Browsing by Author "Melik, R."
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Item Open Access Bio-implantable passive on-chip RF-MEMS strain sensing resonators for orthopaedic applications(Institute of Physics Publishing Ltd., 2008) Melik, R.; Perkgoz, N. K.; Unal, E.; Puttlitz, C.; Demir, Hilmi VolkanOne 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 mm2 with a quality factor of ∼60 and the other has an area of ∼0.07 mm2 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.Item Open Access Circular high-Q resonating isotropic strain sensors with large shift of resonance frequency under stress(2009) Melik, R.; Unal, E.; Perkgoz, N.K.; Puttlitz, C.; Demir, Hilmi VolkanWe present circular architecture bioimplant strain sensors that facilitate a strong resonance frequency shift with mechanical deformation. The clinical application area of these sensors is for in vivo assessment of bone fractures. Using a rectangular geometry, we obtain a resonance shift of 330 MHz for a single device and 170 MHz for its triplet configuration (with three side-by-side resonators on chip) under an applied load of 3,920 N. Using the same device parameters with a circular isotropic architecture, we achieve a resonance frequency shift of 500 MHz for the single device and 260 MHz for its triplet configuration, demonstrating substantially increased sensitivity. © 2009 by the authors.Item Open Access Design and realization of a fully on-chip High-Q resonator at 15 GHz on silicon(Institute of Electrical and Electronics Engineers, 2008-12) Melik, R.; Perkgoz, N. K.; Unal, E.; Dilli, Z.; Demir, Hilmi VolkanWe develop and demonstrate an on-chip resonator working at 15 GHz with a high quality factor (Q-factor) of 93.81 while only requiring a small chip size of 195 mu m x 195 mu m on Si by using our new design methodology. In our design, unlike previous approaches, we avoid the need for any external capacitance for tuning; instead, we utilize the film capacitance as the capacitor of the LC tank circuit and realize a fully on-chip resonator that shows a strong transmission dip of > 30 dB on resonance as required for telemetric-sensing applications. We present the design, theory, methodology, microfabrication, experimental characterization, and theoretical analysis of these resonators. We also demonstrate that the experimental results are in excellent agreement with the theoretical (both analytical and numerical) results. Based on our proof-of-concept demonstration, such high-Q on-chip resonators hold great promise for use in transmissive telemetric sensors.Item Open Access Development and biocompatibility characterization of a biomems sensor for monitoring the progression of fracture healing(2009-06) Santoni, B. G.; Melik, R.; Ünal, Emre; Perkgöz, N. K.; Kamstock, D. A.; Ryan, S. D.; Dernell W. S.; Demir, Hilmi Volkan; Puttlitz, C. M.Orthopaedic extremity injuries present a large medical and financial burden to the United States and world-wide communities [1]. Approximately six million long bone fractures are reported annually in the United States and approximately 10% of these fractures do not heal properly. Though the exact mechanism of impaired healing is poorly understood, many of these non-unions result when there is a communited condition that does not proceed through a stabilized healing pathway [2]. Currently, clinicians may monitor healing visually by radiographs, or via manual manipulation of the bone at the fracture [3]. Unfortunately, the course of aberrant fracture healing is not easily diagnosed in the early period when standard radiographic information of the fracture is not capable of discriminating the healing pathway. Manual assessment of fracture healing is also an inadequate diagnostic tool in the early stages of healing [4].Item Open Access Flexible metamaterials for wireless strain sensing(American Institute of Physics, 2009-11-04) Melik, R.; Unal, E.; Perkgoz, N. K.; Puttlitz, C.; Demir, Hilmi VolkanWe proposed and demonstrated flexible metamaterial-based wireless strain sensors that include arrays of split ring resonators (SRRs) to telemetrically measure strain. For these metamaterial sensors, we showed that a flexible substrate (e.g., Kapton tape) delivers greater sensitivity and a more linear response as compared to using silicon substrates. Specifically, these tape-based flexible SRR sensors exhibit a significantly improved sensitivity level of 0.292 MHz/kgf with a substantially reduced nonlinearity error of 3% for externally applied mechanical loads up to 250 kgf. These data represent a sixfold increase in sensitivity and a 16-fold reduction in error percentage.Item Open Access Implementation of high quality-factor on-chip tuned microwave resonators at 7GHz(WILEY, 2009) Melik, R.; Demir, Hilmi VolkanWe report on the design, analytical modeling, numerical simulation, fabrication, and experimental characterization of chip-scale microwave resonators that exhibit high quality-factors (Q-factors) in the microwave frequency range. We demonstrate high Q-factors by tuning these microwave resonators with the film capacitance of their LC tank circuits rather than the conventional approach of using external capacitors for tuning. Our chip-scale resonator design further minimizes energy losses and reduces the effect of skin depth leading to high Q-factors even for significantly reduced device areas. Using our new design methodology, we observe that despite the higher resonance frequency and smaller chip size, the Q-factor is improved compared with the previous literature using traditional approaches. For our 540 m 540 m resonator chip, we theoretically compute a Q-factor of 52.40 at the calculated resonance frequency of 6.70 GHz and experimentally demonstrate a Q-factor of 47.10 at the measured resonance frequency of 6.97 GHz. We thus achieve optimal design for microwave resonators with the highest Q-factor in the smallest space for operation at 6.97 GHz.Item Open Access Metamaterial based telemetric strain sensing in different materials(Optical Society of American (OSA), 2010) Melik, R.; Unal, E.; Perkgoz, N.K.; Puttlitz, C.; Demir, Hilmi VolkanWe present telemetric sensing of