A. F. Silva

Simultaneous cardiac and respiratory frequency measurement based on a single fiber Bragg grating sensor

A respiratory and cardiac-frequency sensor has been designed and manufactured to monitor both components with a single fiber Bragg grating (FBG) sensor. The main innovation of the explored system is the structure in which the FBG sensor is embedded. A specially developed polymeric foil allowed the simultaneous detection of heart rate and respiration cycles. The PVC has been designed to enhance the sensor sensitivity. In order to retrieve both components individually, a signal processing system was implemented for filtering out the respiratory and cardiac frequencies. The developed solution was tested along with a commercial device for referencing, from which the proposed system reliability is concluded. This optical-fiber system type has found an application niche in magnetic resonance imaging (MRI) exam rooms, where no other types of sensors than optical ones are advised to enter due to the electromagnetic interference.

Hydrogel-based photonic sensor for a biopotential wearable recording system.

Wearable devices are used to record several physiological signals, providing unobtrusive and continuous monitoring. These systems are of particular interest for applications such as ambient-assisted living (AAL), which deals with the use of technologies, like brain-computer interface (BCI). The main challenge in these applications is to develop new wearable solutions for acquisition of electroenchephalogram (EEG) signals. Conventional solutions based on brain caps, are difficult and uncomfortable to wear. This work presents a new optical fiber biosensor based on electro-active gel - polyacrylamide (PAAM) hydrogel - with the ability to measure the required EEG signals and whose technology principle leads to contactless electrodes. Experiments were performed in order to evaluate the electro-active properties of the hydrogel and its frequency response, using an electric and optical setup. A sinusoidal electric field was applied to the hydrogel while the light passes through the sample. An optical detector was used to collect the resultant modulated light. The results have shown an adequate sensitivity in the range of μV, as well as a good frequency response, pointing the PAAM hydrogel sensor as an eligible sensing component for wearable biopotential recording applications.

A Smart Skin PVC Foil Based on FBG Sensors for Monitoring Strain and Temperature

Electronic products, including sensors, are often used in harsh environments. However, many parameters, such as severe weather conditions, high electronic noise, or dangerous chemical compounds in situ, may compromise the required high reliability. Therefore, development of a reliable sensing solution for monitoring those extreme conditions may become a very challenging task. This paper presents a smart skin foil developed to meet this specific need. Fiber Bragg grating sensors, one of the most reliable sensor solutions nowadays, were embedded in a thin foil made of polyvinyl chloride, giving rise to a smart structure with high durability and high resistance, and a dimensional stability above 99%. In addition, the fabrication processes used are based on a technology that allows the development of large sensing areas. The sensing foil shows a linear stretching profile, with a slope of 7.8 nm per 1% elongation. After submitting the developed structure to temperature cycles, it revealed a thermal behavior of 0.1 nm/°C. Since the smart sensing structure was fabricated using available industrial fabrication processes, it is a feasible and ready-to-market solution.

Neural Electrode Array Based on Aluminum: Fabrication and Characterization

A unique neural electrode design is proposed with 3 mm long shafts made from an aluminum-based substrate. The electrode is composed by 100 individualized shafts in a 10 × 10 matrix, in which each aluminum shafts are precisely machined via dicing-saw cutting programs. The result is a bulk structure of aluminum with 65 ° angle sharp tips. Each electrode tip is covered by an iridium oxide thin film layer (ionic transducer) via pulsed sputtering, that provides a stable and a reversible behavior for recording/stimulation purposes, a 40 mC/cm2 charge capacity and a 145 Ω impedance in a wide frequency range of interest (10 Hz-100 kHz). Because of the non-biocompatibility issue that characterizes aluminum, an anodization process is performed that forms an aluminum oxide layer around the aluminum substrate. The result is a passivation layer fully biocompatible that furthermore, enhances the mechanical properties by increasing the robustness of the electrode. For a successful electrode insertion, a 1.1 N load is required. The resultant electrode is a feasible alternative to silicon-based electrode solutions, avoiding the complexity of its fabrication methods and limitations, and increasing the electrode performance.

Integrated thin-film rechargeable battery in a thermoelectric scavenging microsystem

Thin-film solid-state rechargeable batteries are ideal power sources for microsystems applications, where a high level of integration is required. The technology and the steps involving the fabrication of such a battery are discussed in this paper. A DC reactive sputtering technique was used in the thin-films depositions. The battery uses SnO2, Li3PO4 and LiCoO2 materials in the anode, electrolyte and cathode, respectively. The application of the battery is for use in thermoelectric energy scavenging microsystems, which converts the small thermal power available in human-body. This Lithium solid-state thin-film battery is integrated in the same device as well as the ultra low-power electronics to charge battery and perform DC-DC conversion.

