Robust microphone arrays using subband adaptive filters

A new adaptive beamformer which combines the idea of subband processing and the generalised sidelobe canceller structure is presented. The proposed subband beamformer has a blocking matrix that uses coefficient-constrained subband adaptive filters to limit target cancellation within an allowable range of direction of arrival. Simulations comparing the fullband and subband adaptive beamformers show that the subband beamformer has better performance than the fullband beamformer when the target and/or interfering signals are coloured. In reverberant environments, the proposed subband beamformer also performs better than its fullband counterpart     

Long-term stimulation and recording with a penetrating microelectrode array in cat sciatic nerve

We studied the consequences of long-term implantation of a penetrating microelectrode array in peripheral nerve over the time course of 4-6 mo. Electrode arrays without lead wires were implanted to test the ability of different containment systems to protect the array and nerve during contractions of surrounding muscles. Treadmill walking was monitored and the animals showed no functional deficits as a result of implantation. In a different set of experiments, electrodes with lead wires were implanted for up to 7 mo and the animals were tested at 2-4 week intervals at which time stimulation thresholds and recorded sensory activity were monitored for every electrode. It was shown that surgical technique highly affected the long-term stimulation results. Results between measurement sessions were compared, and in the best case, the stimulation properties stabilized in 80% of the electrodes over the course of the experiment (162 days). The recorded sensory signals, however, were not stable over time. A histological analysis performed on all implanted tissues indicated that the morphology and fiber density of the nerve around the electrodes were normal.     

Ultrastructural study of the A-W GC-bone interface after long-term implantation in rat and human bone

The interface between apatite- and wollastonite-containing glass-ceramic (A-W GC) and bone after long-term implantation was studied by scanning and transmission electron microscopy (SEM and TEM) using rat and human specimens. First, particles of A-W GC (100-220 microns in diameter) were implanted into rat tibiae, and specimens were prepared for observation at 24, 48, 72, and 96 weeks after the operation. These long-term specimens showed an A-W GC-bone interface different from that at an earlier stage, which was investigated in our previous studies. SEM showed that the Ca-P-rich layer was wider, suggesting that leaching of ions from the A-W GC had continued even after bonding with bone. In some regions, the material particles were evidently replaced by the bone. TEM showed that the intervening apatite layer had become indistinct, and that A-W GC had intermingled with bone at the interface. In some regions, the surface of the A-W GC was degraded. These findings suggest that the surface region of A-W GC is slowly replaced by bone. Second, a human bone specimen, which included A-W GC particles (300-700 microns in diameter) implanted as a bone filler for about 75 weeks was harvested and investigated. Excellent A-W GC-bone bonding was observed, and the ultrastructure of the interface was similar to that in rats after long-term implantation. This finding demonstrated that A-W GC possibly worked in human bone in the same way as in rat bone, showing excellent bioactivity.     

Synthesis and functionalities of poly(N‐vinylalkylamide). XIV. Polyvinylamine produced by hydrolysis of poly(N‐vinylformamide) and its functionalization

The molecular weights of poly(N‐vinylformamide) [poly(NVF)] obtained by free‐radical polymerization were expanded from being in the range of thousands to hundreds of thousands. Primary amino groups were introduced by the hydrolysis of poly(NVF) under both acidic and basic conditions. After 2 h polyvinylamine [poly(VAm)] was given at 60°C under a 2N NaOH solution. The apparent activation energy of poly(NVF) hydrolysis was 61.8 kJ/mol. Furthermore, alkyl side chains were partly introduced by a polymer modification reaction in poly(VAm) with carboxylic acid, using WSC (water‐soluble carbodiimide) as the activating agent to produce the stimuli‐responsive poly(VAm) derivative. The effects of external stimuli such as temperature and pH on the phase‐transition behavior of the copolymers were then studied. The lower critical solution temperature at pH 12 decreased depending on the alkyl group content. The phase‐transition behavior of the resulting polymers was also found to vary depending on the side‐chain length of the alkyl groups. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 1277–1283, 2003     

Effect of anodic oxidation of coal tar pitch-based carbon fibre on adhesion in epoxy matrix: Part 1. Comparison between H2SO4 and NaOH solutions

Anodic oxidation of high modulus coal tar pitch-based carbon fibre in alkaline and sulfuric solutions was investigated. X-ray photoelectron spectroscopy (XPS) analysis was used to evaluate the oxygen concentration (O_1S/C_1S) and surface functional groups (---OH, C=O and COOH). The interfacial shear strength between the epoxy matrix and carbon fibre was measured by a fragmentation test. The results showed that the oxygen concentration on fibre surfaces increased rapidly as electrical charge increased, in both alkaline and acidic solution. The best bonding between epoxy matrix and carbon fibre was achieved in alkaline solution. The Raman spectra of carbon fibre oxidized in alkaline and sulfuric solutions suggested that the weak adhesive strength between the epoxy resin and oxidized carbon fibre in sulfuric solution was due to the existence of an oxidized graphite layer, which might easily come off the surface.     

Material characterization of fluorosilicone gels for automotive application

Fluorosilicone gel is commonly used in die passivation. This paper studies the characteristics of fluorosilicone gel applied on the manifold air pressure (MAP) sensor die. The cure mechanism and material characterization of the three types of gels were analyzed using differential scanning calorimeter (DSC), thermogravimetric analysis (TGA), and rheometer. The temperature and time relationships were derived for each material type. In the process of characterization, it was discovered that characterized material does not always behave as expected in the production confirmation run. It was found that the gel selected interacted with the thermoplastic packaging material hence leading to further findings of cure inhibitation. This paper concludes with the valuable lessons learnt from this material characterization project and explains the importance of these lessons learnt to actual manufacturing experience.     

Smith chart approach to the design of multilayer resistive sheet

The design of the multilayer resistive sheet is often given in some formulae or in some tabulated forms. The electrical engineer or material scientist often cannot visualize how the design really works or the achievable bandwidth. In this paper, we attempt to give a good understanding of the design of the multilayer resistive sheet by using the Smith Chart approach. The Smith Chart approach offers more flexibility to the design of the multilayer resistive sheet, as compared to published formulae or tables.