I have tried to make a phantom with gelatine and gelly. As there is no information online for the ratio of the two, I have tried combinations of 1 part of gelatine to 5 parts of gelly to pure gelatine. More gelly would offer the benefit of bounciness, but soft and fragile. If only gelatine is used, the outcome is firmer. Comparing the phantoms with my stomach, pure gelatine gives the best matching result.
Considering its softness, magnification of sensitivity of the load cell is required, I have tried to achieve this by increase the gain of the differential amplifier. The resistors I am using currently are 260Ohm and 560kOhm, it brought a 4V offset while magnifying the output from the load cell. Once read by the controller, the freeload voltage is 875 in 16 bits.
For the data collection, I have placed the probe on my own stomach, and judging with my own experiences of undergoing an abdominal ultrasound test. When the maximum level of force is applied, the reading rise to 880. The change is not very significant, one of the reason could be that the probe is not secured onto the backing properly, the force is not fully transferred to the tip of the probe. This point will need to be considered when reviewing the mechanical design.
At this point of time, it is hard to see any difference caused by the orientation of the system, thus an accelerometer may not be necessary.
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