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A transducer is an electronic device that converts energy from one form to another. The transducer has two primary functions during transmission and reception. During transmission, the transducer is responsible for converting electrical energy into sound. During reception, the transducer is responsible for converting reflected sound pulses into electricity.

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1. Mechanical Transducers

2. Linear Phased Array Transducers

3. Annular Phased Array Transducers

4. Linear Sequential Transducers

5. Convex/Curvilinear Transducers

6. Vector Transducers

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Mechanical transducers convert physical quantities into mechanical outputs or vice versa. It contains a single, circular, disc-shaped active element that is physically moved. This movement creates a scan plane.

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The image created by a mechanical transducer is fan or sector-shaped. 

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The two-dimensional image is built up by rotating the crystal with a motor. Sound beams are emitted as the crystal moves, otherwise known as mechanical steering.

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Mechanical transducers have a fixed focal depth, this is called Conventional Mechanical, or Fixed Focusing.

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There are two methods of fixed focusing: Internal and External Focusing.

Internal - with the use of a curved active element

External - with the use of an acoustic lens

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Mechanical transducers have only a single crystal, therefore the entire image is lost when the crystal malfunctions.

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What is a Linear Phased Array Transducer?

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What is a Linear Phased Array Transducer?

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The linear phased array transducer is rather compact with a small square about 1 centimeter on each side that comes into contact with the skin. It has no moving parts, and the beam is steered and focused using an electrical technique called phasing.

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The footprint of a phased array probe is small, however, as many as 100 to 300 elements are arranged along the face of the probe. Placed compactly side-by-side, each element is rectangular and narrow. The width of each element is 1/4 to 1/2 of the sound's wavelength.

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The image created by a phased array transducer is fan or sector-shaped, similar to that produced by the mechanical transducer.

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This type of transducer utilizes electronic steering, which is also known as phasing.

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Linear phased array transducer's sound beams are focused electronically. This specific transducer has a phased array system with controls that allows the sonographer to modify the depth and amount of focusing of the sound beam.

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The damage to the crystal in this specific transducer results in inconsistent or erratic beam steering and focusing.

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The annular phased array transducer is composed of multiple ring-shaped elements with a common center.

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Annular phased array transducer utilizes mechanical steering to create a 2-D image.

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This type of transducer has the capability of multi-focusing with a primary advantage of multiple transmit focal zones that create each scan line of the image.

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Since the transducer utilizes mechanical steering, the image is fan or sector-shaped.

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Due to the way the transducer is composed, one section of the image will be lost when one crystal is damaged. This is known as horizontal dropout.

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What is a Linear Sequential Array Transducer?

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What is a Linear Sequential Array Transducer?

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This type of transducer utilizes 120 to 250 rectangular-shaped strips of material that are arranged in a line.

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The active elements in linear sequential arrays are much larger than those found in linear phased arrays. Each crystal is 1 wavelength in width. The array is large, up to 10 cm long.

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With this type of transducer, a small group of the crystals are fired at the same time to create each individual sound beam. Sound beams are parallel to one another.

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In earlier models, linear sequential arrays utilized fixed focusing, making it not adjustable by the sonographer.

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Beam Focusing: The New & Improved Models 

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Beam Focusing: The New & Improved Models 

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In modern linear sequential arrays, focusing is achieved electronically. They perform both transmit and receive focusing using electronic phase delays.

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Image shaped for the linear sequential array transducer is a rectangular image as shown in the picture above.

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Due to the way the transducers in composed when one of the elements is damage only one portion of the image will be lost. Since the elements are parallel, the loss results in vertical dropout from the top to the bottom of the image.

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A convex array is made up of 120 to 250 rectangular-shaped strips of piezoelectric material placed onto a bowed line side-by-side.

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In some of the convex sequential arrays, the crystals are fired at the same time to create a sound beam, as shown in the picture above.

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The modern convex transducers utilize electronic focusing and dynamic receive focusing.

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As shown in the picture above, the image shape for this transducer is a blunted sector-shape.

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Similar to linear sequential array transducers, convex arrays result in one portion of the of the image to be lost due to the way they are composed. It resembles the image above, with a portion of the image lost from the top of screen to the bottom, otherwise known as vertical dropout.

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Vector array transducers combine linear, sequential, and linear phased array transducers. They are composed of 120 to 250 rectangular-shaped strips of PZT side-by-side.

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Similar to linear and phased array transducers, some of these transducers fire their crystals simultaneously to create a sound beam.

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Vector array transducers utilize electronic focusing.

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The image produced from these transducers is a trapezoidal shape, as pictured above.

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Edelman, S. K. (2012). Understanding Ultrasound Physics (4th ed.). Esp.

LBN Medical. (2019, May 13). Ultrasound Transducer Types (Updated 2019) - LBN Medical. LBN Medical. https://lbnmedical.com/ultrasound-transducer-types/

Transducers (2 of 2). (n.d.). E-Echocardiography.com. https://e-echocardiography.com/page/page.php?UID=1429454172