506 research outputs found

    A practical theorem on using interferometry to measure the global 21-cm signal

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    The sky-averaged, or global, background of redshifted 2121 cm radiation is expected to be a rich source of information on cosmological reheating and reionizaton. However, measuring the signal is technically challenging: one must extract a small, frequency-dependent signal from under much brighter spectrally smooth foregrounds. Traditional approaches to study the global signal have used single antennas, which require one to calibrate out the frequency-dependent structure in the overall system gain (due to internal reflections, for example) as well as remove the noise bias from auto-correlating a single amplifier output. This has motivated proposals to measure the signal using cross-correlations in interferometric setups, where additional calibration techniques are available. In this paper we focus on the general principles driving the sensitivity of the interferometric setups to the global signal. We prove that this sensitivity is directly related to two characteristics of the setup: the cross-talk between readout channels (i.e. the signal picked up at one antenna when the other one is driven) and the correlated noise due to thermal fluctuations of lossy elements (e.g. absorbers or the ground) radiating into both channels. Thus in an interferometric setup, one cannot suppress cross-talk and correlated thermal noise without reducing sensitivity to the global signal by the same factor -- instead, the challenge is to characterize these effects and their frequency dependence. We illustrate our general theorem by explicit calculations within toy setups consisting of two short dipole antennas in free space and above a perfectly reflecting ground surface, as well as two well-separated identical lossless antennas arranged to achieve zero cross-talk.Comment: 17 pages, 6 figures, published in Ap

    Signal Attenuation in V.H.F. Biotelemetry

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    In this paper, the change in loop resistance is examined when the loop is placed at the center of a spherical air cavity which is in turn surrounded by a sphere of physiological saline solution, as shown. The functional dependence of the magnitude of the dissipation resistance on the cavity radius will be studied. The validity of introducing a dissipation resistance will be experimentally tested by immersing a loop in a physiological saline solution and directly measuring the change in resistance with an r.f. bridge. Once the increase in resistance is established, the resultant reduction in radiated power will be mathematically calculated and compared with the reduction in radiated power caused by radiated power absorption, in an effort to determine which effect predominates. The analysis will begin with the derivation of the electro-magnetic fields in the space around the loop in air and in a lossy medium. An analysis of the fields in the cavity and in the saline solution will be made with the goal of obtaining a good approximation for the fields in the solution, from which the Joule heat liberated in the solution can be found and the dissipation resistance determined

    ๋ฐฉ์‚ฌ ๋ฌด์„ ์ „๋ ฅ์ „์†ก์„ ์œ„ํ•œ ๋ฌด์ง€ํ–ฅ์„ฑ ์•ˆํ…Œ๋‚˜ ๋ฐ ์ „์†ก ํšจ์œจ ํ•œ๊ณ„์— ๋Œ€ํ•œ ์—ฐ๊ตฌ

