Progress 07/01/23 to 02/29/24

Outputs
Target Audience:The target audience for this research is greenhouse scientists and greenhouse operators. Changes/Problems: Nothing Reported What opportunities for training and professional development has the project provided?This project included enabling training of a multidisciplinary bioengineering intern who was working with IFOS full-time for one year as part of her undergraduate program. How have the results been disseminated to communities of interest?We plan to disseminate the results to the greenhouse community during the Phase II program. What do you plan to do during the next reporting period to accomplish the goals? Nothing Reported

Impacts
What was accomplished under these goals? Phase I had the following successfully met objectives: 1. Application/design analysis (sensing requirements and performance). 2. Fabrication of representative FBG-based sensors for temperature and humidity. 3.Proof-of-concept demonstration of distributed sensor system with sub-degrees-celsius . To realize these objective, Phase I involved five technical tasks, the highlights of which are discussed below. Task 1: Kickoff, Requirements and Specifications. FOS held a kickoff meeting with USDA technical monitor Dr. Victoria Finkenstadt. IFOS also met with Professor Heiner Lieth of UCD both by Zoom (multiple times) and in person at the UCD greenhouse facility to discuss greenhouse monitoring needs and target specifications. From our discussion with Professor Lieth, generally the most important parameters are temperature, humidity, CO2, and sunlight. With multipoint 3D temperature distribution being the most important and sunlight measurements only needed at a limited number of points in the greenhouse. Task 2: Application Design Analysis. In this Task, IFOS performed (a) sensor design analysis, and (b) cost-effective instrumentation optimization for greenhouse application. Unlike other sensor system applications that IFOS works on involving dynamic strain, vibration and acoustics, greenhouse monitoring of temperature, humidity does not need to be as rapid, i.e., seconds or even minutes are adequate in comparison with milliseconds or microseconds for some other IFOS system. This allows the relatively fast interrogation core to be switched around a large network of sensors without any performance limitations. In particular, we determined that by combining our interrogation core we will be able to examine 20 sensors on a single fiber at our baseline sampling rate of 6 kilosamples per second (ksps) with an optical switch having a large fiber channel count (1x64 or 1x256), but switching between channels relatively slowly (10 Hz) we could examine a network of 1280 or 5120 sensors at acceptable rates (in 6.4 or 25.6 seconds respectively). If the greenhouse being instrumented would benefit from more sensors per fiber, that can be cost-effectively increased up to four-fold from 20 sensors per fiber to 80 sensors per fiber using IFOS's patented optical band multiplexing technology [7-9] providing support for on the order of 20,000 sensors. Task 3. FBG Sensor Array Design and Fabrication. In this task, IFOS fabricated packaged FBG sensors for air temperature and humidity sensing. The temperature sensing was based on FBGs having approximately 10 pm/ºC wavelength shift with humidity independent fiber coatings. While uncoated silica fiber FBGs are insensitive to humidity, some coatings over the silica can lead to humidity-dependent wavelength shifts. This is due to the coating absorbing moisture from the air which causes the coating to swell, which in turn results in apparent strain on the fiber and FBG. Figure 3 considers the effect of different diameter coatings of Ormocer [6]. The largest shift 3.7 pm / %RH are seen for an 80-μm fiber with a 190-μm Ormocer coating. To get both temperature and humidity, we use side-by-side standard fiber and humidity-coating-sensitive fiber. IFOS also investigated possible surface contamination and determine the best means of protection in the greenhouse environment. Task 4. Proof-of-Concept Demonstration Fabrication and Configuration. In this task, as proof-of-concept demonstration, the IFOS team assembled and instrumented a small-scale greenhouse enclosure.This feasibility demonstration unit was first instrumented with five pairs of temperature and five humidity sensors, each type multiplexed on an optical fiber. The purpose was to provide an experimental testbed to demonstrate the feasibility of the distributed sensor concept. In addition, several vertical sensor arrays were used for demonstrating the height dependence of temperature under certain conditions in the greenhouse. IFOS upgraded the software of one of its I*Sense® FBG sensor interrogators to support temperature and humidity monitoring. Sensor arrays were deployed in a lattice-type configuration to provide maximum coverage of the greenhouse area Task 5. Sensor Network Test and Evaluation. The IFOS team tested and evaluated the fabricated feasibility prototype's performance in sensing quasi-distributed air temperature and humidity. We comparedtwo of the elevated fiber optic temperature sensors, one of which was part of an unobtrusive sensor array vertically attached to metal shelving. The other was one of multiple sensors in an array suspended from the roof in the air and so also subject to air currents. We note that during the day when the door and roof vents were opened to keep the greenhouse cooler, the sensor in the suspended array gave a "noisier" signal due to the air currents imparting strain on the fiber as well as temperature variation. The actual temperature would be an averaged version of the blue trace. We also noticed that during the day (depending on sun/cloud conditions), there could be significant variation in temperature depending on elevation and proximity to walls of the greenhouse, whereas when the structure was closed at night all sensors read a similar temperature.While we generally plan sensor array implementation to avoid strain effects, the results for the blue trace do show the potential for measurement of air currents in cases where that could be of value due to plants that are susceptible to air dying effects. Following our experiments, we evaluated minimum detectable sensitivity (~0.1ºC), accuracy (~1ºC depending on calibration), and measurement speed - base speed for a single sensor array can be 6 ksps. However, measuring all sensors every 10 seconds was determined as sufficient. In conclusion, we conclusively demonstrated the capability of measuring any-point distructed temperaure and humdisity readings within a greenhouse with significantadvantage over traditional sensors that require separte wiring for each sensor or periodic changing of batteries.

Publications