An improvement to surface acoustic wave (SAW) sensor devices by Center for Nanoscale Materials users from the University of South Florida, working with the CNM Theory & Modeling Group, has significantly reduced energy losses by up to 50 percent. Zinc oxide filled microcavities were designed to trap energy near the SAW surface that otherwise would be lost to bulk waves.
SAW sensors detect frequency changes in waves that propagate through their crystalline structure. This makes them ideal for detecting the presence of chemicals or biomarkers present in a liquid or gas. The initial wave is created by the piezoelectric effect, in which an initial electric signal is converted into a mechanical displacement. This displacement takes the form of a wave transmitted through the crystal.
In the SAW sensor, the signal wave travels from the input transducer through the material to an output transducer, where it is converted back into an electrical signal. The wave’s frequency is determined by the velocity of sound through the material. The usefulness of these devices as sensors comes from their ability to detect frequency, or pitch, changes in the waves as they propagate. The pitch changes are caused by changes in the density of the crystalline medium, which result from bonding of chemicals to receptors on the crystal or of proteins to antigens.
First-generation SAW sensors lost much of the input signal due to properties of the crystal lattice. By adding the zinc oxide filled microcavities, power consumption was reduced by up to 50 percent while simultaneously improving their sensitivity.
One of the benefits of this sensor design is they potentially could be made battery-operated and portable. To do so, however, requires reducing the power the device needs to operate. The new result takes research one step closer to this goal.
M. Richardson et al., Applied Physics Letters, 104, 253501 (2014). Online