Browsing by Author "Taylor, Zachary"
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- 650 GHz imaging as alignment verification for millimeter wave corneal reflectometry
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä(2022-03-01) Hu, Yong; Baggio, Mariangela; Dabironezare, Shahab; Tamminen, Aleksi; Toy, Brandon; Ala-Laurinaho, Juha; Brown, Elliot; Llombart, Nuria; Deng, Sophie; Wallace, Vincent; Taylor, ZacharyA system concept for online alignment verification of millimeter-wave, corneal reflectometry is presented. The system utilizes beam scanning to generate magnitude-only reflectivity maps of the cornea at 650 GHz and compares these images to a precomputed/measured template map to confirm/reject sufficient alignment. A system utilizing five off-axis parabolic mirrors, a thin film beam splitter, and two-axis galvanometric mirror was designed, simulated, and evaluated with geometric and physical optics. Simulation results informed the construction of a demonstrator system which was tested with a reference reflector. Similarity metrics computed with the aligned template and 26 misaligned positions, distributed on a 0.5 mm x 0.5 mm x 0.5 mm mesh, demonstrated sufficient misalignment detection sensitivity in 23 out of 26 positions. The results show that positional accuracy on the order of 0.5 mm is possible using 0.462 mm wavelength radiation due to the perturbation of coupling efficiency via beam distortion and beam walk-off. - Calibration Alignment Sensitivity in Corneal Terahertz Imaging
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä(2022-05-01) Zarrinkhat, Faezeh; Baggio, Mariangela; Lamberg, Joel; Tamminen, Aleksi; Nefedova, Irina; Ala-Laurinaho, Juha; Khaled, Elsayed E.M.; Rius, Juan M.; Romeu, Jordi; Taylor, ZacharyImproving the longitudinal modes coupling in layered spherical structure contributes significantly to corneal terahertz sensing, which plays a crucial role in the early diagnosis of cornea dystrophies. Using a steel sphere to calibrate reflection from the cornea sample assists in enhancing the resolution of longitudinal modes. The requirement and challenges toward applying the calibration sphere are introduced and addressed. Six corneas with different properties are spotted to study the effect of perturbations in the calibration sphere in a frequency range from 100 GHz to 600 GHz. A particle-swarm optimization algorithm is employed to quantify corneal characteristics considering cases of accurately calibrated and perturbed calibrated scenarios. For the first case, the study is carried out with signal-to-noise values of 40 dB, 50 dB and 60 dB at waveguide bands WR-5.1, WR-3.4, and WR-2.2. As expected, better estimation is achieved in high-SNR cases. Furthermore, the lower waveguide band is revealed as the most proper band for the assessment of corneal features. For perturbed cases, the analysis is continued for the noise level of 60 dB in the three waveguide bands. Consequently, the error in the estimation of corneal properties rises significantly (around 30%). - Calibration of a Two-Port Millimeter-wave Quasioptical Measurement System
A4 Artikkeli konferenssijulkaisussa(2024) Masyukov, Maxim; Tamminen, Aleksi; Nefedova, Irina; Ala-Laurinaho, Juha; Palli, Samu Ville; Generalov, Andrey; Taylor, ZacharyA quasioptical setup based on a Gaussian beam telescope system has been created to analyze the room-temperature and cryogenic millimeter-wave S-parameters of materials and devices for astronomical instrumentation, simulated and tested. The room temperature tests were performed in the WR-3.4 (220-330 GHz) frequency range after completing the thru-reflect-line calibration with a set of custom calibration standards. The system capabilities have been tested during the characterization of the planar devices and materials. - Characterization of Corneal Phantoms
Sähkötekniikan korkeakoulu | Bachelor's thesis(2023-09-22) Levander, Stella - Contactless Terahertz Sensing of Ultrafast Switching in Marx Generator Based on Avalanche Transistors
