Ultrasound Transducers Lecture Review

Comprehensive vocabulary flashcards covering ultrasound transducer construction, physics principles, beam anatomy, and various array types based on lecture Page 1 through Page 55.

Transducer

A device that converts one form of energy to another (e.g., electricity to ultrasound energy).

Piezoelectric Element

Also called the ceramic, active element, or crystal, it is typically $\frac{1}{2}$ a wavelength thick and has an average propagation speed of $4-6\,mm/ms$.

Curie Point

The temperature ($360^{\circ}C$ or $680^{\circ}F$) at which PZT is polarized; heating above this point causes depolarization and loss of piezoelectricity.

Piezoelectric Principle/Effect

The property of certain materials to create a voltage when mechanically deformed by pressure.

Reverse Piezoelectric Effect

The phenomenon where piezoelectric materials deform or change shape when a voltage is applied to them.

Transducer Case

Protects internal components and insulates the patient from shock, often lined with metal to reduce electrical interference and rubber/cork to reduce vibrations.

Matching Layer

A component that is one-quarter ($\frac{1}{4}$) a wavelength thick used to increase the efficiency of sound transmission between the active element and the body by reducing reflection.

Damping Element (Backing Material)

Commonly made of epoxy resin with tungsten, it limits the ringing of the pulse to shorten Spatial Pulse Length (SPL) and Pulse Duration (PD), thereby improving axial resolution.

Bandwidth

The useful range of frequencies in a pulse between the highest and lowest frequency emitted ($\text{Bandwidth} = \text{Max Frequency} - \text{Minimum Frequency}$).

Quality Factor (Q-Factor)

A unitless number representing the extent of damping, calculated as $\text{Q Factor} = \frac{\text{resonant frequency (MHz)}}{\text{Bandwidth (MHz)}}$.

PW Frequency Formula

$\text{PW Frequency (MHz)} = \frac{\text{materials propagation speed (mm/us)}}{2 \times \text{thickness (mm)}}$.

Focus (Focal Point)

The location where the sound beam is at its narrowest or minimum diameter, providing the best image resolution.

Near Zone (Fresnel Zone)

The region extending from the transducer to the minimum beam width where sound beams converge.

Far Zone (Fraunhofer Zone)

The region deeper than the focus where the sound beam diverges and the beam width increases with distance.

Near Zone Length (Focal Depth) Formula

$\text{Focal Length (cm)} = \frac{(\text{transducer diameter})^2 \times \text{frequency}}{6}$.

Sound Beam Divergence Formula

$\sin(\text{divergence angle}) = \frac{1.85}{\text{Diameter(mm)} \times \text{frequency(MHz)}}$.

Huygen’s Principle

Explains the hourglass shape of the beam; a large active element is viewed as millions of tiny sources creating V-shaped wavelets that interfere constructively.

Mechanical Transducer

Features one disc-shaped active element with a fixed focus depth and mechanical steering; a defective crystal destroys the whole image.

Linear Phased Array

Uses rectangular elements ($\frac{1}{4}$ wavelength wide) with electronic steering and focusing; produces a rectangular or parallelogram image.

Dynamic Receive Focusing

A non-adjustable focusing technique occurring during reception in array-based systems where time delays are applied to elements to improve lateral resolution.

Annular Phased Array

Elements are arranged as concentric rings (bullseye); features mechanical steering and electronic multi-focusing, with defective crystals causing a horizontal band of dropout.

Linear Sequenced (Switched) Array

Large transducer with approximately 200 side-by-side elements generating a rectangular image; defective crystals cause a vertical band of dropout.

Vector Array

A transducer with 120-250 crystals that combines linear sequential and phased array techniques to create a trapezoidal (flat-top sector) image.

Pedof or Pencil Probe

A single crystal transducer cut in two for CW Doppler; it lacks imaging capabilities but is extremely sensitive.

Therapeutic Transducers

Transducers used in physical therapy that lack damping material, have high Q-factor, and utilize thermal absorption/cavitation for healing.

1.5 Dimensional Array

A transducer with elements etched parallel to the long axis to allow for multiple elements in the short axis, enabling variable elevation focus.

Two-Dimensional Array

Features thousands of elements in a checkerboard pattern for real-time 3D (4D) imaging and electronic steering/focusing in both lateral and thick planes.