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Energy harvesting on paper for flexible wearables KBy Julien Happich orean researchers from the University of Ulsan have demonstrated ultra-flexible and low-frequency polymer based energy-harvesting on paper substrates. The researchers spin-coated a 80μm thick paper substrate with a co-polymer solution to yield a thin piezoelectric film of poly(vinylidene fluoride trifluoroethylene) or P(VDF-TrFE), only 1μm thin. The deposition process was layered between two platinum electrodes deposited at a 200nm thickness (see figure 1). Key to obtaining the right piezoelectric film density and efficiency was thermal annealing, carried out at 150ºC with a specific cooling profile. Flexing back and forth the very thin structure, the researchers were able to generate an open-circuit voltage of 1.5V at a frequency of about 1Hz, with a short-circuit current of 0.38μA for a device only a few centimetres square. Under this test scenario, the output power density was evaluated to be 2.85mW/cm3. The piezoelectric potential is generated in the P(VDF-TrFE) thin film from tensile stress-induced deformation, making the electrons flow and accumulate at the bottom electrode to balance the electric field induced by dipoles. Repeated bending and releasing of the device generates output voltages and current pulses as shown in figure 2. Attached to the back of a human hand underneath a latex glove, the energy harvester was able to generate a maximum output open-circuit voltage of 0.4V at low bending frequencies of 0.25 Hz (say closing and opening your hand once every four seconds) and that despite the lower deformation of the piezoelectric structure as it conformed to the skin. The output opencircuit voltage reached 0.6V at a 2Hz bending frequency. As well as being flexible, the structure is lightweight and easier to fabricate compared with the typical ZnO-based paper device structures described in other research papers. The device can easily be made biocompatible for implantable medical use. Fig. 1: The flexible P(VDF-TrFE) thin filmbased paper power generators in (a) bending and (b) releasing modes. Power is generated both during the bending (c) and the releasing processes. Fig. 2: The energy harvester attached to the back of a human hand underneath a latex glove. Flexible sensor detects multiple ions in fluids By IJulien Happich mec and Holst Centre have demonstrated a prototype of a single-chip electrochemical sensor for simultaneous detection of multiple ions in fluids. The generic platform consists of conductive inks, hydrogels and ion-selective membranes that can be tailored towards specific applications. Depending on the amount of sensors integrated, the chips can span across an area roughly 10x10mm. The ion-selective membranes can be tuned based on the ionophores they contain, which selectively bind the ion of interest and creates a potential which is then measured by the sensor chip. The researchers have been able to miniaturize the concept and integrate multiple membranes on a single sensor, hence broadening the ions detection capabilities of the sensor. The new sensor chip could enable efficient and low-cost monitoring, such as monitoring of nutrient concentrations in surface and waste water, both for agricultural applications and water quality. In the healthcare and lifestyle applications, it could provide disposable point-of-care solutions, or conformable solutions for integration into patches. Depending on the application and the form factor, it can be mass produced through microfabrication or through screen-printing on inexpensive substrates such as glass or plastic foils, making this solution very cost competitive and very small compared to today’s ions sensors. Currently, The prototype demonstrated is a handheld device that integrates a single-chip sensor with different electrodes that detect pH levels in a range from 2 to 10 at a 0.1 pH accuracy. For the chemical elements chloride (Cl-), sodium (Na+), potassium (K+), and nitrate () -ranging from 10-4 M to 1 M ions- the sensor detects at a 10 percent accuracy. It was benchmarked against other available single-ion sensors, and the researchers found comparable sensitivity and accuracy for their multiple-ion solution. The flexible solution could join the ranks of the ever expanding IoT legion and imec invites the industry to join its R&D program. www.electronics-eetimes.com Electronic Engineering Times Europe December 2015 17


EETE DEC 2015
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