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The Internet-of-Things (IoT) infrastructure is made of uniquely identifiable wireless-enabled smart devices that use the Internet to communicate with each other as well as people, on a large scale. These IoT devices require power to operate, and to communicate with other smart devices. The optical bands have the capacity to provide power and wireless communication to the IoT devices. Simultaneous lightwave information and power transmission (SLIPT) is a technology through which information and optical power are received simultaneously by the receiver. SLIPT is made possible by solar cell-based SLIPT receivers. In this thesis, for the first time, the trade-off between the achievable data rate and the harvested power in solar cell-based SLIPT systems is quantified and analysed. It is known that the amount of power harvested using a solar cell is dependent on its operating voltage. By utilizing a realistic electrical model of the solar cells, an expression for the bandwidth and a lower bound on the data rate of a solar cell receiver as function of the operating voltage is derived. Using the dependency of rate and power on the operating voltage, the rate-power trade-off in solar cell based SLIPT receivers are studied in this thesis. This work proposes a novel solar cell based SLIPT receiver that includes a DC-DC boost converter, which allows control over the operating voltage of the solar cell. Finally, this thesis proposes an optimization problem to compute the optimum operating voltage for a SLIPT system located indoor where a desired trade-off between the data rate and harvested power can be attained based on the battery state of charge. / Thesis / Master of Applied Science (MASc)

With the advent of energy harvesters, supporting fast and efficient computation on energy harvesting devices has become a key challenge in the field of energy harvesting on ubiquitous devices. Computation on energy harvesting devices is equivalent to spreading the execution time of a lasting application over short, frequent cycles of power. However, we must ensure that results obtained from intermittently executing an application do produce results that are congruent to those produced by executing the application on a device with a continuous source of power. The current state-of-the-art systems that enable intermittent computation on energy harvesters make use of novel compiler analysis techniques as well as on-board hardware on devices to measure the energy remaining for useful computation. However, currently available programming models, which mostly target devices with FRAM as the NVM, would cause failure on devices that employ the Flash as primary NVM, thereby resulting in a non-universal solution that is restricted by the choice of NVM. This is primarily the result of the Flash's limited read/write endurance. This research aims to contribute to the world of energy harvesting devices by providing solutions that would enable intermittent computation regardless of the choice of NVM on a device by utilizing only the SRAM to save state and perform computation. Utilizing the SRAM further reduces run-time overhead as SRAM reads/writes are less costlier than NVM reads/writes. Our proposed solutions rely on programmer-guidance and compiler analysis to correct and efficient intermittent computation. We then extend our system to provide a complete compiler-based solution without programmer intervention. Our system is able to run applications that would otherwise render any device with Flash as NVM useless in a matter of hours. / Master of Science / As batteries continue to take up space and make small-scale sensors hefty, battery-less devices have grown increasingly popular for non-resource intensive computations. From tracking air pressure in vehicle tires to monitoring room temperature, battery-less devices have countless applications in various walks of life. These devices function by periodically harvesting energy from the environment and its surroundings to power short bursts of computation. When device energy levels reach a lower-bound threshold these devices must power off to scavenge useful energy from the environment to further perform short bursts of computation. Usually, energy harvesting devices draw power from solar, thermal or RF energy. This vastly depends on the build of the device, also known as a microprocessor (a processing unit built to perform small-scale computations). Due to these devices constantly powering on and off, performing continuous computation on such devices is rather more difficult when compared to systems with a continuous source of power. Since applications can require more time to complete than one power cycle of such devices, by default, applications running on these devices will restart execution from the beginning at the start of every power cycle. Therefore, it is necessary for such devices to have mechanisms to remember where the were before the device lost power. The past decade has seen many solutions proposed to aid an application in restarting execution rather than recomputing everything from the beginning. Solutions utilize different categories of devices with different storage technologies as well different software and hardware utilities available to programmers in this domain. In this research, we propose two different low-overhead, long-life computation models to support intermittent computation on a subset of energy harvesting devices which use Flash-based memory to store persistent data. Our approaches are heavily dependent on programmer guidance and different program analysis techniques to sustain computation across power cycles.

Energy harvesting technologies have drawn much attention as an alternative power source of roadway accessories in different scales. Piezoelectric energy harvesting consisting of PZT piezoceramic disks sealed in a protective package is developed in this work to harness the deformation energy of pavement induced by traveling vehicles and generate electrical energy. Six energy harvesters are fabricated and installed at the weigh station on I-81 at Troutville, VA to perform on-site evaluation. The electrical performance of the installed harvesters is evaluated by measuring the output voltage and current generated under real traffic. Instant and average power outputs are calculated from the measured waveforms of output voltage and current. The analysis of the testing results shows that the electrical productivity of the energy harvesters are highly relevant to the axle configuration and magnitude of passing vehicles. The energy transmission efficiency of the energy harvester is also assessed. / Ph. D.

