J. P. Carmo

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.

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.

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.

Wireless instrumentation system based on dry electrodes for acquiring EEG signals.

This paper presents a complete non-invasive Wireless acquisition system based on dry electrodes for electroencephalograms (WiDE-EEG) with emphasis in the electronic system design. The WiDE-EEG is composed by a 2.4 GHz radio-frequency (RF) transceiver, biopotential acquisition electronics and dry electrodes. The WiDE-EEG can acquire electroencephalogram (EEG) signals from 5 unipolar channels, with a resolution of 16 bits and minimum analog amplitude of 9.98 μV(pp), at a sampling rate of 1000 samples/s/channel and sends them to a processing unit through RF in a 10 m range. The analog channels were optimized for EEG signals (with amplitudes in the range 70-100 μV) and present the following characteristics: a signal gain of 66 dB and a common mode rejection ratio of 56.5 dB. Each electrode is composed by 16 microtip structures that were fabricated through bulk micromachining of a <100>-type silicon substrate in a potassium hydroxide (KOH) solution. The microtips present solid angles of 54.7°, a height of 100-200 μm and 2 μm spaced apart. The electrodes have a thin layer (obtained by sputtering) of iridium oxide (IrO) to guaranty their biocompatibility and improve the contact with the skin. These dry electrodes are in direct contact with the electrolyte fluids of the inner skin layers, and avoid the use of conductive gels. The complete WiDE-EEG occupies a volume of 9 cm×8.5 cm×1 cm, which makes it suitable for true mobility of the subjects and at the same time allows high data transfer rates. Since the WiDE-EEG is battery-powered, it overcomes the need of galvanic isolation for ensuring patient safety observed on conventional EEG instrumentation systems. The WiDE-EEG presents a total power consumption of 107 mW, divided as follows: the acquisition system contributes with 10 mW per channel, whereas the commercial MICAz module contributes with 57 mW (e.g., 24 mW from the microcontroller and 33 mW from the RF chip). The WiDE-EEG also presents autonomy of about 25 h with two class AA 1.5 V batteries.

Thermoelectric generator and solid-state battery for stand-alone microsystems

This paper presents a thermoelectric (TE) generator and a solid-state battery for powering microsystems. Prototypes of TE generators were fabricatedand characterized. The TE generator is a planar microstructure based on thinfilms of n-type bismuth telluride (Bi 2Te 3) and p-type antimony telluride (Sb 2Te 3), which were deposited using co-evaporation. The measurements on selected samples of Bi 2Te 3and Sb 2Te 3thinfilms indicated a Seebeck coefficient in the range of 90–250 ¹ V K −1 and an in-plane electrical resistivity in the range of 7–17 ¹A m. The measurements also showed TEfigures-of-merit, ZT, at room temperatures (T =300 K) of 0.97 and 0.56, for thinfilms of Bi 2Te 3and Sb 2Te 3, respectively (equivalent to a power factor, PF, of 4.87 mW K −2 m −1 and 2.81 mW K −2 m −1 ). The solid-state battery is based on thinfilms of: an anode of tin dioxide (SnO 2), an electrolyte of lithium phosphorus oxynitride (Li xPO yNz, known as LiPON) and a cathode of lithium cobaltate (LiCoO 2, known as LiCO), which were deposited using the reactive RF (radio-frequency) sputtering. The deposition and characterization results of these thin-films layers are also reported in this paper. (Somefigures in this article are in colour only in the electronic version)

A 2.4-GHz Low-Power/Low-Voltage Wireless Plug-and-Play Module for EEG Applications

This paper presents a plug-and-play module for wireless electroencephalogram (EEG) applications. The wireless module is composed by an electrode, processing electronics, a radio-frequency (RF) transceiver, and an associated antenna. The RF transceiver was fabricated in the UMC RF 0.18 mum CMOS process, and operates in the 2.4-GHz ISM band. The receiver has a sensitivity of -60 dBm and a power consumption of 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, for a range of 10 m. It is also presented the electrical performance and comparison between different electrodes for EEG applications, namely sputtered titanium nitride (TiN) electrodes, standard sintered silver/silver chloride (Ag/AgCl) ring electrodes and sputtered iridium oxide (IrO2) electrodes. The experimental results show a better performance of the sputtered IrO2 electrodes compared with the standard sintered Ag/AgCl ring electrodes. These results promise a new opportunity for the application of a dry IrO2 electrodes in wireless modules for using in a wearable EEG braincap. These wireless EEG modules will allow patients to wear a brain cap and maintain their mobility, while simultaneously having their electrical brain activity monitored.

