10 research outputs found
Characterization of photonic crystals at microwave frequencies
Ankara : Department of Physics and Institute of Engineering and Science, Bilkent Univ., 1996.Thesis(Master's) -- Bilkent University, 1996.Includes bibliographical references.VVe investigated the surface reflection properties of layer-by-layer photonic
crystals, for dielectric and metallic based photonic crystals. By using a FabryPerot
cavity analogy with the reflection-phase information of the photonic
crystals, we predicted defect frequencies of planar defect structures. Our
predictions were in good agreement with the measured defect frequencies. The
Fabry-Perot cavity analogy was also used to relate the quality factors of the planar
defect structures to the transmission of the mirrors of the cavity. A simple model
was used to simulate the transmission spectra of planar defect structures, which
agreed well with the experimental data. We also investigated the transmission
and reflection properties of two different metallic crystal structures (face-centeredtetragonal
and simple tetragonal). We obtained rejection rates of 7-8 dB per layer
from metallic crystals. Defect modes created by removing rods resulted in high
peak transmission (80%), and high quality factors (1740). Our measurements
were in good agreement with theoretical simulations of metallic structures. Planar
defect structures built around metallic structures resulted in higher quality factors
(2250). We observed high reflection-rejection ratios (-80 dB) at defect frequencies for planar defect structures, which was explained by using the Fabry-Perot
analogy. Finally, the enhanced field inside the defect volume was measured,
by using a monopole receiver antenna inserted inside the defect. The maximum
observed enhancement with respect to the incident field was around 200 for a
planar defect structure. By placing a Schottky diode detector inside planar and
box-like defects, we built resonant cavity enhanced (RCE) detectors and measured
the enhanced field inside the defect.Temelkuran, BurakM.S
Physics and applications of photonic crystals
Ankara : Department of Physics and the Institute of Engineering and Science of Bilkent Univ., 2000.Thesis (Ph.D.) -- Bilkent University, 2000.Includes bibliographical references leaves 72-79We first fabricated a dielectric based layer-by-layer photonic crystal, with a
three-dimensional photonic band gap at microwave frequencies. We investigated the
transmission, reflection and defect characteristics of the crystal. A Fabry-Perot cavity
analogy was used to understand the localization of the electromagnetic (EM) fields
around defects. We then showed the enhancement of the EM held within the defect
volumes, and suggested a possible application: resonant cavity enhanced detectors built
around photonic crystals. We demonstrated that a detector inserted inside the defect
volume benefits from the frequency selectivity and the highly enhanced field of the cavity.
Next, we investigated the radiation of the EM fields from a source inserted in the defect
volume, and observed that the radiated field has a very high directivity and efficiency.
The experimental results agreed well with the theoretical expectations.
We demonstrated waveguiding structures built around photonic crystals. We showed
that EM waves could be guided through a planar air gap between two photonic crystals,
in which the wave is coupled inside the defect volume, and having no where else to go,
propagates through this opening. The dispersion diagrams for these planar waveguide
structures also agreed well with the theoretical expectations of our waveguide model. We
also showed that, the wave could be guided along a single missing rod, and demonstrated
the bending of the EM waves for these waveguide structures with “L” shaped openings. We tested metallic photonic crystals built in different dimensions and diflferent
filling ratios. We observed many superiorities of these structures when compared to
dielectric-based photonic crystals. A full characterisation of various metallic photonic
crystals was performed. We also showed that metallic photonic crystals are suitable
for some of the applications we have demonstrated for dielectric structures. We
also fabricated a new layer-by-layer photonic crystal using highly doped silicon wafers
processed by semiconductor micromachining techniques, with a band gap at millimeter
wave frequencies. We showed that the transmission and defect characteristics of these
structures are analogous to metallic photonic crystals, as we have predicted. The
experimental results agree well with the predictions of the transfer matrix method
(TMM) simulations. The method can be extended to fabricate these crystals at THz.
frequencies.Temelkuran, BurakPh.D
Widely tunable resonant cavity enhanced detectors built around photonic crystals
We report a resonant cavity enhanced (RCE) detector built around a three-dimensional photonic band gap crystal. We have demonstrated the resonant cavity enhanced (RCE) effect by placing microwave detectors in defect structures built around dielectric and metallic based photonic crystals. We measured a power enhancement factor of 3450 for planar cavity structures built around dielectric based photonic crystals. The tuning bandwidth of the RCE detector extends from 10.5 to 12.8 GHz. We also demonstrated the RCE effect in cavities built around metallic structures. The power enhancement for the EM wave within these defect structures were measured to be around 190. These measurements show that detectors embedded inside photonic crystals can be used as frequency selective RCE detectors with increased sensitivity and efficiency when compared to conventional detectors
New detection method for capacitive micromachined ultrasonic transducers
Capacitive micromachined ultrasonic transducers (cMUT) have become an alternative to piezoelectric transducers in the past few years. They usually consist of many small membranes all in parallel. In this work we report a new detection method for cMUT's. We arrange the membranes in the form of an artificial transmission line by inserting small inductances between the membranes. The vibrations of the membranes modulate the electrical length of the transmission line, which is proportional to the total capacitance and the frequency of the signal through it. By measuring the electrical length of the artificial line at a RF frequency in the GHz range, the vibrations of the membranes can be detected in a very sensitive manner. For the detector structure we considered a minimum detectable displacement in the order of 10-7 angstroms/√Hz is expected
Highly directional receiver and source antennas using photonic band gap crystals
