Surface Acoustic Waves

1. 02.09.2020

2.  SAWs were first explained in 1885 by Lord Rayleigh,
who described the surface acoustic mode of
propagation and predicted its properties.
 Named after their discoverer, Rayleigh waves have a
longitudinal and a vertical shear component that can
couple with any media in contact with the surface.
 This coupling strongly affects the amplitude and
velocity of the wave.

3.  A surface acoustic wave (SAW) is an
acoustic wave traveling along the surface of
a material exhibiting elasticity, with an
amplitude that typically decays
exponentially with depth into the material.
 Type of mechanical wave motion travels
along the surface of the solid material.
 Frequency of SAW
 F=V/λ
 V= Velocity of SAW
 λ= Wavelength.

4.  Based on Piezoelectric Effect
(Piezoelectric Effect is the ability of certain
materials to generate an electric charge in
response to applied mechanical stress)
 Based on Acoustic Wave( type of Longitudinal
Waves that Propagated by means of Adiabatic
compression and decompression).

5. For applications in electronics, the
piezoelectric effect is used to convert
electrical energy into acoustic wave
energy and vice versa.
Information carried by the surface
acoustic waves along the surface of a
crystal substrate may be processed
during propagation.

7. The IDT comprises two
sets of interpenetrating
metallic electrodes
fabricated photo
lithographically on the
surface of a
piezoelectric substrate.
A typical SAW device
contains two such IDTs,
one as input transducer,
the other as output
transducer to convert
the SAW back to the
electrical domain, e.g.
delay or filtering.

9. QUARTZ
LiNbO3
LiTaO3

10.  Ideally one wants zero temperature
coefficient of delay and high piezo
electric coupling from SAW devices.
 QUARTZ has zero temperature
coefficient of delay and its cost is low,
its coupling is very low.

11.  Delay lines and Memories
 Frequency Filters
 Surface Acoustic Wave Resonators
 Narrow Band Filters Employing SAW
Resonators
 Oscillators
 Saw Pressure and Temperature Sensors