Construction of an Ultrasonic Probe

An ultrasonic probe (transducer) converts electrical energy into ultrasound and returning ultrasound echoes back into electrical signals.

Basic Construction

        Probe Face
   ┌──────────────────┐
   │ Acoustic Lens    │
   ├──────────────────┤
   │ Matching Layer   │
   ├──────────────────┤
   │ Piezoelectric    │
   │ Crystal / Array  │
   ├──────────────────┤
   │ Backing / Damping│
   ├──────────────────┤
   │ Electrodes       │
   └────────┬─────────┘
            │ Cable

Main Components

1. Piezoelectric Element

Usually made from a piezoelectric ceramic or other piezoelectric material. It converts electrical pulses into mechanical vibrations and converts returning echoes back into electrical signals.

2. Electrodes

Electrodes apply the excitation voltage and collect the electrical signal generated by received echoes.

3. Matching Layer

The acoustic impedance of the piezoelectric element is much higher than that of soft tissue. A matching layer reduces acoustic reflection at the probe-tissue interface and improves energy transmission.

4. Backing/Damping Material

The backing absorbs backward-directed acoustic energy and shortens the pulse duration. This improves axial resolution and controls ringing.

5. Acoustic Lens

The lens focuses the ultrasound beam and protects the probe face.

6. Housing and Cable

The housing mechanically supports the components, while the cable carries electrical excitation and received signals to the ultrasound system.

Working

1. The scanner applies a short electrical pulse to the piezoelectric element.
2. The element expands and contracts because of the piezoelectric effect, producing ultrasound.
3. The acoustic lens/matching layers transmit the sound efficiently into tissue.
4. Echoes return from tissue boundaries.
5. The piezoelectric element converts the echoes into electrical signals.
6. The scanner amplifies and processes these signals to form the image.

Array Probes

Modern probes often contain many small elements. Electronic beam steering and focusing can produce rapid scanning without mechanically moving the probe.

Conclusion

The probe's piezoelectric element, electrodes, matching layer, backing material, acoustic lens and housing work together to transmit and receive diagnostic ultrasound.