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Basic operation
An acoustic wave sensor uses mechanical (acoustic) waves to sense multiple phenomena from the device's environment, which are registered as changes in the wave's phase, amplitude, and/or frequency relative to some reference. For surface acoustic wave (SAW) sensors, the device operation itself is fairly simple:
- An electromagnetic impulse signal is sent to the device via wired connection or wireless antenna
- An input interdigital transducer (IDT) transduces the The electromagnetic signal is transduced into a surface acoustic wave by an interdigital transducer (IDT)
- The surface acoustic wave propagates along the delay line and is affected by its environment along the waysurface of the substrate
- The An output IDT transduces the acoustic impulse response wave is transduced back into an electromagnetic signal
- The electromagnetic response signal is transmitted for processing
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Figure 1: Overview of surface acoustic wave sensor operation. Graphics edited from source7.
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The electromagnetic response is then analyzed to determine what changes the acoustic wave underwent during its propagation. These changes in compare its frequency, phase, and amplitude can in turn be used to determine the to some reference. Based on this comparison, certain properties of the environment through which the acoustic wave traveled when compared to some referencedevice's environment may be deduced, such as temperature, strain, pressure, force, and mass.
SAW sensors may also include a filtering element as a first step to sensing, for example, a particular chemical or biological compound. The acoustic wave sensor in this case is not directly sensing the compound, but instead sensing the response of the filtering element to the presence of the compound.
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The one-port resonator configuration includes only one IDT element for transducing both impulse and response signals. In these devices, the area of propagation leads to a reflector element, which reflects the acoustic wave back into the same IDT that produced it. The slow propagation speed of the mechanical wave (compared to the electromagnetic impulse) along the delay line allows sufficient time for a short the electromagnetic impulse input to dissipate to be completely transduced (or dissipated) before the reflected acoustic response is captured by the single IDT.
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