Broadband Printed Antenna for Radiofrequency Energy Harvesting

In this work a broadband UHF antenna with high inductive input impedance for radiofrequency energy harvesting is presented. It consists of a small feeding loop and a biconical radiating dipole. A prototype has been fabricated on a FR4 substrate and tested. Experimental results show a - 3dB power transmission bandwidth of about 135MHz (840MHz−975MHz)

Single-Ended Broadband Antenna for Radiofrequency Energy Harvesting

A single-ended broadband UHF antenna with high inductive input impedance for radiofrequency energy harvesting is here presented. It consists of a small feeding loop and a conical radiating monopole. A prototype has been fabricated on a FR4 substrate and tested. Experimental results show a -3dB power transmission bandwidth of about 130MHz (860MHz−990MHz)

Reconfigurable RF Energy Harvester with Customized Differential PCB Antenna

In this work, a RF Energy harvester comprised of a differential RF-DC CMOS converter realized in ST130nm CMOS technology and a customized broadband PCB antenna with inductive coupling feeding is presented. Experimental results show that the system can work with different carrier frequencies and thanks to its reconfigurable architecture the proposed converter is able to provide a regulated output voltage of 2 V over a 14 dB of RF input power range. The conversion efficiency of the whole system peaks at 18% under normal outdoor working conditions

Design of Integrated Neural/Modular Stimulators

Ph.DDOCTOR OF PHILOSOPH

Uma metodologia de projeto de filtros Butterworth passa-baixa utilizando FDDTAs

This work presents a design methodology for the Butterworth low-pass filter of any order, based on the differential-difference transconductance amplifier building blocks. Moreover, a similar design methodology for the high-pass Butterworth filter, using FDDTA, is also investigated. At first, the proposed methodology, the low-pass and high-pass Butterworth filter theories are presented, including state-of-the-art implementations and possible limitations of Butterworth filters. Then, the FDDTA is stated and its operation is evaluated, and a practical implementation using two fully differential inverter-based operational transconductance amplifiers (OTAs) is also investigated. This particular FDDTA implementation relies on two main features: the intrinsically matched transistors that assure similar transconductances and output conductances for both inverter-based OTA instances; and the inverter-based approach without internal nodes that reduces circuit complexity and power consumption since it requires no supplementary external calibration circuit such as tail current or bias voltage sources. Next, the Butterworth low-pass methodology, using FDDTAs, is demonstrated, showing that the proposed topology presents the expected transfer function according to the Butterworth low-pass filter theory. Following, the high-pass Butterworth filter architecture based on the FDDTA instance is also verified, demonstrating its possible feasibility, implementation, and limitations. Finally, intended to demonstrate the methodology functionality for the low-pass Butterworth, a fifth-order filter is implemented, which consists of one inverter-based OTA input stage and five FDDTAs in a cascade connection, showing that it presents the expected fifth-order transfer function according to the Butterworth theory. The prototype, implemented in a 130nm CMOS process, operates in weak inversion supplied with 0.25V and consumes 603nW. Furthermore, the filter features a DR of 57dB in a 100Hz bandwidth and a maximum THD of 54dB, therefore, accomplishing specifications that suit for low-frequency applications.Agência 1Este trabalho apresenta uma metodologia de projeto de filtros Butterworth passa-baixa de qualquer ordem, baseada no bloco de construção amplificador de transcondutância diferencial de diferenças de saída diferencial (FDDTA). É investigada, também, uma metodologia de projeto similar para o filtro Butterworth passa-alta utilizando o FDDTA. A princípio, são apresentadas a metodologia a ser seguida e as teorias de filtro Butterworth passa-baixa e passa-alta, incluindo as implementações do estado da arte de filtros Butterworth e possíveis limitações. Em seguida, o FDDTA é apresentado e sua operação é avaliada e, também, é investigada uma implementação prática usando dois amplificadores operacionais de transcondutância de saídas diferenciais (OTAs), baseados em inversores. Essa implementação específica do FDDTA se baseia em duas características principais: os transistores intrinsecamente casados que asseguram transcondutâncias e condutâncias de saída semelhantes para ambas as instâncias OTAs; e a abordagem baseada no inversor sem nós internos que reduz a complexidade do circuito e o consumo de potência, uma vez que não requer circuito de calibração externo suplementar, como corrente de cauda ou fontes de tensão de polarização. A seguir, a metodologia do filtro Butterworth passa-baixa, usando FDDTAs, é demonstrada, mostrando que a topologia proposta apresenta a fun- ção de transferência esperada de acordo com a teoria de filtros. Na sequência, também, é verificada a arquitetura do filtro Butterworth passa-alta, através da instância FDDTA, demonstrando sua possível viabilidade, implementação e limitações. A fim de demonstrar a funcionalidade da metodologia para o filtro Butterworth passa-baixa, é implementado um filtro de quinta ordem, em que tal topologia consiste em um estágio de entrada diferencial OTA baseado no inversor e cinco instâncias FDDTAs em conexão cascata, evidenciando que a topologia apresenta as características da teoria de filtro Butterworth passa-baixa. O protótipo, implementado em um processo CMOS de 130nm, opera na região de inversão fraca, sob tensão de alimentação de 0,25V e consome 603nW. Além disso, o filtro apresenta uma faixa dinâmica (DR) de 57dB em uma largura de banda de 100Hz e uma distorção harmônica total (THD) máxima de 54dB, cumprindo, portanto, especificações adequadas para aplicações de baixa frequência