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä(2022-10-01) Masyukov, Maxim; Vainshtein, Sergey; Mallat, Juha; Taylor, ZacharyIn this paper, we have studied the temporal evolution of switching for each stage of the Marx generator with picosecond temporal and millimeter spatial resolutions employing terahertz measurements. The Marx circuit utilizes collapsing-field-domain (CFD)-based avalanche switches, which are formed in a bipolar GaAs structure and result in the picosecond speed of powerful carrier generation and electrical switching. The application of the CFD-based avalanche switches emitting mm-wave pulsed radiation in the Marx generator provides a unique opportunity to accurately track the switching instants for each of the circuit stages with a picosecond time precision. The collapsing domains cause the sub-THz pulses radiated by each of the avalanche switches, and the same domains generate the electron-hole plasma thus causing simultaneously the electrical switching. In this work, we report the direct measurements of the switching instants for each of the four stages Marx generator and suggest an interpretation of non-trivial experimental results. - Cross polarization and aberrations with Dragonian and equivalent off-axis parabolic mirrors for beam collimation in THz imaging systems
A4 Artikkeli konferenssijulkaisussa(2022) Rezapoor, Pouyan; Tamminen, Aleksi; Ala-Laurinaho, Juha; Dabironezare, Shahab Oddin; Llombart, Nuria; Taylor, ZacharyThe relative benefits of an offset Dragonian reflector compared to equivalent off-axis parabolic (OAP) mirrors for feeding collimated beam to a scanned beam imaging system are investigated. Physical-optics simulation of the Dragonian are performed at 500 GHz. The input is a Gaussian beam with a frequency dependent waist radius fit to the output of a standard Pickett-Potter horn. The collimated output beam properties are characterized, including cross-polarization, beam waist radius, Gaussicity, and M-squared parameter. Next, by sweeping the parameters of an OAP reflector (parent focal length and incidence angle) in the physical-optics simulations, we find the geometry in which the properties of the output beam best match the Dragonian geometry. This reflector is found to be an OAP with 108.22 mm parent focal length and 30. incidence angle. An additional OAP reflector is also considered in these simulations, which is the most often used 90. OAP. The parent focal length is 56.95 mm for this mirror, so that we have a similar beam waist radius in the detector plane. Finally, physical optics simulations reveal that the Dragonian geometry produces much smaller cross-polarization in the detector plane (-23 dB at the beam waist) in comparison with OAP reflector (being -14 dB and -8 dB for 30 degrees and 90 degrees off-axis mirrors, respectively). The 30. OAP reflector is able to produce similar beam quality in terms of phase variation, Gaussicity, and beam waist radius at the detector plane. - Cross polarization in swept beam THz imaging systems using off-axis parabolic mirrors
A4 Artikkeli konferenssijulkaisussa(2022) Rezapoor, Pouyan; Tamminen, Aleksi; Nefedova, Irina; Ala-Laurinaho, Juha; Llombart, Nuria; Rodilla, Helena; Stake, Jan; Taylor, ZacharyThe optical behavior of a terahertz imaging system employing a train of four identical off-axis parabolic mirrors with oblique incidence angle illumination is investigated in this work. The aperture filling and aberrations of a single off-axis parabolic mirror when illuminated by a Gaussian terahertz beam at its focus point is measured and simulated. The amplitude of E-field in transverse electric (TE) and transverse magnetic (TM) polarizations at target plane reveals a significant cross polarization, even when there is zero cross polarization at the source beam, amplitude of which is ∼ 33% of TE polarization. The investigation of the E-field on the detector plane reveals that this ratio is ∼ 1.5% at the detector plane, and the cross polarized E-field at the target plane is rotated back to co polarization. Although its amplitude is negligible, the TM distribution at detector plane is bimodal and tilted about the optical axis. - Curved boundary integral method for electromagnetic fields
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä(2023-12-18) Lamberg, Joel; Zarrinkhat, Faezeh; Tamminen, Aleksi; Ala-Laurinaho, Juha; Rius, Juan; Romeu, Jordi; Khaled, Elsayed E. M.; Taylor, ZacharyThe angular spectrum method is a rigorous method to synthesize near and far-field electromagnetic beams from planar field distributions. However, this limitation of planar surfaces has restricted its applicability to beams with simple focal planes. We propose a curved boundary integral method (CBIM) to synthesize electromagnetic beams from arbitrary surfaces to address this limitation and expand the method’s scope to synthesize beams from and between shaped objects. This study presents a detailed theoretical framework behind the CBIM and validates its effectiveness and accuracy with a comprehensive set of simulations. Additionally, we present mathematical proof to support our proposal. The proposed method satisfies Maxwell’s equations and significantly benefits optical systems and inverse beam design. It allows for analyzing electromagnetic forward/backward propagation between optical elements using a single method. It is also valuable for optical force beam design and analysis. - Curved boundary integral method for off-axis parabolic reflector analysis
