using a drum kit sensor to detect an egg pulse?

[ghostman11]

hi guys, another strang one for you
ok quick outline...
I am doing some proffessional work in conjunction with the university (exstension of previous research), and i need to monitor/detect the heartrate of an embryo in a egg without using light!
presently on the odd occasion we need to do this we use one of 2 comcercial units that use IR or laser to detect the pulse, unfortunately due to the nature of the research in this instance we wont be able to use light as the wavelenghs of light the embryo's are exposed to is part of the research. so the only thing i can come up with is a piezo drum kit type sensor that the egg would sit on. maybe going through a differential op amp?? and maybe another opamp to boost the signal to finaly the ADC of a micro?
i figured a differential opamp would be needed to cancell out the inherent vibrations present in the incubator.
any thoughts and suggestions? maybe some recomendations for parts! i have some drum kit type piezo sensors already but obviously i am not tied to using this method so any other sugestions gratefully recieved.
sorry about the lack of detail regarding why light cant be used but this is for a paper that will be published late summer so cant realy give much detail on the overal project

 

[JimB]

I dont think that a differential amplifier will cancel out the noise of the incubator as such.

However, if you use the technique which is used in noise cancelling microphones as used in aircraft headsets etc.
There are two microphone capsules, one facing the mouth and one facing away from the mouth.
Electrically the two are wired is series but in opposite phase, so the noise which is all around is cancelled, but the speech which is coming from one direction is louder in one capsule than the other.

JimB

 

[ghostman11]

thanks for that jim, i have a few weeks before i hve to atart building the thing so gives me a little time to look into the noise. although i am not convinced theese sensors are sensitive enough to pick up the tiny vibration of a embryo thru an egg shell anyway! but i am kind of stuck for other ideas