Introduction

A device that uses a foil (in particular a membrane, a micro-lever or cantilever) to guide a probe in order to measure an interaction with the sample to be measured. This interaction can be used in scanning probe microscopy systems, microbalances, detectors of environmental characteristics such as chemical concentration and pressure. It also allows you to scan surfaces in dynamic mode, to study their topography and physical properties with sub-microscopic resolution. This detection system can also be used both wirelessly and in liquid or cryogenic conditions. It is based on the generation and simultaneous detection of surface acoustic waves (SAW) generated and detected by one or more interdigitated transducers (IDT) present on the surface of the foil, having a piezoelectric layer. Compared to other existing devices, it uses a robust technology without moving parts that exploits the variation in the speed of sound in the material caused by deformation, a technology that allows its use in different working conditions with great reliability.

Technical features

The device exploits the variation in the speed of sound produced in a given material as a result of a deformation. It comprises at least one pair of interdigitated transducers (IDTs), which transmit / receive surface acoustic waves on a piezoelectric plate arranged on the microlift so as to flex together with it. By identifying the resonant frequency fr of the receiving IDT, which is related to the speed of sound u according to the relationship fr = u / 2d, d being the pitch between the elements of the IDT. To do this, an appropriate exciting frequency, preferably sinusoidal, is imposed on the transmitting IDT, creating a surface acoustic wave which, thanks to the piezoelectric properties of the foil, generates a potential difference across the receiving IDT, and which is maximum when the exciting frequency is equal to the resonant frequency of the device.

Possible Applications

• Scanning probe microscopy (position sensor);
• Microbalance (mass sensor);
• Environmental characteristics detectors (chemical or pressure sensor);
• Wireless position and mass sensor, also in liquids and under cryogenic conditions.

Advantages

• High detection sensitivity;
• Possibility to selectively excite proper modes of the membrane or micro-lever;
• Possibility to work wirelessly, also in liquids and under cryogenic conditions;
• Possibility to work in array, exploiting different systems having different frequencies of use.