Start Date

2016 12:00 AM

Description

Air-coupled ultrasonics (ACU) has had an increasing importance in non-destructive evaluation (NDE), particularly for inspection of composite materials for example in the aerospace industry [1]. The main problem for ACU is the large impedance mismatch between piezoelectric ceramics and air, and a lack of suitable materials for impedance matching [2]. Many different solutions to this problem have led to a range of transducer technologies and designs, e.g. composite transducers and capacitive micromachined ultrasonic transducers (CMUTs). In previous work by the authors three designs of a novel ACU transducer, combining electromagnetic coupling and flexural mode vibrations, so called electrodynamic flexural transducers (EDFTs), were investigated [3]. In this work, the most promising design of those three EDFTs is characterized and analyzed in depth. The manufacturing process is outlined and the characterization is done in terms of electrical impedance, absolute pressure measurements, beam profile and transducer surface displacement measurements. The results are compared to those from a finite element (FE) model, and there is good agreement between the FE simulations and the experimental results. The transducer has a directivity with -3 dB at ±10° in receive mode and ±13° in transmit mode. Using a standard electromagnetic acoustic transducer (EMAT) amplifier the transducer has a sensitivity of 1.0 mV/Pa and a LPF single shot SNR of 15 dB. Overall the transducer does not have as high electromechanical efficiency as some other available alternatives, such as CMUTs or piezoelectric flexural transducers. However, the EDFT is robust, simple to manufacture, has relatively low cost components and does not rely on a piezoelectric element being bonded to the internal emitting face, which make it a relevant addition to the field of ACU, particularly for non-contact measurements at elevated temperatures.

Language

en

File Format

application/pdf

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Jan 1st, 12:00 AM

Characterization of an Electrodynamic Flexural Transducer for Air-Coupled Ultrasonics

Air-coupled ultrasonics (ACU) has had an increasing importance in non-destructive evaluation (NDE), particularly for inspection of composite materials for example in the aerospace industry [1]. The main problem for ACU is the large impedance mismatch between piezoelectric ceramics and air, and a lack of suitable materials for impedance matching [2]. Many different solutions to this problem have led to a range of transducer technologies and designs, e.g. composite transducers and capacitive micromachined ultrasonic transducers (CMUTs). In previous work by the authors three designs of a novel ACU transducer, combining electromagnetic coupling and flexural mode vibrations, so called electrodynamic flexural transducers (EDFTs), were investigated [3]. In this work, the most promising design of those three EDFTs is characterized and analyzed in depth. The manufacturing process is outlined and the characterization is done in terms of electrical impedance, absolute pressure measurements, beam profile and transducer surface displacement measurements. The results are compared to those from a finite element (FE) model, and there is good agreement between the FE simulations and the experimental results. The transducer has a directivity with -3 dB at ±10° in receive mode and ±13° in transmit mode. Using a standard electromagnetic acoustic transducer (EMAT) amplifier the transducer has a sensitivity of 1.0 mV/Pa and a LPF single shot SNR of 15 dB. Overall the transducer does not have as high electromechanical efficiency as some other available alternatives, such as CMUTs or piezoelectric flexural transducers. However, the EDFT is robust, simple to manufacture, has relatively low cost components and does not rely on a piezoelectric element being bonded to the internal emitting face, which make it a relevant addition to the field of ACU, particularly for non-contact measurements at elevated temperatures.