Peel resistance of adhesive joints with elastomer–carbon black composite as surface sensing membranes

The peel resistance of four adhesives (“J-B Weld” by J-B Weld (adhesive A), 3 M Scotch-Weld DP 125 Gy (adhesive B), Loctite PL Premium (3x) Construction Adhesive (adhesive C), and Henkel Hysol EA9394 (adhesive D)) is investigated for their bonding performance of a styrene‐ethylene/butylene‐styrene– carbon black (SEBS–CB) composite membrane used in structural health monitoring (SHM) applications. Tests are performed on membrane samples bonded on four common structural materials, namely aluminium, steel, concrete, and fiberglass, to obtain the peel resistance of adhesives. Results show that adhesive B has the highest strength for aluminium, steel, and fiberglass substrates, and that adhesive C has the highest strength for the concrete substrate. The performance is also evaluated versus adhesive cost, a critical variable in SHM applications. Here, adhesive C performed best for all substrates. Lastly, membrane residuals resulting from the peel tests are compared. Tests show that Adhesive B resulted in the highest residual percentage for aluminium, while adhesive C performed better for all other substrates. However, membrane residuals for adhesive C do not show a positive correlation with the peel resistance

Pulse Signal System: Sensing, Data Acquisition and Body Area Network

Heart rate variability (HRV) is an important physiological signal of the human body, which can serve as a useful biomarker for the cardiovascular health status of an individual. There are many methods to measure the HRV using electrical devices, such as ECG and PPG etc. This work presents a novel HRV detection method which is based on pressure detection on the human wrist. This method has been compared with existing HRV detection methods. In this work, the proposed system for HRV detection is based on polyvinylidene difluoride (PVDF) sensor, which can measure tiny pressure on its surface. Three PVDF sensors are mounted on the wrist, and a three-channel conditioning circuit is used to amplify signals generated by the sensors. An analog-to-digital converter and Arduino microcontroller are used to sample and process the signal. Based on the obtained signals, the HRV can be processed and detected by the proposed PVDF-sensor-based system. Another contribution of this work is in designing a wireless body area network (WBAN) to transmit data acquired on the human body. This WBAN combines two different wireless network protocols, for both efficient power consumption and data rate. Bluetooth Low Energy protocol is used for transmitting data from the microcontroller to a personal device, and Wi-Fi is used to send data to other terminals. This provides the potential for remote HRV signal monitoring. A dataset consisting of two subjects was used to experimentally validate the proposed system design and signal processing method. ECG signals are acquired from subjects with wrist pulse signals for comparison as standard signal. The waveforms of ECG signals and wrist pulse signals are compared and HRV values are calculated from these two signals separately. The result shows that HRV calculated by wrist pulse has low error rate. A test of movement effect shows the sensor can resist mild motions of wrist. Some future improvements of system design and further signal processing methods are also discussed in the last chapter

Solvent Evaporation-Assisted Three-Dimensional Printing of Piezoelectric Sensors from Polyvinylidene Fluoride and its Nanocomposites

