Matchable Loads from S-Parameters Defined Matching Networks

This post compares two different ways for finding the matchable loads \(Z_L^{'}\) that provide the desired impedance \(Z_G^{*}\) to the generator.

I will show the difference between two approaches, one rigorous and the other approximate, by using a set of S-parameters obtained by a black box network. The only requirement is that the black-box is linear, as the S-parameters requires linearity. For the curious, they are obtained from a binary weighted sweep of a lossy \(LL\) network composed of 1024 states in total from SimSmith.

STM32CubeIDE programmer and ST-LINK GDB server on Linux

This article discusses how to create a minimal set-up for running a gdb server on Linux using ST tools.

ST provides the STM32CubeIDE, which is an IDE based on Eclipse and designed to include the entire STM32 workflow. I am not super fan of all this super complex and bloated IDEs, as they tend force a fixed development strategy on the user. I therefore tried to look for alternatives.

Tandem Directional Coupler: Circuit Theory Approach

This document discusses the analysis of an ideal “tandem” directional coupler using lumped element circuit theory.

A directional coupler is a four port device that is used to sample the forward and reflected wave in a transmission line. It is a key component of a VNA and can be used to measure power flowing in a transmission line, but it can have countless possible uses. Generally they are built using distributed elements structures, but there are also versions built using lumped elements.

The tandem directional coupler, or also tandem bridge, is one of those directional couplers that is built using a lumped element approach. This kind of directional coupler, famous for radio-hams, has inherently large bandwidth and can handle a lot of power. It is also well suited for low frequency scenarios, down to the kHz range. It is composed of two current transformers, or two transformers with a high turn ratio, and two termination resistors with the desired characteristic impedance \(Z_0\), which can be arbitrary but usually 50\(\Omega\).

The Ideal Problem Solver, Second Edition - John D. Bransford, Barry S. Stein

ISBN: 0716722054, 9780716722052

This is a very well written must read book, very interesting and with tons of useful hints to improve creativity, problem solving abilities and to become better students, where student means who tries to learn.

The authors stress the difference between being able to memorize and being able to learn, while providing a method for proper problem solving.

I particularly enjoyed this claim:

Successful learners are not worried of making errors

In the following I will list some hints that I found valuable and worth keeping in mind. I hope you will also find those enlightening.

Coupled coils and coupling coefficient: from fraction of total flux to inductance definition

It is possible to relate the coupling coefficient \(k\) to both the total (\(\phi_{1}\) or \(\phi_{2}\)) and shared flux (\(\phi_{12}\) or \(\phi_{21}\)) or to the self (\(L_{1}\) and \(L_{2}\)) and mutual (\(M\)) inductances: \[ k = \frac{M}{\sqrt{L_{1} L_{2}}} = \frac{\phi_{12}}{\phi_{1}} = \frac{\phi_{21}}{\phi_{2}} \]

Simple proof:

Publication List using BibTeX and BibTeX-js

Sometimes it is useful to display a list of publications on a personal website.

There are many ways to do that, with the easiest being to write down each one by hand. While it is quite simple, it is also quite annoying and probably would leave the list not updated after few days (not a big issue for my few publications, but this is a different story).

One of the ways to deal with references is using BibTeX and the associated .bib files, which are the standard for \(\LaTeX\) and used also by JabRef as the default database format.

There is a nice Javascript library, BibTeX-js, which is able to parse and display .bib files, with the rendering done on the client side when the page is loaded. The only thing to do is to keep an updated .bib file, which is not too demanding, since it is also used for references in the papers.

I therefore decided to share my template, which I personally feel quite clean and nice and would be maybe useful to someone else. It is responsive and the bib link acts as a button to show the bibtex code of the single entry. The books, journal papers and conference papers are separated automatically and ordered by the year, with the newest being first. The clickable link on the DOI is automatically added using the doi value, while the link on the publication title is retrieved from the url value.

As an example see my publication list (Alex Pacini’s Publications).

Appunti Laurea Magistrale e Triennale, Ingegneria Elettronica, Università di Bologna, Cesena

A volte le vacanze natalizie sono utili per riordinare un po’ e così, per liberare spazio, ho deciso di digitalizzare gli appunti. In realtà solo quelli più decenti, quindi non sono tutti i corsi ma solo alcuni.

Meglio sempre prendere il contenuto con senso critico, non dovrebbero esserci errori, ma nel caso lasciare un commento 🤓. Se pensate vi siano stati utili, accetto ben volentieri una birra! 🍻

Load- and Position-Independent Moving MHz WPT System Based on GaN-Distributed Current Sources

This paper describes the modelling, analysis, and design of a complete (dc-to-dc) inductive wireless power transfer (WPT) system for industrial moving applications. The system operates at 6.78 MHz and delivers up to 150 W to a load moving along a linear path, providing a quasi-constant dc output voltage and maintaining a zero voltage switching operation, regardless of position and load, without any retuning or feedback.

