Electrokinetic and magnetic fields generated by flow through a fractured zone a sensitivity
磁共振(磁谐振耦合)无线充电技术鼻祖级文章-英文原文
Wireless Power Transfer via Strongly Coupled Magnetic ResonancesAndré Kurs,1* Aristeidis Karalis,2 Robert Moffatt,1 J. D. Joannopoulos,1 Peter Fisher,3Marin Soljačić11Department of Physics, Massachusetts Institute of Technology, Cambridge, MA 02139, USA. 2Department of Electrical Engineering and Computer Science, Massachusetts Institute of Technology, Cambridge, MA 02139, USA. 3Department of Physics and Laboratory for Nuclear Science, Massachusetts Institute of Technology, Cambridge, MA 02139, USA.*To whom correspondence should be addressed. E-mail: akurs@Using self-resonant coils in a strongly coupled regime, we experimentally demonstrate efficient non-radiative power transfer over distances of up to eight times the radius of the coils. We demonstrate the ability to transfer 60W with approximately 40% efficiency over distances in excess of two meters. We present a quantitative model describing the power transfer which matches the experimental results to within 5%. We discuss practical applicability and suggest directions for further studies. At first glance, such power transfer is reminiscent of the usual magnetic induction (10); however, note that the usual non- resonant induction is very inefficient for mid-range applications.Overview of the formalism. Efficient mid-range power transfer occurs in particular regions of the parameter space describing resonant objects strongly coupled to one another. Using coupled-mode theory to describe this physical system (11), we obtain the following set of linear equationsIn the early 20th century, before the electrical-wire grid, Nikola Tesla (1) devoted much effort towards schemes to a&m(t)=(iωm-Γm)a m(t)+∑iκmn a n(t)+F m(t)n≠m(1)transport power wirelessly. However, typical embodiments (e.g. Tesla coils) involved undesirably large electric fields. During the past decade, society has witnessed a dramatic surge of use of autonomous electronic devices (laptops, cell- phones, robots, PDAs, etc.) As a consequence, interest in wireless power has re-emerged (2–4). Radiative transfer (5), while perfectly suitable for transferring information, poses a number of difficulties for power transfer applications: the efficiency of power transfer is very low if the radiation is omnidirectional, and requires an uninterrupted line of sight and sophisticated tracking mechanisms if radiation is unidirectional. A recent theoretical paper (6) presented a detailed analysis of the feasibility of using resonant objects coupled through the tails of their non-radiative fields for mid- range energy transfer (7). Intuitively, two resonant objects of the same resonant frequency tend to exchange energy efficiently, while interacting weakly with extraneous off- resonant objects. In systems of coupled resonances (e.g. acoustic, electro-magnetic, magnetic, nuclear, etc.), there is often a general “strongly coupled” regime of operation (8). If one can operate in that regime in a given system, the energy transfer is expected to be very efficient. Mid-range power transfer implemented this way can be nearly omnidirectional and efficient, irrespective of the geometry of the surrounding space, and with low interference and losses into environmental objects (6).Considerations above apply irrespective of the physical nature of the resonances. In the current work, we focus on one particular physical embodiment: magnetic resonances (9). Magnetic resonances are particularly suitable for everyday applications because most of the common materials do not interact with magnetic fields, so interactions with environmental objects are suppressed even further. We were able to identify the strongly coupled regime in the system of two coupled magnetic resonances, by exploring non-radiative (near-field) magnetic resonant induction at MHzfrequencies. where the indices denote the different resonant objects. The variables a m(t) are defined so that the energy contained in object m is |a m(t)|2, ωm is the resonant frequency of thatisolated object, and Γm is its intrinsic decay rate (e.g. due to absorption and radiated losses), so that in this framework anuncoupled and undriven oscillator with parameters ω0 and Γ0 would evolve in time as exp(iω0t –Γ0t). The κmn= κnm are coupling coefficients between the resonant objects indicated by the subscripts, and F m(t) are driving terms.We limit the treatment to the case of two objects, denoted by source and device, such that the source (identified by the subscript S) is driven externally at a constant frequency, and the two objects have a coupling coefficient κ. Work is extracted from the device (subscript D) by means of a load (subscript W) which acts as a circuit resistance connected to the device, and has the effect of contributing an additional term ΓW to the unloaded device object's decay rate ΓD. The overall decay rate at the device is therefore Γ'D= ΓD+ ΓW. The work extracted is determined by the power dissipated in the load, i.e. 2ΓW|a D(t)|2. Maximizing the efficiency η of the transfer with respect to the loading ΓW, given Eq. 1, is equivalent to solving an impedance matching problem. One finds that the scheme works best when the source and the device are resonant, in which case the efficiency isThe efficiency is maximized when ΓW/ΓD= (1 + κ2/ΓSΓD)1/2. It is easy to show that the key to efficient energy transfer is to have κ2/ΓSΓD> 1. This is commonly referred to as the strongcoupling regime. Resonance plays an essential role in thisDS S D'' power transfer mechanism, as the efficiency is improved by approximately ω2/ΓD 2 (~106 for typical parameters) compared to the case of inductively coupled non-resonant