Summary
Ultrasound is produced using the piezoelectric effect, where certain materials convert mechanical energy into electrical energy. It is used in medical imaging to create images of tissues and organs by sending sound waves into the body and analyzing the echoes.
- Piezoelectric Effect — Certain materials convert mechanical energy to electrical energy. Example: Quartz crystals generate voltage when deformed.
- Ultrasound — Sound waves beyond human hearing, used in medical imaging. Example: Frequencies above 20 kHz are used to create detailed images.
- Specific Acoustic Impedance — Product of ultrasound speed and material density, measuring resistance to ultrasound. Example: Higher impedance means more reflection at boundaries.
- Intensity Reflection Coefficient (α) — Ratio of reflected wave's intensity to incident wave. Example: Large impedance difference results in higher reflection.
- Attenuation — Reduction in ultrasound energy due to absorption in a medium. Example: 0.5 dB/cm is lost per MHz increase in frequency.
Exam Tips
Key Definitions to Remember
- Piezoelectric Effect: Conversion of mechanical energy to electrical energy.
- Ultrasound: Sound waves with frequencies above 20 kHz.
- Specific Acoustic Impedance: Resistance to ultrasound beam passage.
- Intensity Reflection Coefficient: Ratio of reflected to incident wave intensity.
- Attenuation: Reduction in ultrasound energy due to absorption.
Common Confusions
- Confusing ultrasound frequency with intensity.
- Misunderstanding impedance matching and its role in reducing reflection.
Typical Exam Questions
- What is the piezoelectric effect? It is the conversion of mechanical energy into electrical energy by certain materials.
- How does ultrasound create images? By sending sound waves into the body and analyzing the returning echoes.
- What affects the intensity reflection coefficient? The difference in acoustic impedance between two media.
What Examiners Usually Test
- Understanding of how piezoelectric transducers work.
- Ability to explain the role of acoustic impedance in ultrasound.
- Calculation of intensity reflection coefficients.