Initially it was quite disheartening as we kept thinking that we had a result only to discover that there was some kind of electromagnetic interference effecting the sensor and what we were seeing was not bone vibration after all. This was not helped by the fact that, to begin with, we were working in a room with a noisy computer fan so it was very difficult to avoid acoustic interference as well. We have since moved room and been through numerous set ups trying to electromagnetically isolate the sensor. The first set up we began working with was using a vibration sensor pictured below.
However, we found that all we were picking up on was the electromagnetic field generated by the unshielded connections. We then tried using a condenser microphone running through a mixing desk pre-amp into the oscilloscope. However, we found that it was not sensitive enough and was only displaying ambient noise.
We then tried using a piezo bi-morph sensor suggested by Rob Muir and we have shielded all the connections as best we can. At first we tried using the sensor on its own but the connections were too fragile and broke easily, so I made up two prototypes to support the sensor and provide more solid connections, one with polystyrene and one with glass coverslips.
We have settled on the polystyrene one as being the better option as it is more resilient. However, despite the shielding and the greater sensitivity of the sensor we are still getting electromagnetic interference, which we have determined is due to the conductive coated bone and tendon operating as capacitors. We determined that this was the case by the fact that the transducers output a rapidly falling voltage once disconected from the power supply.
Finally after much stuffing around, we have determined that we can actually hear the bone. Ironically, but not surprisingly, our ears turn out to be the best sensors. The sound is soft and present at 120 volts between about 5-14kHz, depending on the transducer.
Next, Will is designing a laser interferometer to try and get quantative results without the electromagnetic interference