objects. Theoretical model for self-resonant coils. Ourexperimental realization of the scheme consists of two self- resonant coils, one of which (the source coil) is coupled inductively to an oscillating circuit, while the other (the device coil) is coupled inductively to a resistive load (12) (Fig. 1). Self-resonant coils rely on the interplay between distributed inductance and distributed capacitance to achieve resonance. The coils are made of an electrically conducting wire of total length l and cross-sectional radius a wound into Given this relation and the equation of continuity, one finds that the resonant frequency is f 0 = 1/2π[(LC )1/2]. We can now treat this coil as a standard oscillator in coupled-mode theory by defining a (t ) = [(L /2)1/2]I 0(t ).We can estimate the power dissipated by noting that the sinusoidal profile of the current distribution implies that the spatial average of the peak current-squared is |I 0|2/2. For a coil with n turns and made of a material with conductivity σ, we modify the standard formulas for ohmic (R o ) and radiation (R r ) µ0ω l a helix of n turns, radius r , and height h . To the best of our knowledge, there is no exact solution for a finite helix in the literature, and even in the case of infinitely long coils, the solutions rely on assumptions that are inadequate for our R o = 2σ 4πa µ πωr 42 ωh 2 (6)system (13). We have found, however, that the simple quasi- R =0 n 2 + (7)static model described below is in good agreementr ε 12 c3π3 c(approximately 5%) with experiment.We start by observing that the current has to be zero at the ends of the coil, and make the educated guess that the resonant modes of the coil are well approximated bysinusoidal current profiles along the length of the conducting wire. We are interested in the lowest mode, so if we denote by s the parameterization coordinate along the length of the conductor, such that it runs from -l /2 to +l /2, then the time- dependent current profile has the form I 0 cos(πs /l ) exp(i ωt ). It follows from the continuity equation for charge that the linear charge density profile is of the form λ0 sin(πs /l ) exp(i ωt ), so the two halves of the coil (when sliced perpendicularly to its axis) contain charges equal in magnitude q 0 = λ0l /π but opposite in sign.As the coil is resonant, the current and charge density profiles are π/2 out of phase from each other, meaning that the real part of one is maximum when the real part of the other is zero. Equivalently, the energy contained in the coil is 0The first term in Eq. 7 is a magnetic dipole radiation term(assuming r << 2πc /ω); the second term is due to the electric dipole of the coil, and is smaller than the first term for our experimental parameters. The coupled-mode theory decay constant for the coil is therefore Γ = (R o + R r )/2L , and its quality factor is Q = ω/2Γ.We find the coupling coefficient κDS by looking at the power transferred from the source to the device coil,assuming a steady-state solution in which currents and charge densities vary in time as exp(i ωt ).P =⎰d rE (r )⋅J (r ) =-⎰d r (A&S (r )+∇φS (r ))⋅J D (r ) at certain points in time completely due to the current, and at other points, completely due to the charge. Usingelectromagnetic theory, we can define an effective inductance L and an effective capacitance C for each coil as follows:=-1⎰⎰d r d r ' µJ &S(r ')+ρS(r ') 4π |r -r |ε0≡-i ωMI S I Dr '-r|r '-r |3⋅J D (r )(8)L =µ04π |I 0 |⎰⎰d r d r 'J (r )⋅J (r ')|r -r '|where the subscript S indicates that the electric field is due to the source. We then conclude from standard coupled-mode theory arguments that κDS = κSD = κ = ωM /2[(L S L D )1/2]. When 1 1 ρ(r )ρ(r ') the distance D between the centers of the coils is much larger= C 4πε 0 |q 0 | ⎰⎰d r d r ' |r -r '|(4)than their characteristic size, κ scales with the D -3dependence characteristic of dipole-dipole coupling. Both κ and Γ are functions of the frequency, and κ/Γ and the where the spatial current J (r ) and charge density ρ(r ) are obtained respectively from the current and charge densities along the isolated coil, in conjunction with the geometry of the object. As defined, L and C have the property that the efficiency are maximized for a particular value of f , which is in the range 1-50MHz for typical parameters of interest. Thus, picking an appropriate frequency for a given coil size, as we do in this experimental demonstration, plays a major role in optimizing the power transfer.1 2Comparison with experimentallydeterminedU =2 L |I 0 |parameters. The parameters for the two identical helical coils built for the experimental validation of the power 1 2 transfer scheme are h = 20cm, a = 3mm, r = 30 cm, and n = =2C|q 0 | (5)5.25. Both coils are made of copper. The spacing between loops of the helix is not uniform, and we encapsulate theuncertainty about their uniformity by attributing a 10% (2cm) uncertainty to h . The expected resonant frequency given these22dimensions is f0 = 10.56 ± 0.3MHz, which is about 5% off from the measured resonance at 9.90MHz.The theoretical Q for the loops is estimated to be approximately 2500 (assuming σ = 5.9 × 107 m/Ω) but the measured value is Q = 950±50. We believe the discrepancy is mostly due to the effect of the layer of poorly conductingcopper oxide on the surface of the copper wire, to which the current is confined by the short skin depth (~20μm) at this frequency. We therefore use the experimentally observed Q and ΓS= ΓD= Γ = ω/2Q derived from it in all subsequent computations.We find the coupling coefficient κ experimentally by placing the two self-resonant coils (fine-tuned, by slightly adjusting h, to the same resonant frequency when isolated) a distance D apart and measuring the