At present, most of the small-scale equipments used in monitoring underground oil exploration pipelines are powered by disposable or rechargeable batteries. These traditional chemical batteries have been unable to meet the needs of the system due to their large mass and volume, limited energy supply and possible environmental pollution. In addition, the huge depth of the oil wells can lead to a great deal of inconvenience during the replacement of the batteries. To solve these problems, a piezoelectric vibrator based on MEMS is proposed to achieve continuous supply of small downhole equipment in the process of oil/gas development.
In this study, after analyzing and optimizing the structural parameters of the device, a prototype is designed and fabricated through MEMS processing techniques including bulk silicon micro fabrication, bonding, and thinning. The prototype consists of a support layer, a piezoelectric film layer and a tip mass-block. Copper or silicon with appropriate stiffness and suitable for MEMS processing techniques are selected to make the support layer; PMN-PT with superior performance is selected to fabricate the piezoelectric film layer, whose working mode is d31. By running the energy acquisition test, the characteristics of the prototype's output voltage, power, and frequency are studied, as well as the possible requirements for the matching circuit.
The study shows that the test results are in good agreement with the calculated results of the theoretical model. The test results show that when the acceleration is 1.5g, the frequency bandwidth of the proposed prototype is 34.6Hz in air and 50.3Hz in silicon oil, and the output power can reach 35.4μW in air and 4.96μW in silicon oil.
Compared with the current mainstream piezoelectric thin film MEMS devices, this energy harvester based on MEMS technology has the advantages of superior output performance, simple fabrication, high anti-electromagnetic interference reliability, and easy integration with support circuit. This device will provide a new solution for the energy supply of downhole small-scale monitoring equipment.