Limits...
MEMS Microphone Array Sensor for Air-Coupled Impact-Echo.

Groschup R, Grosse CU - Sensors (Basel) (2015)

Bottom Line: By using an array of MEMS (micro-electro-mechanical system) microphones, instead of a single receiver, several operational advantages compared to conventional sensing strategies in IE are achieved.The MEMS microphone array sensor is cost effective, less sensitive to undesired effects like acoustic noise and has an optimized sensitivity for signals that need to be extracted for IE data interpretation.The MEMS microphone array will make air-coupled IE measurements faster and more reliable.

View Article: PubMed Central - PubMed

Affiliation: Technische Universität München (TUM), Chair of Non-destructive Testing, Baumbachstr. 7, 81245 Munich, Germany. robin.groschup@tum.de.

ABSTRACT
Impact-Echo (IE) is a nondestructive testing technique for plate like concrete structures. We propose a new sensor concept for air-coupled IE measurements. By using an array of MEMS (micro-electro-mechanical system) microphones, instead of a single receiver, several operational advantages compared to conventional sensing strategies in IE are achieved. The MEMS microphone array sensor is cost effective, less sensitive to undesired effects like acoustic noise and has an optimized sensitivity for signals that need to be extracted for IE data interpretation. The proposed sensing strategy is justified with findings from numerical simulations, showing that the IE resonance in plate like structures causes coherent surface displacements on the specimen under test in an area around the impact location. Therefore, by placing several MEMS microphones on a sensor array board, the IE resonance is easier to be identified in the recorded spectra than with single point microphones or contact type transducers. A comparative measurement between the array sensor, a conventional accelerometer and a measurement microphone clearly shows the suitability of MEMS type microphones and the advantages of using these microphones in an array arrangement for IE. The MEMS microphone array will make air-coupled IE measurements faster and more reliable.

No MeSH data available.


Raw data of a single impact (Left Column) and Fourier spectra (Right Column) of the Impact-Echo test measurement. The arrows indicate the frequency of the Impact-Echo resonance.
© Copyright Policy
Related In: Results  -  Collection

License
getmorefigures.php?uid=PMC4541815&req=5

sensors-15-14932-f010: Raw data of a single impact (Left Column) and Fourier spectra (Right Column) of the Impact-Echo test measurement. The arrows indicate the frequency of the Impact-Echo resonance.

Mentions: The microphones measure air pressure changes. These pressure changes are proportional to the out-of-plane velocity of the concrete surface [10,12]. Therefore, before further data analysis and sensor comparisons, the recordings from the accelerometer were numerically integrated to get the surface velocity. As in conventional IE processing, the recorded data was converted to the frequency domain by means of a Fourier transformation. Figure 10 (right column) shows the frequency spectra of ten single impacts and the average spectrum of these impacts. Records where taken with a sampling frequency of 200 kHz for 6 ms. The amplitude resolution of the digitizer was 16 bit. The Fourier spectra of the accelerometer data clearly show a single resonance peak. Assuming a typical P-wave velocity for structural concrete (≈4000 m/s), this peak at 9.3 kHz can be unambiguously identified as the IE thickness resonance (ZGV-S1 Lamb mode). This peak is also very pronounced in the recordings of the MEMS microphone array. In the recordings of the measurement microphone, no dominant single frequency peak can be easily identified. A peak at 9.3 kHz is visible but it is weaker than many other spectral peaks. These peaks are most likely the effect of direct impact noise, reverberations of the impact device and multiple reflections of such sound waves. The recorded data show that the MEMS microphone array has a much higher and more selective sensitivity to the acoustic waves originating from the concrete wall than the measurement microphone. In the MEMS microphone recordings, the peak at 9.3 kHz has the highest amplitude in the averaged spectrum and most of the single spectra.


MEMS Microphone Array Sensor for Air-Coupled Impact-Echo.

Groschup R, Grosse CU - Sensors (Basel) (2015)

Raw data of a single impact (Left Column) and Fourier spectra (Right Column) of the Impact-Echo test measurement. The arrows indicate the frequency of the Impact-Echo resonance.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4541815&req=5

sensors-15-14932-f010: Raw data of a single impact (Left Column) and Fourier spectra (Right Column) of the Impact-Echo test measurement. The arrows indicate the frequency of the Impact-Echo resonance.
Mentions: The microphones measure air pressure changes. These pressure changes are proportional to the out-of-plane velocity of the concrete surface [10,12]. Therefore, before further data analysis and sensor comparisons, the recordings from the accelerometer were numerically integrated to get the surface velocity. As in conventional IE processing, the recorded data was converted to the frequency domain by means of a Fourier transformation. Figure 10 (right column) shows the frequency spectra of ten single impacts and the average spectrum of these impacts. Records where taken with a sampling frequency of 200 kHz for 6 ms. The amplitude resolution of the digitizer was 16 bit. The Fourier spectra of the accelerometer data clearly show a single resonance peak. Assuming a typical P-wave velocity for structural concrete (≈4000 m/s), this peak at 9.3 kHz can be unambiguously identified as the IE thickness resonance (ZGV-S1 Lamb mode). This peak is also very pronounced in the recordings of the MEMS microphone array. In the recordings of the measurement microphone, no dominant single frequency peak can be easily identified. A peak at 9.3 kHz is visible but it is weaker than many other spectral peaks. These peaks are most likely the effect of direct impact noise, reverberations of the impact device and multiple reflections of such sound waves. The recorded data show that the MEMS microphone array has a much higher and more selective sensitivity to the acoustic waves originating from the concrete wall than the measurement microphone. In the MEMS microphone recordings, the peak at 9.3 kHz has the highest amplitude in the averaged spectrum and most of the single spectra.

Bottom Line: By using an array of MEMS (micro-electro-mechanical system) microphones, instead of a single receiver, several operational advantages compared to conventional sensing strategies in IE are achieved.The MEMS microphone array sensor is cost effective, less sensitive to undesired effects like acoustic noise and has an optimized sensitivity for signals that need to be extracted for IE data interpretation.The MEMS microphone array will make air-coupled IE measurements faster and more reliable.

View Article: PubMed Central - PubMed

Affiliation: Technische Universität München (TUM), Chair of Non-destructive Testing, Baumbachstr. 7, 81245 Munich, Germany. robin.groschup@tum.de.

ABSTRACT
Impact-Echo (IE) is a nondestructive testing technique for plate like concrete structures. We propose a new sensor concept for air-coupled IE measurements. By using an array of MEMS (micro-electro-mechanical system) microphones, instead of a single receiver, several operational advantages compared to conventional sensing strategies in IE are achieved. The MEMS microphone array sensor is cost effective, less sensitive to undesired effects like acoustic noise and has an optimized sensitivity for signals that need to be extracted for IE data interpretation. The proposed sensing strategy is justified with findings from numerical simulations, showing that the IE resonance in plate like structures causes coherent surface displacements on the specimen under test in an area around the impact location. Therefore, by placing several MEMS microphones on a sensor array board, the IE resonance is easier to be identified in the recorded spectra than with single point microphones or contact type transducers. A comparative measurement between the array sensor, a conventional accelerometer and a measurement microphone clearly shows the suitability of MEMS type microphones and the advantages of using these microphones in an array arrangement for IE. The MEMS microphone array will make air-coupled IE measurements faster and more reliable.

No MeSH data available.