Ultrasound is sound waves with frequencies above the human hearing range (above 20 kHz). Think of it as a super‑fast whisper that can travel through solids, liquids, and gases.
When an electric field is applied across a piezo‑electric crystal, its internal lattice distorts, causing the crystal to change shape. Conversely, when the crystal is mechanically deformed, it generates an electric voltage.
Analogy: Imagine a rubber band that stretches when you pull on it. If the band is made of a special material, pulling it will also create a tiny electric charge.
The crystal is connected to an alternating voltage source. As the voltage oscillates, the crystal vibrates at the same frequency, producing sound waves.
Tip: The frequency of the ultrasound is set by the driving voltage, not by the crystal itself.
When ultrasound waves hit the crystal, they cause it to deform. This deformation induces a voltage across the crystal:
\$V_{\text{induced}} = d \cdot F\$
where \$d\$ is the piezoelectric coefficient and \$F\$ is the applied force from the sound wave.
Analogy: Think of the crystal as a tiny microphone that turns vibrations into electrical signals.
Ultrasound waves create images of internal organs. The reflected waves are detected by the same piezo‑crystal transducer.
Ultrasound checks for cracks or defects in materials by measuring reflected wave patterns.
Used in parking sensors to detect obstacles by sending and receiving ultrasonic pulses.
“Explain how a piezo‑electric crystal can be used to both generate and detect ultrasound waves. Include a diagram of the process (you can describe it in words).”
Answer tip: Describe the crystal as a transducer, mention the alternating voltage, the resulting vibration, the propagation of sound, and the induced voltage from reflected waves.