Principles of Underwater Acoustic Transducer Design (Part 7)

VOLUME 4, APRIL 2011

Principles of Underwater Acoustic Transducer Design (Part 7)

By : Mohd Ikhwan Hadi Yaacob (PhD Student)

Single Element Transducer Design

The simplest design of ultrasonic transducer is a single element piston-transducer as shown in Figure 1. Core component inside the transducer is the piezoelectric layer, sandwiched by top and bottom electrodes. Bottom part of the electrode piezoelectric layer contains conductive backing material. On top of the transducer, at least two or three matching layers are placed for two reasons; as acoustic impedance matching layer and to avoid ringing of the housing material that follows the vibration [1] of electroded piezo layer. Bottom and side parts of the transducer are covered with insulating epoxy. Whole transducer is then placed inside the housing. Several common materials for housing are brass, aluminum and nickel aluminum bronze. Top part of the transducer is finally covered with acoustic lens (Epoxy or parylene).

apr 2a
Figure 1: Cross section of single element acoustic transducer

Modern transducer usually comes with complementary processing electronics circuit, hidden inside the housing. Main concern regarding transmitting and receiving efficiencies of acoustics signal is on top of the transducer. According to Figure 1, acoustic waves need to pass through at least three layers of different materials (matching) before reaching or leaving piezo layer; which is the vital part where energy conversion occurs. Without matching layers, maximum power transfer seems to be impossible, and with several matching layers laid on top of the transducer, responses and sensitivity was reduced significantly. By using MEMS based transducer design, this problem can be rectified. Next issue will discuss detail design of single element micro-acoustic transducer.

References

[1] Diagnostic Ultrasound: Ultrasonic transducers & Array, Taylor & Francis 2006.