49. Ultrasound

1. How Ultrasound Works

• Partial Reflection: When ultrasound waves reach a boundary between two different mediums (e.g., air and water), some waves are reflected and some are transmitted (and refracted).

• Internal Imaging: By measuring the time it takes for these reflections to return to a detector, we can calculate the distance to each boundary. This allows us to map the internal structure of an object.

• Safety: Unlike X-rays, ultrasound is non-ionizing and completely safe, making it ideal for medical use.

2. Key Uses of Ultrasound

Prenatal Scanning

• Process: A device transmits ultrasound into the body. Waves reflect every time they hit a boundary, such as between the surrounding fluid and the fetus.

• Result: A computer processes the timing of these echoes to create a live image, allowing doctors to check the health and development of the fetus.

Industrial Imaging

• Process: Ultrasound is fired through solid materials (like metal pipes).

• Fault Detection: In a solid object, waves should only reflect at the far edge. If a reflection is detected earlier, it indicates an internal crack or flaw in the material.

Sonar (Echo Sounding)

• Process: Boats and submarines fire ultrasound pulses at the sea floor or underwater objects.

• Calculation: Used to determine depth or locate objects like shipwrecks or schools of fish.

3. Example Calculation: Sonar Distance

To find the distance of an object using sonar, use the formula:

$\text{Distance} = \text{Speed} \times \text{Time}$

Crucial Step: Because the sound travels to the object and back, the calculated distance must be divided by 2 to find the distance to the object.

Example:

• Speed of sound in water: 1,400 m/s

• Time for echo to return: 6 seconds

• Total distance traveled: $1,400 × 6 = 8,400 meters

• Distance to sea floor: $8,400 / 2 = 4,200 meters

4. Summary Table