Experimental evidence of variable-order behavior of ladders and nested ladders

TL;DR

This study experimentally investigates domino and nested ladder circuits, revealing their variable fractional order behavior in time domain, with the nested ladder being introduced for the first time, and fitting data using Mittag-Leffler functions.

Contribution

First experimental demonstration of nested ladder circuits exhibiting variable fractional order behavior, with a novel data fitting approach using Mittag-Leffler functions.

Findings

Domino ladder behaves as a 0.5 order system in frequency domain.

Nested ladder behaves as a 0.25 order system in frequency domain.

Both systems show order variation from less than 1 to nearly 1 in time domain.

Abstract

The experimental study of two kinds of electrical circuits, a domino ladder and a nested ladder, is presented. While the domino ladder is known and already appeared in the theory of fractional-order systems, the nested ladder circuit is presented in this article for the first time. For fitting the measured data, a new approach is suggested, which is based on using the Mittag-Leffler function and which means that the data are fitted by a solution of an initial-value problem for a two-term fractional differential equation. The experiment showed that in the frequency domain the domino ladder behaves as a system of order 0.5 and the nested ladder as a system of order 0.25, which is in perfect agreement with the theory developed for their design. In the time domain, however, the order of the domino ladder is changing from roughly 0.5 to almost 1, and the order of the nested ladder is changing in a similar manner, from roughly 0.25 to almost 1; in both cases, the order 1 is never reached, and both systems remain the systems of non-integer order less than 1. Both studied types of electrical circuits provide the first known examples of circuits, which are made of passive elements only and which exhibit in the time domain the behavior of variable order.