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LDC1614: Sensor Coil + PCB dielctic

Rob Priestley
Prodigy 230 points

Part Number: LDC1614

My application requires sensing a moving target at a distance of up to 40mm.

I am using a PCB circular sensor coil with a diameter of 40mm (0.1mm track, 0.1mm spacing).  Using LDC1614 for proximity detection.

I still need to increase the sensitivity at this distance.

Any suggestions on coil design to improve sensitivity ?

What is the relationship between Q of a coil and sensitivity/distance sensing.  I'm struggling to get a Q of 10, my understanding is the higher the better.

How does the dietetic contact of the PCB affect the sensitivity/Q of the coil ? 

If i change from FR4 to an RF type dielectric board will that make any significant impact ?

there is quite a bit of ferrous material in close proximity to the coil (70mm away). 

If i place a ferrite sheet at the back of the sensor will this increase the sensing distance top side of the pcb coil ?

Any light any one can shed on this would be much appreciated.

Rod

 

  • 0
    TI__Genius 17440 points

    Hi Rob,

    The primary determination of the sensor's range is the diameter of the coil. The closer a target is to the coil, the more sensitive the sensor will be to its movements. This is not just absolute distance, but also target distance as a percentage of the coil diameter. If you are able to increase the diameter of your coil, this will improve that ratio and will improve your sensitivity. If you do not have room for this, decreasing your sample rate (increasing RCOUNT) will also improve your resolution. The target material and size will also affect the strength of the sensor's response. The ideal target is very conductive (like copper) and roughly the same size as the coil. For more detailed information, you should review LDC Sensor Design and LDC Target Design.

    The inductor's Q does not affect the sensor's range. The Q value of your inductor isn't nearly as important as its Rp. This also won't affect the sensing range, but the LDC1614 requires a minimum Rp in order to supply enough current to keep the sensor oscillating.

    Changing from FR4 to a different material will likely only affect the self-resonant frequency of your coil (and the cost of your board). FR4 should be fine.

    If the ferrous material is 70mm away in the same plane as the coil, this should not be a problem. If it is behind your target, this would only be an issue if the ferrous material is moving.

    A ferrous sheet at the back of your coil would shield the coil from any moving metal behind it, but it would not change its range or sensitivity.

    Regards,