This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

DRV425: nT resolution magnetic sensor or mmWave radar for underwater application

Part Number: DRV425
Other Parts Discussed in Thread: IWR6443,

Hello,
I’m contacting you because I need information about the avalaibility magnetic sensor with resolution in the order of nT.
They will create a sensor network that will be placed undewater (10-20mt depth) to detect the transision of objects, over the network/barrier, from ships to a scuba divers (for this reason is requested nT resolution).

Obviously they must be able to differentiate the “signal” produced by the object by the earth magnetic field. 

In my preliminary research I saw that the best technology is flux gate, but I’m not sure and need an expert techinician.
Here below you can find the preliminary project architecture in which my magnetic networ must coexist with an acoustic barrier.

Some questions:

  1. Could I have some P/N in addition to DRV425, quotation or suggestion for other technologies in sensor selection for undewater applications?
  2. I already talk with a TI technician (ticket case CS0411747) but he says to me that for magnetic solution I have to talk with expert people in magnetic devices.
  3. The same technician suggests mmWave radar sensor as IWR6443. Could it be a valid solution for underwater application?
  4. I prefer magnetic flux gate approach but I can take in account also mmWave radar sensor if they, according to your opininion, work well. 

Thank you 

Best regards

Piero Mistretta

  • Hello Piero,

    1. Could I have some P/N in addition to DRV425, quotation or suggestion for other technologies in sensor selection for undewater applications?

      -->The DRV425 would be the only device for flux-gate that would even come close.  Our other magnetic sensors are hall and would not work in measuring nT

    2. I already talk with a TI technician (ticket case CS0411747) but he says to me that for magnetic solution I have to talk with expert people in magnetic devices.

      This is where you can speak with me and I can talk to you about the issue you can expect.  The first is distinguishing from earth field and your signal.  Are you going to modulate the signal you are concerned about?  If so I would then recommend a filter to avoid noise as the noise density will limit your limitation for the DRV425.  See this post.

    3. The same technician suggests mmWave radar sensor as IWR6443. Could it be a valid solution for underwater application?

      --> I do not think mmWave will work underwater but I would post this question on E2E with IWR6443 as the subject line.  This is one of the ways on how we filter to get questions to the correct person/group.  That is why I have read this due to the DRV425.

    4. I prefer magnetic flux gate approach but I can take in account also mmWave radar sensor if they, according to your opininion, work well.

      -->I think noise will be the limitation on using the DRV425 and removing the unwanted fields.  I think if you modulate the signal if my be possible.  Other than that the DRV425 will measure any field presented to it and will not distinguish form other magnetic sources such as earth magnetic field.

  • Hello Javier,

    thank you for your answer but I need more help because, according to the previous post I undestand that (correct me if I'm wrong) the DRV425 could reveal nT variations of earth magnetic field caused by a near (10mt) ferromagnetic object underwater:

    • you talk about modulation of the overall signal to filter the earth magnetic field but I think that it is impossible because the earth field changes with a frequency under mHz and my target objects move with a frequency of Hz and the design of this filter is almost impossbile (but I hope that this is not true with hearth).
    • Do you have an example of this modulation approach?
    • Do you have any suggestion about other techniques for example a differential approach to subtract the earth magnetic field?
    • Finally I see the evaluation board DRV425EVM: is it the only eval board?

    Thank you for all

    Have a nice day

    Piero Mistretta

  • Hello Piero,

    I did not know how you were applying the field but if you could change it/ vary it then you could distinguish it.  For example if the field was generated through a signal I would vary it at a frequency that then you could filter out.  If the field is magnetic I do not know how you could remove the earth field unless you calibrate it and use that as your offset in your system.  Also be careful of how much your source will change with time/temperature.  

    • you talk about modulation of the overall signal to filter the earth magnetic field but I think that it is impossible because the earth field changes with a frequency under mHz and my target objects move with a frequency of Hz and the design of this filter is almost impossbile (but I hope that this is not true with hearth).
      • The higher the frequency the easier it will be to filter the mHz(close to DC) out.  
    • Do you have an example of this modulation approach?
      • This is what I mentioned above in applying the field at a frequency that you can filter out the signal you can determine that is coming from your source rather than form earth or another signal.

    • Do you have any suggestion about other techniques for example a differential approach to subtract the earth magnetic field?
      • Normally making a differential measurement may help. Using two DRV425 and look at the differential.  Normally you would need to calibrate the differential as the package variation of the DRV425 sensor location can vary by a couple degrees between each DRV425.
    • Finally I see the evaluation board DRV425EVM: is it the only eval board?

  • Hello Piero,

    I will assume I answered your questions about the DRV425 as I am not sure if it would work for your application.  Please post further questions on the DRV425 on this post or start another thread.

  • Thank you Javier,

    I bought a DRV425EVM board to test the device. If it answers as I expect I have to decide between two ways:

    1. sample the raw signal (earth magnetic field plus useful signal created by the objetc to be revealed) with a 24 sigma-delta ADC and leave to the SW all data processing. In that case could you suggest an adequate DSP or micrcontroller?
    2. modulate the low frequence signal (considering that DRV42 have maximum noise at low frequencies) filter and sample the analog signal.

    Attached you can find how this problem was treated by other users (and part of this basic scheme is used in DRV425 device).

    Thank you for support and for the dissertation about noise.

    Best regards

    Piero Mistretta