) will radically make over the physical world into one that is as “graspable” and comprehensible as the digitalized one. In the specific case of plants, agricultural fields with dense environmental sensor networks savvying how plants communicate, how they suffer and how their biological clock “ticks” will occasion to maximum irrigation efficiency and plant health at the lowest energy and monetary cost. Are you ready to tune with the greens?