RÉSUMÉ Les matériaux piézoélectriques sont connus pour générer des charges électriques lors de leur déformation. Leur capacité à transformer linéairement l'énergie mécanique en énergie électrique, et vice versa, est utilisée dans la détection, l'actionnement, la récupération et le stockage d'énergie. Ces appareils trouvent des applications dans les domaines de l'aérospatiale, de la biomédecine, des systèmes micro-électromécaniques, de la robotique et des sports, pour n'en nommer que quelques-uns. On retrouve la propriété de piézoélectricité dans certaines céramiques, roches, monocristaux et quelques polymères. Le poly(fluorure de vinylidène) (PVDF) est un polymère piézoélectrique qui présente un coefficient piézoélectrique très élevé par rapport aux céramiques, ce qui laisse présager des applications de détection et de récupération d'énergie. La facilité de fabrication, la flexibilité et la biocompatibilité du PVDF sont autant de qualité qui en font un très bon candidat pour ces applications. Les dispositifs actuels à base de PVDF commercial sont disponibles en films plats ou en fibres unidimensionnelles (1D). L'impression tridimensionnelle (3D) du PVDF peut amener à des sensibilités, souplesses et capacités de fabrication accrues des capteurs embarqués en cas d'impression multi-matériaux. Le PVDF est un polymère semi-cristallin possédant cinq polymorphes, dont la phase β polaire qui présente les meilleures propriétés piézoélectriques. Malheureusement, le PVDF, provenant de la fusion ou de la dissolution, cristallise en une phase α non polaire thermodynamiquement stable. Diverses transformations physiques telles que le recuit, l'addition de charge, l'étirement ou le polissage sont effectuées pour transformer la phase α en phase β. En raison de la cristallisation inhérente du PVDF dans la phase α, il y a eu très peu de tentatives de fabrication de structures 3D à partir du PVDF. L'électrofilage en champ proche et la Déposition de Filament Fondu ont permis de fabriquer certaines structures 3D couche par couche avec du PVDF, soit avec l'application de hautes tensions électriques, soit avec la fusion à haute température du polymère. Et les deux nécessitent un traitement de polarisation pour conférer la piézoélectricité aux structures imprimés. Pour fabriquer des capteurs incorporés ou conformes, sur des substrats donnés, il est essentiel de ne pas avoir d'effets négatifs sur les matériaux adjacents à cause de la polarisation pendant le processus d'impression. Ainsi, dans ce travail, nous avons développé un procédé d'impression 3D qui crée des structures PVDF principalement en phase β, à température ambiante et sans application de tension de polarisation.----------ABSTRACT Piezoelectric materials are known to generate electric charges upon deformation. Their ability to linearly transform mechanical energy into electrical energy and vice versa, is utilized in sensing, actuation, transducing, energy harvesting and storage. These devices find applications in aerospace, biomedicine, micro electromechanical systems, robotics and sports, to name a few. Piezoelectricity is found in some ceramics, rocks, single crystals and a few polymers. Polyvinylidene fluoride (PVDF) is a piezoelectric polymer that exhibits a very high piezoelectric stress coefficient as compared to the ceramics, making it the forerunner for sensing and energy harvesting applications. PVDF’s formability, flexibility and biocompatibility, further reinforce its candidature. Present commercial PVDF-based devices come in flat films or one-dimensional (1D) fibers. Three-dimensional (3D) printing of PVDF leads to higher sensitivity, better compliance, and ability to print embedded sensors in case of multi-material printing. PVDF is a semi-crystalline polymer possessing five polymorphs, of which the polar β-phase exhibits highest piezoelectric properties. Unfortunately, PVDF from melt or solution crystallizes into a thermodynamically stable non-polar α-phase. Various physical transformations like annealing, filler addition, stretching or poling are carried out to transform the α-phase into β-phase. Due to the inherent crystallization of PVDF into α-phase, there have been very few attempts in fabricating 3D structures from PVDF. Near-field electrospinning and fused deposition modelling have demonstrated some layer-by-layer 3D structures with PVDF, either with application of high electric voltages or high temperature melting of the polymer, respectively. Also, both these techniques require a poling treatment to impart the desired piezoelectricity to the printed features. To fabricate embedded or conformal sensors on given substrates, it is essential to not have any adverse effects on the adjacent or substrate materials due to poling during the printing process. Thus, in this work, we develop a 3D printing process, that creates PVDF structures that inherently crystallize in the piezoelectric oriented β-phase at room temperature without any applied voltages. Solvent-evaporation assisted 3D printing is employed to print 3D piezoelectric structures of PVDF based solutions. In this process, the polymer solution is filled into a syringe which is inserted into a pneumatic dispenser. The pneumatic dispenser is mounted on a robotic arm that is controlled via a computer program