The electromagnetic fields radiated from a monolithic spiral coil acoustic transduction sensor

The monolithic spiral coil acoustic transduction (MSCAT) sensor platform is a novel bulk acoustic wave (BAW) device which is excited by a gold spiral coil antenna photolithographically deposited on one side of an AT-quartz wafer. The MSCAT platform can operate at very high frequencies by efficiently exciting high harmonic transverse shear modes (TSMs) with the application of a high frequency RF signal to the spiral coil. Since one surface of the MSCAT device is bare, this device can be used as a sensing platform upon which one deposits analyte selective chemical or biological films. The bare surface allows the detection of analyte induced mechanical (mass and viscoelasticity) and electrical (conductivity and dielectric constant) property changes in the film. Although previous work has shown that the MSCAT sensor is a highly sensitive sensor platform for chemical and biological analyte detection, the form of the electric field in the AT-quartz substrate is not well understood. In this work finite element analysis (FEA) was used to obtain the electromagnetic fields radiated by the spiral coil antenna deposited on AT-cut quartz. The theoretical results were compared to experimental measurements for specific spiral coil geometries. The spiral coil antenna was shown to produce electric fields that have components in both the lateral and thickness directions. These fields were responsible for exciting the TSM in the MSCAT sensor platform. Further, it was also shown that liquid properties on the sensor surface significantly alter the form of the radiated electric field. Also, the relative magnitude of the electric field in the AT-cut quartz vary significantly dependent on operating frequency and the spiral coil geometry.