Harvesting energy from ultra-low-power vibration energy sources typically employs a rectifier circuit as the first power conditioning stage. The Schottky diode has a 0.15 V - 0.2 V threshold voltage and can not extract energy efficiently at low voltage. Other technologies such as MOSFET bridge or active diode are designed to minimize the voltage drop to reduce the conduction loss. However, these designs require either additional power supplies to operate comparators or have a larger threshold turn-on voltage than Schottky. Therefore, most rectifiers have an unresponsive or significant low-efficiency zone when the input power is low. This dissertation will elaborate on a backward diode based self-powered micro-circuit diode that will operate in the extremely weak or low alternating source applications, where the existing approaches offer poor outcomes. This proposed micro-circuit diode was compared to a Schottky diode in several experiment setup. The micro-circuit based half-wave rectifier circuit harvested 3.1 mV DC at a 239.5 Ohm load when the input magnitude is 50 mV while the Schottky diode was unable to convert this ultra-low AC power. This dissertation also provides the analysis of two alternating sources, the oscillatory electromagnetic generator and the piezoelectric energy harvester, to conduct experiments in a more realistic context. The micro-circuit diode shows excellent advantages in electromagnetic generator experiment, the micro-circuit based half-wave rectifier circuit harvested 5.16 mV DC at a 0.5 kOhm load when the input magnitude is 40 mV. However, due to the large leakage current in negative resistance region, this micro-circuit is unable to show advantages in piezoelectric energy harvester applications.

The Internet of Things (IoT) is an infrastructure of physical objects connected via the Internet that can exchange data to achieve efficient resource management. Billions of devices must be self-powered and low-cost considering the massive scale of the IoT. Thus, there is a need for low-cost ambient energy harvesters to power IoT devices. It is a challenging task since ambient energy might be unpredictable, intermittent and insufficient. For example, solar energy has limitations such as intermittence and unpredictability despite utilizing the highest power availability and relatively mature technology. Designing a multi-source energy harvester (MSEH) based on continuous and ubiquitous ambient energy sources might alleviate these issues by providing versatility and robustness of power supply. However, combining several energy harvesters into one module must be done synergistically to ensure miniaturization, compactness and more collected energy. Also, additive manufacturing techniques must be used to achieve low-cost harvesters and mass manufacturability. This dissertation presents two different kind of ambient energy harvesters, namely radio frequency energy harvester (RFEH) and thermal energy harvester (TEH). Each harvester is individually optimized and then synergistically combined into a MSEH. First, RFEH is designed for triple-band harvesting (GSM900, GSM1800, 3G2100) using the antenna-on-package concept and fabricated through 3D and screen printing. TEH collects energy from temperature fluctuations of ambient environment through a combination of thermoelectric generators and phase change materials. It is adapted specifically for the desert conditions of Saudi Arabia. Later, TEH and RFEH are combined to realize MSEH. Smart integration is achieved by designing a dual-function component, heatsink antenna, that serves as a receiving antenna of RFEH and a heatsink of TEH. The heatsink antenna has been optimized for both antenna radiation performance and heat transfer performance. Field tests showed that the MSEH can collect 3680μWh energy per day and the outputs of TEH and RFEH have increased 4 and 3 times compared to the independent TEH and RFEH respectively. To validate the utility of the MSEH, a temperature/humidity sensor has been successfully powered by the MSEH. Overall, sensor’s data can be wirelessly transmitted with time intervals of 3.5s, highlighting the effectiveness of the synergistic MSEH.

From the results of this study the following conclusions can be drawn. All conclusions are based on statistical ABOVA tests at a five percent level of significance. 1. Baaed on 108 detachment tests, it can be concluded that the difference in rate at which the loads were applied to the stem, which were 0.175 and 0.350 in./sec did not affect the force of removal. 2. Based on 108 detachment tests, it can be concluded that the angle at which the load was applied to the stem did affect the force of removal. The loading angles used were 90, 60, 30 and 0 degrees. 3. Two, 4-day differences in the stage of maturity did not affect the detachment force. 4. Each individual stem exhibited non-linear stress-strain properties since the calculated apparent elastic modulus in bending decreased as stem deflection increased. S. The rate of applying the load to the stem influenced the calculated apparent elastic modulus values. / Master of Science

