Characterization of a Wireless Vacuum Sensor Prototype Based on the SAW-Pirani Principle

Abstract

A prototype of a wireless vacuum microsensor combining the Pirani principle and surface acoustic waves (SAW) with extended range and sensitivity was designed, modelled, manufactured and characterised under different conditions. The main components of the prototype are a sensing SAW chip, a heating coil and an interrogation antenna. All the components were assembled on a 15 mm × 11 mm × 3 mm printed circuit board (PCB). The behaviour of the PCB was characterised under ambient conditions and in vacuum. The quality of the SAW interrogation signal, the frequency shift and the received current of the coil were measured for different configurations. Pressures between 0.9 and 100,000 Pa were detected with sensitivities between 2.8 GHz/Pa at 0.9 Pa and 1 Hz/Pa close to atmospheric pressure. This experiment allowed us to determine the optimal operating conditions of the sensor and the integration conditions inside a vacuum chamber in addition to obtaining a pressure-dependent signal.

Overview of the MEMS Pirani Sensors

“…For traditional and the thermistor-based Pirani sensors, they work because their resistance changes with the varying pressure, while for a SAW-based Pirani sensor, it is the wave frequency that changes with the varying pressure [94][95][96]. As is known, propagation Figure 6b is a three-dimensional diagram of a diode-based Pirani sensor proposed by Wei et al [91].…”

Special Issue on “Advances in Microfluidics Technology for Diagnostics and Detection”

“…The wireless nature of these concepts simplifies sealing and contamination issues, which justifies the extra effort. Many properties can today be measured wirelessly, as shown in Toto et al [2] where they describe the development and miniaturization of a wireless vacuum sensor, which is enabled by combining the Pirani principle and surface acoustic waves (SAWs).…”