Water loss in the original coupling bags occur primarily through the seams, the Velcro seal, and naturally through the pores of the silk cloth. The Final bag design shown in Figure 1 addresses all three of these areas of water loss. The new bag design is composed of two silk bags, one of which is slightly smaller and placed inside the other silk bag. The inner silk bag is covered with a windowed, pink, anti-static bag (made of Polyethylene). The anti-static bag experiences negligible water loss and during testing it did not appear to negatively affect the ground sensor's performance, which is why it was chosen as a supplementary material for our bag. A window is cut into the anti-static bag to allow the damp silk to make electrical contact with the eCube electrode and the soil.
The new coupling bag design shows a ~85% water loss reduction compared to the original silk bags, which can be verified from the results of Figure 2 and Figure 3. The results were acquired from performing tests in our test environment (often referred to the "test jig") and a "real-word" outdoor test environment using the actual ground sensor & equipment used by Ground Metrics Inc.
In addition to recording the water loss from the tests, humidity and temperature data was collected as well. This information was used to approximate the permeability of each of the bags seen in Figure 4, then the permeability values of the bags were compared to each other to determine which coupling bag design was the best (the best design was the coupling bag with the lowest permeability).
The humidity and temperature values needed to perform this permeability comparison were obtained from Arduino R3 using eight RHT03/DHT22Â humidity and temperature sensors (the model is the same, even through the name is different) seen in Figure 5. For each bag being tested, one sensor was placed inside the bag and another was placed on the outside of the bag; the odd numbered sensors were placed on the outside of each respective bag, and the even numbered sensors were placed on the inside of each respective bag (ex: bag#1: sensor#1 outside & sensor#2 inside, bag#2: sensor#3 outside & sensor#4 inside, etc.).