A. Larky

Bio: A. Larky is an academic researcher from Lehigh University. The author has contributed to research in topics: Electronic circuit & Transistor. The author has an hindex of 1, co-authored 1 publications receiving 90 citations.

Negative-Impedance Converters

Abstract: The conditions under which an active device exhibits an input impedance at one terminal pair which is exactly the negative of the load impedance connected to the other terminal pair are discussed. There are an infinite number of ways by which such a device, which is called a negative-impedance converter (NIC), can be made. One of the limits of this set is represented by a transistor circuit which was discussed previously by Linvill; the other limit, by a new circuit introduced recently. Practical negative-impedance converters are not exact; however, they may be made so by the addition of a pair of compensating impedances. The parameters of the NIC which most affect circuit performance are indicated as a guide to NIC design. Two typical transistor NIC circuits are compared on this basis. Experimental results are given.

Realisation of gyrators using operational amplifiers, and their use in RC-active-network synthesis

Abstract: The realisation of negative-impedance convertors (n.i.c.s) and invertors (n.i.i.s) using the bridge-type circuit is briefly surveyed. An equivalence relating the nullor to infinite-gain controlled sources is first proved, and is then used for the derivation of nullator-norator equivalent circuits for n.i.c.s and n.i.i.s. Some properties of networks containing singular elements, which are used in the realisation of gyrators, are investigated. Nullator-norator equivalent circuits for gyrators are derived by using the n.i.c.s and n.i.i.s. They are converted into physical networks by using the proved equivalence. Gyrator circuits are obtained by replacing nullors by operational amplifiers. A stability analysis of the gyrator circuits is produced and a relevant theorem concerning passivity is proved. The feasible Qfactors and the accuracy of the gyrator circuits are indicated by some experimental results. A generalised-impedance convertor (g.i.c.) is defined by generalising the n.i.c. theory, and it is shown that the gyrator circuits described can be used as g.i.c.s. The application of the gyrator and g.i.c. circuits in the synthesis of RC-active networks is considered. Finally, a highpass filter using gyrators and a bandpass filter using g.i.c.s are designed, and the experimental results are given.

Broadband, Efficient, Electrically Small Metamaterial-Inspired Antennas Facilitated by Active Near-Field Resonant Parasitic Elements

Abstract: The possibility of using an active internal matching element in several types of metamaterial-inspired, electrically small antennas (ESAs) to overcome their inherent narrow bandwidths is demonstrated. Beginning with the Z antenna, which is frequency tunable through its internal lumped element inductor, a circuit model is developed to determine an internal matching network, i.e., a frequency dependent inductor, which leads to the desired enhanced bandwidth performance. An analytical relation between the resonant frequency and the inductor value is determined via curve fitting of the associated HFSS simulation results. With this inductance-frequency relation defining the inductor values, a broad bandwidth, electrically small Z antenna is established. This internal matching network paradigm is then confirmed by applying it to the electrically small stub and canopy antennas. An electrically small canopy antenna with k? = 0.0467 that has over a 10% bandwidth is finally demonstrated. The potential implementation of the required frequency dependent inductor is also explored with a well-defined active negative impedance converter circuit that reproduces the requisite inductance-frequency relations.

A New Theory of Cascade Synthesis

Abstract: This paper presents a new result generalizing Richards' theorem. It is shown that this result leads to a complete, simple and unified theory of cascade synthesis which yields the types A, B, Brune, C and D sections in a direct and natural manner. The element values of the various sections are obtained in closed form in terms of three or six indexes. Thus the extraction cycle is performed once and for all for the whole class of positive-real functions. Several problems are worked out in detail and a chart is constructed to facilitate the computations. The formulas are easily programmed on a digital computer.

Superluminal Waveguides Based on Non-Foster Circuits for Broadband Leaky-Wave Antennas

Abstract: Non-Foster circuits such as negative capacitors can be used to create superluminal waveguides for broadband leaky-wave antennas. The negative capacitors effectively cancel part of the dielectric constant within the waveguide to provide a broadband relative permittivity between 0 and 1. When used as a leaky-wave antenna, the beam angle is independent of frequency over a broad bandwidth because the waveguide provides a frequency-independent phase velocity greater than the vacuum speed of light. Thus, this approach eliminates beam squint, which is a primary drawback of passive leaky-wave antenna designs. Simulation results using ideal negative capacitors are presented, and the effects of causality are analyzed.

Robust and efficient wireless power transfer using a switch-mode implementation of a nonlinear parity–time symmetric circuit

Abstract: Stationary wireless power transfer has been deployed commercially and can be used to charge a variety of devices, including mobile phones and parked electric vehicles. However, wireless power transfer set-ups typically suffer from an inherent sensitivity to the relative movement of the device with respect to the power source. Nonlinear parity–time symmetric circuits could be used to deliver robust wireless power transfer even while a device is moving rapidly, but previous implementations have relied on an inefficient gain element based on an operation-amplifier circuit, which has inherent loss, and hence have exhibited poor total system efficiency. Here we show that robust and efficient wireless power transfer can be achieved by using a power-efficient switch-mode amplifier with current-sensing feedback in a parity–time symmetric circuit. In this circuit, the parity–time symmetry guarantees that the effective load impedance on the switch-mode amplifier remains constant, and hence the amplifier maintains high efficiency despite variation of the transfer distance. We experimentally demonstrate a nonlinear parity–time symmetric radiofrequency circuit that can wirelessly transfer around 10 W of power to a moving device with a nearly constant total efficiency of 92% and over a distance from 0 to 65 cm. A parity–time symmetric circuit that uses a switch-mode amplifier and current-sensing phase-delay feedback can wirelessly transfer around 10 W of power to a moving device with a nearly constant total efficiency of 92%.