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Abstract-Wireless sensor networks are increasingly being used for continuous monitoring of patients with chronic health conditions such as diabetes and heart problems. As biomedical sensor nodes become more wearable, their battery sizes diminish, necessitating very careful energy management. This paper proposes feedback-based closed-loop algorithms for dynamically adjusting radio transmit power in body-worn devices, and evaluates their performance in terms of energy savings and reliability as the data periodicity and feedback time-scales vary. Using experimental trace data from body worn devices, we first show that the performance of dynamic power control is adversely affected at long data periods. Next for a given data period we show that modifying the transmit power at too long timescales (around a minute) reduces the efficacy of dynamic power control, while too short a time-scale (few seconds or less) incurs a high feedback signaling overhead. We therefore advocate an intermediate range of time-scales (when permitted by the data periodicity), typically in the few tens of seconds, at which the control algorithms should adapt transmit power in order to achieve maximal energy savings in body-worn sensor devices used for medical monitoring.

Abstract:The design and performance of an inset feed modified hexagonal patch antenna for possible applications in ultrawideband communication systems is reported. The inset feed hexagonal patch antenna is modified by introducing a fractal up to the second iteration. A right-angled isosceles triangular microstrip antenna is used in the Koch fractal structure on the edges. The proposed antenna is a combination of two standard fractal structures, i.e. Sierpinski and Koch. A rectangular defect in the ground has also been done. The antenna is simulated by applying CST Microwave Studio simulation software. The results are verified by fabricating the antenna and tested using a vector network analyzer.The developed design shows good matching with the feed network at frequencies of 3.1 GHz, 6.9 GHz, 7.3 GHz, 8.5GHz, and 9.1 GHz. The simulated peak gain of the antenna at resonant frequencies is 4.08 dB, 4.79 dB, 3.85 dB, 3.46 dB, and 3.01 dB. The antenna is fabricated on FR-4 substrate having size 30 × 35 × 1.59 mm 3 . It covers the S and X band range. It can be used for microwave applications as it is a part of the microwave spectrum, for wireless networking devices coming under IEEE standards. It can also be used for multimedia applications like mobile TV and satellite radio that use the S band as their frequency range and in home-based consumer electronics like microwave ovens, cordless phones, and wireless headphones. For higher ranges, i.e. in the X band, it can be used in radars, satellites, and military appliances.

The recent developments in the era of low-cost and compact communication systems have largely been due to the advent of small weight and size antennas that are capable of giving good output characteristics over a large frequency range. Microstrip patch antenna has become very famous and has attracted much attention towards the research because of these reasons. In this paper, the comparison of three widely popular designs of microstrip patch antennas has been done. Designing begins with the design of patches and then its analysis. Rectangular, square and hexagonal micro strip patch antennas are analyzed using HFSS and a comparison is made between them. In addition to low computational complexity, enhanced connectivity and high speed, modern wireless communication networks also offer advantages such as low profile structures, lightweight, gain must be high and compact size that assures reliability, mobility, and good efficiency. The compact design of patch antennas is due to conventional micro-strip fabrication technique.

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This paper presents the design, fabrication, and measurement of a novel ultra-wideband (UWB) hexagonal fractal patch antenna. This antenna uses hexagonal shape with Koch snowflake fractal at its edges. The proposed antenna has been excited using microstrip feed. The measured result of this antenna offers the ultra wideband characteristics from 3.265 GHz to 8.2 GHz. The antenna is practically fabricated and tested. Measured results show a good agreement with simulated results. The measured radiation patterns of this antenna are nearly omnidirectional in H-plane and bidirectional in E-plane. This antenna holds applications in many satellite communication transmissions, some Wi-Fi devices, cordless telephones, and weather radar systems. In this paper, an approach for multi-band antennas is proposed. First, a hexagonal patch is taken, it is fractured using Koch structure. The antenna shows compact dimensions with good S11 and pattern performance to be adopted for UWB applications.