Piezoresistive Pressure Sensor for application in e-skin devices

(ENG) In recent years, the advancement of science and technology tends to evolve towards the exploitation of electronic skin (e-skin) and functional prosthetic devices, enabling innovating applications in various fields such as biomedical systems, sports health-monitoring and healthcare. Owing to their significant role in health monitoring, pressure sensors come as essential components in the development of artificial systems that can mimic the impressive human skin. The development of such sensors comprises the search for flexible and stretchable materials suitable for implementation in robust devices that enable the integration of multiple sensingfunctionalities. To quantitatively monitor pressure, these sensors use transduction methods based on piezoresistivity, capacity, piezoelectricity, and triboelectricity. In this work, piezoresistive devices were chosen over others due to their ease in structure design and readout mechanism. The mechanism of such piezoresistive pressure sensor relies on the transduction of a pressure change into a change in resistance that, in this case derives from variations in the contact area. In the approach presented in this work, a semi-sphere microstructuring patterning made by laser engraving on hard-poly(dimethylsiloxane) (h-PDMS) was introduced. h-PDMS works as a mold from which standard-poly(dimethylsiloxane) (s- PDMS) microstructured membranes with approximately 200 μm thickness are peeled off. Carbonink, working as active material, was deposited on top of the microstructured s-PDMS membranes. The fabrication of such pressure sensors based on organic membranes combines advantages such as the production in a low-cost and fast way, device flexibility, and tunability of the sensor’s design. Moreover, sensitivities of 2.4 × 10-1 kPa-1 were reached for the sensors developed.(PT) Nos últimos anos, o avanço da ciência e da tecnologia tende a evoluir para a exploração da pele eletrónica (e-skin) e próteses funcionais, possibilitando aplicações inovadoras em vários campos, nomeadamente sistemas biomédicos, saúde desportiva, e monitorização da saúde. Devido ao seu papel significativo na monitorização da saúde, os sensores de pressão são componentes essenciais no desenvolvimento de sistemas artificiais que conseguem imitar a impressionante pele humana. O desenvolvimento destes sensores requer a procura por materiais flexíveis e extensíveis adequados para implementação em dispositivos robustos que permitam a integração de múltiplas funcionalidades de detecção. Para monitorizar a pressão, estes sensores usam métodos de transdução baseados em piezoresistividade, capacidade, piezoelectricidade e triboeletricidade. Neste trabalho, dispositivos piezoresistivos foram escolhidos em detrimento dos outros devido à sua fácil implementação e mecanismo de leitura. Este mecanismo consiste na transdução de uma diferença de pressão numa diferença de resistência que, neste caso, deriva de variações na área de contato. Na nova abordagem apresentada neste trabalho, introduziu-se um método de microestruturação de semi-esferas baseado na gravação a laser em poli(dimetilsiloxano)-duro (h-PDMS). O h- PDMS funciona como um molde a partir do qual se retiram membranas microestruturadas de poli(dimetilsiloxano)-standard (s-PDMS) com aproximadamente 200 μm de espessura. O material ativo em cima do domínio microestruturado é tinta de carbono. A fabricação destes sensores de pressão com base em membranas orgânicas combina vantagens como a produção de forma rápida, fabricação de baixo custo, flexibilidade do dispositivo e flexibilidade na mudança do design do sensor. Para além disso, para estes sensores foram conseguidas sensibilidades de 2.4 × 10-1 kPa-1

E-skin bimodal sensors for robotics and prosthesis using PDMS molds engraved by laser

Electronic skin (e-skin) is pursued as a key component in robotics and prosthesis to confer them sensing properties that mimic human skin. For pressure monitoring, a great emphasis on piezoresistive sensors was registered due to the simplicity of sensor design and readout mechanism. For higher sensitivity, films composing these sensors may be micro-structured, usually by expensive photolithography techniques or low-cost and low-customizable molds. Sensors commonly present different sensitivities in different pressure ranges, which should be avoided in robotics and prosthesis applications. The combination of pressure sensing and temperature is also relevant for the field and has room for improvement. This work proposes an alternative approach for film micro-structuration based on the production of highly customizable and low-cost molds through laser engraving. These bimodal e-skin piezoresistive and temperature sensors could achieve a stable sensitivity of -6.4 × 10-3 kPa-1 from 1.6 kPa to 100 kPa, with a very robust and reproducible performance over 27,500 cycles of objects grasping and releasing and an exceptionally high temperature coefficient of resistance (TCR) of 8.3%/°C. These results point toward the versatility and high benefit/cost ratio of the laser engraving technique to produce sensors with a suitable performance for robotics and functional prosthesis

Sea lamprey (Petromyzon marinus L.) spawning migration in the Vouga river basin (Portugal): poaching impact, preferential resting sites and spawning grounds.

Historical spawning grounds for sea lampreys (Petromyzon marinus L.) in most Portuguese river basins are becoming inaccessible due to the construction of impassable dams and/or weirs. Studies like the one described in this paper are particularly important in areas like the Vouga river basin, where there is a considerable fishing effort from both professional fishermen and poachers. In fact, for management and conservation purposes, it is important to clarify several aspects of the sea lamprey spawning run in this particular watershed. Therefore, a total of 30 radio tagged, migrating sea lampreys were released in the River Vouga and some of its main tributaries during 2004 and 2005. Results from the tracking sessions were used to determine the effect of poaching on the spawners’ population and the characteristics of the resting sites used during the upstream movement. The rivers’ stretches were also characterized according to the type of substrate present in the riverbed and flow type, in order to determine its aptitude to constitute appropriate spawning habitats for sea lampreys. We have identified in the upstream stretches of River Vouga, and in the tributary River Caima, characteristics that are particularly suitable for the construction of nests by the spawners. Presence of larvae provided evidence that spawners migrated into the River Vouga’s upper reaches. However, abundance and age class diversity appeared to be higher downstream of Sernada and Carvoeiro weirs, corroborating the telemetry data which suggested difficulty in passing these obstacles during low precipitation years. In the River Caima, migration was most predictable, which might be related to daily water releases from a small hydropower dam at dusk, that stimulated the lampreys to resume migration. Poaching has had a considerable negative effect on the success of the tagged lampreys’ migration: 76% of the animals released during 2005 were capture

E-Skin Pressure Sensors Made by Laser Engraved PDMS Molds

This work describes the production of electronic-skin (e-skin) piezoresistive sensors, which micro-structuration is performed using laser engraved molds. With this fabrication approach, low-cost sensors are easily produced with a tailored performance. Sensors with micro-cones and a high sensitivity of −1 kPa−1 under 600 Pa are more adequate for the blood pressure wave detection, while sensors micro-structured with semi-spheres and a maximum sensitivity of −6 × 10−3 kPa−1 in a large pressure range (1.6 kPa to 100 kPa) are more suitable for robotics and functional prosthesis