Multiband properties of a fractal tree antenna generated byelectrochemical deposition

Experimental results on a fractal tree-like antenna are reported. The fractal structure is generated by electrochemical deposition. The antenna presents a multiband behaviour with a denser band distribution than the previously reported Sierpinski fractal antenna. The matched frequencies are related to the length distribution over the fractal shape     

Corrosion resistance of anodic oxides on the Ti-50Zr and Ti-13Nb-13Zr alloys

Electrochemical analyses on the biocompatible alloys Ti-50Zr and Ti-13Nb-13Zr, as-cast and heat-treated, in distinct electrolytes (simulating or not physiological media: pH 7, Ringer, PBS, phosphate buffer and Na₂SO₄ solutions; pH 1, H₂SO₄, HNO₃, CH₃SO₃H, HClO₄ and H₃PO₄ solutions) are reported. Analyses of the open-circuit potential values indicated that either as-cast or heat-treated samples of both alloys present the same tendency to spontaneously form an oxide film on their surfaces and that the oxide grown in the Na₂SO₄ solution presents better protection characteristics than those formed in the phosphate buffer, Ringer and PBS solutions, in this order. Cyclic voltammograms obtained in the Ringer and PBS solutions showed that the Ti-13Nb-13Zr alloy does not transpassivate up to potentials of 8 V (versus SCE), while the Ti-50Zr alloy presents corrosion at potentials lower than 2 V (versus SCE), indicating that this alloy is less resistant to corrosion in solutions simulating physiological conditions. The obtained pit potential values showed that the heat treatment has very little influence on the corrosion behavior of the alloys. Finally, both alloys did not present transpassivation at potentials up to 8 V (versus SCE) in the H₂SO₄, HNO₃, CH₃SO₃H and H₃PO₄ solutions; however, when immersed in the HClO₄ solution the Ti-50Zr alloy underwent pit corrosion while the Ti-13Nb-13Zr alloy remained corrosion resistant in this potential range.     

Voltammetric stability of anodic films on the Ti6Al4V alloy in chloride medium

The biocompatibility and mechanical integrity of Ti and Ti6Al4V alloy can be affected by corrosion processes. This paper presents studies on the stability of anodic oxide films on Ti6Al4V and Ti in chloride medium. The oxides were grown potentiodynamically up to 8.0 V in the phosphate buffer saline (PBS) solution (pH 6.8) at 25 and 37 °C. The morphology of the obtained anodic oxides and the type of corrosion that occurred were analyzed by SEM–EDS. The Ti6Al4V alloy presented less corrosion resistance than pure Ti. Elemental analyses showed that the decrease of the alloy corrosion resistance is due mainly to the corrosion of Al.     

The Koch monopole: a small fractal antenna

Fractal objects have some unique geometrical properties. One of them is the possibility to enclose in a finite area an infinitely long curve. The resulting curve is highly convoluted being nowhere differentiable. One such curve is the Koch curve. In this paper, the behavior the Koch monopole is numerically and experimentally analyzed. The results show that as the number of iterations on the small fractal Koch monopole are increased, the Q of the antenna approaches the fundamental limit for small antennas     

盐水介质中Ti12Mo5Ta合金的电化学特性(英文)

比较了未再结晶和再结晶Ti12Mo5Ta合金、未再结晶Ti12Mo合金和工业用纯钛(cp-Ti)在0.9%生理盐水(pH 2.3)中37°C下的电化学行为。从阳极极化曲线中得到了极低的钝化电流密度(10-6 A/cm2),这表明所有样品在酸性0.9%NaCl溶液中具有高的耐蚀性能。采用扫描电子显微镜(SEM)观察样品的表面形貌,发现所有样品表面受到了相同的腐蚀,而且经阳极动电位极化测试后的样品表面没有出现点蚀、裂纹或其它缺陷。使用等效电路模拟电化学阻抗谱(EIS)数据,以表征样品表面且更好地理解Mo和Ta的添加对cp-Ti及再结晶的影响。EIS结果证实,在开路电位下,所有样品在0.9%NaCl溶液(pH 2.3)中产生钝化(极化电阻约为105Ω·cm2)。在37°C时,样品在0.9%NaCl溶液中(pH 2.3)的耐蚀性顺序为:再结晶Ti12Mo5Ta未再结晶Ti12Mo5Ta未再结晶Ti12Mocp-Ti。     

Bilayered nanofilm of polypyrrole and poly(DMcT) for high-performance battery cathodes

Bilayered nanofilm electrodes made of polypyrrole (Ppy) and poly-2,5-dimercapto-1,3,4-thiadiazole (poly-DMcT) are produced by electrochemical means onto a carbon-fiber substrate, with the goal of preventing the loss of the electroactive mass of the disulfide and improving the electrode stability during the charge/discharge cycling process. Lightweight and high surface area composites are obtained by potentiostatically depositing a nanometric layer of Ppy onto a carbon fiber piece already supporting a layer of a potentiodynamically obtained poly(DMcT) film. The growth charge/mass ratio for the bilayered polymeric electrode is optimized, leading to a high electrochemical performance cathode with a stable specific capacity of ∼320 mA h g⁻¹ after 100 cycles.     

Infrared thermograms applied to near-field testing

Electromagnetic fields close to radiant structures can be measured quickly using an infrared camera. Examples of induced fields by wire antennas over a detection screen at distances shorter than one wavelength are presented. The measured thermograms agree with simulations that take into account heat propagation on the detection screen.