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    ํ•™์œ„๋…ผ๋ฌธ (๋ฐ•์‚ฌ) -- ์„œ์šธ๋Œ€ํ•™๊ต ๋Œ€ํ•™์› : ๊ณต๊ณผ๋Œ€ํ•™ ์ „๊ธฐยท์ •๋ณด๊ณตํ•™๋ถ€, 2020. 8. ๋‚จ์ƒ์šฑ.๋ณธ ๋…ผ๋ฌธ์—๋Š” ๋ฐฉ์‚ฌํ•˜๋Š” ์ „์žํŒŒ๋ฅผ ์ด์šฉํ•œ ๋ฌด์„  ์ „๋ ฅ ์ „์†ก์— ๋Œ€ํ•ด ์ง‘์ค‘์ ์œผ๋กœ ์—ฐ๊ตฌ๋ฅผ ์ง„ํ–‰ํ•˜์˜€๋‹ค. ๋ณด๋‹ค ๊ตฌ์ฒด์ ์œผ๋กœ๋Š”, ๋ฌด์ง€ํ–ฅ์„ฑ ์•ˆํ…Œ๋‚˜์˜ ๋ถ„์„๊ณผ ์„ค๊ณ„, ์ž์œ ๊ณต๊ฐ„๊ณผ ์†์‹ค๋งค์งˆ์—์„œ์˜ ์ตœ์  ์†ก์‹  ์ „๋ฅ˜ ๋ถ„ํฌ, ์ „์†ก ํšจ์œจ์˜ ํ•œ๊ณ„์— ๋Œ€ํ•œ ์—ฐ๊ตฌ๋ฅผ ๊ธฐ์ˆ ํ•˜์˜€๋‹ค. ์ถ”๊ฐ€์ ์œผ๋กœ, ์ „์žํŒŒ์˜ ์ธ์ฒด ์˜ํ–ฅ์— ๋Œ€ํ•œ ๋น„๊ต ๋ฐ ์ด๋ก ์ ์ธ ์ตœ์  ์ „๋ฅ˜ ๋ถ„ํฌ์˜ ํšจ๊ณผ์  ๊ตฌํ˜„์— ๋Œ€ํ•œ ์—ฐ๊ตฌ๋ฅผ ์ง„ํ–‰ํ•˜์˜€๋‹ค. ๋ณธ ์—ฐ๊ตฌ์—์„œ๋Š” ๋ฐฉ์‚ฌํ˜• ๋ฌด์„ ์ „๋ ฅ์ „์†ก์„ ์ „์›์„ ๊ณต๊ธ‰ ์œ ๋ฌด์— ๋”ฐ๋ผ ์ˆ˜๋™ํ˜•๊ณผ ๋Šฅ๋™ํ˜• ๋ฌด์„ ์ „๋ ฅ์ „์†ก์œผ๋กœ ๊ตฌ๋ถ„ํ•˜๊ณ , ์ˆ˜๋™ํ˜• ๋ฐฉ์‚ฌ ๋ฌด์„ ์ „๋ ฅ์ „์†ก๋ถ€ํ„ฐ ๋Šฅ๋™ํ˜• ๋ฐฉ์‚ฌ ๋ฌด์„ ์ „๋ ฅ์ „์†ก๊นŒ์ง€์˜ ์—ฐ๊ตฌ๋ฅผ ์ˆœ์ฐจ์ ์œผ๋กœ ๊ธฐ์ˆ ํ•˜์˜€๋‹ค. ๋จผ์ €, ์ˆ˜๋™ํ˜• ๋ฐฉ์‚ฌ ๋ฌด์„ ์ „๋ ฅ์ „์†ก ์—ฐ๊ตฌ์—์„œ๋Š” ์ „์žํŒŒ ์—๋„ˆ์ง€ ํ•˜๋ฒ ์ŠคํŒ…์šฉ ์•ˆํ…Œ๋‚˜์— ๋Œ€ํ•œ ๋ถ„์„ ๋ฐ ์„ค๊ณ„์— ๋Œ€ํ•œ ์—ฐ๊ตฌ๋ฅผ ์ง„ํ–‰ํ•˜์˜€๋‹ค. ์ˆ˜๋™ ๋ฐฉ์‚ฌ ๋ฌด์„ ์ „๋ ฅ์ „์†ก์˜ ์ƒํ™ฉ์„ ๊ณ ๋ คํ•˜์—ฌ ๋“ฑ๋ฐฉ์„ฑ ํŒจํ„ด, ์ „๊ธฐ์ ์œผ๋กœ ์ž‘์€ ํฌ๊ธฐ, ๋†’์€ ํšจ์œจ ํŠน์„ฑ์„ ๋‚˜ํƒ€๋‚ด๋Š” ์•ˆํ…Œ๋‚˜๋ฅผ ์ œ์•ˆํ•˜์˜€๋‹ค. ์ „๊ธฐ์ ์œผ๋กœ ์†Œํ˜•์ด๋ฉด์„œ ๋“ฑ๋ฐฉ์„ฑ ํŒจํ„ด์„ ๋ฐฉ์‚ฌํ•˜๋Š” SRR์ด ๊ธฐ๋ณธ ๊ตฌ์กฐ๋กœ ํ™œ์šฉ๋˜์—ˆ๋‹ค. SRR์— ๋Œ€ํ•œ ์ด๋ก ์  ๋ถ„์„์„ ์ง„ํ–‰ํ•˜์˜€๊ณ , ์‹œ๋ฎฌ๋ ˆ์ด์…˜ ๊ฒฐ๊ณผ์™€ ์ž˜ ๋งž๋Š” ๊ฒƒ์„ ํ™•์ธํ•˜์˜€๋‹ค. ๋ถ„์„์— ๊ธฐ์ดˆํ•˜์—ฌ FSRR ์•ˆํ…Œ๋‚˜๋ฅผ ์„ค๊ณ„ํ•˜์˜€๊ณ , ์ธก์ •์„ ํ†ตํ•ด ์ œ์•ˆํ•œ ์•„์ด๋””์–ด๋ฅผ ๊ฒ€์ฆํ•˜์˜€๋‹ค. ์ˆ˜์‹  ํŒŒ์›Œ์˜ ํฌ๊ธฐ๋ฅผ ํ–ฅ์ƒ์‹œํ‚ค๊ธฐ ์œ„ํ•ด, ์ด์ค‘ ๋Œ€์—ญ ๋ฐ ํ™•์žฅ๋œ ๋Œ€์—ญ์—์„œ ๋™์ž‘ํ•˜๋Š” FSRR ์•ˆํ…Œ๋‚˜๋ฅผ ์ถ”๊ฐ€๋กœ ์„ค๊ณ„ํ•˜์˜€๋‹ค. ์ œ์•ˆ๋œ ๊ตฌ์กฐ๋Š” ์„ ํ–‰์—ฐ๊ตฌ์™€ ๋น„๊ตํ•˜์˜€์„ ๋•Œ, ์ƒ๋Œ€์ ์œผ๋กœ ์šฐ์ˆ˜ํ•œ ์„ฑ๋Šฅ์„ ๋ณด์—ฌ์ฃผ์—ˆ๋‹ค. ํ•œํŽธ ์ˆ˜๋™ํ˜• ๋ฐฉ์‚ฌ ๋ฌด์„  ์ „๋ ฅ์ „์†ก์˜ ๊ฒฝ์šฐ, ์ฃผ๋ณ€์˜ ๋‚ฎ์€ ์ „๋ ฅ ๋ฐ€๋„๋กœ ์ธํ•ด ์ˆ˜์‹  ์ „๋ ฅ์ด ๋งค์šฐ ๋‚ฎ์€ ํ•œ๊ณ„์ ์ด ์กด์žฌํ•œ๋‹ค. ๋”ฐ๋ผ์„œ, ์†ก์‹  ํƒ€์›Œ๋ฅผ ์ด์šฉํ•ด ๋ชจ๋ฐ”์ผ ์•ˆํ…Œ๋‚˜๋กœ ๋ฌด์„  ์ „๋ ฅ์„ ์ „์†กํ•  ์ˆ˜ ์žˆ๋Š” ๋Šฅ๋™ํ˜• ๋ฐฉ์‚ฌ ๋ฌด์„ ์ „๋ ฅ์ „์†ก์— ๋Œ€ํ•œ ํ›„์† ์—ฐ๊ตฌ๋ฅผ ์ง„ํ–‰ํ•˜์˜€๋‹ค. ๋Šฅ๋™ํ˜• ๋ฐฉ์‚ฌ ๋ฌด์„ ์ „๋ ฅ์ „์†ก์—์„œ๋Š”, ์†ก์‹  ํƒ€์›Œ๋ฅผ ํ™œ์šฉํ•˜์—ฌ ๋ชจ๋ฐ”์ผ ๊ธฐ๊ธฐ์— ํšจ๊ณผ์ ์œผ๋กœ ๋ฌด์„ ์ „๋ ฅ์ „์†ก์„ ์ˆ˜ํ–‰ํ•˜๋Š” ๋ฐฉ๋ฒ•์— ๋Œ€ํ•œ ์—ฐ๊ตฌ๋ฅผ ์ง„ํ–‰ํ•˜์˜€๋‹ค. ๋ณธ ์—ฐ๊ตฌ์—์„œ๋Š” ๋ฐฉ์‚ฌํ˜• ๋ฌด์„ ์ „๋ ฅ์ „์†ก์˜ ํšจ์œจ์„ ์ตœ๋Œ€ํ™” ํ•˜๋Š” ์†ก์‹  ์ „๋ฅ˜๋ถ„ํฌ์™€ ์ฃผ์–ด์ง„ ๋ฉด์ ์„ ํ™œ์šฉํ•  ๋•Œ ์–ป์„ ์ˆ˜ ์žˆ๋Š” ์ตœ๋Œ€ ํ•œ๊ณ„ ํšจ์œจ์„ ์ด๋ก ์ ์œผ๋กœ ๋„์ถœํ•˜์˜€๋‹ค. ๋ณธ ์—ฐ๊ตฌ์˜ ๊ฒฐ๊ณผ๋ฅผ ํ†ตํ•ด, ๊ธฐ์กด์˜ ๋ฐฉ์‹์œผ๋กœ๋Š” ํŒŒ์•…ํ•  ์ˆ˜ ์—†์—ˆ๋˜ ์ค‘๊ฑฐ๋ฆฌ ๋ฌด์„ ์ „๋ ฅ์ „์†ก ํšจ์œจ์˜ ์ตœ๋Œ€ ํ•œ๊ณ„์น˜์™€ ์†ก์‹  ์ „๋ฅ˜๋ถ„ํฌ์˜ ์ตœ์  ํ˜•ํƒœ๋ฅผ ํŒŒ์•…ํ•  ์ˆ˜ ์žˆ๋‹ค. ์—ฐ๊ตฌ์˜ ๊ฒฐ๋ก ์— ๋”ฐ๋ฅด๋ฉด, ์ˆ˜์‹ ํ•˜๋Š” ์•ˆํ…Œ๋‚˜์˜ ์†ก์‹  ๋ฐฉ์‚ฌ ํŒจํ„ด์ด ํšจ์œจ์„ ๊ฒฐ์ •ํ•จ์— ์žˆ์–ด ์ค‘์š”ํ•œ ์—ญํ• ์„ ํ•˜์˜€๋‹ค. ์ œ์•ˆํ•œ ์ด๋ก ์„ ์‹ค์ œ ์•ˆํ…Œ๋‚˜์— ์ ์šฉํ•˜์—ฌ ์„ ํ–‰์—ฐ๊ตฌ์™€ ๋น„๊ต๋ฅผ ํ•˜์˜€๊ณ , ์„ ํ–‰ ์—ฐ๊ตฌ๋กœ ํŒŒ์•…ํ•  ์ˆ˜ ์—†๋Š” ์ด๋ก ์  ํ•œ๊ณ„ ํšจ์œจ์„ ๋„์ถœํ•˜์˜€๋‹ค. ์ œ์•ˆํ•œ ์—ฐ๊ตฌ๋ฅผ ์ผ๋ฐ˜์ ์ธ ์ƒํ™ฉ์œผ๋กœ ํ™•์žฅํ•˜๊ธฐ ์œ„ํ•ด ์†์‹ค ๋งค์งˆ ๋‚ด๋ถ€์—์„œ์˜ ๋ฌด์„ ์ „๋ ฅ์ „์†ก์— ๋Œ€ํ•œ ์ถ”๊ฐ€ ์—ฐ๊ตฌ๋ฅผ ์ง„ํ–‰ํ•˜์˜€๋‹ค. ์†์‹ค ๋งค์งˆ์ด ์žˆ๋Š” ๊ฒฝ์šฐ์—์„œ๋„ ์ตœ์  ์ „๋ฅ˜ ๋ถ„ํฌ์™€ ํšจ์œจ์˜ ์ตœ๋Œ€ ํ•œ๊ณ„์น˜๋ฅผ ๋„์ถœํ•˜์˜€๋‹ค. ์ตœ์  ์†ก์‹  ์ „๋ฅ˜๋ฅผ ํ™œ์šฉํ•˜์—ฌ, ์‹ค์ œ ์•ˆํ…Œ๋‚˜ ์–ด๋ ˆ์ด๋ฅผ ๊ตฌํ˜„ํ•˜๊ณ  ์ธ์ฒด ํŒฌํ…€์— ๋ฏธ์น˜๋Š” ์˜ํ–ฅ์„ ํŒŒ์•…ํ•ด๋ณด์•˜๋‹ค. ๋งˆ์ง€๋ง‰์œผ๋กœ, ์•ž์„œ ๋„์ถœํ•œ ์ด๋ก ์ ์ธ ์ „๋ฅ˜๋ถ„ํฌ๋ฅผ ์‹ค์ œ ์•ˆํ…Œ๋‚˜๋กœ ๊ตฌํ˜„ํ•˜๋Š” ๋ฐฉ๋ฒ•์— ๋Œ€ํ•ด ์—ฐ๊ตฌ๋ฅผ ์ง„ํ–‰ํ•˜์˜€๋‹ค. ์„ ํ–‰ ์—ฐ๊ตฌ๋ฅผ ์ฐธ๊ณ ํ•˜์—ฌ, ์ด์ƒ์ ์ธ ์ „๋ฅ˜๋ถ„ํฌ๋ฅผ thinned ๋ฐฐ์—ด๋กœ ๊ตฌํ˜„ํ•˜๋Š” ๋‘๊ฐ€์ง€ ๋ฐฉ๋ฒ•์„ ์ œ์•ˆํ•˜์˜€๋‹ค. ์ด๋ก ์ ์ธ ์ „๋ฅ˜ ๋ถ„ํฌ์— ์œ ์ „ ์•Œ๊ณ ๋ฆฌ์ฆ˜์„ ํ™œ์šฉํ•œ ๋ฐฉ๋ฒ•๊ณผ, density tapering์„ ์‘์šฉํ•œ ๋ฐฉ๋ฒ•์„ ์ ์šฉํ•˜์˜€๋‹ค. ๋‘ ๋ฐฉ๋ฒ• ๋ชจ๋‘ ๋™์ผํ•œ ๊ฐœ์ˆ˜์˜ ๊ท ๋“ฑ ์–ด๋ ˆ์ด์— ๋น„ํ•ด ์„ฑ๋Šฅ์ด ๊ฐœ์„ ๋˜๋Š” ๊ฒฐ๊ณผ๋ฅผ ๋ณด์˜€๋‹ค. ํŠนํžˆ density tapering์„ ์ด์šฉํ•˜๋ฉด ๊ฐ™์€ ๊ฐœ์ˆ˜ ๋ฐ ๊ฐ™์€ ๋ฉด์ ์˜ ๊ฒฉ์ž๊ตฌ์กฐ๋ณด๋‹ค ๋น„์šฉ, ๋ฌด๊ฒŒ, ํšจ์œจ ๋“ฑ์—์„œ ์žฅ์ ์ด ์žˆ์œผ๋ฉฐ, ์ˆ˜์‹ ๊ธฐ์˜ ์œ„์น˜๊ฐ€ ๋ณ€ํ•  ๋•Œ์—๋„ ๋” ๋†’์€ ํšจ์œจ๋กœ ์†ก์‹ ์ด ๊ฐ€๋Šฅํ•˜๋‹ค.In this thesis, research on the radiative-wireless power transmission (R-WPT) using radiated electromagnetic(EM) fields is presented. More specifically, the analysis and design of quasi-isotropic antennas, the analytical study on the optimal transmitting current, and the efficiency bounds are described. In addition, research on the comparison of the EM effects on the human phantom, and the effective implementation of the optimal current distribution are conducted. The research is described sequentially from the passive R-WPT to active R-WPT, which indicate the absence or presence of the power supplying base station. First, research is conducted on the analysis and design of the passive R-WPT antenna. Considering the ambient environment, an antenna with quasi-isotropic pattern, electrically small size, and high efficiency is proposed. A split-ring resonator (SRR) that radiate quasi-isotropic pattern with electrically small size is used as a basic structure. The analysis on the SRR is well matched with the simulation results. Based on the analysis, folded split-ring resonator (FSRR) is proposed and designed for the passive R-WPT antennas, and verified through the measurement. A dualband and wideband FSRR that can harvest more ambient power is designed as an extended work. The proposed antennas are compared with recent studies showing superior performances. On the other hand, the receiving power of the passive R-WPT is very low due to low power density of ambient field, a study on the active R-WPT, which can transfer wireless powers from the base station to the mobile antenna, is conducted as a next step. In the active R-WPT, a study on the way to effectively transfer wireless power to the mobile devices by using a transmitting tower is described. The optimal current distribution of the transmitting surface, and maximum power transfer efficiency (PTE) bounds when the transmitting