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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.


Time-frequency representation of a single impact (Left Column) and Fourier spectra of time windowed recordings (Right Column). The arrows indicate the frequency of the Impact-Echo resonance.
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sensors-15-14932-f011: Time-frequency representation of a single impact (Left Column) and Fourier spectra of time windowed recordings (Right Column). The arrows indicate the frequency of the Impact-Echo resonance.

Mentions: However, compared to the accelerometer data, the array recordings are not totally free from disturbances, most likely due to impact noise influences. For further analysis, a time-frequency representation of the data was produced by means of a Choi–Williams transformation (Figure 11, left column). The MEMS microphone array sensor and the accelerometer data clearly show high values at the IE resonance frequency (see arrows). In the recordings of the measurement microphone energy values at this frequency barely rise above the background level. As a further observation, it can be noted that the recordings of both microphone based sensors show pronounced high-energy values in the frequency range between 10 and 15 kHz. This energy is concentrated at time instants <2 ms and can be attributed to direct impact noise. Based on these observations, in the time-frequency representations a time window can be selected that separates the IE resonance peak from other energy and again a Fourier transformation is computed (Figure 11, right column). Only samples from a time window between 1.8 ms and 6 ms where passed to the Fourier transformation. Now the IE resonance peak is clearly the most prominent peak in the spectra of the array recordings. This is the case for the averaged spectra, but it also holds true for single impact measurements. Time windowing brings no improvement regarding the ambiguity in the spectral peaks of the measurement microphone.


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

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

Time-frequency representation of a single impact (Left Column) and Fourier spectra of time windowed recordings (Right Column). 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-f011: Time-frequency representation of a single impact (Left Column) and Fourier spectra of time windowed recordings (Right Column). The arrows indicate the frequency of the Impact-Echo resonance.
Mentions: However, compared to the accelerometer data, the array recordings are not totally free from disturbances, most likely due to impact noise influences. For further analysis, a time-frequency representation of the data was produced by means of a Choi–Williams transformation (Figure 11, left column). The MEMS microphone array sensor and the accelerometer data clearly show high values at the IE resonance frequency (see arrows). In the recordings of the measurement microphone energy values at this frequency barely rise above the background level. As a further observation, it can be noted that the recordings of both microphone based sensors show pronounced high-energy values in the frequency range between 10 and 15 kHz. This energy is concentrated at time instants <2 ms and can be attributed to direct impact noise. Based on these observations, in the time-frequency representations a time window can be selected that separates the IE resonance peak from other energy and again a Fourier transformation is computed (Figure 11, right column). Only samples from a time window between 1.8 ms and 6 ms where passed to the Fourier transformation. Now the IE resonance peak is clearly the most prominent peak in the spectra of the array recordings. This is the case for the averaged spectra, but it also holds true for single impact measurements. Time windowing brings no improvement regarding the ambiguity in the spectral peaks of the measurement microphone.

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.