M. S. Martins

Touchscreen based on acoustic pulse recognition with piezoelectric polymer sensors

This article describes the concept, design, fabrication and experimental results of a touchscreen based on acoustic pulse recognition. It uses piezoelectric transducers fabricated from the piezoelectric polymer poly(vinylidene fluoride), PVDF, in its beta phase. The transducers are located at the edges of the panel in order to receive the acoustic pulses generated by the touches. Each transducer is connected to a readout electronic circuit composed by a differential charge amplifier and a comparator, whose output signal is attached to a microcontroller. The microcontroller uses an algorithm to determine the location of the touch, based on the time differences of the transducer signals. The touchscreen itself is made of ordinary glass, providing good durability and optical transparency. The experimental results obtained with the first prototype demonstrate the effectiveness of the method.

Glycerol/PEDOT:PSS coated woven fabric as a flexible heating element on textiles

A polyamide 6,6 (PA66) fabric pre-treated with a double barrier dielectric (DBD) atmospheric plasma in air was coated with 1 and 5 layers of an intrinsically conducting glycerol-doped PEDOT:PSS polymer (PEDOT:PSS + GLY) with the final objective of developing a cost-competitive and temperature controllable flexible-heating element to be used in clothing encapsulated between an outer and an inner separator layer in order to provide heat-reflecting properties and uniform temperature distribution, respectively. FTIR, DSC, TGA, SEM, EDS, XRD and DMA analyses show significant changes in morphology, chemistry, enthalpy, crystallinity and glass transition temperature confirming that PEDOT:PSS and glycerol are not only spread over the PA66 yarn surfaces but are dispersed in the bulk facilitating relaxation and increasing structure and chain flexibility. Electrochemical and electrical resistivity (ρ) measurements confirm that the plasma treated PA66 coated with 5 layers of PEDOT:PSS + GLY presents the highest stability, resistance and capacitive behaviour, and the best capability of storing electrical energy. This configuration needs only 7.5 V to induce a temperature change up to 38 °C at a current density of 0.3 A g−1. The desired temperature is easily adjustable as a function of the applied voltage and by the number of coated layers of PEDOT:PSS + GLY. Despite the need to improve the uniformity of the coating thickness on the fabric for uniform heat generation, the observed results are quite impressive since they can be compared to the temperature obtained in carbon nanotube composites using similar voltages. This cost-competitive, safe, highly flexible and stable thermoelectric fabric has potential for use in large area textiles as a heating element in a wide range of applications such as garments, carpets, blankets and automotive seats.

Development of a 1 Mbps low power acoustic modem for underwater communications

Underwater wireless communication systems are becoming a priority in terms of research and technological development due to the increasing demand for exploring the oceans in areas such as pharmaceutical, oil, minerals, environmental and biodiversity. This demand is increasing exponentially with the need for high data rate and near-real-time communications. In this work an underwater low power acoustic modem to operate over tens of meters, achieving a maximum data rate of 1 Mbps, is presented. This solution allows for reprogramming the digital signal processing block enabling the use of different types of digital modulations in order to improve the modems performance. The system is based on a poly(vinylidene fluoride) PVDF ultrasonic emitter transducer which is capable of sending high quality signals needed for digital modulations with high symbol rates per carrier period. BPSK, BFSK and OOK modulations have been tested. The results registered were 3×10-3 BER with 1 Mbps OOK, 2.3×10-5 with 512 kbps and 1×10-8 with 256 kbps.

Tracking sound source localization for a home robot application

The future of robotics is now trending for home servicing. Nursing homes and assistance to elder people are areas where robots can provide valuable help in order to improve the quality of life of those who need it most. Calling a robot, for a person of age, can be a daunting task if the voice is failing and any resort to battery operated devices fails to comply. Using a simple mechanical apparatus, such as a Click trainer for dogs, a person can call a robot by pressing the button of a powerless device. The high pitch sound produced by this device can be captured and tracked down in order to estimate the person’s location within a room. This paper describes a method that provides good accuracy and uses simple and low cost technology, in order to provide an efficient positional value for an assistance robot to attend its caller. The robot does not need to search for the person in a room as it can directly travel towards the Click’s sound source. Keywords-localization; sound source; interaural sound difference; time difference of arrival

Energy harvesting to supply moored oceanographic monitoring stations

This work aims to study a new energy harvesting device to be anchored on the ocean floor and convert any type of currents, tides or oscillation movement into electrical energy using linear electromagnetic generators. The final application is to supply energy to a set of moored monitoring sensors that collects data and allowing the system to be energetically autonomous. The proposed setup is a spherical buoy with no external moving parts, to be more biofouling proof. The maximum output power measured for a 4 Hz movement was 9.9 mW with only one linear electromagnetic generator.

High data rate acoustic modem for underwater aplications

The development of an underwater wireless communication systems is becoming a research and a technological priority due to the increasing demand for exploring the potential of oceans in fields such as pharmaceutics, oil, minerals, environmental and biodiversity. However, underwater wireless communications still fail to ensure high data-rate connections which support real time applications. In this work a low power high data-rate acoustic modem is presented, based on a piezoelectric poly (vinylidene fluoride) polymer as a transducer and a Xilinx Field Programmable Gate Array (FPGA) that can be programmed to work with different types of modulations. The system has been validated by the implementation of a full duplex point-to-point communication at 1 Mbps using On-Off Keying (OOK) modulation with a 1 MHz single carrier and it represents a major advance in the state of the art and a breakthrough in underwater acoustic communications, being the first to show the possibility to achieve data rates up to 1Mbps. It was successfully tested with a 1 Mbps rate, achieving a 3×10-3 Bit Error Rate (BER) using just 1.4 μW of power consumption per bit.

Design and Development of a Prototype Electrotherapy Device

This article describes a complete prototype system that can be used in electrotherapy treatments, that is, in medical treatments involving electric currents. The system is composed of two main blocks: the master and the slave. The Master block, whose main component is a CPU, controls the user interface. The Slave block, which is composed of a microcontroller and a wave generator, produces the appropriated voltages and currents compatible with the desired treatment. The whole system is powered by a 12 V power supply and the output signal voltage ranges between -100 V and 100 V. Despite the prototype being able of performing all the electrotherapy treatments in the low-medium frequency ranges, it was tested in aesthetic mesotherapy, namely in anticellulite, located anticellulite, antistretch, and antiflaccidity. In these treatments, the output signal is composed of an overlap of two frequencies: the first one is selected in the range of 1.2 kHz - 1.8 kHz and the second in the range of 0.07 Hz - 2 Hz. The system was tested in a clinical environment with real patients. It showed good results both in effectiveness of treatments and in terms of pain suffered by the patients.

Dilatometer for characterization of thermal expansion of ceramic samples

This article describe the design, fabrication steps and experimental results of a dilatometer that will be used to characterize ceramic samples in terms of thermal expansion. The basic idea is to heat a 25 mm ceramic sample up to 1000oC and register its dimension variations during the rising and the falling of the temperature. The device prototype consists in a master-slave structure since there are two control units: the high-level one (master) and a low-level one (slave). The highlevel control unit will be responsible for supporting the user interface, exchanging and processing the necessary information between the user and the low-level control unit. The low-level control unit main component is a microcontroller. It is responsible for acquiring data from the strain and temperature sensors and controlling the temperature of the samples. The experimental results show that the prototype is appropriate for dilatometry essays once the maximum error was 0.037% of full-scale.