SAW-Based Wireless Measurements of the Fast- Varying Deformations in Rotating Vibrating Objects Andrey Merkulov Dept. of Radio Engineering Fundamentals National Research University “MPEI” Moscow, Russia aamerkulovv@gmail.com Alexander Shvetsov Dept. of Radio Engineering Fundamentals National Research University “MPEI” Moscow, Russia shvetsov_as@mail.ru Sergei Zhgoon Dept. of Radio Engineering Fundamentals National Research University “MPEI” Moscow, Russia zhgoon@gmail.com Abstract—Measurement of vibration characteristics with SAW-sensors is attractive in applications for power generation, transport and aviation. The possibility of wireless data acquisition is especially useful for interrogation of sensors fixed on rotating vibrating objects, such as turbine blades for example. This paper reports on details of experimental wireless acquisition of vibration related information from rotating tuning forks which simulate the behavior of the vibrating objects at room temperature. SAW-resonators are used as sensors for fast- varying deformations measurements. Tuning forks with known frequencies of mechanical resonances equal to 512 Hz were fixed on a rotating shaft of an electrical motor. Commercial 224 MHz quartz SAW resonators were glue-bonded to tuning forks shoulders in the area of maximal strain. The resonators were wire-bonded to intermediate PC-boards. They could be connected either as feedback circuits to a miniature oscillator circuit with the output connected to rotating electromagnetic couplers (near-field antennas), or directly to the couplers for interrogation by external signals without the battery and the oscillator electronics. The oscillator had a miniature battery fixed on the same shaft and its output signal was frequency modulated by the tuning fork vibration, inducing fast varying deformations in the SAW resonator. The 512 Hz vibration of rotating at 900- 2700 rpm tuning forks was excited by compressed air flow or by hammer shocks. After demodulation of the oscillator signal about 15 s long exponentially decaying bursts were digitized by a computer sound card and recorded. This approach to data acquisition, although applicable only to low temperature experiments, has shown a better frequency resolution (0.005% in initial experiments) than the interrogation with external signals, and a much larger working distance: above 10 m with vibrator- type antennas and oscillator power of only 10 μW. The spectrum of the output signal contained the rotation related contribution. Keywords—vibration measurements, surface acoustic wave, SAW deformation sensor, wireless interrogation I. INTRODUCTION The long period of workability is one of the important parameters for the expensive construction or its parts. Vibration is one of the important parameters for monitoring in equipment with moving parts. Meanwhile controlled objects can be in motion described by different and complicated pathways. This complicates the measurements and sometimes excludes the use of the wired connections for the sensors monitored objects conditions. This paper reports on investigation of the sensor based on the surface acoustic waves (SAW) for vibrations monitoring of moving objects. The sensor based on the SAW resonator has a number of advantages for example the capability to work in harsh environments like high temperature, radiation and other. Measurement of vibration characteristics with SAW-sensors is attractive in applications for power generation, transport and aviation. High temperature vibration measurements by SAW- sensors were reported in [1]. This suggests the possibility of using the sensor in a hot area above 100°С. The possibility of wireless data acquisition is especially useful for interrogation of sensors fixed on rotating vibrating objects, such as turbine blades for example. This paper reports on details of experimental wireless acquisition of vibration related information from rotating tuning forks which simulate the behavior of the vibrating objects at room temperature. SAW-resonators are used as sensors for fast-varying deformations measurements. Section II presents the sensor design. Section III contains the description of the test setup and the experiment part details. The results and their discussion are described in Section IV. II. SENSOR CONFIGURATION The SAW device used in this work as a sensor for fast- varying deformations measurements is a single-port SAW- resonator. Commercial 224 MHz quartz SAW resonators were used as well as specially designed resonators on ST-quartz. It contains aluminum interdigital transducer and short-circuited reflectors. The connection of the sensor interdigital transducer to a PC-board is made with gold wires by ultrasonic welding (Fig. 1). Fig. 1. Wire bonding connection of the sensor PC-board and SAW- resonator sensor interdigital transducer with a gold conductor.