A4 Artikkeli konferenssijulkaisussa(2024) Lamberg, Joel; Rezapoor, Poyan; Tamminen, Aleksi; Ala-Laurinaho, Juha; Taylor, ZacharyWe recently introduced a new boundary integral method for numerical electromagnetic beam synthesis on curved surfaces. This study applies the methodology to computing gaussian beam reflection from an off-axis parabolic mirror and validates the results with physical optics simulation. Good agreement was observed. - Design of a quasioptical test bench for VNA extenders
A4 Artikkeli konferenssijulkaisussa(2020-11-08) Nefedova, Irina; Moradikouchi, Anis; Baggio, Mariangela; Tamminen, Aleksi; Hu, Yong; Ala-Laurinaho, Juha; Rodilla, Helena; Stake, Jan; Taylor, ZacharyThe CAD design, simulated optical performance, and test measurements of a quasioptical test bench for VNA extenders are presented. The system allows straightforward integration of off axis parabolic mirrors and VNA extenders. The mirror orientation reduces aberrations and results suggest optical properties are close to what is expected with geometric ray tracing. - Design of double-reflector objective for corneal sensing in the 220-330 GHz band
A4 Artikkeli konferenssijulkaisussa(2022) Baggio, Mariangela; Tamminen, Aleksi; Ala-Laurinaho, Juha; Taylor, ZacharyAn all reflective, Schwarzschild objective design for corneal reflectometry is evaluated in the WR3.4 (220-330 GHz) frequency band. The shadow created by the 60-mm diameter secondary mirror is sufficiently large to mount a standard, OCT system to enable concomitant data acquisition with both modalities while avoiding beam obscuration. The system was fed with a bottle beam comprised of a p= 0, ell = 4 Laguerre-Gaussian mode with a 12.5-mm beam waist radius for increased throughput. The 50-mm focal length system was determined with ray tracing and simulated with an in-house physical optics code using a PEC sphere as a test target. The power coupling coefficient between the feed beam and scattered beam varied from 0.35 at 220 GHz to 0.48 at 330 GHz. While the system demonstrated a clear phase center at less than 1 λ from the geometric focal point, significant edge diffraction prevents the formation of a spherical phasefront, which is needed to achieve phase front matching. - Distributed beamsteering at millimeter waves for imaging and localization
Sähkötekniikan korkeakoulu | Master's thesis(2020-10-19) Pälli, Samu-VilleThe challenge of current millimeter-wave and submillimeter-wave imaging systems is the scalability of the imaging technology. At millimeter wavelengths, dense detector arrays are either bulky in size or require cryogenic temperatures to operate. Lack of detectors or transceivers is often compensated by use of electronic or mechanical scanning system, increasing cost and complexity. Computational imaging methods with frequency-diverse antennas present a method where a single transceiver can be used to image a scene effectively without moving parts, as the system complexity shifts from the hardware to software. In this master's thesis, a dual-band, frequency-diverse, phase hologram for millimeter-wave imaging system applications is designed and measured. The hologram is designed to operate at frequencies of 60 and 250 GHz with emphasis on enhancing efficiency and frequency diversity. First, a literature review of conventional beamsteering methods in millimeter-wave imaging systems is presented. In addition, computational imaging theory is studied together with previous studies of frequency-diverse antennas. The frequency-diverse phase hologram is designed using MATLAB-based physical-optics simulations. With simulations, the possibility of dual-band operation is studied. Furthermore, a thorough analysis of the effects of different hologram design parameters to efficiency, frequency diversity, and manufacturability is carried out. Based on the simulation results, two holograms are chosen for manufacturing, one with