A directional antenna made with photonic band gap structures has been presented. The directional antenna is formed with two photonic band gap structures oriented back to back and separated from each other by a distance to form a resonant cavity between the photonic band gap structures. An antenna element is placed in the resonant cavity. The resonant frequency of the cavity is tuned by adjusting the distance between the photonic band gap structures. The resonant cavity can be asymmetrical or symmetrical
Intraoperative robotic-assisted large-area high-speed microscopic imaging and intervention
Objective: Probe-based confocal endomicroscopy is an emerging high-magnification optical imaging technique that provides in-vivo and in-situ cellular-level imaging for real-time assessment of tissue pathology. Endomicroscopy could potentially be used for intraoperative surgical guidance, but it is challenging to assess a surgical site using individual microscopic images due to the limited field-of-view and difficulties associated with manually manipulating the probe. Methods: In this paper, a novel robotic device for large-area endomicroscopy imaging is proposed, demonstrating a rapid, but highly accurate, scanning mechanism with image-based motion control which is able to generate histology-like endomicroscopy mosaics. The device also includes, for the first time in robotic-assisted endomicroscopy, the capability to ablate tissue without the need for an additional tool. Results: The device achieves pre-programmed trajectories with positioning accuracy of less than 30um, the image-based approach demonstrated that it can suppress random motion disturbances up to 1.25mm/s. Mosaics are presented from a range of ex-vivo human and animal tissues, over areas of more than 3mm², scanned in approximate 10s. Conclusion: This work demonstrates the potential of the proposed instrument to generate large-area, high-resolution microscopic images for intraoperative tissue identification and margin assessment. Significance: This approach presents an important alternative to current histology techniques, significantly reducing the tissue assessment time, while simultaneously providing the capability to mark and ablate suspicious areas intraoperatively
Precise Hybrid-Actuation Robotic Fiber for Enhanced Cervical Disease Treatment
Treatment for high-grade precancerous cervical lesions and early-stage
cancers, mainly affecting women of reproductive age, often involves
fertility-sparing treatment methods. Commonly used local treatments for
cervical precancers have shown the risk of leaving a positive cancer margin and
engendering subsequent complications according to the precision and depth of
excision. An intra-operative device that allows the careful excision of the
disease while conserving healthy cervical tissue would potentially enhance such
treatment. In this study, we developed a polymer-based robotic fiber measuring
150 mm in length and 1.7 mm in diameter, fabricated using a highly scalable
fiber drawing technique. This robotic fiber utilizes a hybrid actuation
mechanism, combining electrothermal and tendon-driven actuation mechanisms,
thus enabling a maximum motion range of 46 mm from its origin with a sub-100
{\mu}m motion precision. We also developed control algorithms for the actuation
methods of this robotic fiber, including predefined path control and
telemanipulation, enabling coarse positioning of the fiber tip to the target
area followed by a precise scan. The combination of a surgical laser fiber with
the robotic fiber allows for high-precision surgical ablation. Additionally, we
conducted experiments using a cervical phantom that demonstrated the robotic
fiber's ability to access and perform high-precision scans, highlighting its
potential for cervical disease treatments and improvement of oncological
outcomes
Highly directional resonant antennas built around photonic crystals
A monopole resonant antenna with a very high directivity and gain was fabricated based on a layer-by-layer dielectric photonic crystal having a 3D band gap with mid-gap frequency around 12 GHz. The radiation patterns of the antenna, inserted into the planar defect structures built around a 20-layer photonic crystal, was investigated by H-plane measurements and finite difference time domain simulations. When the antenna was inserted in the cavity, the resonance frequency in the reflection dropped sharply from -5 to -35 dB, indicating that most of the power is radiated out in the presence of the cavity. Assuming negligible absorption, the maximum gain has a value around 300
Comparison of fiber delivered CO2 laser and electrocautery in transoral robot assisted tongue base surgery
WOS: 000399177100026PubMed ID: 28190091To compare intra-operative and post-operative effectiveness of fiber delivered CO2 laser to monopolar electrocautery in robot assisted tongue base surgery. Prospective non-randomized clinical study. Twenty moderate to severe obstructive sleep apnea (OSA) patients, non-compliant with Continuous Positive Airway Pressure (CPAP), underwent Transoral Robotic Surgery (TORS) using the Da Vinci surgical robot in our University Hospital. OSA was treated with monopolar electrocautery in 10 patients, and with flexible CO2 laser fiber in another 10 patients. The following parameters in the two sets are analyzed: Intraoperative bleeding that required cauterization, robot operating time, need for tracheotomy, postoperative self-limiting bleeding, length of hospitalization, duration until start of oral intake, pre-operative and post-operative minimum arterial oxygen saturation, pre-operative and post-operative Epworth Sleepiness Scale score, postoperative airway complication and postoperative pain. Mean follow-up was 12 months. None of the patients required tracheotomy and there were no intraoperative complications related to the use of the robot or the CO2 laser. The use of CO2 laser in TORS-assisted tongue base surgery resulted in less intraoperative bleeding that required cauterization, shorter robot operating time, shorter length of hospitalization, shorter duration until start of oral intake and less postoperative pain, when compared to electrocautery. Postoperative apnea-hypopnea index scores showed better efficacy of CO2 laser than electrocautery. Comparison of postoperative airway complication rates and Epworth sleepiness scale scores were found to be statistically insignificant between the two groups. The use of CO2 laser in robot assisted tongue base surgery has various intraoperative and post-operative advantages when compared to monopolar electrocautery
Highly directional receiver and source antennas using photonic band gap crystals
A directional antenna made with photonic band gap structures has been presented. The directional antenna is formed with two photonic band gap structures oriented back to back and separated from each other by a distance to form a resonant cavity between the photonic band gap structures. An antenna element is placed in the resonant cavity. The resonant frequency of the cavity is tuned by adjusting the distance between the photonic band gap structures. The resonant cavity can be asymmetrical or symmetrical.</p