Tall fescue (Festuca arundinacea Schreb.) often becomes dormant in the hot summer months. Switchgrass (Panicum virgatum L.) has potential to supplement the limited carrying capacity of tall fescue in mid-summer. The objective of this study was to determine the seasonal dry matter distribution and quality of tall fescue and switchgrass as influenced by different harvest managements. Switchgrass and tall fescue were studied on a fine-loamy, mixed, mesic Ultic Hapludalf of the Duffield soil series at Blacksburg, VA during 1987 and 1988. Normal harvest management included harvests taken from the first growth in spring until mid to late August. Delayed management included harvests taken from regrowth after a hay crop in mid-May for tall fescue and early June for switchgrass until mid to late August. Three and four harvest intensities were imposed on tall fescue and switchgrass, respectively. Plots were harvested in 1989 to determine the accumulative influence of treatments. Yield, crude protein, neutral detergent fiber, and invitro dry matter digestibility were measured for each harvest of both species. Digestible yield and protein were calculated for each harvest. Clipping either switchgrass or tall fescue at any harvest intensity reduced potential yield compared to forage not clipped. Accumulated forage resulted in high yields but unsatisfactory quality. Delayed harvest management resulted in higher total yield than normal harvest management because of high hay yields. This study indicated that considerable overlap of forage production of tall fescue and switch grass occurred in late spring but abundant high quality switchgrass was available in midsummer when available tall fescue was low. Switchgrass warrants consideration in southwest Virginia as a solution to the problem of limited cool-season forage in midsummer. / Master of Science

Doctor of Philosophy / Department of Biological & Agricultural Engineering / Donghai Wang / In 2008 AGCO began a project to develop machinery to harvest biomass for a DOE project called “Integration of Advanced Logistical Systems and Focused Bioenergy Harvesting Technologies to supply Crop Residues and A Herbaceous Energy Crops in a Diversified Large Square Bale Format”. The project considered the harvest of corn stover, wheat straw, switchgrass and energy sorghum. AGCO modified some existing pieces of production hay harvesting equipment and developed a new larger square baler for single pass crop residue harvesting. Field scale tests of the developed equipment occurred in the years 2010, 2011, and 2012. Data collected during these tests included crop harvested, field location, number of hectares harvested, moisture content of harvested biomass, number of bales produced, weight of each bale, time to harvest, model(s) and sizes of machine(s) used, and fuel consumed. Data was collected for different harvesting techniques for crop residues: two-pass vs single-pass harvesting for corn stover and wheat straw. Data was collected for harvesting switchgrass and energy sorghum for comparison purposes. The cropping years were very different over the course of the project due rain fall amounts. The data was analyzed using American Society of Agricultural and Biological Engineer machinery management standards and accepted Agriculture & Applied Economics Association assumptions. Excel spreadsheets were developed to calculate the harvesting costs on a dry Mg basis for each crop that was harvested. Results from the data analysis was used to modify the Integrated Biomass Supply Analysis and Logistics model to predict harvesting costs for crop residues at different yield levels, harvest conditions, and machine settings for single-pass harvesting. A number of conclusions can be drawn from this analysis. First, “take rates” for crop residues can have a significant effect on harvest costs. Low “take rates” can make it economically unfeasible to harvest crop residues in some instances. Second, single-pass harvesting of crop residues is less labor and fuel intensive than multi-pass harvesting. Third, the large yields potential of energy sorghum, which requires more operations to harvest than switchgrass, more economically to harvest than switchgrass. Fourth, operational techniques can be used to offset some crop variability to reduce harvest cost of crop residues. Lastly, a decision tool has been developed to aid producers in the decision of whether to harvest corn stover or not based on cost return estimates.