optimal results and one sub-optimal for comparison. To validate the performance of manufactured holograms, a quasi-optical measurement setup is built for millimeter-wave measurements at 50-75 GHz and 220-330 GHz. The optimal version of the manufactured holograms achieved efficiency of 20-40% at 50-75 GHz and 40-50% at 220-330 GHz. Although less than predicted by the simulations, the measured efficiency is sufficient for imaging. The measured frequency diversity of both holograms exceeded what was predicted in simulations. Results indicate that the hologram performs well as a frequency-diverse element in millimeter-wave imaging system at both frequency bands. Future work includes imaging experiments of simple targets using the hologram with trained deep-neural-network backend. - Dual View Capsule Endoscope Optics with Metallic Mirrors that Can Serve as Loop Antennas for Wireless Power Transfer
Sähkötekniikan korkeakoulu | Master's thesis(2023-03-20) Kiviharju, PyryFor approximately twenty years, Wireless Capsule Endoscopy has been used as a standard technique for small intestine imaging. Because of the small size of the entirely wireless capsule, it has alleviated various problems related to conventional endoscopy. Despite this success, the capsule still suffers from various problems such as restricted field of view and low resolution. These problems can be seen as consequences of a limited capsule battery. Since the capsule real estate is constrained, it is difficult to increase the battery capacity. Recently, wireless power transfer from outside of the body into the capsule has been considered to alleviate the problem of a limited battery. This approach is potential. However, the limited real estate of a wireless capsule endoscope poses a challenge for introducing of a power transfer antenna into the capsule. The aim of this thesis is to develop a novel dual view optical system for wireless capsule endoscope and evaluate the feasibility of integrating a power transfer antenna into it. Integration in this context means designing an optical mirror in such a manner that its impedance as an antenna would be reasonable for dual-use as a wireless power transfer antenna. To accomplish the aim, a literature review is performed and a suitable optical system template is chosen based on the review. This template design is subsequently modified and optimized appropriately in order to facilitate an antenna. Furthermore, the length of the template design is reduced and its field of views are widened. Reasonable sized mirrors and their impedances as antennas are simulated in an electromagnetic simulator to verify the integration feasibility. The developed dual view optical system achieves an MTF value of 0.38 for the side, and 0.44 for the forward viewing optics at 100 lp/mm spatial frequency. At the nominal focus, the RMS spot radii are 3.6 micrometers for the side, and 3.3 micrometers for the forward view, respectively. The achieved F-numbers of 2.8 and 3 assure sufficient light collection in the dark small intestine. Simulated in a realistic environment, the integrated antennas' resistances lie in the range of 0.2 Ohms -- 2 Ohms for reasonable sized loops at 1 GHz. Correspondingly, the reactances are between 20 Ohms -- 40 Ohms, at the same frequency. - Dynamic optical contrast imaging (DOCI): System theory for rapid, wide-field, multispectral optical imaging using fluorescence lifetime contrast mechanism
A4 Artikkeli konferenssijulkaisussa(2019-01-01) Cheng, Harrison; Xie, Yao; Pellionisz, Peter; Pearigen, Aidan; Rangwalla, Khuzaima; Stafsudd, Oscar; Taylor, Zachary; St John, Maie; Grundfest, WarrenDynamic Optical Contrast Imaging (DOCi) is an imaging technique that generates image contrast through ratiometric measurements of the autouflorescence decay rates of aggregate uorophores in tissue. This method enables better tissue characterization by utilizing wide-field signal integration, eliminating constraints of uniform illumination, and reducing time-intensive computations that are bottlenecks in the clinical translation of traditional fluorescence lifetime imaging. Previous works have demonstrated remarkable tissue contrast between tissue types in clinical human pilot studies [Otolaryngology-Head and Neck Surgery 157, 480 (2017)]. However, there are still challenges in the development of several subsystems, which results in existing works to use relative models. A comprehensive mathematical framework is presented to describe the contrast mechanism of the DOCi system to allow intraoperative quantitative imaging, which merits consideration for evaluation in measuring tissue characteristics in several important clinical settings. - Electromagnetic beam synthesis from spherical surface electric field distributions using modified Fourier optics method
