Mr Bodie Fuller, Professor Drew Evans
Sensors, and the data they provide, are becoming increasingly important in shaping the way people live their daily lives. As sensors become more advanced, they are being deployed in varied environments to provide insights and information in locations that were previously inaccessible. Sensing in remote locations and/or environments is one area that is rapidly growing in importance. Such remote sensing applications provide (near) real-time input to the decision-making regarding processes such as mining operations, agriculture, and military operations such as intruder detection and battlefield surveillance. In order for stable sensor operation, a source of power is required – an energy storage device (ESD).
Owing to the importance of longevity and high energy density of ESDs, it seems logical that enhancing the performance of ESDs can be considered a core priority for remote sensing applications.
While sensors detect their area of interest, the data produced from a sensor needs to be analysed at a base terminal. Some sensors are within the vicinity of their terminal and can be connected via cables. However, remote sensors, such as those in the middle of a vineyard, the ocean, or a deep underground mine, do not have the luxury of short distance for cabled connections. A common strategy used to communicate data wirelessly is to implement telemetry technologies. Telemetry is not particularly new and has been used for many years in Bluetooth, ZigBee, Wi-Fi (2G, 3G and 4G) and Long Range wide-area-network (LoRa), among various others. The key issue with wireless telemetries is the requirement of the additional energy that is needed to transmit their data. Wireless sensor networks (WSN) use telemetry technologies to transmit the data obtained by the sensor, to the analyst via the internet of things (IoT) as seen in Figure 1. The IoT is a cloud-based storage protocol that allows WSNs to communicate data from the sensors to the analyst in a matter of seconds. Pivotal to the next phase in the Industry 4.0, modern smart technologies such as IoT for remote sensing is a step above in procuring optimal use of Earths precious resources such as water and arable soils.
As remote sensors using WSNs run on rechargeable battery storage devices, the limited lifetime and energy density of battery technologies of today are just two of the main challenges for continuous remote sensing applications. It is typical that such batteries are not easily reachable for replacement when the life of that battery has ended. Some successful attempts have been made to increase energy efficiency by implementing low energy protocols within the WSN for various applications. The bottleneck of life longevity remains the lack of sufficient energy density within commercial battery technologies.
Today, there are many sources of rechargeable secondary batteries produced from various materials such as nickel, lead, or lithium, due to their high energy density and performance characteristics. The rechargeable battery has revolutionized commercial personal devices, making the mobile phones and laptops the effective devices to communicate, share ideas and control equipment on a daily basis. In the context of remote sensing, however, the current commercial batteries do not meet the requirement of a long-life sensing system, nor are the current testing methods adequate for this application. Renewable energy harvesting such as solar or wind may be used for recharging the batteries, however energy harvesting may not be practical in remote locations. Even with the WSN low energy protocols, current lithium-ion battery technologies struggle to uphold the needs of the ever-growing industry of remote sensing.
The higher energy densities in battery systems is one of the major safety concerns that need to be addressed. Theoretically, lithium metal has the highest energy density of all currently known materials, however, the use of lithium metal at room temperature (25°C) has recently resulted in combustions and fires. Lithium-ion batteries have optimal temperature ranges between 10 °C – 45 °C before degradation of internal components begins, which can also lead to combustion. When operating in remote locations, these energy storage devices (ESD) are subject to environmental conditions which may exceed the optimal operating range of current commercial ESDs. The daily maximum ambient air temperature over the year of 2019 in Riverland South Australian fluctuated from a high of 48 °C in the summer months to a low of 12 °C in the winter months, as seen in Figure 2. Each day, the temperatures vary significantly, where some cases this change may be as large as ± 15 °C from one day to the next. This is just one example to highlight the importance of considering the operational conditions of ESDs beyond just temperature-controlled environments, especially for existing and emerging remote sensing applications.
Several challenges must be overcome to ensure an appropriate translation of prior R&D and scientific knowledge to ESDs for remote sensing applications. Much of the ESD development (and proposed improvements) arise from their application in consumer electronic devices such as tablets and smart phones – hence not necessarily aligned with remote sensing requirements. Overall, the conditions a remote sensor ESD is subject to differ greatly from commercialised battery technologies used in personal devices of today. The current view of energy harvesting is not applicable in every remote sensing scenario (underground mining for example). These special conditions lead to the requirement of high energy density batteries that are capable of long, slow, and safe discharging during operation in variable climatic conditions.
Mr Bodie Fuller’s PhD project focuses on the investigation of ESDs for use in remote sensing, in partnership with Sentek Pty Ltd.