Design and Dynamics of Oil Filled Flexural Ultrasonic Transducers for Elevated Pressures

Abstract

The flexural ultrasonic transducer has traditionally been limited to proximity measurement applications, such as car-parking systems and industrial metrology. Principally, their classical form is unsuitable for environments above atmospheric 1 bar pressure, due to an internal air cavity which creates a pressure imbalance across the transducer's vibrating membrane. This imbalance leads to physical deformation and degradation of the transducer's structure, restricting the membrane's capacity to vibrate at resonance to transmit and receive ultrasound. There is a requirement for ultrasonic sensors which can withstand environments of elevated pressure, for example in ultrasonic gas metering. Recent research demonstrated the dynamic performance of flexural ultrasonic transducers with vented structures, allowing the pressure to balance across the transducer membrane. However, a hermetically sealed transducer is a more practical and robust solution, where the internal components of the transducer, such as the piezoelectric ceramic disc, will be protected from harmful environmental fluids. In this research, the design and fabrication of a new form of flexural ultrasonic transducer for environments of elevated pressure is demonstrated, where the internal air cavity is filled with an incompressible fluid in the form of a non-volatile oil. Dynamic performance is measured through acoustic microphone measurements, electrical impedance analysis, and pulse-echo ultrasound measurement. Together with finite element analysis, stable ultrasound measurement is achieved above 200 bar in air, opening the possibility for reliable ultrasound measurement in hostile environments of elevated pressure.

Measurement Stability of Oil-Filled Flexural Ultrasonic Transducers Across Sequential In Situ Pressurization Cycles

“…The OFFUT used for this research is fabricated with an aluminium thin plate with a nominal diameter of 10 mm, consistent with prior research and adhering to the same general fabrication process [27], where the complete schematics and images of the internal components can be viewed in [27]. An aluminium case is attached to the cap rear, through which silicone oil (Polydimethylsiloxane, CAS 63148-62-9) is injected, before being sealed with potting epoxy resin (Electrolube ER1448).…”

“…The pressure imbalance in the traditional FUT was successfully eliminated in the vented FUT, an adapted form of the FUT where the cavity is vented to the external environment [23][24]. Overcoming the pressure imbalance led to the oil filled FUT (OFFUT), which addressed key design and operation limitations associated with the vented design [27], including likely vent blockage or the exposure of the piezoelectric ceramic disc to harmful particles or fluids. Through filling the FUT cavity with oil, a quasi-incompressible system boundary condition was created, thus enabling operation in elevated pressure environments.…”

“…In prior research [27], the authors outlined a suitable fabrication process for the OFFUT, giving a general insight into how aspects of transducer performance such as the resonance frequency can be affected. Key dynamic characteristics of the OFFUT when operating at atmospheric 1 bar conditions were also demonstrated, complemented by a selection of A-scans obtained at several environmental pressure levels above atmospheric, using the pitch-catch approach.…”

“…The first investigative step in the study was to construct a representative finite element model of the OFFUT, beyond what has been demonstrated in prior research. The OFFUT was defined in COMSOL Multiphysics ® software, consistent with the physical parameters and geometry shown above and in the preliminary study [27], where the model is illustrated in Fig. 3.…”

Applying a Novel Image Recognition Curve-Fitting Control Strategy Combined with a Cloud Monitoring Technique into an Electric Self-Driving Vehicle (ESDV) to Improve Its Operation Efficiency

“…Small-and medium-sized computers and control boards are the indispensable key components of the automatic driver assistance system. The mini-computer and the control board receive the environmental data for calculations through different sensors, such as a camera, ultrasonic sensor, infrared, and LiDAR [8][9][10][11]. The computed results subsequently serve as navigational instructions for electric self-driving vehicles (ESDVs), ensuring safe and stable operation.…”