發(fā)布時(shí)間：2018-03-27 07:05

  本文選題：低頻電磁波　切入點(diǎn)：甚低頻電磁波　出處：《浙江大學(xué)》2015年碩士論文

【摘要】：低頻(LF:30-300kHz)電磁波在地面(或海面)-空氣組成的兩層介質(zhì)中傳播以及甚低頻(VLF:3-30kHz)電磁波在“地-電離層波導(dǎo)”模型中傳播問題均可看作電磁波在分層介質(zhì)中的傳播問題。當(dāng)觀察點(diǎn)與源點(diǎn)距離較小時(shí),可忽略地球曲率的影響,采用平面半空間地波傳播模型或平面波導(dǎo)模型來求解；隨著傳播距離增大,需要考慮地球曲率的影響,當(dāng)滿足球面模型適用條件時(shí),可采用球面分層介質(zhì)的傳播模型進(jìn)行求解。然而,在現(xiàn)有的地波傳播與“地-電離層波導(dǎo)”傳播理論尚無法解決過渡區(qū)內(nèi)電磁場的理論計(jì)算,當(dāng)觀察點(diǎn)與源點(diǎn)的距離既不滿足平面模型的距離條件,也不滿足球面模型的條件時(shí),現(xiàn)有的低頻、甚低頻電磁波的理論均不適用。對(duì)LF/VLF頻段而言,過渡區(qū)范圍很大,如何解決過渡區(qū)內(nèi)的波傳播問題有著十分重要的意義。 為此,本文將針對(duì)LF地波傳播及“地-電離層波導(dǎo)”中VLF波傳播問題提出了一種新的解析計(jì)算公式,使得過渡區(qū)中的傳播計(jì)算問題得到了較好的解決。本文主要工作簡述如下： 1、精確定義了三種傳播模型,及過渡區(qū)的截止傳播距離。通過對(duì)經(jīng)典低頻、甚低頻電磁波理論的重新審視,推導(dǎo)出過渡區(qū)的中心距離ρCn,并以此確定了過渡區(qū)的上下距離截止范圍ρ1n、ρ2n。 2、分別提出了適用于低頻電波的地波傳播和適用于甚低頻電波的地-電離層波導(dǎo)傳播的分段解析模型,其中,對(duì)于過渡區(qū)的理論計(jì)算進(jìn)行了明確定義與理論論證。 3、將本文所提出的理論計(jì)算模型的數(shù)值結(jié)果與King等人在地波傳播過渡內(nèi)的計(jì)算結(jié)果進(jìn)行對(duì)比,數(shù)值結(jié)果基本一致。同時(shí),所給出甚低頻過渡區(qū)計(jì)算模型在取低階傳播模式時(shí)可退化為地波傳播的過渡區(qū)模型。數(shù)值結(jié)果表明,該計(jì)算模型具有較高的數(shù)值穩(wěn)定性和收斂性。 綜上所述,本文在現(xiàn)有對(duì)低頻、甚低頻電磁波傳播問題的理論基礎(chǔ)上,進(jìn)一步提出并準(zhǔn)確區(qū)分了過渡區(qū)的概念,引入模式加權(quán)的方法,提出了一種工程計(jì)算中適用于低頻、甚低頻電波在過渡區(qū)傳播模型的解析表達(dá)式。通過與現(xiàn)有結(jié)果的對(duì)比,在與現(xiàn)有理論模型的求解區(qū)域數(shù)值結(jié)果吻合,并解決了現(xiàn)有理論中部分區(qū)域無法理論計(jì)算的不足。
[Abstract]:The propagation of low frequency LF: 30-300kHz) electromagnetic wave in the surface (or in a two-layer medium consisting of sea surface / air and very low frequency VLF: 3-30kHz) can be regarded as the propagation problem of electromagnetic wave in stratified medium. When the distance between the observation point and the source point is small, The influence of earth curvature can be ignored and solved by plane half-space ground wave propagation model or plane waveguide model. With the increase of propagation distance, the influence of earth curvature needs to be considered. The propagation model of spherical layered medium can be used to solve the problem. However, the theoretical calculation of electromagnetic field in transition zone can not be solved by the existing theories of ground wave propagation and "ground-ionospheric waveguide" propagation. When the distance between the observation point and the source point does not satisfy the distance condition of the plane model or the spherical model, the existing theories of low frequency and very low frequency electromagnetic waves are not applicable. For the LF/VLF band, the transition region is very large. How to solve the problem of wave propagation in transition zone is of great significance. In this paper, a new analytical formula for LF ground wave propagation and VLF wave propagation in earth-ionospheric waveguide is proposed. The problem of propagation calculation in the transition zone is well solved. The main work of this paper is as follows:. 1. Three kinds of propagation models are defined accurately, and the cut-off propagation distance of transition region is defined. The classical theory of low frequency and very low frequency electromagnetic wave is reexamined. The center distance 蟻 C n of the transition region is derived, and the cutoff range 蟻 1 n, 蟻 2 n of the upper and lower distances of the transition region is determined. 2. The piecewise analytical models of ground wave propagation suitable for low frequency wave wave and ground ionospheric waveguide propagation for very low frequency wave wave are presented respectively. The theoretical calculation of transition zone is clearly defined and theoretically demonstrated. 3. The numerical results of the theoretical model proposed in this paper are compared with those of King et al in the ground wave propagation transition. The model of very low frequency transition region can be degenerated into a transition zone model of ground wave propagation when the low order propagation model is taken. The numerical results show that the model has high numerical stability and convergence. To sum up, on the basis of the existing theories on the propagation of low and very low frequency electromagnetic waves, the concept of transition zone is further proposed and accurately distinguished. A method of mode weighting is introduced, and a method suitable for low frequency in engineering calculation is proposed. The analytical expression of the VLF wave propagation model in the transition region. By comparing with the existing results, the numerical results agree well with the existing theoretical model, and solve the deficiency that some regions of the theory can not be calculated theoretically.
【學(xué)位授予單位】：浙江大學(xué)
【學(xué)位級(jí)別】：碩士
【學(xué)位授予年份】：2015
【分類號(hào)】：TN011

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本文編號(hào)：1670500