Have you heard of brainwave entrainment for sleep? It is an innovative way to go to sleep. (It can do more than induce sleep but for now let's stick to sleep induction.) This article explains what it is all about.
Your brain uses electrical signals to communicate with all the systems in your body. The electrical pulses vary in the their rhythm depending on what you are doing. When you are wide awake your brain waves pulse faster than when you are relaxed.
The rate of these electrical pulses can be measured using an EEG (electroencephalograph) machine. They are called brainwaves because that is how they appear.
When we are alert and busy the activity in our brains is faster and the waves are closer together. When we are relaxed the wave pattern is much slower and when we first drop off to sleep it is slower still.
If, when you go to bed you are tense and anxious, or perhaps trying to solve the problems of the day, your brain waves will be running quite fast. The waves captured on an EEG will show waves that are close together and spiky. They are known as beta waves.