The romantic notion of grizzled ranchers out riding the range on horseback to shepherd their herd of cattle may soon be a distant memory, as cloud-based sensor technology now permits real-time animal tracking from the comfort of home or office, or by smartphone.
The transformation of modern ranching is just one example of how remote wireless connectivity is impacting virtually all aspects of modern life as part of the burgeoning Industrial Internet of Things (IIoT).
Riding the Range
A prime example of IIoT interconnectivity is CattleWatch, a cloud-based hardware/software technology that utilizes energy harvesting to power sensor and communication tools to enable remote monitoring of livestock. The CattleWatch system deploys a small number of hub collars equipped with small photovoltaic panels, which are placed on roughly 2% of the cattle, while the rest of the herd is outfitted with collar units or ear tags powered by primary lithium batteries. Cows are exceptionally large animals, so the added size and weight of an energy harvesting device does not cause significant discomfort.
All collars communicate with the solarpowered hub collars to create an in-herd wireless mesh network that provides valuable, near-real-time insight regarding animal behavior, including herd location, walking time, grazing time, resting time, water consumption, in-heat condition, and other health events. The system even broadcasts alerts if predatory animals or poachers are detected (see Figure 1).
The energy harvested from miniaturized photovoltaic cells is stored in industrial-grade lithium-ion (Li-ion) rechargeable batteries that handle the high pulses required to communicate with the Iridium satellite network, accessible from the rancher’s computer or smartphone via the Internet “cloud.”
Energy Harvesting’s Role in IoT Expansion
While the CattleWatch example demonstrates the dynamic potential for energy harvesting technology, in reality, wireless devices intended for long-term deployment draw low average daily current; the technologies are predominantly powered by primary bobbin-type lithium thionyl chloride (LiSOCl2) batteries, which are generally preferred due to their very high energy density, high capacity, and wide temperature range.
Certain bobbin-type LiSOCl2 cells feature an annual self-discharge rate of less than 1% per year, permitting 40-year battery life. The cells can also be modified with a patented hybrid layer capacitor (HLC) to provide the high pulses required for advanced two-way wireless communications. The standard LiSOCl2 cell delivers long-term low-rate current to power the device in “standby” mode, while the HLC stores and sends periodic high pulses to support data interrogation and transmission. The hybrid technology offers significant advantages over supercapacitors, which have limitations, including short duration power, limited energy discharge, low capacity, low energy density, and high self-discharge. Supercapacitors linked in series also require cell balancing circuits.
The use of an energy harvesting device over a primary lithium battery is dependent on several factors, including a reliable source of energy (such as light, vibration/motion, heat differential, or RF/EM signals), the reliability and expected operating life of the device, environmental requirements, size and weight considerations, as well as the total cost of ownership.
The typical energy harvesting device consists of five basic components: the sensor; the transducer; the energy processor; the microcontroller; and an optional radio link. The sensor detects and measures environmental parameters such as motion, proximity, temperature, humidity, pressure, light, strain vibration, and pH. The transducer and energy processor work in tandem to convert, collect, and store the electrical energy either in a rechargeable battery or a supercapacitor. The microcontroller collects and processes data, and the radio link communicates with a host receiver or data collection point via RF or cell phone technology.
The amount of daily energy harvested can be small. For example, ambient RF/EM energy may create only a few microamps per day. As a result, the wireless device needs to conserve energy by remaining mainly in a “dormant” state, drawing little or no energy, then periodically querying the data to “wake up” and become fully operational only when pre-programmed data point thresholds are exceeded.
Challenging Applications: When to Use Industrial-Grade Li-ion Batteries
Energy harvesting devices are usually paired with rechargeable lithiumion (Li-ion) batteries that store the harvested energy. The most popular consumer-grade Li-ion battery is the 18650 cell, which was created by laptop computer manufacturers to provide inexpensive power for their devices. The batteries have a life expectancy of less than 5 years and 500 recharge cycles, and operate within a moderate temperature range of 0°C - 40°C, making them ill-suited for many remote applications.