Flow Rate, Waves, and Sound Types

• The aim of work is to explore flow rate measurement methods, and the relationship between pressure drop and:
  • Flow rate
  • Fluid velocity
  • Signal frequency of an ultrasound

Waves

• General types
  • Electromagnetic
  • Mechanical
• Electromagnetic waves
  • Examples include;
    • Radio Waves
    • Microwaves
    • Infrared
    • Visible Light
    • X-Ray
    • Ultraviolet
    • Gamma-ray
  • Do not require a medium
• Mechanical Waves
  • Require a medium
• Transverse Waves
  • Particles vibrate perpendicularly to the direction of wave propagation
• Longitudinal Waves
  • Particles vibrate parallel along to the direction of the wave propagation

Types of Sounds

• There are many different types of sounds;
  • Audible
  • Inaudible
  • Unpleasant
  • Pleasant
  • Soft
  • Loud
  • Noise
  • Music
• Infrasonic Waves (Infrasound)
  • Frequencies below 20 Hz
  • Inaudible for humans
  • Used to detect earthquakes and volcanic eruptions
  • Used to map rock and petroleum formations underground
  • Used to study activity in the human heart
• Human Audio Spectrum
  • Sounds such as a dog whistle, are inaudible because they are below the human hearing range
  • Normal range is 20 Hz to 20,000 Hz
• Ultrasonic Waves (Ultrasound)
  • Sound waves that have frequencies higher then 20,000 Hz
  • Occurs at frequencies outside human hearing range and is inaudible

Differences from the Ordinary Sound

• Ultrasound (US) is a form of mechanical energy propagating through collisions between adjacent molecules
  • It has compressions
  • It has rarefactions
• Ultrasound is a longitudinal wave
  • Has wavelength
    • The distance between two consecutive sound wave peaks
  • Has frequency
    • The number of sound wave cycles per second

Characteristics of Ultrasound Waves

• Sound waves, including ultrasound, are mechanical waves and require a medium for propagation
• Ultrasound is not audible, high frequencies above 20 kHz
• The wavelength of waves is inversely proportional to its frequency
  • Higher frequencies produce smaller wavelengths
• Shorter wavelengths provide better resolution for imaging small structures
• Longer wavelengths penetrate deeper into materials or tissues
• The speed of ultrasound waves depends on the medium through which they travel

Ultrasound vs Ultra-Sonography

• Ultrasound
  • Refers to the sound waves themselves, typically those with frequencies above the audible range for humans, greater than 20,000 Hz
• Ultra-Sonography
  • Refers to the technique or process of using ultrasound waves to create images of internal body structures

Production of Ultrasonic Wave

• The principle of ultrasonic generation is based on the piezoelectric effect
• Can use piezoelectric crystals;
  • Well defined arrangement, a crystal lattice
  • It is possible by applying an alternating potential to a crystal its molecules configuration changes
  • To produce an ultrasound wave by rapid periodic change of a crystal shape
• Applying an alternating voltage to a piezoelectric crystal causes the compressive and tensile stresses alternate permanently
• The oscillation of the crystal results in ultrasonic generation based on the piezoelectric effect
  • The piezoelectric effect is the generation of a voltage by mechanical deformation of certain materials, piezoelectric crystal examples
• The piezoelectric effect can also be reversed
  • When an external voltage is applied, the crystal is deformed
  • Depending on the polarity, the piezoelectric crystal is either compressed or stretched
  • This can convert electrical energy into mechanical energy

Ultrasound Interaction with the Body

• Acoustic impedance is the resistance experienced by the ultrasound beam as it passes through tissues; z = p X vs
• (Z) depends on:
  • p is the density of the medium (in kg/m3)
  • v is the speed of sound in the medium (in m/s)
• When the acoustic impedance (Z) of two materials (Z1 and Z2), are different, several key phenomena occur at the interface between media.
• When sound interfaces between materials:
  • Part is reflected back into the first medium, part is transmitted into the second medium
  • Amount of reflection and transmission, depends on the relative difference in acoustic impedance
  • Can be described by the reflection coefficient and the transmission coefficient
• Reflection Coefficient (R): R = (Z2-Z1 / Z2 + Z1) 2
  • Gives the proportion of the wave's intensity that is reflected back into the first medium
  • The larger the difference between Z1 and Z2, the greater then the reflection
• Transmission Coefficient (T): T = 1-R
  • Gives the proportion of the wave's intensity that is transmitted into the second medium

Acoustic Impedance with tissue

• If Z