splitting in the frequencies of the two resonant modes. According to coupled-mode theory, this splitting should be ∆ω = 2[(κ2-Γ2)1/2]. In the present work, we focus on the case where the two coils are aligned coaxially (Fig. 2), although similar results are obtained for other orientations (figs. S1 and S2).Measurement of the efficiency. The maximum theoretical efficiency depends only on the parameter κ/[(L S L D)1/2] = κ/Γ, which is greater than 1 even for D = 2.4m (eight times the radius of the coils) (Fig. 3), thus we operate in the strongly- coupled regime throughout the entire range of distances probed.As our driving circuit, we use a standard Colpitts oscillator whose inductive element consists of a single loop of copper wire 25cm in radius(Fig. 1); this loop of wire couples inductively to the source coil and drives the entire wireless power transfer apparatus. The load consists of a calibrated light-bulb (14), and is attached to its own loop of insulated wire, which is placed in proximity of the device coil and inductively coupled to it. By varying the distance between the light-bulb and the device coil, we are able to adjust the parameter ΓW/Γ so that it matches its optimal value, given theoretically by (1 + κ2/Γ2)1/2. (The loop connected to the light-bulb adds a small reactive component to ΓW which is compensated for by slightly retuning the coil.) We measure the work extracted by adjusting the power going into the Colpitts oscillator until the light-bulb at the load glows at its full nominal brightness.We determine the efficiency of the transfer taking place between the source coil and the load by measuring the current at the mid-point of each of the self-resonant coils with a current-probe (which does not lower the Q of the coils noticeably.) This gives a measurement of the current parameters I S and I D used in our theoretical model. We then compute the power dissipated in each coil from P S,D=ΓL|I S,D|2, and obtain the efficiency from η = P W/(P S+ P D+P W). To ensure that the experimental setup is well described by a two-object coupled-mode theory model, we position the device coil such that its direct coupling to the copper loop attached to the Colpitts oscillator is zero. The experimental results are shown in Fig. 4, along with the theoretical prediction for maximum efficiency, given by Eq. 2. We are able to transfer significant amounts of power using this setup, fully lighting up a 60W light-bulb from distances more than 2m away (figs. S3 and S4).As a cross-check, we also measure the total power going from the wall power outlet into the driving circuit. The efficiency of the wireless transfer itself is hard to estimate in this way, however, as the efficiency of the Colpitts oscillator itself is not precisely known, although it is expected to be far from 100% (15). Still, the ratio of power extracted to power entering the driving circuit gives a lower bound on the efficiency. When transferring 60W to the load over a distance of 2m, for example, the power flowing into the driving circuit is 400W. This yields an overall wall-to-load efficiency of 15%, which is reasonable given the expected efficiency of roughly 40% for the wireless power transfer at that distance and the low efficiency of the Colpitts oscillator.Concluding remarks. It is essential that the coils be on resonance for the power transfer to be practical (6). We find experimentally that the power transmitted to the load drops sharply as either one of the coils is detuned from resonance. For a fractional detuning ∆f/f0 of a few times the inverse loaded Q, the induced current in the device coil is indistinguishable from noise.A detailed and quantitative analysis of the effect of external objects on our scheme is beyond the scope of the current work, but we would like to note here that the power transfer is not visibly affected as humans and various everyday objects, such as metals, wood, and electronic devices large and small, are placed between the two coils, even in cases where they completely obstruct the line of sight between source and device (figs. S3 to S5). External objects have a noticeable effect only when they are within a few centimeters from either one of the coils. While some materials (such as aluminum foil, styrofoam and humans) mostly just shift the resonant frequency, which can in principle be easily corrected with a feedback circuit, others (cardboard, wood, and PVC) lower Q when placed closer than a few centimeters from the coil, thereby lowering the efficiency of the transfer.When transferring 60W across 2m, we calculate that at the point halfway between the coils the RMS magnitude of the electric field is E rms= 210V/m, that of the magnetic field isH rms= 1A/m, and that of the Poynting vector is S rms=3.2mW/cm2 (16). These values increase closer to the coils, where the fields at source and device are comparable. For example, at distances 20cm away from the surface of the device coil, we calculate the maximum values for the fields to be E rms= 1.4kV/m, H rms= 8A/m, and S rms= 0.2W/cm2. The power radiated for these parameters is approximately 5W, which is roughly an order of magnitude higher than cell phones. In the particular geometry studied in this article, the overwhelming contribution (by one to two orders of magnitude) to the electric near-field, and hence to the near- field Poynting vector, comes from the electric dipole moment of the coils. If instead one uses capacitively-loaded single- turn loop design (6) - which has the advantage of confining nearly all of the electric field inside the capacitor - and tailors the system to operate at lower frequencies, our calculations show (17) that it should be possible to reduce the values cited above for the electric