SAW Technology

Glossary

Basics on SAW How it works Features & Benefits Glossary

Acoustic wave sensing key words 

Piezoelectricity: the charge which accumulates in certain solid materials like crystals or ceramics in response to applied mechanical strain, result of piezoelectric effect.

Piezoelectric effect: linear electromechanical interaction between the mechanical and the electrical state in crystalline materials with no inversion symmetry

Direct piezoelectric effect: internal generation of electrical charge resulting from an applied mechanical force

Inverse or reverse piezoelectric effect: internal generation of a mechanical force resulting from an applied electrical field

RF Radio frequency: a rate of oscillation in the range of about 30 kHz to 300 GHz, which corresponds to the frequency of electrical signals normally used to produce and detect radio waves.
 
Radio waves: a type of electromagnetic radiation with wavelengths in the electromagnetic spectrum longer than infrared light. Like all other electromagnetic waves, they travel at the speed of light. Naturally-occurring radio waves are made by lightning, or by astronomical objects. Artificially-generated radio waves are used for fixed and mobile radio communication, broadcasting, radar and other navigation systems, satellite communication, computer networks and innumerable other applications like SAW sensing.

SAW Surface Acoustic Waves: acoustic waves propagating on the surface of a material (like piezoelectric material) exhibiting elasticity, with amplitude that typically decays exponentially with depth into the substrate.

BAW Bulk Acoustic Waves: acoustic waves propagating through the piezoelectric material.

Wafer: thin slice of semiconductor material, such as a silicon crystal, used in the fabrication of integrated circuits and other microdevices like sensor chips.

Photolithography: process used in microfabrication to selectively remove parts of a thin film or the bulk of a substrate like a crystal wafer. It uses light to transfer a geometric pattern from a photo mask to a light-sensitive chemical photo resist, or simply "resist," on the substrate. A series of chemical treatments then engraves the exposure pattern into the material underneath the photo resist.

IDT Inter Digital Transducer: device which consists of two interlocking comb-shaped metallic coatings applied to a piezoelectric substrate. IDTs are primarily used to convert microwaves to surface acoustic waves (SAW).

Sensor chip: die using a piezoelectric substrate incorporating SAW devices such as resonators or delay lines used to convert changes of physical parameters such as mechanical stress or temperature into electrical signals.

SAW Resonator: SAW device based on piezoelectric material on which is deposited at least one  Inter Digital Transducer (IDT) surrounded by a sufficient number of reflectors in order to create a resonant cavity.

1 port SAW delay line: SAW device based on piezoelectric material on which are deposited one IDT  (input/output transducer) and reflectors or other IDTs separated by certain distances from the input/output transducer in order to generate different delayed signals.

2 port SAW delay line: SAW device based on piezoelectric material on which are deposited two  IDTs (input and output transducers) separated by a certain distance which generates a delayed signal due to propagation time between the two transducers.

Differential structure: addition of a reference SAW device on a sensor chip, to provide a differential measurement that compensates for unwanted effects due to other physical parameter variations. For example, a differential temperature sensor uses two resonators operating at two different frequencies. Frequency difference (being furthermore less sensitive to ageing) is considered as input data for temperature computation.

Package: material/components assembly where the sensor chip is incorporated for protection and easy mounting in sensing systems. Example: ceramic package, metallic package, all quartz package.

Mounting: assembly of packaged sensor chip on material/components allowing antenna connection and fixing for industrial use. Example: thermowell or PCB

Partial contribution from en.wikipedia.org