Waves

Sound Waves

Sound waves are mechanical waves, and there are actually particles bouncing into each other which cause the wave to travel. We're going to transition at some point to electromagnetic waves, so at this point just know there's a difference. I'm going to talk about some characteristics of waves, and I'm going to talk about it in the sense of sound waves to begin with.

Here we have a speaker, and then we have somebody that's listening to the speaker. This speaker has a cone on it, and this cone is vibrating. The cone vibrates back and forth and creates a wave through the air where particles are actually bouncing into each other, and it goes all the way to the ear, into the ear canal. Then we have a sensor in there that gets vibrated within our ear, and our brain interprets those vibrations and turns it into some sort of audible sound that we can understand. That's how sound waves work.

Frequency

Frequency is a measurement of cycles per second. So what is a cycle? I have an example of it here on the left. It's an up and down; it's a full rotation. If we were to think about a speaker and it's vibrating, a full cycle would be the time it takes for that speaker to fully extend out, then fully extend back, and then return back to the original spot. So it's a full extension out, full extension in, and then back to its original spot. That is one cycle. A frequency would be how many times it does that every second.

In my example here on the left, let's say we're measuring a frequency, and that speaker goes all the way out, then comes all the way in, and then back to zero. There's one cycle right there, and if this is 1 second, we have 1, 2, 3, 4, 5, 6, 7. That's seven cycles in that 1 second, and so that would be seven hertz. A hertz is a cycle per second, so this is a seven hertz signal. A seven hertz signal would be pretty low, and we probably wouldn't be able to hear that low of a cycle per second.

Here's an example of two frequencies. This is a much lower frequency. Our ear is going to hear this lower frequency on the left-hand side and determine that it is a low pitch, so this is a lower note, a deep note. Versus if we have a higher frequency, our ear hears that and determines it's a much higher pitch and hears it as a higher sound. A lower frequency makes a lower sound, and a higher frequency makes a higher sound.

The Ranges We Hear

Let's take a look at some frequencies and what our ear would actually determine that frequency is going to be. Here we have this range from 0 to 20 hertz, so that is up to 20 cycles per second. Most people are not going to hear this, so this is called subsonic. Subsonic is the sub sound; we really don't interpret these wavelengths as being sound at all.

Then we have the bass range. Bass is everything from 20 to 120. This is the range where we hear those really low rumbles, or off in a distance you hear some car that has big bass speakers, and these are probably the sounds that you're hearing. Notice that those sounds travel further. You hear the bass before you hear the high-end noises, and that's important, and we'll get into it in a little bit.

Then we see this range here they call the upper bass. And then we've got the mid-range, the upper mid-range, the high-end, and then supersonic. Supersonic is the above-sound range, the things that our ear really can't interpret. Depending on how well our hearing is, we may not even hear up to 20,000 hertz, but that's what this is — this is 20,000 hertz. So your hearing range is probably somewhere between 20 and 20,000 hertz. That is the range. You'll notice that we actually have different speakers that will play each of these ranges, because they're purpose-built for those different ranges.

That's a little bit about audio waves and how audio waves get formed by the speaker, go through the air, and come into our ear. Our ear has an eardrum which senses those vibrations, and then our brain interprets those vibrations, those signals, and puts it into some sort of audible sound that we can then hear.

Amplitude

We talked about frequency, but with music we also have amplitude, and amplitude is the sound. We could have a really low frequency across here that's really quiet, so we talk about a frequency that's low and it's quiet. But we can also have a frequency that's very loud, and that's amplitude. So we have frequency and amplitude, and we can vary both the frequency and the amplitude. We can have bigger amplitudes and smaller amplitudes with the same frequency. Those are the two things that we can control with these waves.

Electromagnetic Waves

Now let's take what we learned about sound waves and apply it to electromagnetic waves. Electromagnetic waves are really interesting, really fascinating stuff. They aren't mechanical. They're not particles that are bouncing off of each other in the air. They're waves that go through the air, and it uses an electromagnetic field that goes through the air. I can't explain it, I can't do it justice. It's pretty mind-boggling how these waves actually travel through the air. But what they do behaves very similar to other mechanical waves.