Sähkötekniikan korkeakoulu | Master's thesis(2021-06-16) Lamberg, JoelConventional methods for evaluating electromagnetic beams created from spherical electric surface distribution may include full-wave simulations, geometric optics (GO), or physical optics (PO). These methods are extensively studied and accurate given the model fidelity and a suitable wavelength range. However, they cannot assess the incident and scattered electric field from multi-layered spherical objects without considerable computational effort. Fourier optics is a powerful method to obtain incident electric field, which can be easily expanded to vector spherical harmonics (VSH) presentation to accommodate spherical geometry. The VHS presentation is mapped with the T-matrix method to evaluate the internal and scattered fields from the multi-layered dielectric sphere. The limitation of this method is that it is nominally compatible with planar interfaces. In this study, the Fourier-optics method is expanded to model beam propagation from arbitrary electric field distributions positioned on spherical surfaces. This method can be applied to synthesize beams from any surface shape within reasonable frequency-dependent surface details. The method’s main idea is that Riemann’s surface integral combines differential surface elements, which can be approximated as locally planar elements. The Fourier-optics method is applied to each of these differential elements, and the total electric field is the sum of the fields created from them by the superposition principle. The method is readily applicable to the field of THz sensing of corneal tissue hydration and geometry due to the cornea’s layered spherical shell. First, a literature review of the general theory of Fourier optics, vector spherical harmonics, and the T-matrix method is presented. The new modified Fourier-optics method is derived, and the result is mathematically proved. The simulation algorithm was implemented in the MATLAB programming language. The simulations with the new method are compared with corresponding wave optics simulations or known analytical solutions. The method differs from the results given by physical optics by -41 dB in the case of a constant field at the calotte, and the difference from the theoretical result is -24 dB in the case of a rectangular aperture. Finally, the minimum size of the quasi-optics focusing element required to achieve sufficient resolution and efficiency for THz imaging is estimated. Reflection simulations at 275 GHz show an efficiency of 80 % when the aperture diameter of the focusing element was 100 mm and was 40 mm from the origin of the spherical mirror. The results suggest that the desired electric field on the spherical surface can be produced with an aperture of this size. In this case, up to 80 % of the reflected power returns to the aperture. In the future, the frequency dependence of the simulation method and field synthesis will be investigated on a spherical surface to analyze the cornea’s reflection spectrum. The work involves iterative optimization, in which case the developed algorithm has to be rewritten without a VSH extension to provide lighter computational capacity. - Exploration of cross-polarization generation and coupling efficiency degradation in OAP mirror pairs
Sähkötekniikan korkeakoulu | Bachelor's thesis(2019-08-28) Lamberg, Joel - Extended legality of curved boundary integral method
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä(2024-07-29) Lamberg, Joel; Lamberg, Lasse; Tamminen, Aleksi; Ala-Laurinaho, Juha; Taylor, ZacharyThe angular spectrum method is an efficient approach for synthesizing electromagnetic beams from planar electric field distributions. The electric field definition is restricted to a plane, which can introduce inaccuracy when applying the synthesized beam to curved surface features. The angular spectrum method can also be interpreted as a pure source method defining the field symmetrically with respect to the creation plane. Recently, we generalized that symmetric field method to arbitrary source distributions, which are valid at any point on compact, regular surface Ω in