Hi all,
I am writing to inquire about the performance characteristics of the MEMS Omnidirectional Microphones Audio Evaluation Board, specifically the ICS-40180.
Our application involves emitting Linear Frequency Modulated (LFM) signals in the 18-22 kHz. During our experiments, we observed that the microphone's detection capability seems to be limited to objects directly in front of it, with a maximum effective range of approximately 4.5 meters. We noticed a significant drop in detection efficiency when the objects were not positioned directly in front of the microphone, such as when an object is 1 meter away from the microphone and laterally shifted by 0.3 meters to the left or right, resulting in an approximate angle of 15 degrees from the microphone's central axis.
Given these observations, we are curious about the actual beam angle of this microphone chip. The product was advertised as omnidirectional, but our experience suggests a more limited detection range. Could you please provide us with detailed specifications regarding the beam angle or directivity pattern of the ICS-40180 microphone? This information is crucial for us to understand the limitations of the product and to adjust our project requirements accordingly.
We appreciate your prompt response and any technical insights you can offer regarding this matter.
Thank you.
Best regards,
Xiaoxuan
Hello,
Thank you for your question. In order to better help, I'm hoping that you might be able to provide a little but more detailed information on your test conditions.
One specific question that comes to mind is regarding how the source of the sound is being offset. Given the frequency range of your signal I would assume that the signal itself would be fairly directional and so if the source is not being aimed at the microphone then less of the signal would reach the microphone. I'm attaching a couple of quick drawings to try to illustrate this. In the case that the source is shifted laterally but not aimed at the microphone, it is possible that the directionality of the high frequency signal may result in the sound passing by the microphone. By shifting the sound source laterally and then aiming it, I would expect that this situation would be improved. Note, if this is the case, in your experiments, it is a function of the directionality of the signal and not necessarily the microphone itself.
Another possibility is that, in the range you're using, the microphone response includes a resonant peak slightly above 20 kHz which could be affecting the measurements.
I do not currently have measurement data on the directionality of this model, but I will review the historical data to determine if directionality was measured in the frequency range in question.
If you have any additional information, e.g. test setup photographs and/or measurement results, that you can share, that might be helpful in better guiding you.
Regards,
Mike