7th Forum on New Materials - Part F
7th Forum on New Materials - Part E
7th Forum on New Materials - Part D
7th Forum on New Materials - Part C
7th Forum on New Materials - Part B
7th Forum on New Materials - Part A
6th Forum on New Materials - Part D
6th Forum on New Materials - Part C
6th Forum on New Materials - Part B
6th Forum on New Materials - Part A
13th International Ceramics Congress - Part F
13th International Ceramics Congress - Part E
13th International Ceramics Congress - Part D
6th Forum on New Materials - Part D
摘要: ZrO2 and Al2O3 are monolithic ceramics used today in a wide variety of structural components. However, both materials present important drawbacks for some specific applications. In the case of Al2O3, its moderate strength (500 MPa) and toughness (4 MPa.√m) makes it unsuitable for high loading conditions. On the other hand, ZrO2 presents higher strength and toughness values (900 MPa and 6 MPa.√m) than Al2O3 but it is a material limited in its long-term behaviour due to its bad response to hydrothermal ageing and a pronounced tendency for subcritical crack growth. Due to this fact, ceramic nanocomposites made of Al2O3 and ZrO2 (ATZ and ZTA) have been developed in the last years in order to overcome the main drawbacks of the monolithic materials as they can combine the properties of both, strong and tough materials, simultaneously, with null ageing and even higher biocompatibility. In this work, several amounts of Al2O3 disperse phase (15, 35 and 50 vol %) were added to one ZrO2 matrix (CeO2 - 10 mol %) in order to see their effect on the mechanical properties, subcritical crack propagation and long-term reliability.
摘要: Ceramic composites developed for glass infiltration in ceramic substract has as main advantage the reduction of fabrication temperatures of ceramic parts compared to the solid state sintering. In this work, spinell based-ceramics infiltrated with glass rich in lanthanum, aiming applications in dental ceramics, were developed and studied. Pre-sintered spinell substrates with porosity of 10, 15 and 20% were infiltrated with glass at temperature 1120°C-120min, using heating and cooling rate of 10°C/min. The composites present relative density superior 98.6% in every investigated condition, and X-ray diffraction indicated the phase MgAl2O4, as unique crystalline phase detected. Hardness Vickers varying between 850-1000HV and fracture toughness varying between 3.0 to 4.5MPa.m1/2 were obtained for composites with variation of intergranular phase quantity. The evaluation of residual thermal stress indicates that compressive thermal stress are generated in every composition varying from 70-90MPa, for compositions containing between 10 to 20% of infiltrated glass, respectively. Theoretical calculations indicate that the excellent quantity of inter-granular phase infiltrated must be 17%, for obtaining better resistance to crack propagation in this material.
摘要: Assistive devices have been used to improve the quality of life in elderly society, and information and communication technology (ICT) and robotics have been applied extensively to this end. Falls are a common problem and fall risk assessments are created. This study involved assessment related to an application of information technology. First, to monitor and record falls during daily activities, wearable inertial sensors were used . The threshold of acceleration was used to detect falls. To prevent injury during falls, we also developed a wearable airbag system using an accelerometer, angular velocity, and airbags. The subjects wore the airbag vest with a motion detection belt. When the subject fell, the combination of acceleration and angular velocity signals detected the fall and inflated the airbag.
摘要: In recent years, there has been significant progress in a number of sensing technologies related to on-body measurements, such as platforms for monitoring respiration, heart rate, location and movement. In these cases, the sensing element (s) are based on highly effective transducers that are increasingly integrated into garments such that they are becoming innocuous to the user. In contrast, the area of on-body chemical sensing remains highly under-developed. In this paper, we will address the significant challenges that are inhibiting the practical realisation of reliable chemical sensors and biosensors capable of generating accurate data in real time.
摘要: As part of the goal of developing wearable sensor technologies, we have continued the development of a headset system for monitoring activity across the primary motor cortex of the brain. Through the combination of electroencephalography (EEG) and near-infrared spectroscopy (NIRS), the headsets are capable of monitoring event-related potentials and hemodynamic activity, which are wirelessly transmitted to a computer for real-time processing to generate control signals for a motorized prosthetic limb or a virtual embodiment of one or more limbs. This paper focuses on recent observations that have been made regarding the frequency content of EEG data, which we believe is responsible for the high performance we have previously reported using artificial neural networks to infer user’s intentions. While the inference engine takes advantage of frequency content from 0-128 Hertz (Hz), distinct fluctuations in alpha (8-13 Hz), beta (13-30 Hz), and gamma (30-100 Hz) frequency bands are human-observable across varying upper limb motor exercises when observed at the group level. In addition to prosthetic limbs, this technology is continuing to be investigated for application in areas including pain treatment, robotic arm control, lie detection, and more general brain-computer interfaces.
