Answers.Body: <p>As your Q indicates, you are not referring to constructing hydrophones using MEMS technology as described e.g. by
  <a href="https://www.academia.edu/download/101657425/TIE.2018.287458320230430-1-rwi75u.pdf" rel="nofollow noreferrer">https://www.academia.edu/download/101657425/TIE.2018.287458320230430-1-rwi75u.pdf</a>
  and
  <a href="https://www.mdpi.com/2077-1312/8/10/784" rel="nofollow noreferrer">https://www.mdpi.com/2077-1312/8/10/784</a>
  but you consider terrestrial products,e.g. MEMS microphone, accelerator as potential hydrophones.
  <a href="https://www.acoustics.asn.au/conference_proceedings/AAS2018/papers/p66.pdf" rel="nofollow noreferrer">https://www.acoustics.asn.au/conference_proceedings/AAS2018/papers/p66.pdf</a> gives you a first answer. Yes, it is possible but with constrains that make them nearly useless.</p>
  <p>To be more precise:
  As you wanted to cover the whole soundscape, your receiving bandwidth will most likely reach 100 kHz (192 kHz sampling). A good hydrophone has the lowest resonance above the band of interest. This excludes all piezo benders,buzzers, which have resonances in the kHz band (you can hear a bender,buzzer, right?).  Foggers have their resonance somewhere in the tens of kHz.</p>
  <p>Most, if not all hydrophones that satisfy scientific requirements are piezoceramic cylinders or spheres, if aimed for greater deployment depth and omnidirectionality.  Spheres are somewhat more expensive, but cylindrical ceramics are affordable, especially if you have the right equipment to solder the wires to piezo-ceramic (short enough time so that ceramic is not heated over Curie temperature and looses polarization).</p>
  <p>There must be a reason why, despite different labs tried to use cheaper MEMS microphones as hydrophones, piezo ceramic cylinders/spheres are still the first choice. The reason lies in the physics. MEMS microphones need a small air volume in order to function, so you have 3 media between the sound source and the sensor (water, polyurethane/epoxy, air). The MEMS is constructed to sense sound in air, but, while underwater sound propagates good from water to polyurethane/epoxy, it does not propagate good from polyurethane/epoxy to air, it is reflected, especially at higher frequencies. OK, as we are talking about waves, there is some exponential decay of sound energy in the air volume, so especially for lower frequencies the MEMS may sense sufficient sound energy to function as hydrophones. Unprotected air volumes finally decrease with increasing deployment depths (Boyls law pressure*volume = constant)</p>
  <p>Some labs have used oil-filled Electret microphones as hydrophones, but again microphones are optimized for in-air operations and piezo-ceramic cylinders/spheres are still found optimal for hydrophones. Maybe in future the MEMS technology that can be encapsulated without air in polyurethane/epoxy becomes affordable in the underwater domain.</p>
  
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Answers.CreationDate: 2024-10-17T07:43:42.933Z
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Answers.LastEditDate: 2024-10-17T08:10:01.503Z
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Body: <p>I am trying to understand which sensors would make good hydrophones, to then have these used by somebody building the circuit.
  I looked up these two piezo MEMS microphones:</p>
  <p>VA1210AA (sensitivity -28dB ±1dB, SNR 59 dB) <a href="https://mm.digikey.com/Volume0/opasdata/d220001/medias/docus/5342/VA1210AA_DS.pdf" rel="nofollow noreferrer">https://mm.digikey.com/Volume0/opasdata/d220001/medias/docus/5342/VA1210AA_DS.pdf</a>
  VM1000 (sensitivity -38dB ±3dB, SNR 62 dB) <a href="https://vespermems.com/wp-content/uploads/2019/03/VM1000_Datasheet-2.pdf" rel="nofollow noreferrer">https://vespermems.com/wp-content/uploads/2019/03/VM1000_Datasheet-2.pdf</a></p>
  <p>I am interested in the whole underwater soundscape, I wonder how these sensors would compare to piezo benders so commonly used as hydrophones or to ultrasound foggers ceramic elements that might also be ok to be used as such.
  Needless to say, the higher SNR and sensitivity, the better.</p>
  <p>Thank you</p>
  
