1. Echoes

2. Reflection  The reflection of sound waves applies to frequencies above human hearing. 20 kHz is human maximum20 kHz is human maximum Bats can reach 100 kHzBats can reach 100 kHz 3.5 to 7 MHz are ultrasonic frequencies3.5 to 7 MHz are ultrasonic frequencies  Ultrasonic waves are short and make clean reflections.

3. Smile  Autofocus cameras use ultrasonic waves. A subject 2 m away Distance is 4 m Time = 4 m / (340 m/s)  Camera measures 12 ms.

4. Medical Ultrasound  Ultrasound transmits well though fluids.  It’s reflected from bone and firm tissues.  The transducer receives the echo and translates the time to depth.

5. Multiple Images  Each measurement reads a single line.  Multiple signals get a complete picture.

6. Sonogram  Each separate echo is a single dot.  The multiple signal traces provide additional dots.  Our brain (or a computer) connects the dots to get the image.