A 200 MHz surface acoustic wave resonator mass microbalance

Abstract

Surface acoustic wave (SAW) piezoelectric sensors typically used by researchers in analytical applications are based on SAW delay lines. We report here the development of a 200 MHz SAW instrument based on a SAW resonator instead of a conventional delay line. The instrument is small, compact and uses two separate 200 MHz resonator crystals which operate in the dual difference mode. The difference frequency stability is better than 55× 10−9 (±1 Hz) which is comparable to a 10 MHz bulk crystal (on an absolute frequency basis) and at least an order of magnitude better than other commercially available SAW delay lines that operate at comparable frequencies. The mass sensitivity is about 9 × 1010 Hz cm2/g. Response to temperature change is found to be about 20 Hz/°C from −30 °C to 30 °C. Response to pressure is found to be linear from 760 to 415 Torr at 3 Hz/Torr. Detection limits for HCl vapors were determined to be in the low ppb range using a SAW resonator coated with triethanolamine.

Surface acoustic wave vapor sensors based on resonator devices

“…These authors had investigated SAW delay lines for use in a cascade impactor for the collection and measurement of aerosols (14), and then developed their resonator-based system in order to improve baseline stability. They have also briefly reported the use of resonator devices with sorbent coatings as gas sensors (13).…”

An EP-SAW for measurements of particulate matter in ambient air

“…A modified SAW device operating in a voltage plateau region would further increase this collection efficiency. For any field instrument the SAW devices need to be incorporated into resonator circuits so that only changes in the resonant frequency 5 need be measured; the use of a third SAW device without a collection plate could also be incorporated to allow for ambient changes such as temperature drift.…”

“…al. [5] using olive oil as the test aerosol. In a previous report EP have been used in conjunction with quartz crystal microbalances (QCM), an acoustic wave device with a lower sensitivity than SAW devices, in a prototype personal dust monitor [6].…”

Acoustic Wave Based MEMS Devices, Development and Applications

“…Any variations to the characteristics of the propagation path affect the velocity or amplitude of the wave. Important application for acoustic wave devices as sensors include torque and tire pressure sensors (Cullen et al, 1980;Cullen et al, 1975;Pohl et al, 1997), gas sensors (Levit et al, 2002;Nakamoto et al, 1996;Staples, 1999;Wohltjen et al, 1979), biosensors for medical applications (Andle et al, 1995;Ballantine et al, 1996;Cavic et al, 1999;Janshoff et al, 2000), and industrial and commercial applications (vapor, humidity, temperature, and mass sensors) (Bowers et al, 1991;Cheeke et al, 1996;Smith, 2001; N. J. Vellekoop et al, 1999;Vetelino et al, 1996;Weld et al, 1999).…”