Abstract
One-port surface acoustic wave (SAW) devices with defined reflector patterns give characteristic signal patterns in the time domain making them identifiable and leading to so-called RFID-Tags. Each sensor responds with a burst of signals, their timed positions giving the identification code, while the amplitudes can be related to the analyte concentration. This paper presents the first combination of such a transducer with chemically sensitive layer materials. These include crosslinked polyvinyl alcohol for determining relative humidity and tert-butylcalix[4]arene for detecting solvent vapors coated on the free space between the reflectors. In going from the time domain to the frequency domain by Fourier transformation, changes in frequency and phase lead to sensor responses. Hence, it is possible to measure the concentration of tetrachloroethene in air down to 50 ppm, as well as 1% changes in relative humidity.
Highlights
Surface acoustic wave (SAW) [1] devices have already been successfully applied as sensors in analytical chemistry [2,3], because their high resonance frequency leads to excellent sensitivity [4,5,6,7]
Common two-port SAW devices usually consist of a piezoelectric substrate (e.g., ST-cut quartz) having two metallic interdigital transducers (IDT) deposited on its surface
RFID-Tags consist of SAW with only one IDT and a distinct reflector pattern [8] leading to time-dependent signal modulation that is suitable for identifying individual devices
Summary
Surface acoustic wave (SAW) [1] devices have already been successfully applied as sensors in analytical chemistry [2,3], because their high resonance frequency leads to excellent sensitivity [4,5,6,7]. In the same way as standard SAW, RFID-Tags can be coated with a sensitive layer to achieve chemical sensors. Such a layer modifies the velocity of the surface acoustic wave resulting in frequency shifts [9]. RFID-Tag sensors proposed in literature usually focus on physical sensing or detect chemical changes rather directly with the device than with a rationally designed recognition material. Supramolecular recognition based on such molecular cavities has already proven to be highly suitable for detecting volatile organics [11]
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