area is limited are analytically derived. Through the results, it is possible to figure out the maximum efficiency bounds for the mid-range R-WPT and the optimal shape of transmission current distribution that could not be found by the conventional method. The results indicate that the optimum current distribution on the transmitting surface and the maximum efficiency of radiative WPT depend on the radiating field pattern of the mobile antenna. To generalize the proposed theory, an additional analysis in lossy environment is carried out. The optimal transmitting current and efficiency bound in lossy media is found for a couple of examples. The results are compared with the previous works to verify the proposed theory. Based on the results in lossy media, the EM effects on the human body is investigated. Lastly, research on the effective implementation of the theoretical current distribution as practical antenna arrays is described. Based on the previous research, two techniques that can effectively realize the ideal current are proposed in designing a thinned array. An optimization using genetic algorithm, and deterministic density tapering are applied to sample the theoretical current distribution. As a results, the proposed thinned arrays show improved performance compared to the same number of densely arranged regular arrays. In particular, the use of density tapering has advantages in cost, weight, efficiency than the same number of the regular array. In addition, it is possible to transmit wireless power with better efficiency even when the position of the receiver changes.Chapter 1. Introduction 1 1.1. Classification of Wireless Power Transmission 1 1.2. Separation of Regions 3 1.3. Passive and Active Radiative-Wireless Power Transmission 6 1.4. References 14 Chapter 2. Passive: RF Energy Harvesting Antenna 18 2.1. Motivation 18 2.2. Analytical Study on RF Energy Harvesting Antenna 19 2.2.1. Previous Research 19 2.2.2. Analysis on Split-Ring