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Wavelength, Frequency, Period and Speed of Sound | Ultrasound Physics | Radiology Physics Course #2
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Wavelength, Frequency, Period and Speed of Sound | Ultrasound Physics | Radiology Physics Course #2

Understanding Sound: Wavelength, Frequency, and Speed

Introduction to Sound Parameters

  • The discussion begins with a recap of previous topics on sound, including comparisons to electromagnetic radiation and key parameters such as wavelength, frequency, and speed.
  • The focus shifts to exploring wavelength and frequency in depth, introducing the concept of the period.

Speed of Sound

  • The speed of sound is independent of frequency; it is determined by the material through which sound travels.
  • Key definitions are provided:
  • Wavelength: Distance between successive peaks in a wave.
  • Frequency: Number of cycles passing a point per unit time (measured in Hertz).

Understanding Period

  • Period (T) is introduced as the time taken for one cycle to pass a point; it is inversely related to frequency.
  • These parameters will be crucial for understanding concepts like attenuation and echo production in ultrasound imaging.

Relationship Between Speed, Frequency, and Wavelength

  • Unlike electromagnetic waves, sound speed varies with medium but frequency remains constant regardless of material changes.
  • A common misconception addressed: changing wavelength does not affect frequency; only speed may change based on medium properties.

Properties Affecting Speed of Sound

Elastic Properties

  • The first major property affecting sound speed is elasticity—how quickly materials return to their resting state after deformation. Stiffer materials allow faster sound travel.

Inertial Properties

  • The second property is inertia, represented by tissue density. Denser tissues require more force to move particles within them but do not necessarily lead to faster sound propagation.

Clarifying Misconceptions About Density

  • It’s clarified that while water has higher density than air, its elastic properties make it less compressible and thus allows faster sound travel compared to air.
  • An example contrasts dry air with humid air; despite humid air being denser, sound travels faster in dry air due to lower density.

Summary of Key Concepts

Bulk Modulus vs. Density

  • Bulk Modulus refers to tissue stiffness—the resistance against compression. Higher bulk modulus means faster sound travel through that tissue.
  • Conversely, greater density typically slows down sound transmission due to increased inertia among tightly packed particles.

Understanding Bulk Modulus and Its Impact on Sound Speed

The Relationship Between Ground Stiffness and Runner Speed

  • The concept of bulk modulus is likened to the ground a runner runs on; stiffer ground allows for faster running speeds at a constant frequency.
  • A runner's stride length increases when running on hard ground, resulting in longer wavelengths due to the higher stiffness of the surface.
  • Transitioning from hard ground to sand (less stiff) causes a decrease in speed, despite maintaining the same step frequency; this illustrates how compressibility affects performance.

Density's Effect on Running Speed

  • Air density impacts running speed; thinner air allows for faster movement, while denser mediums like syrup slow down the runner even if their step frequency remains unchanged.
  • As air density increases, the runner’s speed decreases significantly due to reduced stride length, paralleling how sound behaves in different media.

Sound Speed Variation with Material Properties

  • A graph illustrating various materials used in clinical imaging shows that sound speed varies based on material properties rather than just density alone.
  • While denser tissues generally have higher bulk moduli, it’s crucial to understand that bulk modulus and density are independent factors affecting sound speed.

Implications for Ultrasound Imaging

  • In ultrasound imaging, if all tissues had identical bulk moduli but varied densities, sound speed would decrease as density increased.
  • The process of creating ultrasound images involves sending pulses into tissue and waiting for echoes to return; understanding this mechanism is essential for future discussions.

Key Parameters in Ultrasound Imaging

  • The diagram introduced separates time parameters (above a certain line) from distance parameters (below), aiding clarity as more parameters are added.
  • Key concepts discussed include wavelength (distance of one cycle), frequency (number of cycles per time unit), period (time taken for one cycle), and speed (distance traveled over time).
Playlists: Ultrasound physics
Video description

Please note: I say speed of EM radiation doesn't change in different mediums. This is incorrect! However, in radiology physics we often assume the speed of electromagnetic radiation is constant despite minor material dependent speed changes, as these changes are imperceptible to our detector systems. Creating an ultrasound image relies heavily on accurately knowing the speed of sound; the production of radiographs and CT images do not rely on knowing the speed of electromagnetic radiation. Therefore, although not technically true, the comparison is often stated as electromagnetic radiation speed is constant and acoustic wave speed is variable (such as I've done in the video). *High yield radiology physics past paper questions with video answers* Perfect for testing yourself prior to your radiology physics exam 👇 ➡️ X-RAY, ULTRASOUND AND MRI BUNDLE (SAVE over 25%): https://www.radiologytuts.com/bundles/x-ray-ultrasound-and-mri-question-banks ➡️ X-RAY QUESTION BANK: https://www.radiologytuts.com/courses/xray-physics-question-bank ➡️ ULTRASOUND QUESTION BANK: https://www.radiologytuts.com/courses/ultrasound-physics-question-bank ➡️ MRI QUESTION BANK: https://www.radiologytuts.com/courses/mri-physics-question-bank ========================= *I have also created two RADIOPAEDIA LEARNING PATHWAYS* https://bit.ly/radiopaediaphysics (👈 25% OFF DISCOUNT LINK) WHAT’S INCLUDED? ✅This YouTube series Ad free ✅Constantly updated Radiopaedia articles ✅Summary slides ✅Key take home bullet points throughout ✅Multiple review quizzes ✅Short answer review questions ✅Official Radiopaedia course completion certificate 25% discount using this link: https://bit.ly/radiopaediaphysics ========================= In the last talk we mentioned that the speed of sound changes depending on the medium through which it is travelling. The frequency of that sound wave remains the same. Here we will look at the elastic and inertial properties of the medium that will determine the speed at which sound travels. ========================= SIGN UP TO MY MONTHLY EMAIL NEWSLETTER 👉 https://bit.ly/3ruLh3d *Not sure if the question banks are for you?* If you're here, you're likely studying for a radiology physics exam. I've spent the last few months collating past papers from multiple different countries selecting the most commonly asked questions. You'll be surprised how often questions repeat themselves! The types of questions asked in FRCR, RANZCR AIT, ARRT, FC Rad Diag (SA), ABR qualifying Core Physics and MICR part 1 are surprisingly similar and the key concepts remain the same throughout. I've taken the most high-yield questions and answered them in video format so that I can take you through why certain answers are correct and others are not. Happy studying, Michael #radiology #radres #FOAMrad #FOAMed