Sensor technology to track forces, placement and positioning of Arabin pessary

Objective: This paper introduces a simple wireless method to monitor the orientation and forces exerted by the cervix on the Arabin Pessary without introducing any active circuitry or using complicated imaging methods such as Magnetic Resonance Imaging (MRI) scans. The key technology behind the sensor is based on the measurement of the mutual coupling between two coils as the angle of the coil and the capacitance of the resonant circuit is varied. The change is measured using an external sensor circuit composed of a modified Grid Dip Oscillator (GDO). Methods: The authors have tested the device with a test rig to simulate the tissue barrier and the environment in which the Arabin Pessary is situated. Results: A frequency of approximately 560 kHz was used. The change in voltage with orientation follows a sinusoidal trend with the maximum voltage at 0o being 6.23V and the minimum voltage at 90o being 5.39V. The capacitance force sensor has a baseline capacitance of 32.5pF and yielded approximately 1pF change in capacitance for every 1N of force. This would result in a 0.765kHz/N sensitivity for a system with 560kHz baseline frequency. Conclusion: The designed sensor is capable of detecting, with good accuracy, both the forces exerted and the orientation of the Arabin. Significance: Correct placement of implanted devices can be critical to their function. Possessing the ability to monitor the properties of an implanted device in a noninvasive manner continuously would improve early detection of incorrect or failed placement minimizing negative health impacts and costs associated with complications