field, the Poynting vector, and the power radiated to below general safety regulations (e.g. the IEEE safety standards for general public exposure(18).) Although the two coils are currently of identical dimensions, it is possible to make the device coil small enough to fit into portable devices without decreasing the efficiency. One could, for instance, maintain the product of the characteristic sizes of the source and device coils constant, as argued in (6).We believe that the efficiency of the scheme and the power transfer distances could be appreciably improved by silver-plating the coils, which should increase their Q, or by working with more elaborate geometries for the resonant objects (19). Nevertheless, the performance characteristics of the system presented here are already at levels where they could be useful in practical applications.References and Notes1. N. Tesla, U.S. patent 1,119,732 (1914).2.J. M. Fernandez, J. A. Borras, U.S. patent 6,184,651(2001).3.A. Esser, H.-C. Skudelny, IEEE Trans. Indust. Appl. 27,872(1991).4.J. Hirai, T.-W. Kim, A. Kawamura, IEEE Trans. PowerElectron. 15, 21(2000).5.T. A. Vanderelli, J. G. Shearer, J. R. Shearer, U.S. patent7,027,311(2006).6.A. Karalis, J. D. Joannopoul os, M. Soljačić, Ann. Phys.,10.1016/j.aop.2007.04.017(2007).7.Here, by mid-range, we mean that the sizes of the deviceswhich participate in the power transfer are at least a few times smaller than the distance between the devices. For example, if the device being powered is a laptop (size ~ 50cm), while the power source (size ~ 50cm) is in thesame room as the laptop, the distance of power transfer could be within a room or a factory pavilion (size of the order of a fewmeters).8. T. Aoki, et al., Nature 443, 671 (2006).9.K. O’Brien, G. Scheible, H. Gueldner, 29th AnnualConference of the IEEE 1, 367(2003).10.L. Ka-Lai, J. W. Hay, P. G. W., U.S. patent7,042,196(2006).11.H. Haus, Waves and Fields in Optoelectronics(Prentice- Supporting Online Material/cgi/content/full/1143254/DC1SOM TextFigs. S1 to S530 March 2007; accepted 21 May 2007Published online 7 June 2007; 10.1126/science.1143254 Include this information when citing this paper.Fig. 1. Schematic of the experimental setup. A is a single copper loop of radius 25cm that is part of the driving circuit, which outputs a sine wave with frequency 9.9MHz. S and D are respectively the source and device coils referred to in the text. B is a loop of wire attached to the load (“light-bulb”). The various κ’s represent direct couplings between the objects indicated by the arrows. The angle between coil D and the loop A is adjusted to ensure that their direct coupling is zero, while coils S and D are aligned coaxially. The direct couplings between B and A and between B and S are negligible.Fig. 2. Comparison of experimental and theoretical values for κ as a function of the separation between coaxially aligned source and device coils (the wireless power transfer distance.) Fig. 3. Comparison of experimental and theoretical values for the parameter κ/Γ as a function of the wireless power transfer distance. The theory values are obtained by using the theoretical κ and the experimentally measured Γ. The shaded area represents the spread in the theoretical κ/Γ due to the 5% uncertainty in Q.Fig. 4. Comparison of experimental and theoretical efficiencies as functions of the wireless power transfer distance. The shaded area represents the theoretical prediction for maximum efficiency, and is obtained by inserting theHall, Englewood Cliffs, NJ, 1984).12.The couplings to the driving circuit and the load donot theoretical values from Fig. 3 into Eq. 2 [with Γκ2/Γ2 1/2 W /ΓD= (1 +have to be inductive. They may also be connected by awire, for example. We have chosen inductive coupling in the present work because of its easier implementation. 13.S. Sensiper, thesis, Massachusetts Institute of Technology(1951).14.We experimented with various power ratings from 5W to75W.15.W. A. Edson, Vacuum-Tube Oscillators (Wiley, NewYork,1953).16.Note that E ≠cμ0H, and that the fields are out of phaseand not necessarily perpendicular because we are not in a radiativeregime.17.See supporting material on Science Online.18.IEEE Std C95.1—2005 IEEE Standard for Safety Levelswith Respect to Human Exposure to Radio FrequencyElectromagnetic Fields, 3 kHz to 300 GHz (IEEE,Piscataway, NJ,2006).19. J. B. Pendry, Science 306, 1353 (2004).20. The authors would like to thank John Pendry forsuggesting the use of magnetic resonances, and Michael Grossman and Ivan Čelanović for technical assistance.This work was supported in part by the Materials Research Science and Engineering Center program of the National Science Foundation under Grant No. DMR 02-13282, by the U.S. Department of Energy under Grant No. DE-FG02-99ER45778, and by the Army Research Officethrough the Institute for Soldier Nanotechnologies under Contract No. DAAD-19-02-D0002.) ]. The black dots are the maximum efficiency obtained from Eq. 2 and the experimental values of κ/Γ from Fig. 3. The red dots present the directly measured efficiency,as described in thetext.。
Lecture 1 磁性物理和磁学基本概念
Topics for your report:
Recent progress in advanced -
1. Nanocomposite Rare-earth permanent magnetic materials;
2. Nanocomposite soft magnetic materials; 3. perpendicular magnetic recording; 4. Magnetoelectric materials; 5. Magnetic thin films for microwave absorber; 6. GMR materials; 7. One-dimension magnetic nanostructures;
Pliny the Elder (23-79 AD Roman) wrote of a hill near the river Indus that was made entirely of a stone that attracted iron.
Known in China and Europe 800 BC
When lightning strikes the earth it could create a magnetic field large enough to saturate the magnetization of lodestone .
