Piezo Ceramics in medical devices

Written by: PI (Physik Instrumente) Ltd | Published:

High quality piezo ceramic components with exceptional batch to batch consistency are required in medical applications involving ultrasound. PI Ceramic GmbH has provided piezo products into this demanding market for a number of years. The company's experience includes working on the specification and application of piezo ceramics to atomise liquids, a critical part of a nebuliser. PI Ceramic's expertise includes advising on the control of frequency to optimise the size of the droplets and minimise the power consumption and on ensuring that the mounting and packaging of the piezo element promotes long lifetime.

Ultrasound makes it possible to atomise liquids without increasing the fluid pressure or temperature. This fact is of critical importance where sensitive substances such as drugs are involved. Two aerosol generation processes are used at present.

As with high-frequency ultrasonic cleaning (MHz range), a piezo ceramic disk is fixed to the bottom of a liquid container and is vibrating at resonance. The disc generates high-intensity ultrasonic waves in the fluid and this in turn creates capillary waves on the surface. These waves disturb the surface and stimulate minute droplets to "break off" from the liquid so generating the aerosol.

With direct nebulization, the piezo element vibrating at high frequency (1 to 3 MHz) is in direct contact with the liquid. A special surface finish on the ceramic is typically used to protect it against any aggressive substance. The ultrasonic waves propagating in the medium reach their maximum intensity at a specific height in the liquid, at which point droplets break off.

In both processes, the diameter of the aerosol droplets is determined by the frequency of the ultrasonic waves. The higher the frequency, the smaller are the droplets.

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