Monday, 21 March 2016

CONSTRUCTION OF 2D PROBES



The constructional details of all the modern ultrasound transducer can be explained using the following diagram.The basic component of a modern convex 2D ultrasound transducer is illustrated in below figure.


2D PROBE

The major parts of the transducer includes
  • Acoustic lens
  • Acoustic matching layer
  • Piezoelectric element
  • Backing material
  • Cable
  • connector

  1. Acoustic lens: Ultrasonic waves transmitted from the piezoelectric element are reflected off a target because there is a big difference in acoustic impedance between the piezoelectric element and the object. To avoid this phenomenon, an intermediate material is inserted between the two so that ultrasonic waves can efficiently enter the object. This is the role of the acoustic matching layer. This acoustic matching for less reflection of ultrasonic waves makes it possible to implement highly sensitive probes. The acoustic matching layer is designed to have adequate acoustic impedance value using a combination of different resin materials.
  2. Matching layer: Ultrasonic waves transmitted from the piezoelectric element are reflected off a target because there is a big difference in acoustic impedance between the piezoelectric element and the object. To avoid this phenomenon, an intermediate material is inserted between the two so that ultrasonic waves can efficiently enter the object. This is the role of the acoustic matching layer. This acoustic matching for less reflection of ultrasonic waves makes it possible to implement highly sensitive probes. The acoustic matching layer is designed to have adequate acoustic impedance value using a combination of different resin materials.
  3. Piezoelectric crystals: The piezoelectric element is an essential part of the probe to generate ultrasonic waves. On both sides of the piezoelectric element electrodes are affixed and a voltage is applied. The element then oscillates by repeatedly expanding and contracting, generating a sound wave. When the element is externally applied with vibration (or an ultrasonic wave) in turn, it generates a voltage. Among the several types of piezoelectric elements, piezoelectric ceramic (PZT: lead zirconate titanate) is most commonly used because of its high conversion efficiency.
  4. Backing material: The backing material is located behind the piezoelectric element to prevent excessive vibration. Reducing excessive vibration will cause the element to generate ultrasonic waves with a shorter pulse length, improving axial resolution in images.
  5. Cable: The Coaxial wires Carries power to excite the piezoelectric crystals. For each crystal there will be one cable.
  6. Connector: connect the probe with ultrasound machines. Contains electrical circuits with MUX and other interfacing ICs.

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