SYSTEM DESIGN


problems that the Boeing Dreamliner suffered, and another example of this danger was a farm fire, where several pigs were killed. It seems that a pig ate a pedometer, and the copper in a battery reacted with excrement and bedding to set fire to the farm. A slightly anecdotal story perhaps, but imagine if something similar had happened to a child. So, what’s the solution? We want to make


our products as efficient as possible and to use the smallest possible batteries, so we need to consider if other solutions are possible, perhaps removing the need for batteries completely or at least reducing the size by using the energy in the environment around us as a power source. Until now, the use of energy harvesting has


been limited, but with the latest generation of energy harvesters it becomes possible to consider them as the primary or at the very least, a secondary power source. The latest photovoltaic cells are optimised for both indoor and outdoor light sources. Energy can also be harvested from heat,


using thermal electric generators, these can utilise the waste heat generated by machines or perhaps the difference between the air temperature and the soil temperature to generate power. Just a few degrees of temperature difference is enough to power a typical system. There are many other energy harvesting


technologies available. Vibration harvesters collecting energy from the movement of machines, microturbines and wind generators. With the right technology, energy can be harvested from an almost unlimited range of sources. Table 1 (left) shows a comparison of common energy harvesting power sources. Sometimes the amount of energy we can


harvest is very small and requires specialist electronics to turn it into something useful. Dedicated power management ICs and microcontrollers designed specifically to use these small amounts of energy are now available, so while we may still need a battery in our applications, the use of energy harvesting technology and the appropriate energy storage technologies can allow us to


Figure 2: A soil monitor developed by Renesas, powered by harvesting the energy from the soil temperature


minimise the size of the battery, and perhaps even remove it entirely. Imagine an application where we want to


embed a sensor in a bridge to detect if the structure is starting to fail. Typically, structures are designed to last 50 years or more, and even the best battery technologies, such as lithium thionyl chloride cannot meet these requirements. A sensor, which is powered by a small solar cell will operate for many years, as long the sun shines. Much of our infrastructure was built in the


50s and 60s and is coming to the end of its planned useful life, and the cost of replacing these structures can be immense. The first Forth Road Bridge, opened in 1964 with a planned lifespan of over 100 years. Due to


significant corrosion problems, this has now been replaced by a second crossing, at a cost of £1.35 billion. The use of energy harvesting technologies to power structure health monitoring sensors can help prolong the working life of many structures, minimising these costs.


The new Forth Crossing under construction Until now the use of energy harvesting power sources has been limited to niche applications. However, the development of the latest generation of energy harvesting power sources, combined with advances in ultra-low power semiconductor process technology has allowed the development of higher performance microcontrollers to consume significantly less energy, enabling energy harvesting to reach more mainstream applications, sometimes bringing some significant product advantages. As we leave the current pandemic, product


sustainability and issues around the future of the planet will again have a higher priority. We all have a responsibility to make sure our products don’t continue to place unnecessary demands on the planet and allow us all to have a cleaner and better future. Harvesting the energy to power our products from the environment around them and limiting the use of batteries, is one way that we can all achieve this.


The new Forth Crossing under construction


Renesas Corporation www.renesas.com


DECEMBER/JANUARY 2022 | ELECTRONICS TODAY 27


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