Acoustic-wave based sensor technology has matured allowing for so far impossible applications and replacing existing solutions for higher customer value

Technology Introduction:

• SAW-based sensors exploit Surface Acoustic Waves (SAW) or Bulk Acoustic Waves (BAW) depending on application requirements.
  
  
• SAW-based sensors are built on single-crystal piezoelectric materials like Quartz (SiO2), Lithium Niobate (LiNbO3), Lithium Tantalite (LiTaO3), Langasite and AlN or ZnO/Silicon compounds. In the case of single crystals, different cut-angles produce largely different results.
  
  
• Reverse piezoelectricity induces a mechanical strain (e.g. a surface acoustic wave) on the substrate due to an electrical field generated at the electrodes of the sensor, whereas the direct effect allows for an electrical detection of acoustic wave propagation under the electrodes.
  
  
• The velocity of a surface acoustic wave is very sensitive to surface state. Under the effect of the physical parameter which is sensed, the velocity or the delay length is modified. We can measure: 1. the delay or corresponding phase; 2. the attenuation; 3. the frequency of the sensor’s electrical response.
  
  
• In order to compensate for unwanted effects due to other physical parameter variations an independent reference sensor can be implemented on the same chip in order to benefit from a differential measurement. Also an adequate choice of crystal cut enables one to significantly minimize unwanted sensitivities.
  
  

  The design of the sensor needs to be adapted for each application by selecting the appropriate design alternative: - Wave type: Rayleigh waves, Love waves, Transverse waves, - Choice of the structure: delay lines, resonators, - Choice of the material (high coupling, high velocity, temperature compensation, high quality factor of the resonance, etc.) - Choice of the frequency: from 30MHz up to 2,45GHz and more

One of the outstanding values of AW-sensing is that it allows to create wireless sensors which require no local energy source !

This works as follows:

An electromagnetic wave is sent by an Interrogator and converted into a mechanical wave on the surface of the acoustic wave chip via a so-called IDT structure connected to an antenna. This mechanical wave travels along the surface of the AW-chip, is reflected and resent to the interrogator. - which allows to measure physical phenomena. The big advantage as compared with a passive RFID system is that an AW-based system allows a much farther wireless distance (up to several meters, depending on the frequency operating range).

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