Wireless Accelerometer Using Piezoelectric MEMS Sensing Element

A Wireless Accelerometer Using Micromachined Piezoelectric Sensor

Vibration monitoring is often carried out for machines fault diagnosis. The state of art vibration sensors are manually and repetitively installed, which causes inconsistency in the measurement results. The long cables, large mass and size, protruding profile of the sensors interfere with the testing results. The objective of this project is to realize a miniaturized, low profile wireless battery-powered accelerometer system with a piezoelectric MEMS sensing element for machines vibration monitoring.

The MEMS sensor element comprises a frame, four suspending beams, and a seismic mass. Four sets of interdigited electrodes on the four beams are for charge collection.

Finite element model simulation shows that the fundamental resonance is 7.3 kHz and the charge sensitivity at 1 kHz is 0.13 pC/N.

Microfabrication results

The packaged wireless piezoelectric accelerometer consists of the piezoelectric sensing element, a charge amplifier and attenuator, an analog to digital converter (ADC), a programmable microcontroller (MCU), a battery, and a RF transceiver connected to an antenna. The low profile of the package, with the size of 28.50 cm³ and weight of 67.50 g, is smaller and lighter than the commercial wireless accelerometers found on the market (2014).

The effects of the device package on the dynamic response of the wireless piezoelectric accelerometer are investigated, and two mechanisms been implemented in the package to eliminate the electromagnetic interference (EMI): 1, shielding materials are inserted in the packaging; 2, the ground of the sensing element and the ground of the charge amplifier circuit are shorted to avoid the “ground loop” effect.

The sensitivity frequency spectra with a comparison among the different grounding and shielding conditions. The resonance at 7.7 kHz agrees with the numerical simulation result. The packaging did not introduce any resonance lower than the fundamental resonance of the bending-mode sensing element, which secured the maximum utilization of the dynamic frequency range provided by the sensing element. After noise suppression, the experimentally measured charge sensitivity at 1 kHz is 31.2 mV/g.

Field test: comparison between the vibration spectra detected by our accelerometer and a commercial cabled accelerometer (4525B, Triaxial DeltaTron, B&K, Denmark).

For more information, please refer to:

[1] Zhiyuan Shen, Yi Fan Chen, Lei Zhang, Chin Yaw Tan, and Kui Yao, “A Wireless Accelerometer Using Micromachined Piezoelectric Sensor”. ISAF-ISIF-PFM 2015, (2015), Singapore. (Oral presentation)

[2] Kui Yao, Zhiyuan Shen, Chin Yaw Tan, Yi Fan Chen, and Lei Zhang, “A wireless piezoelectric accelerometer for vibration monitoring”. (filed)

[3] Kui Yao, Chin Yaw Tan, Szu Cheng Lai, Lei Zhang, Zhiyuan Shen, and Yifan Chen, “Ferroelectrics for wireless sensor and transducer applications”, CIMTEC 2014 - 13th International Ceramics Congress, (2014), Montecatini Terme, Italy.