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RFID Moisture

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natclo1 edited this page Feb 10, 2021 · 45 revisions

RFID Moisture | Updates | Github

Project Team:

Electrical & Firmware Lead: Natalie Clouse

Mechanical Lead: Max Chu

Overview

OPEnS RFID aims to address common overwatering and financially demanding issues to agricultural grown by providing a cheap, wireless, battery-less solution to large area moisture sensing. OPEnS RFID integrates the newest advances in ultra-high frequency (UHF) radio frequency identification (RFID) technology into our sensors, which make them a fraction of the cost of other sensors. When set up on an irrigation boom at a common greenhouse, all moisture processing can be done locally onboard a powerful microcontroller, allowing for precise and autonomous control over the watering of these crops.

Current Problem

Overwatering is ubiquitous in agriculture. Whole fields are grossly overwatered to ensure that no single plant experiences water stress. Farmers typically overwater their crops by 20-50% as a precautionary measure. Higher yields and low water costs make this behavior rational. However, recent improvements in water sensors and precision irrigation will make it possible to significantly reduce agricultural water use while maintaining yields.

According to the World Wildlife Fund, agriculture consumes 70% of the planet’s accessible freshwater1. For comparison, 8% of water is used municipally for drinking, sewage and industry. In water strained regions like California, Northern China, and Pakistan, increasing agricultural and municipal demands compete for a finite waters supply.

Another impact of overwatering is agricultural runoff. When soil is oversaturated, the resulting runoff carries environmentally hazardous pollutants and fertilizer into local water systems. Fertilizers consist of nitrogen-based compounds that are harmful to freshwater ecosystems. This runoff also depletes soil of its nutrients, further exacerbating the need for fertilizer.

Precision irrigation systems exist and can substantially reduce agricultural water use; the current bottleneck for these systems is soil moisture data. Without corresponding moisture data the water savings for these systems largely go unrealized. The soil moisture sensors that exist are either too costly, obstructive, or too inaccurate to use in conjunction with precision irrigation. In the following section we describe these limitations.

Block Diagram

Current Solutions

The two primary solutions for soil moisture data have been capacitance probes and satellite imaging. Capacitance probes are the industry standard for taking cheap, accurate soil moisture measurements; however, capacitance probes require a continuous supply of power and often need to be checked manually. These sensors are relatively cheap but installing the number of probes necessary for a precision irrigation grid is costly. For these reasons capacitance probes are impractical for large area moisture sensing.

Satellite imaging is a cost-effective solution, but the results from these images come sporadically (less than once per day) and have low granularity (measure on a hectare scale). For these reasons they are ineffective for managing water usage on a day-to-day basis.

Outcomes

Initial Adafruit STEMMA Soil Moisture Sensor Trial

Initial field testings were done with the Adafruit Capacitive I2C Soil Moisture sensors at Peoria Gardens, mapped to their subjective 1-5 rating scale, where 1 is considered very dry and 5 is considered very wet. The Adafruit Capacitive Soil Moisture sensors contain 10-bits of resolution, designed to serve as the control for the RFID Soil Moisture sensor moisture correlation. The idea behind these data points is to provide accurate mapping of the RFID sensor soil moisture to the proven Adafruit Capacitive I2C Soil Moisture sensor. Updates on these correlations can be found in the Updates page.

Proven Correlation with the 5TM Moisture Sensor

After conducting 48 trials at 9 moisture levels, the data showed a correlation between the RFID tag's sensor values and the 5TM's measure of relative permittivity. This implies that SmarTrac's Dogbone RFID tags are sensitive enough to be used as a moisture sensor. Using the linear, empirically derived equation to map the RFID values to the 5TM,g(x), and then the Topp  equation (Topp et al 1980) to map from relative permittivity to volumetric water content (VWC),f(x), the equation relating the RFID to VWC is below:

f(g(x)) = -8.82803×10^-8x^3 -2.4733710^-5x^2 -3.8844710^-3*x+0.306477

Field Testing

After the correlation was proven in the lab, the team traveled up to OSU's Hermiston Agriculture Research Center to conduct field tests. Using a portable version of the RFID reader that sent data to a companion app over Bluetooth, we read the RFID tags and moisture values as a center pivot irrigation arm passed over. Using this app, we were able to visualize the water seeping down to the depth of the tag.

Future

Market Opportunity

Total Available Market (TAM): International capital-intensive agriculture. Regions that use modern agricultural practices are more likely to adopt our sensor system. To realize the full water savings, it is necessary that the OPEnS RFID System work in tandem with high-precision irrigation systems. Places and industry segments which already use applied irrigation are more likely to adopt our system. For example, center pivots can be easily retrofitted with variable rate nozzles and variable rate rotation motors to provide high precision water application. TAM.PNG

Serviceable Available Market (SAM): Agriculture in California and the Pacific Northwest. Most US agricultural output occurs between the two aforementioned regions. OPEnS Sensors would be ideal for roughly $14 billion of agricultural output.

Serviceable Obtainable Market (SOM): Our first market will be focused on potato growers in Southeastern Washington and Northeastern Oregon, with a regional agricultural annual output of approximately $650 million. We plan to capture 20% of this market in the first two years of commercial production.

It will be a priority for our company to get endorsed by the Potato Commission of Oregon and Washington which will greatly expedite adoption. After the system is tested using potatoes, an ideal crop, we intend to branch out to other water intensive crops with and without canopies.

Additional Projects

The correlation between the SmartTrac Dogbone RFID tags to soil moisture sensor can lead to many different projects for the OPEnS Lab. Currently for RFID Irrigation System, soil moisture data is done locally onto the system via an onboard microSD card, running autonomously. On an Irrigation System with cellular connectivity, a TCP connection can be made on the system, streaming moisture value data onto a Google spreadsheet rather than a local .csv file. This can lead to a more manual control on the irrigation boom as well. With internet connectivity, a GUI can be implemented to adjust different calibration curves of the RFID tags, thus changing the rate of plant watering.

Resource List

Tutorials

Keywords

  • RFID

  • Dogbone

  • Soil Sensor

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