Sound is vibration. When something vibrates, it pushes the air around it in waves. Those waves carry energy to your ears, and your brain hears them as sound.
Two things change how a sound wave looks and sounds: how tall the wave is, and how fast it repeats.
Sound Lab
Tap to start
Amplitude = Volume. Drag up and down to change it.
Nice. You just controlled amplitude: the height of the wave determines how loud the sound is. Now explore how frequency changes the pitch.
Both together now. Amplitude controls volume. Frequency controls pitch. In the combined view you can change both at once.
In Ultrasound
Ultrasound machines use the same wave properties you just explored. The transducer sends sound waves into the body and listens for the echoes. The machine controls amplitude and frequency to build an image.
Amplitude▸
Definition: The height of the wave from the center line to its peak.
In ultrasound: Amplitude relates to the strength of the signal. A stronger pulse (higher amplitude) travels deeper into the body but uses more energy. A weaker pulse (lower amplitude) does not penetrate as far.
Frequency▸
Definition:How many times the wave repeats per second, measured in Hertz (Hz).
In ultrasound: Higher frequency transducers produce sharper images but do not penetrate as deep. Lower frequency transducers penetrate deeper but with less detail. Choosing the right frequency is one of the first decisions a sonographer makes.
Wavelength▸
Definition: The distance from one wave peak to the next. How long one cycle is in space.
In ultrasound: Wavelength determines the smallest detail the machine can resolve. Shorter wavelength means finer detail. Wavelength and frequency are inversely related: when one goes up, the other comes down.
Period▸
Definition:How long it takes for one complete cycle to occur, measured in time.
In ultrasound: Period is the reciprocal of frequency. If frequency is high (many cycles per second), each cycle must be short (small period). You will see this relationship again on the Reciprocals card.
These terms will come back throughout every chapter. Right now, the key idea: amplitude and frequency are the two properties you control to shape the image.
Quick Check
Amplitude controls which quality of sound?
When you increase frequency, the wave cycles become:
In ultrasound, a higher frequency transducer produces: