Hao‐Ming Shen

Spherical reflector as an electromagnetic‐missile launcher

A spherical reflector illuminated by a point source is found to be capable of launching an electromagnetic missile. Since the surfaces of the reflector are not complete spherical surfaces, the problem cannot be solved by simple boundary matching. The electromagnetic fields have to be solved in three regions separately. The general solutions are matched on the boundaries to obtain a set of coefficient equations. Under the conditions for an electromagnetic missile, the coefficient equations are solved asymptotically. The evaluation of the Poynting vector shows that the energy radiated from the reflector has the same slow rate of decay as for the spherical lens.

Plasma waveguide: A concept to transfer electromagnetic energy in space

This paper studies the possibility of using a laser‐generated ‘‘plasma waveguide’’ to transfer electromagnetic (EM) energy. The plasma waveguide is a cylindrical vacuum core surrounded by a plasma cladding. The analysis shows that guided‐mode fields do exist inside the core. Like a general dielectric waveguide, the plasma waveguide is characterized by a ‘‘normalized frequency parameter’’ (also called the V number). Although the permittivity of the plasma varies strongly with frequency, the V number surprisingly remains constant over the entire frequency range. Because of this property, the frequency dependence of the plasma waveguide is different; it has a wider high‐frequency response than the general dielectric waveguide. The EM pulse can propagate in the plasma waveguide at close to the speed of light and keep its profile and shape unchanged. When the V number is smaller than 2.4048 (the first root of the zero‐order Bessel function), only the single HE11 mode exists in the plasma waveguide. Unlike the ...

The properties of the electromagnetic missile

The electromagnetic field from the current in a circular disk and its Poynting vector off the axis of propagation have been investigated both analytically and experimentally. These studies show that the electromagnetic (EM) missile has the following properties: (1) The waveform of the EM field when propagating remains similar in shape but diminishes in size. (2) The transverse distribution of energy around the axis is stable; i.e., when the longitudinal distance increases, the transverse pattern of the energy remains the same. This ‘‘plane‐wave beamlike’’ property is different from continuous‐wave (cw) radiation, in which the energy pattern is like that of a spherical wave. (3) The transverse energy pattern has a cusp on the axis. This property is also different from cw radiation. With cw, the radiation has a flat top on the axis of the main lobe.

The plasma waveguide with a finite thickness of cladding

The properties of the plasma waveguide of finite thickness (plasma tube) have been studied. The analysis indicates that, in the case of finite thickness, most of the properties for the plasma waveguide with infinite thickness are retained. At high frequencies, such a plasma tube is still a nondispersive waveguide system. The losses due to the finite thickness of the cladding and the conductivity of the plasma are both small. The decay coefficient decreases with the thickness exponentially. With a thickness equal to the radius of the central core, the attenuation can be as low as 0.1 dB/km.

Spherical lens as a launcher of electromagnetic missiles

A uniform dielectric sphere, under transient excitation by a point source, is found to be capable of launching an electromagnetic missile, i.e., there is a direction where the decay of the total energy transmitted to a receiver is slower than r−2. The conditions for the presence of an electromagnetic missile have a natural interpretation, which in turn leads to a classification of electromagnetic missiles according to the singularities of differentiable maps in two dimensions.

New sensors for measuring very short electromagnetic pulses

In order to detect very short electromagnetic pulses under 100 ps in width, a wide-band receiving antenna with a bandwidth from 0 to 14 GHz is needed. The usual short dipoles or monopoles do not provide both the required fidelity (bandwidth) and sensitivity. A novel type of electromagnetic pulse (EMP) sensor has been designed, analyzed, and tested. It is simple, inexpensive, and can detect the electromagnetic pulse with both high fidelity and high sensitivity. An approximate analysis is given for better understanding and optimum design of the proposed EMP antenna. >

Generalized analysis of the spherical lens as a launcher of electromagnetic missiles

It is found that, like the directly transmitted radiation field previously investigated, an internally multiply reflected radiation field can also become an electromagnetic missile under certain different electromagnetic‐missile conditions. The analysis is carried out in a general way, i.e., for the point source located either inside or outside the dielectric sphere. The electromagnetic‐missile conditions are obtained for general multiply reflected radiation fields.

The Exciting Mechanism of the Parallel-Plate EMP Simulator

It is said that the parallel-plate electromagnetic-pulse (EMP) simulator is essentially a parallel-plate waveguide. This is not true. An analysis of the subpulses emitted from subregions of the sloping triangular and parallel rectangular plates shows that, when the length b of the parallel-plate section is close to the height h between the two parallel plates (which is true in most practical cases), the simulator is essentially a cone-plate radiator rather than a parallel-plate waveguide. The EMP in the working volume is contributed by the current pulses on the triangular plate near the pulse generator, so that the parallel plate actually plays a rather small role in forming the EMP in the working volume.

The Rhombic EMP Simulator

A complete analysis has been carried out of the twoconductor rhombic antenna as an EMP simulator. The distribution of current along the conductors and the electric field in the working space bounded by rhombic wires have been determined at low, middle, and high frequencies. The analysis indicates that, at low frequencies, when the termination is the characteristic impedance, a traveling-wave current with very low standing-wave ratio propagates along the wires of the rhombic structure; but it is very sensitive to the load. As the frequency is increased, the standing-wave ratio also increases somewhat and it becomes less sensitive to the load. The electric field in the working space exhibits a reasonably constant amplitude with a standing-wave ratio of 1.5 or lower at all three frequencies.

Curved electromagnetic missiles

An interesting topic has been the possible behavior of transient fields in the limit of great distances from their sources. Under the physical restriction that the total energy radiated is finite, it has been shown that the energy reaching a distant receiver can decrease with distance much more slowly than the usual r−2. Such cases of slow decrease have been referred to as electromagnetic missiles. All of the wide variety of known missiles propagate in essentially straight lines. It is shown here that such a missile can follow a path that is strongly curved. An example of a curved electromagnetic missile is explicitly constructed and some of its simpler properties are discussed.