Application of Fiber Bragg Gratings to Wearable Garments

This paper presents a photonic system based on Fiber Bragg Gratings (FBGs) for application to wearable garments. The objective is spanning the FBGs over the whole area of the garments for acting as sensing elements. The FBGs are embedded on a polychloroethanediyl (polyvinyl chloride, commonly abbreviated as PVC) carrier in order to increase their sensitivity to strains and for improving the simultaneous acquisition of respiratory and cardiac frequencies with only one FBG sensor. The global structure comprising FBGs and carrier allow high strain cycles and at the same time present linear behavior with the temperature, 17 pm · °C-1. The measurements show a stable structure for temperatures up to 100°C. This brings excellent perspectives for measuring the temperature with high accuracy and range. A set of tests were done by subjecting the FBG/carrier structure (with FBG stretched and no curves) to strains up to 1.2 mm, and it was also observed a linear behaviour: e.g., displacements of 0.8 pm · με-1. Behind its sensing enhancement operation, the carrier makes easy to mount the sensing structures.

An energy scavenging microsystem based on thermoelectricity for battery life extension in laptops

This paper presents a solution to increase the nominal lifetime of batteries in laptops. New thin-film materials offer potentially greater efficiencies when converting heat to electricity using the thermoelectric effect. Applied to microprocessors, this technology can mitigate a number of critical problems as the critical amount of heat produced by laptops. The use of a thermoelectric scavenging microsystem based on the Seebeck effect can address this problem, by extracting waste heat from a high-end microprocessor, converting the heat to electricity using thin-film technology in silicon compatible materials. Applying a thermoelectric micro converter (that was fabricated using thin-films of bismuth and antimony tellurides) to a temperature gradient of 60 °C, it is possible to obtain an efficiency of 3% and increase in the same amount, the lifetime of batteries.

Low-power/low-voltage RF microsystems for wireless sensors networks

This paper presents radio-frequency (RF) microsystems (MSTs) composed by low-power devices for use in wireless sensors networks (WSNs). The RF CMOS transceiver is the main electronic system and its power consumption is a critical issue. Two RF CMOS transceivers with low-power and low-voltage supply were fabricated to operate in the 2.4 and 5.7GHz ISM bands. The measurements made in the RF CMOS transceiver at 2.4GHz, which showed a sensitivity of -60dBm with a power consumption of 6.3mW from 1.8V supply. The measurements also showed that the transmitter delivers an output power of 0dBm with a power consumption of 11.2mW. The RF CMOS transceiver at 5.7GHz has a total power consumption of 23mW. The target application of these RF CMOS transceivers is for MSTs integration and for use as low-power nodes in WSNs to work during large periods of time without human operation, management and maintenance. These RF CMOS transceivers are also suitable for integration in thermoelectric energy scavenging MSTs.

A Flexible Infrastructure for Dynamic Power Control of Electric Vehicle Battery Chargers

This paper proposes a flexible infrastructure for dynamic power control (FIDPC) of electric vehicle (EV) battery chargers. This infrastructure dynamically adjusts the EV battery charger current, according to the power demand of the home wherein the vehicle is plugged. An infrastructure was implemented to validate this proposal. This infrastructure is composed by an EV battery charger and a communication system based on a radio-frequency (RF) interface. The battery charger has nominal power of 3.6 kVA and operates with sinusoidal current and unitary total power factor, whereas the RF interface provides continuous data flow to the battery charger with information on the home total current consumption (root-mean-square value). Experimental tests were performed under realistic conditions to validate the concept behind the proposed FIDPC. These tests served to assess the behavior of the EV battery charger with dynamic power control on a single-phase 230-V 16-A 50-Hz residential electrical installation. The experimental results confirm the quick time response of the FIDPC, even when working under heavy-home-load variations.