Title: A nonlinear and asymmetric monostable compliant ortho-planar spring piezoelectric vibrational energy harvester using a H-I structure
Authors: Ibnu Taufan, Jeff Punch, Valeria Nico
Journal: Sensor and Actuators A: Physical (Elsevier)
Link to full paper: https://www.sciencedirect.com/science/article/pii/S0924424724009786?via%3Dihub
What is this paper all about?
By 2030, it is estimated that the Wireless Sensor Networks (WSNs), referred as the Internet of Things (IoT), will reach almost 50 billion devices. These sensors can be found in our daily life, such as smartwatches, smoke alarms, and sensors for smart farming. However, most of these sensors are powered by batteries which not only contain material that is harmful to the environment, but also require regular maintenance.
Due to low power requirement of these sensors, ambient energy can be utilised for energy harvesting such as light energy, thermal gradient energy, wind energy, and mechanical energy (vibration). Among other ambient energy sources, mechanical energy is promising because of its abundance in many environments, such as vibration from human activities (running and biking), washing machines, vehicles (car, airplane, and train), bridge, and water pump. In particular, vibrational energy harvesters (PVEHs) can convert mechanical energy to electrical energy and represent an alternative solution for batteries because PVEHs are renewable, reliable, and do not require human intervention. The word piezoelectricity means electricity that comes from pressure. It is derived from Ancient Greek piézō, which means squeeze or press, and ḗlektron which means amber (an ancient source of electric charge). Piezoelectric materials, called piezoelectric effect, can convert mechanical energy (pressure) to electrical energy (voltage) and vice versa. They can be utilised for sensors, actuators, and energy harvesting.
Most PVEHs employ to convert strain (stress) into electricity. A cantilever beam is a structural element that extends horizontally and, is fixed on one end while free on the other end. However, the drawbacks of this type of harvester are a single resonant mode (single voltage response) and narrow frequency bandwidth (see the linear (illustration) in the figure on the top right above) that are not suitable for broadband ambient vibrations. In this paper, a wideband PVEH is proposed. The complex structure combining an ortho-planar spring and H-I structure (see the overview of the harvester on the top left above)to enhance the bandwidth of the harvester at relatively low frequency where most broadband (everyday normal) vibrations are abundant in many environments (human activities, bridge, and railways)
What have you discovered?
As shown on the bottom right (results under 0.6 g (g=9.81 m/s2)) in the figure above, first, the harvester exhibits nonlinear behaviour that has a wider bandwidth of voltage or power output response compared to the linear harvester (see the nonlinear harvester in the figure on the top right above). Second, the harvester shows a chaotic behaviour (due to jump from buckled down (pre-load by gravitation) to buckled up condition (when the excitation level is sufficient)) in low frequency regions (below 15 Hz) that enhance the bandwidth of the harvester. Third, the multi-modal (multi-peaks) behaviour in the output power also increase the bandwidth of the harvester. Finally, all these features enhance the bandwidth of the harvester. This wideband harvester is suitable for scavenging broadband ambient vibration in low frequency region such as human activities, bridge, railways, and vehicles for powering IoT sensors. The harvester can be utilised as alternatives to batteries.
So What?
WEEE Ireland Annual Environmental 2023 reported that 1327 tonnes of portable batteries, which is equivalent with 66 million AA batteries, were sold in Ireland. However, only 49% of these numbers was recycled. In other words, more than 50% of the waste batteries was thrown away to the landfill which can cause the soil and water to be polluted. To tackle the waste batteries problem, we can utilise a piezoelectric vibrational energy harvester (PVEH) to replace the batteries on the IoT devices where the mechanical energy or vibration is available in the environment.
Even though the harvester exhibits high power and wide bandwidth, there are several steps need to be done before realising the IoT sensors powered by the harvester without batteries. First, the power management circuit need to be developed to achieve an optimum power under real vibration. Second, the harvester should be designed in a package that consist of harvester, IoT sensors, and electrical circuit for easy plug and play. Third, the harvester package has to be tested in laboratory scale for powering an IoT sensor before deploying the harvester in real ambient vibration such as air compressor, water pump, or vehicle for smart farming, for example.
CONNECT is the world leading Science Foundation Ireland Research Centre for Future Networks and Communications. CONNECT is funded under the Science Foundation Ireland Research Centres Programme and is co-funded under the European Regional Development Fund. We engage with over 35 companies including large multinationals, SMEs and start-ups. CONNECT brings together world-class expertise from ten Irish academic institutes to create a one-stop-shop for telecommunications research, development and innovation.
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