surface strains on different industrial materials using split-ring-resonator based metamaterials. For wireless strain sensing, we utilize metamaterial array architectures for high sensitivity and low nonlinearity-errors in strain sensing. In this work, telemetric strain measurements in three test materials of cast polyamide, derlin and polyamide are performed by observing operating frequency shift under mechanical deformation and these data are compared with commercially-available wired strain gauges. We demonstrate that hard material (cast polyamide) showed low slope in frequency shift vs. applied load (corresponding to high Young's modulus), while soft material (polyamide) exhibited high slope (low Young's modulus).Item Open Access Metamaterial-based wireless strain sensors(American Institute of Physics, 2009-07-07) Melik, R.; Unal, E.; Perkgoz, N. K.; Puttlitz, C.; Demir, Hilmi VolkanWe proposed and demonstrated metamaterial-based strain sensors that are highly sensitive to mechanical deformation. Their resonance frequency shift is correlated with the surface strain of our test material and the strain data are reported telemetrically. These metamaterial sensors are better than traditional radio-frequency (rf) structures in sensing for providing resonances with high quality factors and large transmission dips. Using split ring resonators (SRRs), we achieve lower resonance frequencies per unit area compared to other rf structures, allowing for bioimplant sensing in soft tissue (e.g., fracture healing). In 5×5 SRR architecture, our wireless sensors yield high sensitivity (109 kHz/kgf, or 5.148 kHz/microstrain) with low nonlinearity error (<200 microstrain).Item Open Access Nested metamaterials for wireless strain sensing(IEEE, 2009-12-28) Melik, R.; Unal, E.; Perkgoz, N. K.; Santoni, B.; Kamstock, D.; Puttlitz, C.; Demir, Hilmi VolkanWe designed, fabricated, and characterized metamaterial-based RF-microelectromechanical system (RF-MEMS) strain sensors that incorporate multiple split ring resonators (SRRs) in a compact nested architecture to measure strain telemetrically. We also showed biocompatibility of these strain sensors in an animal model. With these devices, our bioimplantable wireless metamaterial sensors are intended, to enable clinicians, to quantitatively evaluate the progression of long-bone fracture healing by monitoring the strain on the implantable fracture fixation hardware in real time. In operation, the transmission spectrum of the metamaterial sensor attached to the implantable fixture is changed when an external load is applied to the fixture, and from this change, the strain is recorded remotely. By employing telemetric characterizations, we reduced the operating frequency and enhanced the sensitivity of our novel nested SRR architecture compared to the conventional SRR structure. The nested SRR structure exhibited a higher sensitivity of 1.09 kHz/kgf operating at lower frequency compared to the classical SRR that demonstrated a sensitivity of 0.72 kHz/kgf. Using soft tissue medium, we achieved the best sensitivity level of 4.00 kHz/kgf with our nested SRR sensor. Ultimately, the laboratory characterization and in vivo biocompatibility studies support further development and characterization of a fracture healing system based on implantable nested SRR.Item Open Access Real-Time In Vivo Control of Neural Membrane Potential by Electro-Ionic Modulation(Elsevier, 2019) Soybas, Z.; Şimşek, S.; Erol, F. M. B.; Erdogan, U. Ç.; Şimşek, E. N.; Şahin, B.; Marçalı, M.; Aydogdu, B.; Elbüken, Çağlar; Melik, R.Theoretically, by controlling neural membrane potential (Vm) in vivo, motion, sensation, and behavior can be controlled. Until now, there was no available technique that can increase or decrease ion concentration in vivo in real time to change neural membrane potential. We introduce a method that we coin electro-ionic modulation (EIM), wherein ionic concentration around a nerve can be controlled in real time and in vivo. We used an interface to regulate the Ca2+ ion concentration around the sciatic nerve of a frog and thus achieved stimulation and blocking with higher resolution and lower current compared with electrical stimulation. As EIM achieves higher controllability of Vm, it has potential to replace conventional methods used for the treatment of neurological disorders and may bring a new perspective to neuromodulation techniques.Item Open Access RF-MEMS load sensors with enhanced Q-factor and sensitivity in a suspended architecture(Elsevier, 2010-11-09) Melik, R.; Unal, E.; Perkgoz, N. K.; Puttlitz, C.; Demir, Hilmi VolkanIn this paper, we present and demonstrate RF-MEMS load sensors designed and fabricated in a suspended architecture that increases their quality-factor (Q-factor), accompanied with an increased resonance frequency shift under load. The suspended architecture is obtained by removing silicon under the sensor. We compare two sensors that consist of 195 μm × 195 μm resonators, where all of the resonator features are of equal dimensions, but one's substrate is partially removed (suspended architecture) and the other's is not (planar architecture). The single suspended device has a resonance of 15.18 GHz with 102.06 Q-factor whereas the single planar device has the resonance at 15.01 GHz and an associated Q-factor of 93.81. For the single planar device, we measured a resonance frequency shift of 430 MHz with 3920 N of applied load, while we achieved a 780 MHz frequency shift in the single suspended device. In the planar triplet configuration (with three devices placed side by side on the same chip, with the two outmost ones serving as the receiver and the transmitter), we observed a 220 MHz frequency shift with 3920 N of applied load while we obtained a 340 MHz frequency shift in the suspended triplet device with 3920 N load applied. Thus, the single planar device exhibited a sensitivity level of 0.1097 MHz/N while the single suspended device led to an improved sensitivity of 0.1990 MHz/N. Similarly, with the planar triplet device having a sensitivity of 0.0561 MHz/N, the suspended triplet device yielded an enhanced sensitivity of 0.0867 MHz/N.