Resonator 21 2.2.3. Analysis on the Symmetric Folded Split-Ring Resonator 25 2.2.4. Analysis on the Asymmetric Folded Split-Ring Resonator 30 2.3. Design of RF Energy Harvesting Antenna 34 2.3.1. Antenna Design 37 2.3.2 Results and Discussion 44 2.4. Design of RF Energy Harvesting Antenna with Dual-band Operation 45 2.4.1. Motivation 45 2.4.2 Antenna Design 45 2.4.3. Results and Discussion 48 2.5. RF Energy Harvesting Antenna with Wide-band Operation 53 2.5.1. Motivation 53 2.5.2 Antenna Design 54 2.5.3. Results and Discussion 57 2.6. Conclusion 65 2.7. References 69 Chapter 3. Active: Radiative-WPT in Lossless Medium 73 3.1. Motivation 73 3.2. Previous Research 73 3.3. Theoretical Approach 77 3.3.1. Power Transfer Efficiency 77 3.3.2. Optimum Transmitting Current 80 3.3.3. Minimizing Transmitting Area 84 3.4. Numerical Examples 86 3.3.1. Dipole Antenna 88 3.3.2. Patch Antenna 90 3.3.3. Horn Antenna 91 3.5. Results and Discussion 93 3.5. Conclusion 98 3.6. References 99 Chapter 4. Active: Radiative-WPT in Lossy Media 103 4.1. Motivation 103 4.2. Previous Research 103 4.3. Theoretical Approach 106 4.3.1. Problem Formulation 108 4.3.2. Maximum Power Transfer Efficiency 110 4.4. Practical Examples 114 4.4.1. Planar Inverted-F Antenna 116 4.4.2. Half-Mode Cavity-Backed Antenna 120 4.5. Electromagnetic Human Exposure in Radiative WPT System 125 4.5.1. Motivation 125 4.5.2. Simulation Results 126 4.6. Conclusion 132 4.7. References 134 Chapter 5. Active: Implementation of Optimal Transmitting Current Distribution 138 5.1. Motivation 138 5.2. Theoretical Approach 139 5.2.1. Radiation Pattern Matching 139 5.2.2. Optimal Excitation Coefficient 141 5.2.3. Thinning of Transmitting Array 141 5.3. Implementation of the Optimal Current Sheet 145 5.3.1. Array Thinning using Genetic Algorithm 145 5.3.2. Results and Discussions 148 5.3.3. Array Thinning using Density Tapering 151 5.3.4. Results and Discussions 154 5.4. Conclusion 158 5.5. References 159Docto

