Is vibration energy harvesting the right choice for your application?

How to evaluate your application

Maximising IoT performance vs battery life time

The Internet of Things (IoT), and the Industrial Internet of Things (IIoT) in particular, is alongside Industry 4.0 one of the biggest buzzwords in recent years. More and more R&D departments across traditional industries such as Industrial Monitoring, Railway and Mining are faced with the task of creating IoT applications where focus is on collecting data in hard-to-reach locations. These devices should communicate their data wirelessly and should be powered without the need for external power supply. And this is where most R&D departments run into problem. They will now be faced with the daunting task of compromising data quality and update rate for battery life time, as the simple truth is that the higher the data quality and update rate is, the short will the battery life be. So, the question is worth asking – Is vibration energy harvesting the right choice for your application to get rid of these problems? 

Data quality and update rate eats away from the battery

When designing a sensor node that can be powered by a cable, one does not need to worry about compromising the quality of data and update rate as the power budget is virtually endless. But, as soon as you take the step over to using a battery as the power source, the power budget is by definition limited. Depending on the desired functionality of the sensor, there are a few areas that need to be considered during the development of the IoT node:

Sleep mode

A sensor node that has an endless power supply is usually always active, always measuring and collecting data. This is not the case with an IoT node. Try experimenting with on/off modes where the sensor and other components that aren’t necessary all the time are put to sleep when they are not utilized, all in order to save power.

Choice of communication protocol

One of the components that could consume a substantial part of the power budget is the communication module. There are multiple ways of transmitting data wirelessly, but they all have their pros and cons. Some protocols like WiFi are great for sending large portions of data but use a substantial amount of energy when sending the data. There are several low-power protocols that are specifically designed for IoT applications such as LoRa, NB-IoT, and to some extent Bluetooth Low Energy. But, the limitation of using such protocols is that they can’t send large data packages which means that there is less data (meaning lower quality) to base your analysis on. If choosing the high-power protocols, the point about sleep modes above becomes even more important. 

Computing in the node

Many automatically assumes that all the valuable analytics are made in the cloud, after that the data has been sent from the node. This does not have to be the case. In applications where it is not important to store the raw data, it might be more efficient from a power-budget perspective to carry out the analysis on the raw data in the IoT node and then communicate the results and discard the raw data. This approach is not suitable for all applications but it should be considered if the Micro Control Unit used in the sensor node has the capabilities of carrying out the algorithms necessary to send the analysed data. 

After evaluating the areas above, and other potential ways, of reducing the power consumption an R&D department/team is left with two possibilities: 1) Use a larger battery to reach the desired functionality or 2) find an alternate power source to batteries. And this is where the opportunity of using Vibration Energy Harvesting arises.

Is vibration energy harvesting the right choice for your application?

What if there was a solution that could allow for high-quality data, frequent update rates and still not create the hassle of batteries that are in need of replacement? There is! 

Vibration Energy Harvesting (VEH) units can, in the right circumstances, be the solution that many IoT architects are looking for. Depending on the input vibrations, VEH units can deliver output in the range of 0,1 – 150 mA (milliAmps), which is plenty enough to power IoT systems that have been designed in an intelligent way. But as mentioned above, VEH units are not always the best choice. It really depends on the environment that they are applied in. So how can you evaluate the environment on your own to understand if VEH units are an alternative for you? There are a few criteria that are extra important, and we have outlined them below. 

Continuous vibrations

Are the vibrations continuous? Or is it an intermittent movement that we are looking at? In order for VEH units to function properly, the best application is continuous vibration that continues over time and doesn’t stop. Some fluctuations are OK and can be handled, but the movement should to a larger extent be continuous and not intermittent.

A dominant frequency between 10 - 200 Hz

VEH units function in such a way that they are factory-tuned for a specific resonance frequency. This means that they absorb the vibration at a specific frequency and a small area around this frequency. To find out where this frequency lies in your specific application, we recommend recording the vibrations and performing a FFT (see our article on How to Analyse vibration measurements). If you are not able to do so, please feel free to reach out to us at ReVibe Energy via the button below and we would be happy to help. 

Below is an example of the power output from one of our VEH units which displays the output in mW (milliWatts) and the dependency on a resonance frequency

Output vs resonance frequency

Strong acceleration levels at the dominant frequency

As can be seen in the graph above, the output levels are dependent on two things: the frequency that the harvester is tuned for and the acceleration found in that part of the frequency spectrum. The stronger the acceleration, the higher the output from the VEH unit. Now, there is of course a limit to how strong the acceleration can be before the VEH unit can’t handle it but in most application it is only positive that the acceleration is strong. 

Final conclusion: Is vibration energy harvesting the right choice for your application?

Once you have evaluated the vibrations in your application per the criteria above, it is time to decide whether or not a harvester should be integrated into your IoT application. And the question remains, how should this be done? 

We recommend reaching out to our sales engineers that are trained in assessing your applications and can evaluate your situation and recommend the best VEH unit and how to integrate it.