RESUMO
Piezoelectric composite materials can convert mechanical energy into electrical energy, thus promoting battery-free motion-sensing systems. However, their substandard mechanical performance limits the capability of sensors developed using flexible piezoelectric materials. This study introduces a novel design strategy for preparing high-strength flexible piezoelectric composite materials comprising unidirectional carbon fiber-reinforced potassium sodium niobate (K0.5 Na0.5 NbO3 ) nanoparticle-filled epoxy resin (UDCF/KNN-EP). The fibers significantly improve the Young's modulus of UDCF/KNN-EP along the fiber direction, which reaches 282.5 MPa. Moreover, the composite exhibits excellent stretchability and piezoelectric response ( V pp â¼ 1.1 V ${V}_{{\mathrm{pp}}}\ \sim \ 1.1\ V$ ) in the cross-fiber direction under cyclic tensile loading. Multiscale finite element analysis is performed via simulation, which allows theoretical examination of the experimental results and the material's mechanical response mechanism. Finally, UDCF/KNN-EP is seamlessly incorporated into athletic gear and used to measure the impact caused by baseball catching and track footfall patterns. This study harnesses the superior strength of carbon fibers to enhance the durability and dependability of self-powered sensors without compromising flexibility in specific directions.
RESUMO
Practical applications like very thin stress-strain sensors require high strength, stretchability, and conductivity, simultaneously. One of the approaches is improving the toughness of the stress-strain sensing materials. Polymeric materials with movable cross-links in which the polymer chain penetrates the cavity of cyclodextrin (CD) demonstrate enhanced strength and stretchability, simultaneously. We designed two approaches that utilize elastomer nanocomposites with movable cross-links and carbon filler (ketjenblack, KB). One approach is mixing SC (a single movable cross-network material), a linear polymer (poly(ethyl acrylate), PEA), and KB to obtain their composite. The electrical resistance increases proportionally with tensile strain, leading to the application of this composite as a stress-strain sensor. The responses of this material are stable for over 100 loading and unloading cycles. The other approach is a composite made with KB and a movable cross-network elastomer for knitting dissimilar polymers (KP), where movable cross-links connect the CD-modified polystyrene (PSCD) and PEA. The obtained composite acts as a highly sensitive stress-strain sensor that exhibits an exponential increase in resistance with increasing tensile strain due to the polymer dethreading from the CD rings. The designed preparations of highly repeatable or highly responsive stress-strain sensors with good mechanical properties can help broaden their application in electrical devices.
RESUMO
We focus on research to develop a compact human blood sampling device used for the Self Monitoring of Blood Glucose (SMBG). The SMBG comprises: (1) an indentation system using a shape memory alloy (SMA) actuator to force a microneedle through the skin; (2) a micro electrical pumping system to extract blood using a bimorph type piezoelectric microactuator; (3) a biosensor using an enzyme such as glucose oxidase (GOx) to detect and evaluate the amount of glucose in extracted blood. A titanium microneedle the same size as a female mosquito's labium (60 mum outer diameter, 25 mum inner diameter) was produced by the sputter deposition method. The mechanical design of the device was based upon the mosquito's blood sampling mechanism. The blood extraction system worked well. We measured the performance of the principal components: the indentation load for a microneedle of external diameter 100 mum was found to be 0.1 N. The pumping system has an extraction speed of about 2 mul/min for whole blood. This is similar to that achieved by the mosquito.
