Author Archives: Matthew

Directly downwind faster than the wind

Posted on May 31, 2024 by Matthew

Is it possible to build a wind-powered vehicle that can continuously travel faster than the wind, in the same direction as the wind? Like the airplane-on-treadmill problem and the Feynman sprinkler problem, this question has spawned endless Internet arguments. Continue reading →

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Amplifiers in the real world: a case study

Posted on January 12, 2024 by Matthew

I encountered an interesting problem recently. As part of a personal project related to magnetic resonance, I built a small coil set and pre-amplifier: The pre-amplifier is located on the tiny green PCB; the signal received by the inner coil … Continue reading →

Posted in Electronics | 1 Comment

Electromagnetic radiation from accelerating charges

Posted on November 18, 2023 by Matthew

Electromagnetic radiation is something that has often eluded my intuition. Electrical engineering depends on numerous abstractions: current flowing in wires like a fluid, capacitance/inductance in lieu of near field interactions, antenna theory to model far field interactions, etc. These abstractions … Continue reading →

Posted in Physics | 2 Comments

MEMS oscillator frequency increase from helium

Posted on March 16, 2022 by Matthew

You may have heard of the incident where a helium leak suddenly disabled many iPhones at a medical facility. The root cause — tiny MEMS oscillators being susceptible to helium leaking into their hermetically-sealed casings — is interesting but not … Continue reading →

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Android device encryption hang at Time remaining 00:00

Posted on April 18, 2020 by Matthew

Recently I had a frustrating problem while trying to enable full disk encryption on my Android device (Motorola G3 “osprey”). Every time the encryption process would hang forever at: EncryptingWait while your phone is being encrypted.Time remaining 00:00

Posted in Computing | Leave a comment

WebEx audio input hang on Linux (Chrome/Chromium bug)

Posted on April 13, 2020 by Matthew

If you have been connecting to WebEx meetings on Linux using Chrome/Chromium versions 79 or 80, you might have run into issues where your microphone randomly stops working and other participants cannot hear you. When trying to reconnect to the … Continue reading →

Posted in Computing | Leave a comment

H field and material boundaries

Posted on April 10, 2020 by Matthew

For a long time I thought of the H field as being generated by free currents only. The problem with this view is that it leads us to make erroneous assumptions. We know from the definition of H that:   … Continue reading →

Posted in Physics | 2 Comments

Magnetic field of a ferrite core solenoid

Posted on January 19, 2020 by Matthew

Consider a solenoid made of wire wrapped around a rod made of iron, ferrite, or other ferromagnetic material: It is well known that the magnetic field will be significantly stronger inside such a solenoid, compared to an air core solenoid. … Continue reading →

Posted in Physics | 5 Comments

Designing and making a ring

Posted on October 30, 2017 by Matthew

Recently I designed an engagement ring for my (now-)fiancée, from scratch. This was a fascinating and challenging process, and gave me a new appreciation for both the art and engineering of jewellery design. The first step in the process was … Continue reading →

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Splines in Onshape, part 2

Posted on July 25, 2017 by Matthew

In this second part of the series, I’ll briefly cover drawing splines directly in 3D, and then discuss offset curves, which are the original reason I started on this long journey delving into Onshape curves. Continue reading →

Posted in Computing | 5 Comments

Splines in Onshape, part 1

Posted on July 5, 2017 by Matthew

In this post I talk about splines and various ways they can be represented, with particular reference to Onshape, a web-based CAD system. Continue reading →

Posted in Computing | 5 Comments

Dell Venue 11 Pro travel keyboard troubleshooting

Posted on May 29, 2017 by Matthew

Introduction I recently purchased a pair of Dell Venue 11 Pro 7140 tablet computers — one for myself and one for my girlfriend. I figured this would be a good crossover device between a tablet and a laptop, and so … Continue reading →

Posted in Computing | 2 Comments

Unlocking my Lenovo laptop, part 3

Posted on February 12, 2016 by Matthew

The decryption function If you are just joining this story you may want to start at part 1. In part 2, we discovered that a embedded controller update is performed by uploading a small ‘flasher’ program to the EC. This … Continue reading →

Posted in Computing | 78 Comments

Unlocking my Lenovo laptop, part 2

Posted on February 5, 2016 by Matthew

The embedded controller In part 1, we looked at the communication between a Lenovo Thinkpad X230T laptop and battery, and discovered that there a challenge-response protocol used to authenticate ‘genuine’ Lenovo batteries. On the laptop side, this – and battery … Continue reading →

Posted in Computing | 26 Comments

Unlocking my Lenovo laptop, part 1

Posted on February 1, 2016 by Matthew

Introduction Two months ago, I bought a new battery for my Lenovo laptop (a ThinkPad X230T). I was about to go away on holidays and wanted a battery that could last me through a plane flight; the original battery was … Continue reading →

Posted in Computing | 24 Comments

Introduction to photography slides

Posted on December 16, 2013 by Matthew

These are some slide decks I used to use when I ran introductory courses for the UNSW Photography Club. They are a pretty good set of slides so I figured they should have a home on the Web. Part I: … Continue reading →

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Global food security

Posted on May 17, 2012 by Matthew

I went to a great lecture today by Professor Chris Barrett on “The Global Food Security Challenge in the Coming Decades”. The slides from this lecture are available here. Here are my notes: Current global food demand growth is ~1.25% … Continue reading →

Posted in Other | 1 Comment

Weather balloon physics

Posted on February 27, 2012 by Matthew

One of the simplest solutions for sending measurement instruments up into the stratosphere is a rubber balloon filled with hydrogen or helium. While the physics of such a balloon would seem to be simple, there are actually some interesting considerations.

Posted in Physics | 12 Comments

New site

Posted on January 15, 2012 by Matthew

Welcome to the newly redesigned zmatt.net. I seem to only get around to upgrading my personal website once every decade so this is a special day indeed. The biggest change is that I now have a blog here (powered by … Continue reading →

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