Fiber Bragg Grating Sensors Integrated in Polymeric Foils

Optical sensors have hit their maturity and a new kind of systems is being developed. This paper deals with the development of a new sensing structure based on polymeric foils and optic fiber sensors, namely the Fiber Bragg Grating sensors. Sensor integration in polymeric foils, using industrial process is the proposed goal. To achieve this goal, Finite Element Analysis was used for prototype modeling and simulation. The model was subjected to loads and restraints in order to retrieve information about stress distribution and displacement of specific points. From the simulation was possible to predict the sections where the sensor should be positioned. A prototype was then fabricated using industrial processes. Tests indicate that the polymeric foil influence on the sensor performance may exist. However, the prototype was able of transferring the full deformation to the optical sensor. Moreover, the optical sensor, which is incorporated in the polymeric foil, is fully functional with high sensitivity, 0.6 picometer by microstrain, allowing deformation measurements, up to 1.2 millimeter.

Smart Sensing Polymeric Foil with Integrated Optic Fiber Sensors: Fabrication and Characterization of a Polymeric Foil Sensitive to Strain

A structural integrity monitoring system based on optical fiber sensors is an important development at the smart structures level. However, direct sensors incorporation, without a substrate structure, creates some difficulties in eventual sensor maintenance or replacement. This paper presents an approach to overcome this issue. The fabrication, using industrial processes, and characterization of a polymeric foil able to sense, gather and send sensitive information for remote analysis is explored. The described example uses Fiber Bragg Grating sensors embedded in laminated polymeric sheets commonly used in different industries, as automotive, aeronautic, civil, among others. The fabricated foil is capable of transferring the full deformation to the optical sensor. The presented optical sensor incorporated in the polymeric foil is fully functional with high sensitivity, 0.6 picometer by microstrain, measuring deformation up to 1.2 millimeter. The sensors distribution over the structure is only restricted by the 10 mm sensor length, the desired dynamic range window and interrogation system used.

Manufacturing technology for flexible optical sensing foils

This paper presents the development of an integration technology that offers a breakthrough solution for the industrial manufacturing of flexible smart materials with optical sensing features. Subsequently, it aims the development of a flexible substrate, or foil, in which optical waveguides and sensing elements are integrated in line during the manufacturing process of the substrate itself. This artificial and flexible optical sensing foil can then be applied to regular or irregular surfaces, enabling a quasi-distributed strain map. Fabrication, using industrial processes, and characterization of a polymeric foil able to sense, gather and send sensitive information for remote analysis is explored. The propose smart material uses fiber Bragg grating sensors embedded in standard laminated polymeric sheets used in different industries, as automotive or aeronautic. The definition of the whole integration process as well as the PVC paste custom formulation for better integration results is described. The presented optical sensor incorporated in the polymeric foil is fully functional with high sensitivity, 0.6 pm/¿strain, measuring deformation, up to 1.2 mm.

Design and manufacturing challenges of optogenetic neural interfaces: a review

Optogenetics is a relatively new technology to achieve cell-type specific neuromodulation with millisecond-scale temporal precision. Optogenetic tools are being developed to address neuroscience challenges, and to improve the knowledge about brain networks, with the ultimate aim of catalyzing new treatments for brain disorders and diseases. To reach this ambitious goal the implementation of mature and reliable engineered tools is required. The success of optogenetics relies on optical tools that can deliver light into the neural tissue. Objective/Approach: Here, the design and manufacturing approaches available to the scientific community are reviewed, and current challenges to accomplish appropriate scalable, multimodal and wireless optical devices are discussed. SIGNIFICANCE Overall, this review aims at presenting a helpful guidance to the engineering and design of optical microsystems for optogenetic applications.

Fabrication and mechanical characterization of long and different penetrating length neural microelectrode arrays

This paper presents a detailed description of the design, fabrication and mechanical characterization of 3D microelectrode arrays (MEA) that comprise high aspect-ratio shafts and different penetrating lengths of electrodes (from 3 mm to 4 mm). The arrays design relies only on a bulk silicon substrate dicing saw technology. The encapsulation process is accomplished by a medical epoxy resin and platinum is used as the transduction layer between the probe and neural tissue. The probes mechanical behaviour can significantly affect the neural tissue during implantation time. Thus, we measured the MEA maximum insertion force in an agar gel phantom and a porcine cadaver brain. Successful 3D MEA were produced with shafts of 3 mm, 3.5 mm and 4 mm in length. At a speed of 180 mm min−1, the MEA show maximum penetrating forces per electrode of 2.65 mN and 12.5 mN for agar and brain tissue, respectively. A simple and reproducible fabrication method was demonstrated, capable of producing longer penetrating shafts than previously reported arrays using the same fabrication technology. Furthermore, shafts with sharp tips were achieved in the fabrication process simply by using a V-shaped blade.