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Wireless magnetoelastic sensors offer significant potential for measuring the accumulation of biomass within stents – enabling early detection prior to stent occlusion – but the encapsulation of these sensors remains a critical challenge. The encapsulation must allow the sensors to navigate the curvature and accommodate the contact forces imparted during and after the implantation procedure, while also leaving the sensor open to mechanical interaction with the biomass during the extended period of deployment. This paper is focused on the encapsulation of ribbon-like magnetoelastic sensors (12.5 mm × 1 mm × 60 μm) within plastic biliary stents (inner diameter of 2.54 mm). The compromise between two polymer-based package designs – one mechanically flexible (Type F) and one mechanically stiff (Type S) – is evaluated. The primary advantage of the Type F package is the flexibility during the delivery process while that of the Type S package is in maintaining a strong signal even when the stent is in a curved bile duct. The maximum thicknesses of the Type F and S packages are 0.53 mm and 0.74 mm, respectively. Mechanical tests show that both types protect the sensors from forces imparted by a standard introducer, and allow the encapsulated sensors to accommodate bending with a radius of curvature as small as 3 cm. The Type F package has also been tested in situ, in the bile duct of a porcine carcass. The signal is measurable with a wireless range of ≈10 cm, at a resonant frequency of 159 kHz and a quality factor of 397.

This paper describes the design, fabrication and in situ evaluation of a system developed for interrogation of an actuator-integrated glaucoma valve. An implanted glaucoma valve facilitates drainage of aqueous humor from the eye to help lower intraocular pressure in patients with glaucoma. Here, a customized magnetoelastic actuator is integrated on the valve to limit the fibrosis and encapsulation of the valve that can otherwise lead to implant failure. The system described here excites the actuator magnetically and verifies the actuation by sensing the acoustic signals generated by the vibrating actuator. This work focuses on increasing the wireless range, reducing signal feedthrough, and establishing the clinical utility of the system. In vitro experiments performed with the system demonstrate a signal-to-noise ratio of =140. In situ experiments, performed with the actuator-integrated valves implanted in porcine eyes, achieve a signal to noise ratio of 3–6. These are the first recorded acoustic signatures through tissue from a magnetoelastic device in an implanted environment.

This paper describes a comparative study of sensitivity and non-linearity of conventional and bossed diaphragm piezoresistive pressure sensor along with a performance enhanced design. The proposed structures take into consideration corner compensation to avoid distortion of the mesa structure during fabrication of bossed diaphragm structure using wet bulk micromachining. Optimum piezoresistors locations are calculated with the help of simulations carried out using finite element method (FEM) based tool COMSOL© Multiphysics. Since the sensitivity and non-linearity of conventional and bossed diaphragm structures showed a linear trend, empirical formulae are proposed using linear fit for quick and approximate calculation of sensitivity and non-linearity for a particular sensor structure. It is observed that high stress regions are also present near the boss — diaphragm interface and hence a design with piezoresistors placed at these regions is also proposed. This design is found to be enhancing the performance of piezoresistive pressure sensor compared to the conventional piezoresistor placement.