Once ቤተ መጻሕፍቲ ባይዱn 1 – 10 million years
磁性材料：原理、工艺与应用
Magnetic Materials: Basic theory, Processing and Applications
Lecture 1 磁学基本概念与磁性物理基础
TEM,TE AND TM MODES FOR WAVEGUIDES,RECTANGULAR WAVEGUIDE
Whites, EE 481 Lecture 10 Page 1 of 10© 2011 Keith W. WhitesLecture 10: TEM, TE, and TM Modes for Waveguides. Rectangular Waveguide.We will now generalize our discussion of transmission lines by considering EM waveguides . These are “pipes” that guide EM waves. Coaxial cables, hollow metal pipes, and fiber optical cables are all examples of waveguides.We will assume that the waveguide is invariant in the z -direction:z and that the wave is propagating in z as j z e β−. (We could alsohave assumed propagation in –z .)Types of EM WavesWe will first develop an extremely interesting property of EM waves that propagate in homogeneous waveguides. This will lead to the concept of “modes ” and their classification as• Transverse Electric and Magnetic (TEM),•Transverse Electric (TE), or • Transverse Magnetic (TM).Proceeding from the Maxwell curl equations: ˆˆˆx y zx y zE j H j H xy z E E E ωμωμ∂∂∂∇×=−⇒=−∂∂∂ or ˆx : y z x E E j H y zωμ∂∂−=−∂∂ ˆy : x z y E E j H xz ωμ∂∂⎛⎞−−=−⎜⎟∂∂⎝⎠ ˆz : y x z E E j H x yωμ∂∂−=−∂∂However, the spatial variation in z is known so that()()j z j z e j e zβββ−−∂=−∂ Consequently, these curl equations simplify to z y x E j E j H yβωμ∂+=−∂ (3.3a),(1) z x y E j E j H xβωμ∂−−=−∂ (3.3b),(2) y x z E E j H x yωμ∂∂−=−∂∂ (3.3c),(3)We can perform a similar expansion of Ampère’s equation H j E ωε∇×= to obtain z y x H j H j E yβωε∂+=∂ (3.4a),(4) z x y H j H j E xβωε∂−−=∂ (3.4b),(5) y x z H H j E x yωε∂∂−=∂∂ (3.5c),(6)Now, (1)-(6) can be manipulated to produce simple algebraic equations for the transverse (x and y ) components of E and H . For example, from (1): z x y j E H j E y βωμ⎛⎞∂=+⎜⎟∂⎝⎠Substituting for E y from (5) we find 2221z z x x z z x j E H H j j H y j x j E j H H y xββωμωεββωμωμεωμε⎡⎤∂∂⎛⎞=+−−⎜⎟⎢⎥∂∂⎝⎠⎣⎦∂∂=+−∂∂ or,where 222c k k β≡− and 22k ωμε=. (3.6)Similarly, we can show thatMost important point: From (7)-(10), we can see that all transverse components of E and H can be determined from only the axial components z E and z H . It is this fact that allows the mode designations TEM, TE, and TM.Furthermore, we can use superposition to reduce the complexity of the solution by considering each of these mode types separately, then adding the fields together at the end.TE Modes and Rectangular WaveguidesA transverse electric (TE) wave has 0z E = and 0z H ≠. Consequently, all E components are transverse to the direction of propagation. Hence, in (7)-(10) with 0z E =, then all transverse components of E and H are known once we find a solution for only z H . Neat!For a rectangular waveguide , the solutions for x E , y E , x H , y H , and z H are obtained in Section 3.3 of the text. The solution and the solution process are interesting, but not needed in this course.Therefore,These m and n indices indicate that only discrete solutions for the transverse wavenumber (k c ) are allowed. Physically, this occurs because we’ve bounded the system in the x and y directions. (A vaguely similar situation occurs in atoms, leading to shell orbitals.)Notice something important. From (11), we find that 0m n == means that ,000c k =. In (7)-(10), this implies infinite field amplitudes, which is not a physical result. Consequently, the 0m n == TE or TM modes are not allowed.One exception might occur if 0z z E H == since this leads to indeterminate forms in (7)-(10). However, it can be shown that inside hollow metallic waveguides when both 0m n == and0z z E H ==, then 0E H ==. This means there is no TEM mode.Consequently, EM waves will propagate only when the frequency is “large enough ” since there is no TEM mode. Otherwise β will be imaginary (j βα→−), leading to pure attenuation and no propagation of the wave j z z e e βα−−→.This turns out to be a general result. That is, for a hollow conductor, EM waves will propagate only when the frequency is large enough and exceeds some lower threshold. This minimum propagation frequency is called the cutoff frequency ,c mn f.It can be shown that guided EM waves require at least two distinct conductors in order to support wave propagation all the way down to 0+ Hz.The cutoff frequencies for TE modes in a rectangular waveguide are determined from (12) with 0β= to be,,0,1,(0)c mn m n f m n ===≠… (3.84),(13) In other words, these are the frequencies where 0mn β= and wave propagation begins when the frequency slightly exceeds ,c mn f .For an X-band