    Design Tools for Small Implantable antennas

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    Implantable applications have been increasing in number in an exponential manner since the turn of the millennium. This is largely due to the increasing availability of ultra low power consumption electronics, enabling the emergence of healthcare services using implantable or swallowable sensors. Other fields of applications exist, e.g. in the domains of military, security or sports. A large number of antennas for these implantable or swallowable capsules have been designed, and can be found in the literature. They are however always presented for a specific capsule and application, and are thus very difficult to compare in terms of antenna characteristics. In this paper, we show results obtained for simple canonical implantable radiation sources, obtained using a specifically developed numerical tool presented earlier. These canonical results will allow us to obtain some simple but useful figures of merit that enable an easy assessment of the quality of the radiation characteristic of a specific antenna design in a specific capsul

    Fundamental Limits for Implanted Antennas: Maximum Power Density Reaching Free Space

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    Medical implants with communication capability are becoming increasingly popular with todayโ€™s trends to continuously monitor patientโ€™s condition. This is a major challenge for antenna designers since the implants are inherently small and placed in a communication-wise very lossy environment. Our goal is to determine the fundamental limitations of such antennas when placed inside human bodies and to develop guidelines for most efficient design. We base our findings on in-house analysis tools based on spherical and cylindrical wave expansion applied to simplified spherical and cylindrical body models respectively. These give us insight into wave propagation and show the maximum power density levels that can be reached just outside the body. Based on the obtained limits we can propose a useful upper bound for more complex scenarios

    Wireless powering efficiency assessment for deep-body implantable devices

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    Several frequency-dependent mechanisms restrict the maximum achievable efficiency for wireless powering implantable bioelectric devices. Similarly, many mathematical formulations have been proposed to evaluate the effect of these mechanisms as well as predict this maximum efficiency and the corresponding optimum frequency. However, most of these methods consider a simplified model, and they cannot tackle some realistic aspects of implantable wireless power transfer. Therefore, this paper proposed a novel approach that can analyze the efficiency in anatomical models and provide insightful information on achieving this optimum operation. First, this approach is validated with a theoretical spherical wave expansion analysis, and the results for a simplified spherical model and a bidimensional human pectoral model are compared. Results have shown that even though a magnetic receiver outperforms an electric one for near-field operation and both sources could be equally employed in far-field range, it is in mid-field that the maximum efficiency is achieved, with an optimum frequency between 1-5 GHz, depending on the implantation depth. In addition, the receiver orientation is another factor that affects the efficiency, with a maximum difference between the best and worst-case scenarios around five times for an electric source and over 13 times for the magnetic one. Finally, this approach is used to analyze the case of a wirelessly powered deep-implanted pacemaker by an on-body transmitter and to establish the parameters that lead to the maximum achievable efficiency

    Doctor of Philosophy

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    dissertationThe invention of antennas has revolutionized the world by enabling fast communications over long distances. Since their invention in the 1800s, antennas have been extensively studied at RF and microwave frequencies. The high conductivity of metals coupled with operation in a relatively loss-free environment has fueled the rapid development of antennas designed to operate at particular frequency ranges. Evolution of science and technology has now led to the study of lossy antennas. The ability to create nanometer scale structures has allowed for the creation of antennas for operation at very high (optical) frequencies. At these frequencies, metals are no longer excellent conductors, and their lossiness must be considered in order to effectively design and create resonant antennas. In the RF, the fast development of applications for antennas has led to an artificial allocation of frequency bands to prevent interference. In the nanoworld, electromagnetic spectrum allocation is more natural and is dictated by the particular application. In both cases, the ability to apply antennas relies upon control of their resonances. Lossy materials contribute an additional variable to the creation and control of resonant structures. The purpose of this research is to study the effect of material losses in RF and optical antennas. The investigation is done via the study of implantable spiral antennas at RF frequencies and crescent nanoantennas at optical wavelengths

    The admittance of the infinite cylindrical antenna in a lossy, isotropic, compressible plasma

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    Numerical values for admittance of infinite cylindrical antenna in lossy, isotropic, compressible plasm
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