The ultrasonic probe consists of a piezoelectric element, backing material, an acoustic matching layer and an acoustic lens. The following describes the components and their functions of the convex type probe as an example:
NDK, as a crystal device manufacturer, applies its proprietary technologies to the probe manufacturing processes, such as micromachining of piezoelectric elements and bonding of acoustic matching layers.
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 viblation (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.
The piezoelectric element is divided into strip sections, which are each affixed with electrodes.
Each strip section of the piezoelectric element has a width about a half of that of a piece of hair. The process to cut the element into sections in micron order and affix them is based on the advanced technology of NDK.
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.
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 impeadance value using a combination of different resin materials.
The acoustic lens is a gray colored part looking like rubber attached to the tip of the probe. Ultrasonic waves transmitted from the probe would spread and travel like light. The acoustic lens prevents the ultrasonic waves from spreading and focuses them in the slice direction to improve the resolution.
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