rectangular waveguide, the cross-sectional dimensions are a = 2.286 cm and b = 1.016 cm. Using (13):TE m,n Mode Cutoff Frequenciesm n f c,mn(GHz)1 0 6.5622 0 13.1230 1 14.7641 1 16.156In the X-band region (≈ 8.2-12.5 GHz), only the TE10 mode can propagate in the waveguide regardless of how it is excited. (We’ll also see shortly that no TM modes will propagate either.) This is called single mode operation and is most often the preferred application for hollow waveguides.On the other hand, at 15.5 GHz any combination of the first three of these modes could exist and propagate inside a metal, rectangular waveguide. Which combination actually exists will depend on how the waveguide is excited.Note that the TE11 mode (and all higher-ordered TE modes) could not propagate. (We’ll also see next that no TM modes will propagate at 15.5 GHz either.)TM Modes and Rectangular WaveguidesConversely to TE modes, transverse magnetic (TM) modes have 0z H = and 0z E ≠.The expression for the cutoff frequencies of TM modes in a rectangular waveguide,,1,2c mn f m n ==… (14) is very similar to that for TE modes given in (13).It can be shown that if either 0m = or 0n = for TM modes, then 0E H ==. This means that no TM modes with 0m = or 0n = are allowable in a rectangular waveguide.For an X-band waveguide:TM m ,n Mode Cutoff Frequencies m n f c ,mn (GHz)1 1 16.1561 2 30.2482 1 19.753Therefore, no TM modes can propagate in an X-band rectangular waveguide when f < 16.156 GHz.Dominant ModeNote that from 6.56 GHz f ≤≤ 13.12 GHz in the X-band rectangular waveguide, only the TE 10 mode can propagate. This mode is called the dominant mode of the waveguide.See Fig 3.9 in the text for plots of the electric and magnetic fields associated with this mode.TEM ModeThe transverse electric and magnetic (TEM) modes are characterized by 0z E = and 0z H =.In order for this to occur, it can be shown from (3.4) and (3.5) that it is necessary for 0c f =. In other words, there is no cutoff frequency for waveguides that support TEM waves.Rectangular, circular, elliptical, and all hollow, metallic waveguides cannot support TEM waves.It can be shown that at least two separate conductors are required for TEM waves. Examples of waveguides that willallow TEM modes include coaxial cable, parallel plate waveguide, stripline, and microstrip.Microstrip is the type of microwave circuit interconnection that we will use in this course. This “waveguide” will support the “quasi-TEM” mode, which like regular TEM modes has no non-zero cutoff frequency.However, if the frequency is large enough, other modes will begin to propagate on a microstrip. This is usually not a desirable situation.。
文献翻译(二次电流层)
激光等离子体相互作用中磁重联引起的等离子体与二次电流层生成的研究摘要:以尼尔逊[物理学家、列托人，97，255001，（2006）]为代表的科学家首次对等离子体相互作用引起的磁重联进行了研究，该研究在固体等离子体层上进行，在两个激光脉冲中间设置一定间隔，在两个激光斑点之间可以发现一条细长的电流层（CS），为了更加贴切的模拟磁重联过程，我们应该设置两个并列的目标薄层。
实验过程中发现，细长的电流层的一端出现一个折叠的电子流出区域，该区域中含有三条平行的电子喷射线，电子射线末端能量分布符合幂律法则。
电子主导磁重联区域强烈的感应电场增强了电子加速，当感应电场处于快速移动的等离子体状态时还会进一步加速，另外弹射过程会引起一个二级电流层。
正文:等离子体的磁重联与爆炸过程磁能量进入等离子体动能和热能能量的相互转换有关。
发生磁重联的薄层区域加速并释放等离子体[1-5]。
实验中磁重联速度与太阳能的观察结果大于Sweet-Parker与相关模型[4-6]的标准值，这是由霍尔电流和湍流[7-12]引起的。
二级磁岛以及该区域释放的等离子体可以提高磁重联速度，当伦德奎斯特数S﹥104[13]时二级磁导很不稳定。
这些理论预测值与近地磁尾离子扩散区域中心附近的二级磁岛观察值相符[14]，激光束与物质的相互作用的过程中，正压机制激发兆高斯磁场（▽ne×▽Te）生成[15-16]。
以尼尔逊[17]为代表的科学家首次运用两个类似的的激光产生的等离子体模拟磁重联过程。
尼尔逊[17]与Li[18]等人实验测量数据为磁重联的存在提供了决定性的证据，他们运用了随时间推移的质子偏转技术来研究磁拓扑变化，除此之外尼尔逊[17]等人观察到高度平行双向等离子喷射线与预期的磁重联平面成40°夹角。
本次研究调查了自发磁场的无碰撞重联，激光等离子体相互作用产生等离子体，为了防止磁场与等离子体连接在一起实验过程使用了两个共面有一定间隔的等离子体。
微纳米流动和核磁共振技术
微纳米流动和核磁共振技术英文回答：Microfluidics and nuclear magnetic resonance (NMR) are two important technologies that have revolutionized various fields of science and engineering.Microfluidics refers to the study and manipulation of fluids at the microscale level, typically in channels or chambers with dimensions ranging from micrometers to millimeters. It allows precise control and manipulation of small volumes of fluids, enabling a wide range of applications such as chemical analysis, drug delivery systems, and lab-on-a-chip devices. Microfluidic devices are often fabricated using techniques such as soft lithography, which involve the use of elastomeric materials to create microchannels and chambers.NMR, on the other hand, is a powerful analytical technique that utilizes the magnetic properties of atomicnuclei to study the structure and dynamics of molecules. It is based on the principle of nuclear spin, which is the intrinsic angular momentum possessed by atomic nuclei. By subjecting a sample to a strong magnetic field and applying