摘要: Microelectrode arrays (MEAs) act as an interface between electronic circuits and neural tissues of implantable devices. Biological response to chronic implantation of MEAs is an essential factor in determining a successful electrode design. Finding appropriate coating materials which are biocompatible and improve electrical properties of MEAs are among the main challenges. In this paper, we propose a novel, three-dimensional (3D), high-density, silicon-based MEAs for both neural recording and stimulation. Electrodes were fabricated using micromachining techniques. Geometrical features of these electrodes not only cause less tissue damage during insertion but also provide more contacts between the electrodes and targeted neural tissues. In order to achieve the proposed geometry, we introduce a novel masking method to coat variable-height electrodes with uniform and small tip-exposure. More importantly, compared to conventional techniques, the new masking method significantly improves process time and costs. This technique needs only one step masking and reduces the conventional masking steps from ten to three. In the next step, the active sites of the electrodes were coated with thin-films of molybdenum (Mo) and platinum (Pt) due to their ability to transfer between ionic and electronic current and to resist corrosion. Electrodes were characterized by scanning electron microscopy and impedance measurements. The average impedance of Mo and Pt electrodes at 1 kHz was 350 ± 50 kΩ and 150 ± 10 kΩ, respectively.
摘要: Wet gel electrodes are widely used for ECG/EEG monitoring, their low impedance results in high-quality signals. But they have important drawbacks too, such as time-consuming electrode set-up for EEG followed by a painful removal, skin irritation by the gel and signal degradation due to gel drying. Hence various dry electrode types are investigated, such as hard metal electrodes with low impedance but limited patient comfort/safety. We focus on flexible conductive polymer-based electrodes to combine low impedance, user comfort and safety. The composition of the conductive polymers is optimized to improve various properties such as conductivity, which directly affects signal quality and sensitivity to motion artifacts, and mechanical properties of the electrodes, important with respect to patient comfort. Electrode impedance and ECG/EEG signal recordings are evaluated using various polymer compositions and compared to wet gel electrode results. Additive optimization to improve processability of the conductive formulations is performed by dedicated flow studies, and will result in a high electrode fabrication yield. Very promising results are obtained regarding impedance, EEG/ECG signal quality and user comfort.
摘要: As known, wireless sensing applications can be enabled by using ultra-low-power electronics for sensing, processing and transmitting information, in order to extend the battery lifetime. Battery size is also a limiting factor constrained by the application requirements. In this scenario, energy harvesting is a fascinating solution, which can attenuate the trade-off between battery size, power consumption of the load circuits and battery lifetime. In some particular applications, characterized by long times in which no energy is available in any form, the battery could completely deplete because of the standby current of the load circuits. For that reason, battery-less applications become more and more relevant. In this paper the available circuit techniques for interfacing vibrational energy harvesters are presented and compared.
摘要: Electroactive polymers (EAP) are relatively soft and flexible materials, easy to integrate and able to undergo large deformations by applying an electric field (usually some 10 V/μm). This coupling between strain and electric field (quadratic by nature) as well as particular mechanical properties have already been used advantageously to design actuators. As energy harvesters, EAP have also shown good abilities by providing energy densities up to 0.4 J/g/cycle (generator integrated in a shoe). Moreover, they present some advantages over other techniques as electromagnetic or piezoelectric as they have low resonance frequency response and high elasticity which enable them to be used in situations where large displacements are available. The main drawback of EAP as energy harvesters is that they don't experience direct coupling between strain and electric field, such as the piezoelectric effect. It is therefore essential to use an external electrical polarization source in order to create energy cycles induced by the EAP capacitance variations when it is subject to external stress. The goal of this work is to combine the EAP and piezoelectric materials using the advantages of both, for a hybrid energy harvesting. Different possible configurations and their performances are studied and a comparison with existing techniques is made.