Improving Biocompatibility of Implantable Bioelectronics using Zwitterionic Cysteine

Recent advances in bioelectronics have allowed for faster diagnoses of diseases as well as treatments for disorders that were previously considered incurable. The performance of these devices is, however, severely hindered in-vivo due to the body’s inherent immune response. Surface fouling, rapid oxidation, and fibrous encapsulation are some of the common issues that reduce device performance and lead to device failure. Overcoming these issues becomes especially critical when a bioelectronic is designed for prolonged exposure to the host in the form of an implant. Constant exposure to the host results in rapid deterioration of device functionality and a secondary surgery is often required to replace the dysfunctional device. The inclusion of various surface modifications, specifically zwitterionic coatings, have recently demonstrated promising results in prolonging a device’s performance in-vivo. An extensive literature review indicates that current antifouling coatings are mainly composed of long chain hydrophilic or zwitterionic polymers; however, these thick polymer brushes are often undesirable for bioelectronics, especially devices designed for electrotherapy as the therapeutic electric pulse decays exponentially with respect to coating thickness. There is a growing need for an engineered surface that is biocompatible, resistant to nonspecific protein adsorption, and does not interfere with the device function in order to prolong the bioelectronics’ in-vivo lifetime. This research focuses on developing an ultra-thin and highly zwitterionic antifouling coating that is also biocompatible and versatile. Cysteine is selected as the coating material because it is a small biomolecule, highly zwitterionic at physiological pH, inherently biocompatible, and practical to fabricate. By optimizing the fabrication process, a monolayer cysteine coating of 8.64Å in thickness is achieved. X-ray photoelectron spectroscopy confirms the protonation of the amine group and the deprotonation of the carboxyl group, and that 87.84% of the surface cysteine is zwitterionic when fabricated at room temperature. This zwitterionic percentage is increased to 94.47% by increasing the reaction temperature to 330K. The adsorption kinetics of zwitterionic cysteine onto a gold surface is studied through monitoring a liquid interface quartz-crystal microbalance in real time and the rate constants are calculated. Cysteine is also inherently biocompatible because it is an amino acid that exists in, and is produced by, our body. Fabrication of a cysteine monolayer is also practical; the sulfur headgroup on cysteine allows for a one-step synthesis onto a gold substrate without the need of a linker molecule. The fabrication can be completed in solution, which allows for the coating of curved or ridged surfaces that can be challenging for other coating processes such a vacuum deposition. Investigation towards the antifouling performance of zwitterionic cysteine begins by quantifying the hydration layer around the molecule. Surface hydration is a key attribute that dictates a material’s antifouling performance. The layer of water associated with the surface acts as an energy barrier that proteins must overcome in order to adsorb onto the surface. Molecular dynamic simulations indicate that a zwitterionic cysteine molecule associates 43.89 water molecules per nm3, which is comparable to established zwitterionic coatings. The degree of surface fouling from various plasma proteins and human blood was quantified by a liquid interface quartz crystal microbalance in real time, and a zwitterionic cysteine surface can reduce fouling from BSA by 95%, fibrinogen by 93%, and human blood by 93% compared with an untreated gold surface. This thesis demonstrates that an ultra-thin monolayer of highly zwitterionic cysteine capable of significantly reducing biological fouling can be fabricated through solution chemistry. This technology exemplifies the tremendous potential of engineering at a nanoscopic level and has application in the field of bioelectronics, tissue engineering, contact lenses, marine membranes, and drug delivery