Here I've got a station, a radio station, and it's got an antenna. What it does is it sends a signal to this antenna, and you've got electrons going up and down this antenna, and that creates a wave, and that wave travels through space and time. Then there is another antenna, and it will affect an electron within that antenna and wave up and down. We have a radio that senses it, and it comes out the other side. So we are able to transmit data across these electromagnetic waves by having antennas that will first broadcast or transmit these signals, and then we have antennas that will receive the signal and then interpret that signal.

The Spectrum

Just like sound waves, electromagnetic waves have a really wide range of frequencies. Depending on what the frequency is, we'll have different effects, and we utilize those effects, those behaviors, that physics behind those waves, to do different things.

This is a diagram. You can see it starts out at 50 hertz down here, so 50 cycles per second. We see 500 megahertz, so that'd be 500 million cycles per second. We see a gigahertz; that'd be 1 billion cycles per second. We go all the way up to 30 exohertz, so whatever that is. You can see that there's a real wide range here of different cycles per second that we have.

With these electromagnetic fields, as we send out these different frequencies, we have different effects. These lower frequencies tend to travel a lot further down here. The higher frequencies don't travel as far. The lower frequencies, as you can see, tend to have some safer behaviors, where the higher frequencies can have some harmful behaviors.

VLF would stand for very low frequency. We've defined some of these areas: very low frequency, low frequency. We've got these radio frequencies in here, and these are the frequencies we use for lots of different types of bands that we do use, like AM and FM stations, so we have a lot of different bands within there. We have these microwave ranges that we have in here; we call them microwaves. In fact, what's one of the things that we bombard our food with to heat our food up? That tells you that some of this in concentrated form may not be good. The exposure may not be good. Our cell phones use that. Our wireless uses that. So that's one reason why the 2.4 gigahertz range can interfere sometimes when you have microwaves going, because they operate on a similar frequency.

We have visible light right in here. When we were talking about the lasers and the different colors, shooting them down and then spreading them out on the other end, what that really is is those are different frequencies of these electromagnetic fields, these electromagnetic frequencies. If we can generate an electromagnetic field at a certain rate, at a certain frequency, it will let out that color of light, that light spectrum.

We've got infrared, which means below red. Infra is below, so below red, so it's below visible light. Our visible light range starts with red and goes all the way to violet at the end. And then we have ultraviolet. That means it's above; ultra is above, beyond. Ultraviolet would be the stuff that once again we actually don't see — your UV rays. We talk about our UV rays coming from the sun. That's ultraviolet rays coming from the sun. That's where we start getting into the dangerous and harmful area again. Then we have X-rays that we use for X-rays and can use for medical purposes. And then we have gamma rays, which are radioactive, or they're not ones that you want to be really exposed to. So here are some of those different frequencies and different things that we associate with those frequencies.

Licensed and Unlicensed Bands

Along with these bands — these radio frequencies, these microwave frequencies, and even down into these low frequencies — all of these we use a lot for communication, and there are certain bands that they have said you cannot use because we're using it for air traffic control or we're using it for military purposes. A lot of these frequencies they say that you aren't able to use, but then we have these little slim, narrow channels within here that we are allowed to use. For instance, the 2.4 GHz range, which would be somewhere right in here, is a range that you don't have to have licensing to use, which is why there's a lot of devices that will use that range. So some of those ranges in there is what we commonly use for these different devices, because it's an unlicensed band.

Sending Data on a Wave

If you couldn't tell, I find this stuff really fascinating. When we're sending data through frequencies, through these electromagnetic fields, what we're talking about is that to send data we either have to vary the frequency or the amplitude. We either have amplitude modulation, AM, or frequency modulation, FM. Those are the two ways that we transfer data back and forth. This is how we transfer data from one location to the next: we vary the amplitude or the frequency to get this data over to the other side.