Comments.ContentLicense: CC BY-SA 4.0
Comments.CreationDate: 2024-10-17T04:31:28.473Z
Comments.Text: Can you elaborate on your application - specifically why you want to build your own hydrophone instead of buying a tried and tested existing product? Is this a hobby? personal learning? engineering, art or science project? Have you read the existing threads here on building your own hydrophones with some references to and discussion of sensors  (https://bioacoustics.stackexchange.com/questions/1269/what-affordable-hydrophone-options-exist-for-in-the-field-listening; https://bioacoustics.stackexchange.com/questions/1313/can-i-use-mems-microphones-to-record-underwater-sounds)?
Comments.UserDisplayName: Brian Miller
Comments.ContentLicense: CC BY-SA 4.0
Comments.CreationDate: 2024-10-22T04:53:19.763Z
Comments.Text: Please clarify your specific problem or provide additional details to highlight exactly what you need. As it's currently written, it's hard to tell exactly what you're asking.
Comments.UserDisplayName: Community
Tags: <hydrophone><acoustic-monitoring><sensor>
Title: Suggestions for hydrophone piezo sensor
ThreadText: # Suggestions for hydrophone piezo sensor
  
  (Asked by: username_0 on 2024-10-16)
  
  I am trying to understand which sensors would make good hydrophones, to then have these used by somebody building the circuit.
  I looked up these two piezo MEMS microphones:
  
  VA1210AA (sensitivity -28dB ±1dB, SNR 59 dB) <https://mm.digikey.com/Volume0/opasdata/d220001/medias/docus/5342/VA1210AA_DS.pdf>
  VM1000 (sensitivity -38dB ±3dB, SNR 62 dB) <https://vespermems.com/wp-content/uploads/2019/03/VM1000_Datasheet-2.pdf>
  
  I am interested in the whole underwater soundscape, I wonder how these sensors would compare to piezo benders so commonly used as hydrophones or to ultrasound foggers ceramic elements that might also be ok to be used as such.
  Needless to say, the higher SNR and sensitivity, the better.
  
  Thank you
  
  **Tags:** hydrophone, acoustic-monitoring, sensor
  
  > **Comments:**
  > **username_1**: Can you elaborate on your application - specifically why you want to build your own hydrophone instead of buying a tried and tested existing product? Is this a hobby? personal learning? engineering, art or science project? Have you read the existing threads here on building your own hydrophones with some references to and discussion of sensors  (https://bioacoustics.stackexchange.com/questions/1269/what-affordable-hydrophone-options-exist-for-in-the-field-listening; https://bioacoustics.stackexchange.com/questions/1313/can-i-use-mems-microphones-to-record-underwater-sounds)?  
  > **username_2**: Please clarify your specific problem or provide additional details to highlight exactly what you need. As it's currently written, it's hard to tell exactly what you're asking.  
  
  ---
  
  ## 1 answers
  
  ### Answer by username_3 on 2024-10-17. Score: 1
  
  As your Q indicates, you are not referring to constructing hydrophones using MEMS technology as described e.g. by
  <https://www.academia.edu/download/101657425/TIE.2018.287458320230430-1-rwi75u.pdf>
  and
  <https://www.mdpi.com/2077-1312/8/10/784>
  but you consider terrestrial products,e.g. MEMS microphone, accelerator as potential hydrophones.
  <https://www.acoustics.asn.au/conference_proceedings/AAS2018/papers/p66.pdf> gives you a first answer. Yes, it is possible but with constrains that make them nearly useless.
  
  To be more precise:
  As you wanted to cover the whole soundscape, your receiving bandwidth will most likely reach 100 kHz (192 kHz sampling). A good hydrophone has the lowest resonance above the band of interest. This excludes all piezo benders,buzzers, which have resonances in the kHz band (you can hear a bender,buzzer, right?). Foggers have their resonance somewhere in the tens of kHz.
  
  Most, if not all hydrophones that satisfy scientific requirements are piezoceramic cylinders or spheres, if aimed for greater deployment depth and omnidirectionality. Spheres are somewhat more expensive, but cylindrical ceramics are affordable, especially if you have the right equipment to solder the wires to piezo-ceramic (short enough time so that ceramic is not heated over Curie temperature and looses polarization).
  
  There must be a reason why, despite different labs tried to use cheaper MEMS microphones as hydrophones, piezo ceramic cylinders/spheres are still the first choice. The reason lies in the physics. MEMS microphones need a small air volume in order to function, so you have 3 media between the sound source and the sensor (water, polyurethane/epoxy, air). The MEMS is constructed to sense sound in air, but, while underwater sound propagates good from water to polyurethane/epoxy, it does not propagate good from polyurethane/epoxy to air, it is reflected, especially at higher frequencies. OK, as we are talking about waves, there is some exponential decay of sound energy in the air volume, so especially for lower frequencies the MEMS may sense sufficient sound energy to function as hydrophones. Unprotected air volumes finally decrease with increasing deployment depths (Boyls law pressure\*volume = constant)
  
  Some labs have used oil-filled Electret microphones as hydrophones, but again microphones are optimized for in-air operations and piezo-ceramic cylinders/spheres are still found optimal for hydrophones. Maybe in future the MEMS technology that can be encapsulated without air in polyurethane/epoxy becomes affordable in the underwater domain.
  
  
  ---
  
  