The inductive link consists of an array of stationary transmitting coils and a moving receiving coil whose length is optimized to achieve a constant coupling coefficient along the path. Each Tx coil is individually driven by a constant amplitude and phase sinusoidal current that is generated from a GaN-based coupled load-independent Class EF inverter. Two adjacent transmitters are activated at a given time depending on the receiver’s position; this effectively creates a virtual series connection between the two transmitting coils. The Rx coil is connected to a passive Class E rectifier that is designed to maintain a constant dc output voltage independent of its load and position.

Extensive experimental results are presented to show the performance over different loading conditions and positions. A peak dc-to-dc efficiency of 80% is achieved at 100 W of dc output power and a dc output voltage variation of less than 5% is measured over a load range from 30 to 500 Ω.

The work in this paper is foreseen as a design solution for a high-efficient, maintenance-free, and reliable WPT system for powering sliders and mass movers in industrial automation plants.

This paper is published with Open Access on IEEE Xplore:

A. Pacini, A. Costanzo, S. Aldhaher and P. D. Mitcheson, “Load- and Position-Independent Moving MHz WPT System Based on GaN-Distributed Current Sources,” in IEEE Transactions on Microwave Theory and Techniques, vol. PP, no. 99, pp. 1-10. doi: 10.1109/TMTT.2017.2768031

PhD Tutorial: Position and Load Independent DC to DC Wireless Power Transfer System for Moving Applications

In order to pass to the third year of the PhD at the University of Bologna, it is required to give a 40 minutes presentation to first introduce your field, in the form of a tutorial, and then briefly show your research.

The presentation is organized as follows

• Tutorial
  • Introduction to Wireless Power Transfer (WPT)
  • Inductive Power Transfer (IPT)
  • Class E Resonant Inverter
  • Advantages of Wide Bandgap Semiconductors (WBG)
• Research Contribution
  • Geometry Optimization of Sliding Inductive Links for Position-Independent Wireless Power Transfer
  • Design of a Position-Independent End-to-End Inductive WPT Link for Industrial Dynamic Systems

Introduction to Wide BandGap Semiconductors and Class E rectifier

As an assignment to achieve the PhD credits for the Summer School of Information Engineering, it was requested to write a short report. This is a very simple introduction to Wide BandGap Semiconductors and Class E rectifier.

Python matplotlib: insets and aligned legends

Sometimes it is needed to create a plot with several lines and to assign a legend to each of them, which quite often ends in cumbersome and clunky legends. In my opinion, a more elegant way is include the legend as aligned text aside to each plot line, which is possible using Python and matplotlib.

Furthermore, to better highlight some details it is also possible to use an inset, hence to add a box which zooms a particular detail of the plot.

In the following is the Python code. The style is optimised for an IEEEtran journal.

Peer review template based on IEEEtran and pandoc

When you start to be involved in scientific publishing, one of the side-effects is to become a reviewer for some journals. This side-effect is an extremely important part of the scientific publishing process, which should ensure the quality of the published papers. It has also some other advantages, as to be able to view the papers few months before they would be published. The major downside is the time required for a good review, even days.

To simplify the writing process I decided to create a simple workflow which is based on \(\LaTeX\), IEEEtran and pandoc. The final output will be made up of a .pdf file, formatted as an IEEEtran journal, and a .rst file, formatted as a reStructuredText. The .pdf is ideal for viewing the math, figures, etc., while the .rst file is ideal to be pasted in the comments part, which is the part that will be sent in the email to the authors.

International Morse Code

This is a nerdy post, just to share a cheat-sheet which contains the International Morse Code along with the NATO Phonetic alphabet. I created this, using various resources online, just to lose some time…

Import a RF design (and logos) from svg, png or Gerber files into Kicad

KiCad is a wonderful software for PCB designing, it is open-source and can handle the complete workflow from the schematic to the final layout.

Unfortunately, it is not (yet) intended for RF circuit and antenna design. In these cases, a suitable program should be used, which could be ADS, CST, HFSS, or others. These are expensive but, unfortunately, the open-source tools are still not complete enough. I generally use multiple open-source tools depending of the requirements and quite often compare the results to evaluate the correctness.

Long story short, I was facing with the need to create a PCB by incorporating some custom Inductive Power Transfer coils, which I could export to a Gerber file from CST and some patch antennas and matching circuits, from ADS. The idea was to import the different parts from the Gerbers into different footprints, which are then assigned to schematics blocks and placed on the PCB.

There are no ways (yet) to get it simply by using some pre-baked functions, but some tricks are needed.

This post is a walk-through different options that can be used. I try to compare the options and outline the strengths of each one.

Notice that the same methods can be used to produce custom logos or any custom shape.

Visually engaging periodic plots using Python

In order to obtain periodic images with a technical feel to be embedded in a website, I decided to compose them with Python and Matplotlib. The plots are essentially some sums and multiplications of "noisy" sines.