radiofrequency pulses, NMR can provide information about the chemical composition, molecular structure, and molecular interactions of the sample. NMR has diverse applications in fields such as chemistry, biochemistry, medicine, and materials science.Microfluidics and NMR can be combined to create powerful analytical tools for studying various biological and chemical systems. For example, microfluidic devices can be used to precisely control the flow of samples and reagents, while NMR can provide detailed information about the composition and structure of the samples. This combination has been used in the development ofmicrofluidic NMR systems, which allow rapid and sensitive analysis of small sample volumes. These systems have been applied in areas such as metabolomics, drug discovery, and environmental monitoring.中文回答：微纳米流体力学和核磁共振技术是两种重要的技术，已经在科学和工程的各个领域引起了革命性的变化。
Magnetism and magnetic properties of materials
Magnetism and magnetic properties ofmaterials介绍磁性及其磁性能是材料科学中很重要的一块，磁性是指物质受到磁场作用时表现出来的各种现象，如吸引或排斥等。
而磁性能是指物质在磁场中的一系列特性表现。
磁性不仅影响着我们生活中常用的许多物品，如电视、电脑、磁性材料，而且还对应用在电磁设备、航空航天、生物医学等方面具有重要的应用价值。
磁性基础知识磁性是由原子和分子的磁性质决定的。
原子既具有电子轨道运动所形成的轨道磁矩，又具有自旋运动所形成的自旋磁矩。
物质的磁性取决于自旋磁矩、轨道磁矩的合成，并受到分子结构、晶格结构、温度等因素的影响。
然而，对于许多材料而言，这种合成是非常微弱的，因此物质磁化的来源主要是出现了局域磁时原子间作用的形成及相互偏转。
物质磁化度的计量单位是磁通量密度，即每个单位面积上磁通量的总数。
如果表面积为A, 磁通量为Φ，磁化密度J可以用下式表示：J = Φ/A磁性种类物质的磁性取决于其内部的微观结构，不同结构具有不同的磁性。
根据物质的磁特性，可分为顺磁性、铁磁性、反磁性及亚铁磁性。
顺磁性是指物质受磁场作用后，始终在磁场的方向上产生一个磁矩，而它的方向又是与磁场方向相同的微弱磁性。
顺磁性是由于原子或离子中的未成对电子对磁场的响应所引起的，其性能与温度成正比，并随着温度升高而减小。
反磁性是指物质受磁场作用后，使之形成的磁场方向相反，而且是以极微弱的程度出现。
这种类型的磁性主要是由于原子自旋磁矩和轨道磁矩的相互抵消所引起的。
亚铁磁性是介于顺磁性和铁磁性之间的一种磁性，通常将它称为温和的顺磁性或极弱的铁磁性。
其过渡相变点温度通常在零下20至100度之间正好还接近室温，而且其磁滞回线比较宽，在低温时磁性比较强，而温度升高时磁性明显减弱。
铁磁性是指物质受到磁场作用后，产生与磁场一致方向的强磁性。
铁性铁磁性是由于各个原子磁矩以相同方向排列而形成的。
铁磁性材料在常温下可能具有永久磁性，常见的亲铁磁材料有铁、钴、镍等。
磁能发电技术理论研究
人类的生存离不开能源和能源使用技术。众所周知， 煤炭、石油、天然气是一次能源，是不可再生的能源，然而 这些能源依然是人类使用能源的主要组成部分。随着工业 的发展，能源危机已经是全人类共同面对的一个重大的问 题，事关人类的生死存亡。人类希望找到永不枯竭的能源 来满足人类不断增长的能源需求。随着科学的发展，各钟 新能源理论也应运而生，如真空能理论、零点能理论、扰 场理论、暗能量暗物质理论等等，有些前沿科学理论还没 有 得 到广 泛 认同，更谈 不上实际应 用。但有一点 是可以肯 定的，我们周围存在着各式各样的能量。这些能源是环境 友 好、没有限制、安 全 稳定的可 再 生能源，这为人 类 研 究 利用新能源提供了新思路。
1 磁能发电理论基础 1.1 电磁感应和传统发电机
英国科学家法拉第在1831年发现了电磁感应现象。法 拉 第通 过 实 验 总 结出了如下定律:电 路中感 应电动势的大 小，跟穿过这一们制造了传统的发电机[1]。
传统的发电机是将其他形式的能量转化为机械能，再
文献标识码：A
文章编号：1674-098X(2018)11(c)-0063-03
Abstract: Before the discovery of electric current, people have discovered the phenomenon of magnetism. Magnetic f ield is a special kind of material, which has the properties of force and energy. Magnetic f ield has energy.Traditional generator is based on the law of electromagnetic induction and the law of electromagnetic force, the input mechanical energy into electrical energy output.The eff iciency of the traditional generator is less than 1 because of the loss in the working process of the generator.This paper introduces a new type of power generation which is different from the traditional one -- magnetic energy generation, and makes a theoretical exploration.There are basically two forms of magnetic energy generation, one is called constant magnetic type, the other is called electromagnetic type.The permanent magnet magnetic energy generation is to use the magnetization of the permanent magnet magnetic field to convert the additional magnetic energy (zero energy) into electrical energy, which is fundamentally different from the traditional generation mode of converting mechanical energy into electrical energy.Magnetic energy generation technology and traditional generators with the use of its power generation eff iciency will be greatly improved.The electromagnetic type uses a special magnetic circuit to amplify the input energy so as to realize the output of electric energ y. Key Words: New energy; Magnetic energy; Technology of Power generation
2019年职称英语理工类A级新增文章篇目(三)
2019年职称英语理工类A级新增文章篇目（三） Solar Power without Solar Cells太阳能的太阳能电池A dramatic and surprising magnetic effect of light discovered by University of Michigan1 researchers could lead to solar power without traditional semiconductor-based solar cells.戏剧性的和令人惊讶的磁光效应发现michigan1大学研究人员可能导致太阳能没有传统的半导体太阳能电池。
The researchers found a way to make an "optical battery," said Stephen Rand, a professor in the departments of Electrical Engineering and Computer Science, Physics and Applied Physics.研究人员发现了一种使“光电池，说：”史蒂芬兰德，系教授电气工程与计算机科学，物理和应用物理。
