Extensive review on Supercapacitor cell voltage balancing

This paper explains about the supercapacitor cell voltage balancing circuits by comparing different topologies with regard to parameters like cost, balancing time, weight of the components used and control of switches. The advantage of supercapacitor over battery made to overcome weight and faster responding source problems. In supercapacitor bank cell voltages differ from each other which effects the performance of the device. Passive circuits consume power from cell for balancing but active circuits consume power from source. Many topologies are considered in this paper for different ratings and with different components. Balancing circuit is selected based upon total number of components in the balancing circuit, many components make circuit less reliable, complex and also increase the cost for balancing.

First ten years of active metamaterial structures with “negative” elements

Almost ten years have passed since the first experimental attempts of enhancing functionality of radiofrequency metamaterials by embedding active circuits that mimic behavior of hypothetical negative capacitors, negative inductors and negative resistors. While negative capacitors and negative inductors can compensate for dispersive behavior of ordinary passive metamaterials and provide wide operational bandwidth, negative resistors can compensate for inherent losses. Here, the evolution of aforementioned research field, together with the most important theoretical and experimental results is reviewed. In addition, some very recent efforts that go beyond idealistic impedance negation and make use of inherent non-ideality, instability, and non-linearity of realistic devices, are highlighted. Finally, a very fundamental, but still unsolved issue of common theoretical framework that connects causality, stability, and non-linearity of networks with negative elements is stressed.