Ph.D. (Agriculture)) -- University of Limpopo, 2021 / The rind physiological disorders incidence such as rind pitting is a challenge to the citrus industry as it affects appearance; and ultimately, acceptability and purchase in both local and international markets. Although the internal quality is not directly affected by rind pitting, fruit damaged by this disorder are rejected in the fresh fruit market. The susceptibility to this disorder varies among citrus fruit cultivars. Other factors impacting rind physiological disorders include; pre-harvest environmental conditions and postharvest storage conditions. However, the main cause of this disorder is still unknown. In South Africa, ‘Benny’ valencias are the most prone orange cultivars to rind pitting disorder within the sweet-orange-type. Therefore, the aim of this study was to investigate production site and postharvest treatments’ effect on physico-chemical, biochemical properties, antioxidants, rind soluble sugars and gene expression in relation to rind pitting development of ‘Benny’ valencia citrus fruit. During 2016 and 2017 seasons, the study was conducted, whereby, ‘Benny’ valencia citrus fruit were harvested from Tzaneen, Groblersdal and Musina in South Africa. After harvesting, the fruits were transported to the Agricultural Research Council- Tropical and Subtropical Crops (ARC-TSC) postharvest laboratory in Nelspruit for sorting, grading treatment, cold storage and post-storage quality evaluation. After sorting and grading, fruits were subjected to the following treatments: T1 = no wax plus dehydration, T2 = wax plus dehydration and T3 = wax plus no dehydration. Dehydrated treatments were applied for 3 days at relative humidity of ±45%, thereafter, fruit were stored at -0.6 and 4.5°C for 28 days plus 7 days shelf-life. After removal from cold storage plus 7 days shelf-life, fruit were analysed for rind pitting incidence (RPI), weight loss percentage (WL), firmness, total electrolyte leakage (TEL), total soluble solids (TSS), titratable acidity (TA) and TSS: TA ratio. xxvi Afterwards, fruit were peeled to remove flavedo, thereafter; the flavedo peels were freeze-dried, milled and stored at -21°C for further physiological analysis. Freeze dried flavedo peel was analysed for total flavonoids, total phenolics, vitamin C, soluble sugars (glucose, fructose and sucrose), antioxidant assays (FRAP, DPPH, ABST and ORAC) and genes. The results showed that rind pitting incidence was high on fruit subjected to wax plus no dehydration across all storage temperatures and production sites. Furthermore, results showed that fruit harvested from Musina exposed to T1 had higher incidence of rind pitting than those from Groblersdal and Tzaneen, irrespective of storage temperature. Meanwhile, fruit harvested from Musina had the highest TEL when compared with Groblersdal and Tzaneen irrespective of treatments and storage temperatures. A significantly higher (P<0.05) WL was observed in Musina fruit harvested from Tzaneen exposed to T3 at both storage temperatures. Moreover, increased TSS was observed after storage across all production site and postharvest treatments. The study showed that production site and postharvest treatments had a significant influence on rind pitting and total electrolyte leakage. Additionally, fruit treated with no wax + dehydration was found to be more susceptible to rind pitting. However, fruit sourced from Tzaneen had significantly (P<0.0001) high TPC and TFC, irrespective of postharvest treatments therefore, low rind pitting incidence. While rind vitamin C was higher in fruit from Groblersdal when compared with Tzaneen and Musina. However, low RPI was also observed in fruit sourced from Groblersdal. Fruit from Musina subjected to wax plus dehydration had higher RSA and low RPI at both temperatures when compared with fruit sourced from Groblersdal and Tzaneen. Therefore, wax plus dehydration resulted in low rind pitting with an increased accumulation of rind biochemical concentrations, xxvii irrespective of cold storage temperatures. These results suggested that there is a link between rind pitting and rind biochemical concentrations in the ‘Benny’ valencia citrus fruit. Moreover, fruit from Musina subjected to wax plus dehydration had higher antioxidant measured by DPPH and low RPI at both low storage temperatures when compared with fruit harvested from Groblersdal and Tzaneen. Furthermore, fruit harvested from Musina and treated with no wax plus dehydration, thereafter, stored at -0.6°C had low RPI with high antioxidant activity measured by FRAP than Tzaneen and Groblersdal regions in both seasons. With respect to sugars, fructose was not significantly (P<0.05) affected by production sites, postharvest treatments and cold storage temperature, hence, the low pitting incidence. The highest glucose was observed in fruit harvested from Groblersdal, irrespective of treatments and cold storage temperatures when compared with those from Tzaneen and Musina, low RPI was also observed in fruit harvested from Groblersdal. However, fruit harvested from Groblersdal treated with wax plus dehydration and stored at 4.5°C had higher sucrose and low RPI when compared with Tzaneen and Musina. Moreover, this study suggested that soluble sugars in ‘Benny’ valencia flavedo during cold storage is involved in rind pitting tolerance mediated by wax plus dehydration treatment. Three homologic genes: CsCP gene; CsNAC-domain protein gene; CsCP-F gene; were chosen to examine the relationship between their expression and citrus rind pitting through quantitative RT-PCR analysis in pitting and no-pitting fruits. Results showed that the expression of CsCP, CsNAC and CsCP-F genes were all higher in the pitting rind fruit harvested from Tzaneen and low in fruit with low pitting. Groblersdal and Musina fruit had low expression of genes and low rind pitting was observed. Therefore, findings suggested that CsCP, CsNAC and CsCP-F genes may xxviii be linked to non-chilling rind pitting and could serve as targets for future investigation. Generally, the overall results obtained in this study provided an understanding into the previous unknown complexities of citrus non-chilling rind pitting. Moreover, the study revealed that the studied factors had an influence on non-chilling rind pitting and physico-chemical properties of ‘Benny’ valencia citrus fruit. In addition, postharvest treatments resulted in low non-chilling rind pitting with an increased accumulation of rind biochemical concentrations. The fruit with high antioxidant capacity were found to be tolerant to rind pitting, whereas, fruit with low antioxidant capacity were found to be susceptible to rind pitting. Furthermore, soluble sugars are believed to be involved in the defence mechanisms against non-chilling rind pitting in the fruit. Gene expression changes also provided clues about the possible mechanisms involved in non-chilling rind pitting development. / National Research Fund, Agricultural Research Council Tropical and Subtropical Fruit Crops and Citrus Academy