Circuit modeling of a MEMS varactor including dielectric charging dynamics

Electrical models for MEMS varactors including the effect of dielectric charging dynamics are not available in commercial circuit simulators. In this paper a circuit model using lumped ideal elements available in the Cadence libraries and a basic Verilog-A model, has been implemented. The model has been used to simulate the dielectric charging in function of time and its effects over the MEMS capacitance value.Peer ReviewedPostprint (published version

Qucs-S help documentation release 0.0.21-S

Following the release of Qucs-0.0.18 in August 2014 the Qucs Development Team considered in detail a number of possible directions that future versions of the software could take. Spice4qucs is one of these routes. It addresses a number of problems observed with the current version of Qucs while attempting to combine some of the best features of other GPL circuit simulation packages. The project also aims to add additional model development tools to those currently available in Qucs-0.0.18. Qucs was originally written as an RF and microwave engineering design tool which provided features not found in SPICE, like S parameter simulation, two and multiport small signal AC circuit analysis and RF network synthesis. Since it was first release under the General Public License (GPL) in 2003 Qucs has provided users with a relatively stable, flexible and reasonably functional circuit simulation package which is particularly suited to high frequency circuit simulation. In the years following 2003 the Qucs Development team added a number of additional simulation facilities, including for example, transient simulation, device parameter sweep capabilities and single tone Harmonic Balance simulation, making Qucs functionality comparable to SPICE at low frequencies and significantly extended at high frequencies. Considerable effort has also been made to improve the device modelling tools distributed with Qucs. The recent versions of the software include code for algebraic equation manipulation, Equation-Defined Device (EDD) modelling, Radio Frequency Equation-Defined Device (RFEDD) simulation and Verilog-A synthesised model development plus a range of compact and behavioural device modelling and post simulation data analysis tools that have become central features in an open source software package of surprising power and utility. One of the most often requested new Qucs features is “better documentation”, especially documentation outlining the use and limitations of the simulation and the modelling features built into Qucs. Qucs is a large and complex package which is very flexible in the way that it can be used as a circuit design aid. Hence, however much documentation is written describing its functionality there are always likely be simulation and modelling examples that are missing from the Qucs documentation. In future Qucs releases will be accompanied by two or more basic Qucs documents. The first of these, simply called “Qucs-Help”, provides introductory information for beginners and indeed any other users, who require help in starting to use Qucs. The second Qucs document, called “Spice4qucs-Help”, introduces more advanced simulation and modelling topics. Both documents present a large number of typical circuit simulation and compact device modelling examples

Acoustic Power Transfer Leveraging Piezoelectricity and Metamaterials

Acoustic power transfer, or ultrasonic power transfer (UPT) more specifically, has received growing attention as a viable approach for wireless power delivery to low-power electronic devices. It has found applications in powering biomedical implants, sensors in sealed metallic enclosures, and sensors deep in the ocean. The design of an efficient UPT system requires coupled multiphysics modeling to establish strategies toward maximizing the transferred power. This work, first, investigates different analytical and numerical models to analyze the performance of UPT systems to increase the transferred power. Various electromechanical models are developed to represent the transducer (transmitter or receiver) and overall system dynamics for a broad range of aspect ratios covering the diverse UPT applications. The main challenges that limit UPT system efficiency such as attenuation, power divergence, and reflection due to impedance mismatch issues are investigated using the developed models. These effects are investigated at the system level with an application to transfer power through metallic barriers using bonded piezoelectric disc transducers. A complete system for transferring power from the battery of a transmitter to the DC load of a receiver is designed and simulated, then experimentally tested. The experimental results of the system agree well with the modeling predictions, and the system can deliver 17.5 W to a DC load with a total DC-to-DC efficiency of 66 %. A second system with a portable and detachable dry-coupled transmitter is also experimentally tested. The dry-coupled system can deliver 3 W of DC power with 50 % efficiency from a 9V battery. Novel approaches using acoustic metamaterials/phononic crystals are introduced to enhance the efficiency of UPT through wave focusing. Specifically, two 3D phononic crystal structures based on air in a 3D-printed polymer matrix are introduced to manipulate acoustic waves both under water and in air. Two designs for gradient-index lenses are fabricated and experimentally characterized to focus acoustic waves on a piezoelectric receiver, thereby dramatically enhancing the power output. Finally, acoustic and electrical impedance matching are investigated for sending both power and data using ultrasonic waves. Several impedance matching techniques are proposed to maximize transducer bandwidth, power efficiency, as well as sensitivity for underwater data transfer. A novel approach is introduced for achieving simultaneous power and data transfer using frequency multiplexing with a single transducer. The introduced designs allow for configurable matching for maximizing power efficiency, maximizing data transfer, or simultaneously sending power to the transducer while receiving data with lower bandwidth.Ph.D