Jukka Venermo

Transmission-Line Networks Cloaking Objects From Electromagnetic Fields

We consider a novel method of cloaking objects from the surrounding electromagnetic fields in the microwave region. The method is based on transmission-line networks that simulate the wave propagation in the medium surrounding the cloaked object. The electromagnetic fields from the surrounding medium are coupled into the transmission-line network that guides the waves through the cloak thus leaving the cloaked object undetected. The cloaked object can be an array or interconnected mesh of small inclusions that fit inside the transmission-line network.

Boosting numerical accuracy in calculation of polarizability of two-dimensional scatterers

This article presents an effective way to increase the accuracy of the numerical evaluation of the polarizability of two-dimensional scatterers. It is based on the numerical exploitation of the observation that the polarizabilities of complementary inclusions are closely related: if the permittivity is inverted, the polarizability changes sign. For anisotropic inclusions, the corresponding property cross-connects the orthogonal components, and can be used as well in the numerical calculations. The improvement of the numerical accuracy is several orders of magnitude. The method is also applied to evaluate the polarizability of split rings.

Correction to "Transmission-Line Networks Cloaking Objects From Electromagnetic Fields" [Feb 08 416-424]

In the above titled paper (ibid., vol. 56, no. 2, pp. 416-424, Feb 08), Fig. 1 appeared with a typographical error. The correct version is presented here.

The tangent galvanometer of Johan Jacob Nervander

J.J. Nervander designed the more- sensitive tangent galvanometer in 1834, which led to a great improvement in precise measurements of electric current. Because of its ingenuous coiling arrangements, Nervander was able to use the tangent busol to prove the validity of the law that the tangent of the deviation angle of the needle of the tangent-bussol is proportional to the electric current flowing through its coil. Exploitation of the tangent law provided a way of measuring and comparing currents. The increased sensitivity of the galvanometer was a result of the uniformity of the current-created magnetic field over the cylindrical volume inside the coils. This allowed the use of a long magnetic needle. The reconstructed galvanometer operates with a short needle. For the reconstructed galvanometer, the tangent law is valid up to deflection angles more than 50deg; Nervander reported acceptable deviations only up to 30deg.