Light has electric and magnetic components. Until now, scientists thought the effects of the magnetic field were so weak that they could be ignored. What Rand and his colleagues found is that at the right intensity, when light is traveling through a material that does not conduct electricity, the light field can generate magnetic effects that are 100million times stronger than previously expected. Under these circumstances, the magnetic effects develop strength equivalent to a strong electric effect.光的电场和磁场组成部分。
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However, there has been little quantitative modeling of a precise physical situation, although Fitterman [1978,1979] analyzed the surface electric potential anomaly induced by a buried pressure source in a layered half-space and the surface
Copyright 1999 by the American Geophysical Union.
Paper number 1999GL900095. 0094-8267/99/1999GL900095$05.00
La Fournaise volcano (R´eunion Island), 2630 m high, is one of the most active basaltic volcanoes in the world with one eruption every 18 months. It is characterized by heavy rainfalls reaching 6 m per year and large anomalies in the electric potential, which may be of the order of 2 V [Michel and Zlotnicki, 1998]. A large fracture zone, about 500 m wide, cuts across the whole volcano. As mentionned by Zlotnicki and Le Mouel, [1990], this zone is likely to play an important part in the water circulation through the massif.
magnetic field in the vicinity of a vertical fault (cf also the recent review by Johnston, 1997).
The major s to provide a sensitivity analysis of the electrokinetic effect for La Fournaise volcano. This paper is organized as follows. An idealized model of the system is proposed and the governing equations are presented as well as the method of resolution and the range of parameters. The last section is devoted to a presentation and discussion of the results.
GEOPHYSICAL RESEARCH LETTERS, VOL. 26, NO. 6, PAGES 795-798, MARCH 15, 1999
Electrokinetic and magnetic fields generated by flow through a fractured zone: a sensitivity study for La Fournaise volcano
Abstract. A number of electric and magnetic signals have been observed on La Fournaise volcano, attributed to electrokinetic effects. A simple model is proposed here to check this hypothesis. The volcano is idealized as a 2d heterogeneous structure composed of a fractured zone located between two porous zones through which meteoritic waters flow downwards; flow occurs predominantly in the fractured zone and induces electromagnetic fields. Correct orders of magnitude are obtained for the measured surface fields. The importance of the heterogeneous character of the underground medium is demonstrated; local measurements of various quantities are recommended.
Meteoritic water is assumed to flow through this structure. The upper and lower boundaries of the porous medium (x=0 and L, |y| ≥ h) are assumed to be impermeable; hence, water flows through the central zone and drags along water contained in the porous medium. We investigate the influence of this flow on the electric potential and the magnetic field which can be measured at the volcano surface (x = 0).
When an electrolyte flows through a charged medium, electric and convective phenomena are coupled [de Groot and Mazur, 1969; Nourbehecht, 1963]. The seepage velocity u and the current density I are linearly related to the driving forces which are the gradients of the pressure p and of the
For this study, we adopt the simplified structure shown in Figure 1 which presents a cross-section of the volcano perpendicular to the fracture zone; the topography is simplified so that the cross-section is of a constant height L ∼ 2 km, of the order of the height of the volcano; the top corresponds roughly to the top of the volcano and the bottom to sea level. This cross-section consists of three zones; the two external zones are assumed to be a porous medium with identical properties surrounding a fractured zone of width 2h ≈ 500 m with different properties. For simplicity, the structure is assumed to be translationnally invariant along the z-axis which is perpendicular to the plane of the figure.
2. General
1. Introduction
It has been proposed that anomalous electric and magnetic fields observed before earthquakes and volcanic activity could be generated by the electrokinetic effect induced by water flow resulting from internal stresses, thermal buoyancy effects and meteoritic waters. The order of magnitude and the sign of the magnetic field were correctly obtained for the Matsushiro earthquake swarm [Mizutani and Ishido, 1976]. Self-potentials and magnetic measurements at La Fournaise volcano have been analyzed and interpreted in the same way [Zlotnicki and Le Mouel, 1990; Michel and Zlotnicki, 1998].