R3. We call this approach the Curved Boundary Integral method. The electromagnetic fields synthesized with this method satisfy the Helmholtz equation and are adjusted via amplitude and phase at the desired surface. The fields are obtained as a relatively simple integral. However, restrictions on where in space the synthesized field is valid were included in the mathematical proof length to avoid obscuring the main points. These restrictions can be significant depending on the shape and degree of curvature of surface Ω. In this article, we remove these restrictions so that the integral representation of the electromagnetic beam becomes valid at all points r ∈ R3 \ Ω, with a minor restriction. Its modification can work even on Ω. We demonstrate the importance of this extended legality with a source field parametrized into the torus surface. The electromagnetic radiation of this structure would not be valid at any point in space without this extension. Finally, we show that by changing the order of integration, the field singularity at each source point is eliminated. - Extraction of thickness and water content gradients in hydrogel-based, water-backed corneal phantoms via submillimeter wave reflectometry
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä(2021-11-01) Tamminen, Aleksi; Baggio, Mariangela; Nefedova, Irina; Sun, Qiushuo; Presnyakov, Semyon; Ala-laurinaho, Juha; Brown, Elliot; Wallace, Vincent; Macpherson, Emma; Maloney, Thaddeus; Kravchenko, Natalia; Salkola, Mika; Deng, Sophie; Taylor, ZacharyAbsolute thickness and free-water-content gradients in gelatin-based corneal phantoms with physiologically accurate radii of curvature and aqueous backing were extracted via coherent submillimeter-wave reflectometry at 220-330 GHz. Fourier-domain-based calibration methods, utilizing temporal and spatial gating, were developed and yielded peak-to-peak amplitude and phase clutter of 10-3 and 0.1°, respectively, for signal-to-noise ratios (SNRs) between 40 and 50 dB. Total 12 phantoms were fabricated. Calibration methods enabled quantification of target sphericity that strongly correlated with optical-coherence tomography-based sphericity metrics via image segmentation. The extracted free-water volume fraction varied less than 5% in the five phantoms whose fabrication yielded the most spherical geometry. Submillimeter-wave-based thickness accuracy was better than 111 μm (∼λ/9) with an average of 65 μm (∼λ/17) and standard deviation of 44 μm (∼λ/25) for phantoms with physiologically relevant geometry. Monte-Carlo simulations of measurement noise and uncertainty limits agree with the experimental data analysis and indicate a lower thickness accuracy limit of 33 μm, and water-content sensitivities of 0.5% and 11.8% for the anterior and posterior segments, respectively. Numerical analysis suggests that the measurement fidelity was SNR limited and identified optical path length ambiguities within the cornea where a continuum of thickness/water gradient pairs produces statistically insignificant differences in complex reflection coefficient for finite SNR. This is the first known submillimeter-wave measurement technique, which is able to extract both the thickness and water-content gradients from a soft-tissue phantom, with a water backing, without the need for ancillary measurements. - Filtering Spurious Reflections with Time Domain Gating
Sähkötekniikan korkeakoulu | Bachelor's thesis(2022-01-20) Linnanen, Patrick - Fivefold Peak Power Boost in HBT-driven GaAs Collapsing-Field-Domain-Based Sub-THz Source
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä(2023-10-01) Masyukov, Maxim; Vainshtein, Sergey; Grigorev, Roman; Taylor, ZacharyMiniature on-chip sources based on the collapsing field domain phenomenon in GaAs have advanced compact sub-picosecond time-domain imaging schemes operating in the 100-250 GHz frequency range. Efforts have been done to broaden the emission band of on-chip sources towards 400 GHz, but increasing the peak power of the emitted picosecond-range pulses remains physically challenging but practically important. In this work, a fivefold increase in peak power has been achieved by replacing the previously used hetero-bipolar-based collapsing field domain source operating in self-oscillating mode with a bipolar-based source externally pulsed by a hetero-bipolar driver. Importantly, the suggested solution unaffected the compactness of the source and facilitates its application in time domain imaging.