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The quartz crystal monitor (QCM) is a common sensor platform based on the room temperature compensated pure shear mode (PSM) of thickness field excited (TFE) AT-cut quartz. However, with electrodes on both crystal faces, TFE only allows sensing of mechanical property changes. Lateral field excitation (LFE), where both electrodes are on a single face, enables the detection of both mechanical and electrical changes, potentially leading to higher sensitivity. As lithium tantalate (LT) has an LFE PSM and piezoelectric coupling several times greater than that of quartz, LFE LT was chosen as a possible replacement for TFE quartz. A theoretical search of all LT cuts identified those exhibiting a room temperature compensated PSM. A set of orientations ranging from (YXwl) 0°/-85° to 0°/-90° was chosen for experimental verification. The temperature response of each sample was shown to be parabolic, with a roughly linear relationship between crystal cut angle and temperature inflection point/turnaround temperature. Specifically, the (YXwl) 0°/-87° cut with a turnaround temperature at 26.4°C demonstrates that a room temperature PSM in LT can be excited via LFE. Future work focusing on the development of an LT sensing platform could profoundly impact sensor systems in agriculture, homeland security, global warming, and medical applications. 

The operational modes of lateral field excited (LFE) quartz crystal microbalances (QCMs) under various electrical boundary conditions have been under investigation for use in sensing applications. The present results indicate connections between the behaviors of acoustic plate modes (APMs) and LFE-QCM modes. The influences of deposited thin conducting and semiconducting films on the mode responses of LFE-QCMs strongly agree with reported effects on APMs. Thus the main operating modes of LFE devices are concluded to be laterally varying APMs, which may be close in character to thickness modes. Mode response changes caused by slowly varying surface curvature are explained from this perspective. The consistency of the usual LFE thickness mode coupling formalism is evaluated, and the superposition of partial waves method is found to be more appropriate for analyzing LFE devices. This view of LFE devices operating through APMs supports improved sensing applications and investigations through access to existing APM knowledge.