Hamdi Torun

An antenna-coupled split-ring resonator for biosensing

An antenna-coupled split-ring resonator-based microwave sensor is introduced for biosensing applications. The sensor comprises a metallic ring with a slit and integrated monopole antennas on top of a dielectric substrate. The backside of the substrate is attached to a metallic plate. Integrated antennas are used to excite the device and measure its electromagnetic characteristics. The resonant frequency of the device is measured as 2.12 GHz. The characteristics of the device with dielectric loading at different locations across its surface are obtained experimentally. The results indicate that dielectric loading reduces the resonant frequency of the device, which is in good agreement with simulations. The shift in resonant frequency is employed as the sensor output for biomolecular experiments. The device is demonstrated as a resonant biomolecular sensor where the interactions between heparin and fibroblast growth factor 2 are probed. The sensitivity of the device is obtained as 3.7 MHz/(μg/ml) with respe...

A micromachined membrane-based active probe for biomolecular mechanics measurement

A novel micromachined, membrane-based probe has been developed and fabricated as assays to enable parallel measurements. Each probe in the array can be individually actuated, and the membrane displacement can be measured with high resolution using an integrated diffraction-based optical interferometer. To illustrate its application in single-molecule mechanics experiments, this membrane probe was used to measure unbinding forces between L-selectin reconstituted in a polymer-cushioned lipid bilayer on the probe membrane and an antibody adsorbed on an atomic force microscope cantilever. Piconewton range forces between single pairs of interacting molecules were measured from the cantilever bending while using the membrane probe as an actuator. The integrated diffraction-based optical interferometer of the probe was demonstrated to have <10 fm Hz−1/2 noise floor for frequencies as low as 3 Hz with a differential readout scheme. With soft probe membranes, this low noise level would be suitable for direct force measurements without the need for a cantilever. Furthermore, the probe membranes were shown to have 0.5 µm actuation range with a flat response up to 100 kHz, enabling measurements at fast speeds.

Thermal deflections in multilayer microstructures and athermalization

Exact and approximate analytical solutions are developed for calculating the thermally induced deformation of three-layer cantilever structures. The solution is derived from the closed-form solutions for multilayer films. Thermal deformation and athermalization conditions are derived using dimensionless parameters for film to substrate thickness ratios for three-layer structures. The analytical solution for a narrow beam is applied to a scan mirror plate suspended with two torsional flexures. The results agreed well with finite element method simulations and experiments. Tests are performed using a bulk-micromachined silicon microelectromechanical system scanner that has a thin gold (Au) coil layer on one side and an aluminum (Al) mirror layer on the other side. Useful figures using film-to-substrate thickness ratios and the material independent normalized parameters are introduced for easy thermal deformation computations and performance trades for three-layer structures.

Athermalization in atomic force microscope based force spectroscopy using matched microstructure coupling

The authors describe a method for athermalization in atomic force microscope (AFM) based force spectroscopy applications using microstructures that thermomechanically match the AFM probes. The method uses a setup where the AFM probe is coupled with the matched structure and the displacements of both structures are read out simultaneously. The matched structure displaces with the AFM probe as temperature changes, thus the force applied to the sample can be kept constant without the need for a separate feedback loop for thermal drift compensation, and the differential signal can be used to cancel the shift in zero-force level of the AFM.

Spring constant tuning of active atomic force microscope probes using electrostatic spring softening effect

The authors describe a method to electrically adjust the spring constant of an active atomic force microscopy (AFM) probe using electrostatic spring softening effect. The probe consists of a clamped membrane with interferometric displacement sensing and integrated electrostatic actuation. Using the bias voltage on the integrated electrostatic actuator, the spring constant of the probe is reduced electrically. This increases the force sensitivity of the probe without significant dimensional change, therefore not affecting its noise level. The sensitivity improvement for force spectroscopy is demonstrated by capturing force curves using the membrane probe while it is in interaction with an AFM tip.

