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Help in force-pressure transfer through oil

  1. May 14, 2014 #1
    Hi Guys,

    It Is me again, I am working in the design of a packaging for a MEMS sensor, the package is a oil-based diaphragm, who is basically a chamber that in the bottom has a pressure sensor, the sensor is in the chamber of oil completelly cover by oil, in the other extreme of the chamber there is one membrane (very thin) that is in contact with a uniform pressure. The membrane is design in a way that will not absorb energy and will let pass the pressure from the exterior to the oil inside the chamber (I am attaching a schematic). Here is where I need your help. Which will be the equation to define the transfer of the external pressure to the sensor through the oil considering the properties of the oil (viscosity, etc) and in a worst case a compressibility of 2%. The chamber is closed, there is not interchange of mass. My background is MEMS design, but I need to know how to describe the packaging too.

    I really need your help

    Attached Files:

  2. jcsd
  3. May 15, 2014 #2


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    Science Advisor

    There should be no pressure drop in the transfer through the oil.

    The diaphragm is there to isolate the chemistry of the fluid from the sensor. The oil is there to translate the external pressure to the sensor without distortion due to the diaphragm shape.

    The oil viscosity is not important because the silicon oil is in a 3D capsule and does not need to flow through any small hole. Delay in the pressure signal due to the oil will be due to the speed of sound in the oil.

    The 2% compression of the oil at 13.5MPa will require a volume of fluid be supplied when there is an increase in pressure. If it is significant, the volume of fluid required per MPa should be specified in the data sheet. Since the oil volume can be minimised by minimising the capsule volume, that should be done.
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