J. H. Correia

Thermoelectric Microconverter for Energy Harvesting Systems

This paper presents a solution for energy microgeneration through energy harvesting by taking advantage of temperature differences that are converted into electrical energy using the Seebeck effect. A thermoelectric microconverter for energy scavenging systems that can supply low-power electronics was fabricated using thin films of bismuth and antimony tellurides. Thin films of n-type bismuth (Bi2Te3) and p-type antimony (Sb2Te3) tellurides were obtained by thermal coevaporation with thermoelectric figures of merit (ZT) at room temperature of 0.84 and 0.5 and power factors (PF × 10-3 [W · K-1 ·m-2]) of 4.87 and 2.81, respectively. The films were patterned by photolithography and wet-etching techniques. The goal for this thermoelectric microconverter is to supply individual electroencephalogram (EEG) modules composed by an electrode, processing electronics, and an antenna, where the power consumption ranges from hundredths of microwatts to a few milliwatts. Moreover, these wireless EEG modules allow patients to maintain their mobility while simultaneously having their electrical brain activity monitored.

Bulk-micromachined tunable Fabry-Perot microinterferometer for the visible spectral range

The design, fabrication and measured characteristics of a bulk-micromachined tunable Fabry-Perot microinterferometer FPMI for the visible spectral range are presented. The FPMI is formed by two parallel 40 nm thick silver mirrors supported by a 300 nm low tensile . stress silicon nitride membrane with a square aperture side length of 2 mm and initial cavity gap of 1.2 mm. One of the mirrors is fixed, the other is under tension on a movable Si frame, which is electrostatically deflected, using several distributed electrodes, to control . cavity spacing and mirror parallelism. Performance achieved is: high flatness of the mirrors lr10 for the visible part of the spectrum , .

Fabrication of flexible thermoelectric microcoolers using planar thin-film technologies

The present work reports on the fabrication and characterization of a planar Peltier cooler on a flexible substrate. The device was fabricated on a 12 µm thick Kapton(c) polyimide substrate using Bi2Te3 and Sb2Te3 thermoelectric elements deposited by thermal co-evaporation. The cold area of the device is cooled with four thermoelectric junctions, connected in series using metal contacts. Plastic substrates add uncommon mechanical properties to the composite film–substrate and enable integration with novel types of flexible electronic devices. Films were deposited by co-evaporation of tellurium and bismuth or antimony to obtain Bi2Te3 or Sb2Te3, respectively. Patterning of the thermoelectric materials using lift-off and wet-etching techniques was studied and compared. The performance of the Peltier microcooler was analysed by infrared image microscopy, on still-air and under vacuum conditions, and a maximum temperature difference of 5 °C was measured between the cold and the hot sides of the device.

A 2.4-GHz CMOS Short-Range Wireless-Sensor-Network Interface for Automotive Applications

This paper describes a CMOS interface for short-range wireless sensor networks (CMOS-SRWSN interface). The sensor interface is composed of a sensor readout, electronics for processing and control, a memory, a radio-frequency CMOS transceiver for operation in the 2.4-GHz industrial, scientific, and medical bands, and a planar antenna. The receiver has a sensitivity of -60 dBm and consumes 6.3 mW from a 1.8-V supply. The transmitter delivers an output power of 0 dBm with a power consumption of 11.2 mW. The application of the CMOS-SRWSN interface is in the automotive industry for the reduction of cables and to support the information, communication, and entertainment systems in cars.

Single-chip CMOS optical microspectrometer

Abstract Numerous applications, e.g., systems for chemical analysis by optical absorption and emission line characterization, will benefit from the availability of low-cost single-chip spectrometers. A single-chip CMOS optical microspectrometer containing an array of 16 addressable Fabry–Perot etalons (each one with different resonance cavity length), photodetectors and circuits for read-out, multiplexing and driving a serial bus interface has been fabricated. The result is a chip that can operate using only four external connections (including Vdd and Vss) covering the visible spectral range of the spectrum with FWHM=18 nm. Frequency output and serial bus interface allow easy multi-sensor, multi-chip interfacing using a microcontroller or a personal computer. Power consumption is 1250 μW for a clock frequency of 1 MHz.

FBG Sensing Glove for Monitoring Hand Posture

A wearable sensing glove for monitoring hand gestures and posture has been developed. The glove sensing capability is based on optical fiber Bragg gratings (FBGs) sensors. These sensors, due to their inherent self-referencing and multiplexing capability, are a value-added choice for this application. A single optical fiber would cross all the hand with Bragg structures in specific spots, as the finger joints. The functionality and performance of the glove was fully evaluated. The sensor response was linear to the hand movements for opening and closing down. Through the sensor response, it was possible to retrieve information about the joint angles from which other set of information like finger force can be estimated. The developed glove was able to provide numerical data about the angles of the hand posture in real time. The simplicity of the system and performance makes it well suitable for physical therapy applications, study of the human kinematics during sport activity, virtual reality or even remote control applications, among others.

MAC Protocol for Low-Power Real-Time Wireless Sensing and Actuation

This paper presents LPRT, a new medium access control (MAC) protocol for wireless sensing and actuation systems. Some of the characteristics of the proposed protocol are low power consumption, support for real-time and loss intolerant traffic through contention-free operation and a retransmission scheme, flexibility, and high throughput efficiency. The LPRT protocol was implemented it in the MICAz motes, a platform for the development of wireless sensor networks. We also briefly describe a wireless hydrotherapy application that benefits from the use of the proposed protocol. This paper also provides experimental results and comparison of the proposed protocol with the CSMA/CA protocol of IEEE 802.15.4.

Thermoelectric micro converters for cooling and energy scavenging systems

This paper describes the fabrication process of thermoelectric microconverters, based on n-type bismuth telluride (Bi2Te3) and p-type antimony telluride (Sb2Te3) thin films. The films are fabricated by thermal co-evaporation with thermoelectric properties comparable to those reported for the same materials in bulk form (used in conventional macro-scale Peltier modules). The absolute value of the Seebeck coefficient in the range of 150–250 µV K−1 and an in-plane electrical resistivity of 7–15 µΩ m were obtained. The influence of fabrication parameters on thermoelectric properties is reported. The films were patterned by photolithography and wet-etching techniques, using HNO3/HCl-based etchants. The influence of composition and concentration of etchants in the lithographic process is reported. A microcooler was fabricated.

An array of highly selective Fabry-Perot optical channels for biological fluid analysis by optical absorption using a white light source for illumination

This paper describes a laboratory microsystem (Microlab) used to measure the concentration of biomolecules in biological fluids. Rather than just one measurement channel, it comprises 16 optical channels that enable the measurement of the concentration of 16 different biomolecules with the same device. An array of 16 optical filters based on Fabry–Perot thin-film optical resonators has been designed. Each optical channel is sensitive in a single wavelength with a FWHM less than 6 nm and with a peak intensity higher than 86%. The 16 optical channel array fabrication requires only four masks, used with different deposition time. The Microlab can easily be tuned during fabrication to analyse different biomolecules only by adjusting the deposition times without affecting the device layout. A commercially available passband optical filter with a passband wavelength in the range 450–650 nm is used. Th eM icrolab requires only a white light source for illumination due to the use of selective optical filters. The quantitative measurement of uric acid in urine is demonstrated. Such a device is extremely suitable for clinical diagnosis application in clinical laboratories and at a patient’s home because of its small size, low cost and portability.

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.