Measuring localized viscoelasticity of the vitreous body using intraocular microprobes

Vitrectomy is a standard ophthalmic procedure to remove the vitreous body from the eye. The biomechanics of the vitreous affects its duration (by changing the removal rate) and the mechanical forces transmitted via the vitreous on the surrounding tissues during the procedure. Biomechanical characterization of the vitreous is essential for optimizing the design and control of instruments that operate within the vitreous for improved precision, safety, and efficacy. The measurements are carried out using a magnetic microprobe inserted into the vitreous, a method known as magnetic microrheology. The location of the probe is tracked by a microscope/camera while magnetic forces are exerted wirelessly by applied magnetic fields. In this work, in vitro artificial vitreous, ex vivo human vitreous and ex vivo porcine vitreous were characterized. In addition, in vivo rabbit measurements were performed using a suturelessly injected probe. Measurements indicate that viscoelasticity parameters of the ex vivo human vitreous are an order of magnitude different from those of the ex vivo porcine vitreous. The in vivo intra-operative measurements show typical viscoelastic behavior of the vitreous with a lower compliance than the ex vivo measurements. The results of the magnetic microrheology measurements were validated with those obtained by a standard atomic force microscopy (AFM) method and in vitro artificial vitreous. This method allows minimally-invasive characterization of localized mechanical properties of the vitreous in vitro, ex vivo, and in vivo. A better understanding of the characteristics of the vitreous can lead to improvements in treatments concerning vitreal manipulation such as vitrectomy.

Uncooled thermo-mechanical detector array with optical readout

This paper reports a novel uncooled infrared FPA whose performance is comparable to the cooled FPAs in terms of noise parameters. FPA consist of bimaterial microcantilever structures that are designed to convert IR radiation energy into mechanical energy. Induced deflection by mechanical energy is detected by means of optical methods that measures sub nanometer thermally induced deflections. Analytical solutions are developed for calculating the figure of merits for the FPA. FEM simulations and the analytical solution agree well. Calculations show that for an FPA, NETD of <5mK is achievable in the 8-12 μm band. The design and optimization for the detectors are presented. The mechanical structure of pixels is designed such that it can be possible to form large array size FPAs. Microfabrication of the devices, which can be improved to improve the performance further, employs low cost standard MEMS processes.

A 35-

A thermo-mechanical MEMS detector with 35-μm pixel pitch is designed, fabricated, and characterized. This fabricated design has one of the smallest pixel sizes among the IR thermo-mechanical MEMS sensors in the literature. The working principle of the MEMS detector is based on the bimaterial effect that creates a deflection when exposed to IR radiation in the 8-12-μm waveband. The nanometer level out of plane mechanical motion is observed in response to IR heating of the pixel, which is detected by a diffraction grating-based optical readout. Performance of MEMS sensor arrays with optical readout have been limited by a large DC bias that accompanies a small AC signal. We developed a novel optical setup to reduce the DC term and the related noise using an AC-coupled detection scheme. Detailed noise characterization of the pixel and the readout system is reported in this paper. The noise equivalent temperature difference of our detector is measured as 216 mK using f/0.86 lens with the AC-coupled optical readout. Finally, we obtained a thermal image using a single MEMS pixel combined with a scanning configuration. Despite the reduced pixel size, the measured noise levels are comparable to the state-of-the-art thermo-mechanical IR sensors.

{\mu} \hbox{m}

This paper reports a micro electro-mechanical system (MEMS) based sensor array integrated with CMOS-based optical readout. The integrated architecture has several unique features and reported here for the first time. MEMS devices are passive and there are no electrical connections to the MEMS sensor array. Thus the architecture is scalable to large array formats for parallel measurement applications and can even be made as a disposable cartridge in the future using self-aligning features. A CMOS-based readout integrated circuit (ROIC) is integrated to the MEMS chip. Via holes are defined on ROIC by customized post-processing to enable integrated optical readout. A diffraction grating interferometer-based optical readout is realized by pixel-level illumination of the MEMS chip through the via holes and by capturing the reflected light using a photodetector array on the CMOS chip.

Pitch IR Thermo-Mechanical MEMS Sensor With AC-Coupled Optical Readout

The thermal sensor system presented in this paper is based on the mechanical bending due to the incident IR radiation. A diffraction grating is embedded under each pixel to facilitate optical readout. Typically the first diffraction order is used to monitor the sub-micron mechanical displacement with sub-nanometer precision. In this work; two different optical readout systems based on diffraction gratings are analyzed. First setup employs a conventional 4f optical system. In this one-to-one imaging system, collimated light is propagated through a lens, filtered with an aperture and then imaged onto a CCD by a second lens. Second system is more compact to improve image quality and to reduce noise. This is achieved by using an off-axis converging laser beam illumination that forms the Fourier plane near the imaging lens. This approach has important advantages such as reducing number of optical components and minimizing the optical path. The system was optimized considering parameters such as laser converging angle, laser beam size at MEMS chip, and magnification of the imaging system.