In its main definition, piezoelectrets are polymeric structures with electric charged internal cavities. The bipolar-trapped charges form macro-dipoles that can be mechanically deformed, thus presenting a high piezoelectric coefficient in the order of hundreds of pC/N. Such results outperform most of the traditional piezoelectric polymers. As piezoelectrets can be manufactured by different methods, some of the techniques allow the inner cavities to be geometrically controlled, therefore providing some degree of freedom in the piezoelectric behavior. This report provides a description of the most relevant methods, starting with a brief introduction of piezoelectret origin and reaching recent achievements in piezoelectret production, such as additive manufacturing (3D printing). Materials that are frequently employed in piezoelectret fabrication and methods for improving their characteristics are also presented.

This paper presents an overview of silicon-based optical sensors for the measurement of light in the visible spectrum range. The review is focused on sensors based on CMOS (complementary metal-oxide semiconductor) technology due to the high availability, low cost, ease of prototyping, and well-established fabrication processes. CMOS technology allows integration with the CMOS readout and control electronics in the same microdevice, featuring high-volume fabrication with high-reproducibility and low-cost. This review starts with an explanation of the phenomena behind opto-electronic transduction. It also presents and describes the most common components responsible for optical transduction, readout electronics, and their main characteristics. This review finishes with the presentation of selected applications to grasp where and how these sensors can be used.

This paper presents new perspectives on photonic technologies for capsule endoscopy. It first presents a review of conventional endoscopy (upper endoscopy and colonoscopy), followed by capsule endoscopy (CE), as well as their techniques, advantages, and drawbacks. The technologies for CEs presented in this paper include integration with the existing endoscopic systems that are commercially available. Such technologies include narrow-band imaging (NBI), photodynamic therapy (PDT), confocal laser endomicroscopy (CLE), optical coherence tomography (OCT), and spectroscopy in order to improve the performance of the gastrointestinal (GI) tract examination. In the context of NBI, two optical filters were designed and fabricated for integration into endoscopic capsules, allowing for the visualization of light centered at the 415 nm and 540 nm wavelengths. These optical filters are based on the principle of Fabry-Perot and were made of thin films of titanium dioxide (TiO₂) and silicon dioxide (SiO₂). Moreover, strategies and solutions for the adaptation of ECs for PDT are also discussed.

This paper presents a photovoltaic (PV) sub-module with an optical sensor for angular measurements of incident light. The optical sensor is a CMOS microdevice for accurate tracking of the solar incident angle for application on photovoltaic systems. This microdevice was designed in 0.7μm CMOS and is composed by a matrix of photodiodes and the respective read-out circuits. A set of microstructures on metal with widths of 5μm and 10μm was fabricated on top of the photodiodes to allow the measuring of angles on a wide range of illuminations and for calibration purposes. The measurements done in the laboratory and in realfield open environments confirmed the suitability to track with good precision the maximum sun’s incident angle in the range [0°, 180°], only limited by the servomotor to rotate the system. This PV sub-module measures 12cm×10cm×4cm and presents a total power consumption of 265mW, when supplied by 5V. These features combined with the low-cost of this PV sub-module bring excellent prospects for its installation on photovoltaic cells to achieve maximum efficiency in the solar to electric energy conversion. To finish, this PV sub-module costs less than $130, opening good perspectives for its popularization.

Deep-brain stimulation (DBS) is an emerging research topic aiming to improve the quality of life of patients with brain diseases, and a great deal of effort has been focused on the development of implantable devices. This paper presents a low-noise amplifier (LNA) for the acquisition of biopotentials on DBS. This electronic module was designed in a low-voltage/low-power CMOS process, targeting implantable applications. The measurement results showed a gain of 38.6 dB and a −3 dB bandwidth of 2.3 kHz. The measurements also showed a power consumption of 2.8 μW. Simulations showed an input-referred noise of 6.2 μV_RMS. The LNA occupies a microdevice area of 122 μm × 283 μm, supporting its application in implanted systems.

The imagiology using Narrow Band Light (NBL) is widely employed in detection of mucosa's premature changes of gastrointestinal tract, while taking advantage of light spectral features by enhancing the vascular structures without the application of any type of dye. NBL uses two specific spectral bands centered in blue (415 nm) and green (540 nm). Despite their greater advantages, this technique is not available on intra-corporal imagiology devices yet. Thus, this paper presents a low-cost method to adapt such devices without the need to develop specific and expensive LEDs (Light-Emitting Diodes) centered at 415 nm and 540 nm. The method combines optical filters with commercial LEDs to provide transmitted light with the desired peaks at 415 nm and 540 nm. Two optical filters were designed and fabricated, using 7 thin-films layers of SiO2 and TiO2 deposited by RF sputtering. The measurements showed that the transmitted light through the filters presented relative transmittance peaks located at 414 nm and 542 nm wavelengths with relative transmittances of 31% and 62% and FWHM (Full-Width-Half-Maximum) of 17 nm and 29 nm, respectively. The measurements also showed significant relative transmittances located at NBL central wavelengths of 415 and 540 nm with 30% and 60%.