Waves, Sound & Units
(Chapters 1-3)
(Chapters 1-3)
This type of wave requires a medium to travel through and cannot propagate in a vacuum.
What is a mechanical wave? (or acoustic/longitudinal wave)
As sound travels through soft tissue, its intensity and amplitude decrease. This overall weakening of the sound beam is known by this 11-letter word.
What is attenuation?
The percentage or fraction of time that the ultrasound system is actively transmitting a pulse.
What is the Duty Factor?
Piezoelectric materials convert electrical energy into mechanical energy and vice versa. The most common synthetic material used in modern transducers is known by these three letters.
What is PZT (Lead Zirconate Titanate)?
Axial resolution measures the system's ability to display two structures close together parallel to the sound beam. It can be remembered using the acronym LARRD; name two of the words in LARRD.
What are Longitudinal, Axial, Range, Radial, and Depth?
Sound waves are composed of alternating regions of high pressure and density called this, and low pressure and density called this.
What are compressions and rarefactions?
The average speed of sound in soft tissue is accepted as this value in meters per second.
What is 1,540 m/s?
For reflection to occur at a boundary between two media, the media must have different values of this acoustic property.
What is acoustic impedance?
The primary purpose of the matching layer is to bridge the huge gap in this acoustic property between the PZT crystal and human skin.
What is acoustic impedance?
Unlike axial resolution, lateral resolution varies with depth because the beam width changes. It can be remembered using the acronym LATA; name two of these words.
What are Lateral, Azimuthal, Transverse, and Angular?
Frequency and period are inversely related; if a wave's frequency is doubled, its period does this.
What is halved (or cut in half)?
Attenuation in soft tissue is determined primarily by these two sound beam characteristics.
What are distance (path length) and frequency?
This law mathematically describes the angle of refraction when a sound wave strikes an interface at an oblique angle with different propagation speeds.
What is Snell's Law?
The region of a sound beam from the transducer face to the narrowest point (focus) is called the Near Zone, or by this scientist's name.
What is the Fresnel zone?
In phased array transducers, electronic steering and focusing are accomplished by introducing tiny time delays between electronic pulses called this.
What are phase delays (or delay curves/time delays)?
Metric prefix practice: This term represents 10-6 or one-millionth, commonly paired with seconds to measure pulse duration.
What is micro-?
If an amplifier increases a signal's power by a factor of 100, the gain in decibels is this value.
What is +20 dB?
(Every 10 dB is a 10-fold increase; 10 x 10 = 100, so 10 dB + 10 dB = 20 dB)
Using the 13-microsecond rule: If an echo returns to the transducer in 39 microseconds, the reflector is located at this depth.
What is 3 cm?
39 microseconds / 13 microseconds/cm = 3/cm
For an unfocused single-crystal transducer, the diameter of the sound beam at the focal point is equal to this proportion of the crystal's diameter.
What is one-half (1/2)?
Linear phased array transducers produce a sector-shaped image, whereas linear sequential array transducers produce an image with this shape.
What is a rectangular shape?
The three acoustic variables used to identify sound waves from other types of waves.
What are Pressure, Density, and Distance?
This specific physical property of a medium—defined as its resistance to compression—has the greatest influence on propagation speed.
What is stiffness (or bulk modulus)?
Rayleigh scattering occurs when a reflector's dimensions are much smaller than the wavelength, causing sound to scatter equally in all directions. Rayleigh scattering is proportional to frequency raised to this power.
What is the fourth power?
Heating a PZT crystal above this critical temperature causes it to lose its piezoelectric properties permanently.
What is the Curie point (or Curie temperature)?
Grating lobes are off-axis sound energy artifacts produced by array transducers. Transducer manufacturers reduce them using this technique of dividing each PZT element into smaller sub-elements.
What is subdicing? (Apodization is also acceptable for altering voltage amplitudes to reduce lobes).