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Piezoelectricity holds promise to providing power source, and the use of rubber is helping researchers to optimise that potential in broader applications, says Angelica Buan.
Clean source of energy
When we think of renewable and clean energy, what comes to mind are the energies sourced from the wind, water, sun and, although arguably, nuclear power. However, researchers continue to seek other potential energy that will add to the list of renewable energy sources. Hence, piezoelectricity shows promise in this aspect.
The University of California published online a definition of piezoelectricity as “the effect of mechanical strain and electric fields on a material. The mechanical strain on piezoelectric materials will produce a polarity in the material, and applying an electric field to a piezoelectric material will create strain within the material. When pressure is applied to a piezoelectric material, a dipole and net polarisation are produced in the direction of the applied stress.”
Materials used to harvest energy
According to research, only certain non-conductive materials produce the piezoelectric effect; and although at the time it was discovered in the 1880s to occur by applying mechanical stress on crystals like quartz, ceramics also became known to produce such an effect.
According to the book, Nanotechnology-enabled Sensors authored by RMIT University researchers, some polymeric materials such as rubber, wool, hair, wood fibre and silk also exhibit piezoelectricity to some extent.
A recent study undertaken by Malaysian researchers, Mohd Firdaus Jaafar of the Faculty of Engineering and Technology Infrastructure, Infrastructure University Kuala Lumpur, and Dr Hanim Salleh of the Centre for Renewable Energy, University Tenaga Nasional, has been proven that micro-watts of power can be generated from a piezoelectric energy harvester (PEH)-rubber attachment.
The researchers, presented during a conference held in Putrajaya, a piezoelectric cantilever beam with structural modification using rubber, which was designed to harvest power from a vibrating structure.
Energy from rubber
In a study, Piezoelectric Ribbons Printed onto Rubber for Flexible Energy Conversion, published in Nano Letters in 2010, scientists have developed the piezo rubber, a flexible, biocompatible rubber film, which they said could be suitable for use in implantable or wearable energy harvesting systems, which means that the material may harvest energy from body motions, such as the lungs during breathing.
This potential sees the possibility of enabling pacemakers for heart patients to function for longer time without replacing batteries as frequently as is usual.
Hand-held consumer electronic devices that require smaller amounts of electricity could also benefit from piezo rubber, which can collect energy when flexed or pressure is applied on it.
Manufacturing piezoelectric materials requires very high temperatures of over 538°C, thus making it difficult to work with temperature-sensitive rubber, the study explained. This limitation can be overcome through applying a manufacturing process for transferring crystalline piezoelectric nano-thick ribbons of lead zirconate titanate (PZT) from host substrates onto flexible rubbers over macroscopic areas.
The scientists also suggested that the PZT could be embedded onto clear sheets of silicone rubber. Each PZT strand is about 1/50,000th the width of a human hair.
According to the study, PZT is one of the most efficient piezoelectric materials developed to date and can convert 80% of mechanical energy into electricity.
Developing for larger-scale use
On-going research and developments are taking place to utilise energy-generating rubber on a commercial scale.
Japanese multinational imaging and electronics company, Ricoh, is currently developing an “energygenerating rubber” that it says converts pressure and vibration into electric energy with high efficiency. Working with the Tokyo University of Science that launched mechanism analysis in molecular level using leading computational chemistry, Ricoh says that the mechanism of the energy generating rubber is not the same as that of previous piezoelectric materials.
The company says that the current piezoelectric materials, such as ceramics and polymers, pose certain limitations in terms of tenuous strength and weight.
Combining the beneficial properties of ceramics and plastics, Ricoh’s energy generating rubber may be able to wield a high level of electricity as ceramics, while taking on the soft and flexible nature of plastics. This combination broadens the scope of applications for energy rubber.
Ricoh says that it will further advance research in this technology, targeting to commercialise the material for various purposes, especially flexible sensors, as well as become an energy harvesting staple for devices with the emerging Internet of Things trend. The latter is a scenario in which objects, animals or people are provided with unique identifiers and the ability to transfer data over a network without requiring human-to-human or human-to-computer interaction.
Current applications in healthcare
Recent advancements are paving the way for piezoelectricity for a much larger scale use. It is obvious though that the recent developments are built around medical applications.
Coltene, a Switzerland-headquartered dental manufacturing company, launched in 2013 the BioSonic SUVI piezoelectric ultrasonic scaler and air polisher. The ultrasonic and air polishing devices for professional dental care feature an ergonomic design combined with LED lighting, advanced electronics and high-durability DuraGradeMAX steel tips.
The power tool comes in two models, with the BioSonic Suvi Premier for ultrasonic treatment. Due to its wide power range and a variety of tips, the scaler is adjustable for all treatments. The other model, BioSonic Suvi Elite, combines the various features of the Premier and the air polisher into one versatile appliance that can be used for a wide range of ultrasonic and polishing treatments.
Meanwhile, this year, researchers from the National University of Singapore presented at a conference in Portugal, the skin-based self-powered generator that converts muscle movements into enough power for small electronics. With a size as small as a postage stamp, the device utilises static electricity to convert mechanical energy into electrical energy.
According to the research team, friction-powered generators can launch new types of wearable sensors that do not require batteries but harness the piezoelectric effect of the wearer’s daily activities like walking, talking or holding an object.
The said device can generate 90 V of open circuit voltage and power of 0.8 mW at a slight tapping of the finger.
To enable the friction electrical charge on the sensors to come on contact with the skin, the scientists created a negative layer with thousands of tiny pillar-like structures on a flexible silicone rubber layer. Below it, a 50 nm-thick gold film is bonded to act as the device’s electrode. The pillars increase the surface area of the device that touches the skin, which increases friction and thus generates power.
Thus, although still in its nascent phase, piezoelectricity offers vast opportunities for varied applications, such as electrical transducers and signal devices.
However, with current interest in piezoelectricity, potential applications, as well as viability as efficient direct source of energy, are expanding.