Bio-implantable passive on-chip RF-MEMS strain sensing resonators for orthopaedic applications

Abstract

One out of ten bone fractures does not heal properly due to improper load distribution and strain profiles during the healing process. To provide implantable tools for the assessment of bone fractures, we have designed novel, bio-implantable, passive, on-chip, RF-MEMS strain sensors that rely on the resonance frequency shift with mechanical deformation. For this purpose, we modeled, fabricated and experimentally characterized two on-chip sensors with high quality factors for in vivo implantation. One of the sensors has an area of ∼0.12 mm 2 with a quality factor of ∼60 and the other has an area of ∼0.07 mm 2 with a quality factor of ∼70. To monitor the mechanical deformation by measuring the change in the resonance frequencies with the applied load, we employed a controllable, point load applying experimental setup designed and constructed for in vitro characterization. In the case of the sensor with the larger area, when we apply a load of 3920 N, we obtain a frequency shift of ∼330 MHz and a quality factor of ∼76. For the smaller sensor, the frequency shift and the quality factor are increased to 360 MHz and 95, respectively. These data demonstrate that our sensor chips have the capacity to withstand relatively high physiologic loads, and that the concomitant and very large resonant frequency shift with the applied load is achieved while maintaining a high signal quality factor. These experiments demonstrate that these novel sensors have the capacity for producing high sensitivity strain readout, even when the total device area is considerably small. Also, we have demonstrated that our bio-implantable, passive sensors deliver a telemetric, real-time readout of the strain on a chip. Placing two more resonators on the sides of the sensor to serve as transmitter and receiver antennas, we achieved to transfer contactless power and read out loads in the absence of direct wiring to the sensor. With this model, where telemetric measurements become simpler due to the fact that all sensor system is built on the same chip, we obtain a frequency shift of ∼190 MHz with an increase in the quality factor from ∼38 to ∼46 when a load of 3920 N is applied. Therefore, as a first proof of concept, we have demonstrated the feasibility of our on-chip strain sensors for monitoring the mechanical deformation using telemetry-based systems.

Thin-film sensor based tip-shaped split ring resonator metamaterial for microwave application

“…However, the microwave sensors based on metamaterial have been investigated till date, because they can offer the capability of obtaining higher Q-factors and sharper and deeper resonance dips in transmission, compared with the traditional structure sensors previously reported (Melik et al 2008). For example, the silicon-based metamaterial wireless strain sensors yield high sensitivity of 109 kHz/kgf with low nonlinearity error of less than 200 microstrain (Melik et al 2009a, b).…”

Metamaterial-based wireless strain sensors

“…Among their advantages is the ability to obtain higher quality factors ͑Q factors͒, and sharper and deeper dips on resonance in their transmission using SRR compared to traditional rf structures that we previously used ͑e.g., rectangular and circular coils͒. [17][18][19] This makes metamaterials very well suited for telemetric sensing applications. Furthermore, metamaterial architecture enables us to achieve higher resonance frequency shifts, leading to higher sensitivity and better linearity, compared to our previous rf sensor structures.…”

“…The theoretical rationale of the design has been previously presented in detail for conventional spiral coil architecture. 19 Transmission through the matematerial sensor is shown as a function of the frequency parameterized with respect to the applied load in Fig. 2͑a͒.…”

Metamaterials beyond negative refractive index: Applications in telecommunication and sensing

“…While MFEF may be a disadvantage factor for high power applications, it provides metamaterial essential sensitivity in the sensing technology, both in electromagnetics and beyond [1,35]. As Melik et al pointed out in [36], metamaterials can obtain sharper resonance and higher Q-factors compared with traditional structure sensors. Al-Naib et al [37] demonstrated the interaction between electromagnetic waves and substances under test for chemistry and biological applications.…”