论文标题
关于纵向电流在辐射系统中的作用
On the Role of Longitudinal Currents in Radiating Systems of Charges
论文作者
论文摘要
电荷密度的时间导数通过连续性方程与电流密度相关。但是，它仅具有电流密度的纵向部分，该密度已知不会产生辐射。尽管它构成了看似严重的悖论，但通常仍未引起人们的注意，这表明电荷密度的时间变化也应与辐射无关。我们通过表明即使产生时间依赖的电荷密度也不在空间上限制有效的纵向电流来解决这一悖论。这通过Helmholtz分解强制了电流密度的互补（即横向）的共存。我们说明了在动态电偶极子的情况下，Helmholtz分解的潜在非本地性的机制，讨论了其对水下天线通信的实际意义。更普遍地，我们解释了Helmholtz分解在塑造常规多产膨胀结构中的作用。
The time derivative of the charge density is linked to the current density by the continuity equation. However, it features only the longitudinal part of a current density, which is known to produce no radiation. This fact usually remains unnoticed though it poses a seemingly serious paradox, suggesting that the temporal variation of a charge density should be also irrelevant for radiation. We resolve this paradox by showing that the effective longitudinal currents are not spatially confined even when the time-dependent charge density that generates them is. This enforces the co-existence of the complementary (i.e. transverse) part of the current density through the Helmholtz decomposition. We illustrate the mechanics of the underlying non-locality of the Helmholtz decomposition in the case of a dynamic electric dipole, discussing its practical implication for underwater antenna communications. More generally, we explain the role of the Helmholtz decomposition in shaping the structure of the conventional multipole expansion.
