My last project brought up the subject of capacitive touch sensing. You may not have realized this, but capacitive touch sensing is currently on the forefront of electronics. Mechanical touch sensors are known to wear and ‘push-less’ sensors are just cooler. In case you did not know, the scroll wheel on an Ipod uses an array of capacitive sensors along with the infamous touch lamp.

For the engineer in you, Planet Analog has a lengthy overview. Basically, you design a circuit that is highly dependent on the value of a small capacitor. The capacitance in a finger then causes a significant and detectable change in the circuits output.

The doorknob touch alarm functions in just this manner. It does its job, but is not as precise as more complex circuits. For more schematics, check out Discover Circuits. A recent article on DesignLine proposed that this interface be adapted to mobile phone keypads.

Over the past week, I’ve been really busy with exams and projects. Trying to save time by finding the speed of light on Google, I stumbled upon an extremely interesting article on measuring the speed of light with a microwave. As any decent cook knows, microwaves do not heat evenly. In fact, this article explains their heating patterns are relative to the speed of light!

Understanding how a microwave heats

As we all know, microwaves heat using electromagnetic waves. These waves are at a frequency perfect for rotating water molecules (f = 2.5 GHz). The rotating water molecules create friction and thereby heat.

Two types of electromagnetic waves

Although there are two types of electromagnetic waves, we typically only consider traveling waves. The amplitude of the wave travels forward in position over times. The following animation demonstrates the amplitude of a wave over space and time.

The waves in a microwave are not traveling. If they were, it would be nearly impossible to distinguish any uneven heating patterns!

USA Today was recently asked, “If both electric and magnetic fields can pass through paper why not light?” If you think about it, this is a really good question. The simple answer: paper absorbs/scatters light, but not low or high energy electromagnetics. Read the article if you want to learn more.