Browsing by Subject "Sensing"

Now showing 1 - 4 of 4

Open Access
Bow tie shaped coplanar waveguide microwave resonators for single cell detection, flow rate measurements, and nanopore sensing of viruses
(2020-09) Seçme, Arda
Measurement sensitivity of different biosensing applications can be enhanced by using the microwave resonators. In the first application, microwave sensors based on bow tie shaped coplanar waveguide (CPW) resonator was designed to detect single cells in real-time. While the resonator was kept at its resonance frequency, cells/particles were made a pass through the sensing electrodes and their frequency shift statistics were obtained. For each cell, the geometrical size that is obtained from the optical microscope was correlated to the electrical volume of the cell which was measured by the microwave signals. A linear relationship was observed between the electrical and geometrical volume of a cell. Dispersion caused by the device geometry was elucidated using the standard sized polystyrene microparticles. To observe the single-cell dynamic, a target cell was trapped around the sensing region, and its microwave response was continuously recorded. Then cells were treated with dimethyl sulfoxide (DMSO), a chemical accelerating dehydration, and a decline in the resonance shifts by time was observed as the cell lost total content. Secondly, the same microwave design was patterned on a low-stress thin film membrane and used for flow rate measurements. When the flow is on, there were certain shapes continuously formed on the membrane and after a critical point pulsation of the membrane cause a shift in the resonance frequency. When the flow rate was increased, it was observed that these shapes formed faster so does frequency shifts in the resonance. Therefore, the effective flow rate could be correlated to the pulsation frequency of the membrane. Then, devices with different membrane size and different channel geometry were fabricated to span different flow rate values. As a secondary sensing mechanism, the flow was given from the reset condition where there was no flow. In this case, the amount of frequency shift was related to the flow rate and a monotonically increasing relation was obtained. As a next step, instead of liquid, the air was pressurized to measure the flow rate. Airflow measurements have become important during the COVID19 pandemic as the flow rate sensors are the most essential component of the ventilation machines. Using the secondary mechanism, frequency shifts induced by airflow were recorded and a linear relation was observed between the applied air pressure and frequency modulations. In the last application, the sensing electrodes were patterned down to hundreds of nanometer apart to detect nanoparticles and biological samples such as polystyrene nanoparticles or viruses. A nanopore having a diameter around 400 nm was drilled on the membrane using focused ion beam (FIB) and analytes were translocated using electrokinetic motion. Since the events would be quick in electrokinetic motion, data were collected with CompactRIO (cRIO), however, when the PLL was running, there were spikes in cRIO for this reason after the resonator was locked to zero degrees, LabVIEW was stopped. Yet, since the resonator has low quality factor (≈100), the phase of the resonator dwells around zero degrees and still sensitive to translocations through the pore. In the control run, there were no precipitous jumps, however, when the particles were added sudden jumps induced by the particles were recorded. Therefore, can be optimized and proposed as a biophysical sensor to characterize single viruses.
Open Access
Signal recovery with cost-constrained measurements
(IEE, 2010-03-22) Özçelikkale, A.; Özaktaş, Haldun M.; Arikan, E.
We are concerned with the problem of optimally measuring an accessible signal under a total cost constraint, in order to estimate a signal which is not directly accessible. An important aspect of our formulation is the inclusion of a measurement device model where each device has a cost depending on the number of amplitude levels that the device can reliably distinguish. We also assume that there is a cost budget so that it is not possible to make a high amplitude resolution measurement at every point. We investigate the optimal allocation of cost budget to the measurement devices so as to minimize estimation error. This problem differs from standard estimation problems in that we are allowed to design the number and noise levels of the measurement devices subject to the cost constraint. Our main results are presented in the form of tradeoff curves between the estimation error and the cost budget. Although our primary motivation and numerical examples come from wave propagation problems, our formulation is also valid for other measurement problems with similar budget limitations where the observed variables are related to the unknown variables through a linear relation. We discuss the effects of signal-to-noise ratio, distance of propagation, and the degree of coherence (correlation) of the waves on these tradeoffs and the optimum cost allocation. Our conclusions not only yield practical strategies for designing optimal measurement systems under cost constraints, but also provide insights into measurement aspects of certain inverse problems.
Open Access
Strong light-matter interaction in lithography-free perfect absorbers for photoconversion, photodetection, light emission, sensing, and filtering applications
(2022-01) Ghobadi, Amir
The efficient harvesting of electromagnetic (EM) waves by subwavelength nanostructures can result in perfect light absorption in the narrow or broad frequency range. These metamaterial based perfect light absorbers are of particular interest in many applications, including thermal photovoltaics, photovoltaics, emission, sensing, filtering, and photodetection applications. Although advances in nanofabrication have provided the opportunity to observe strong light-matter interaction in various optical nanostructures, the repeatability and upscaling of these nano units have remained a challenge for their use in large-scale applications. Thus, in recent years, the concept of lithography-free metamaterial absorbers (LFMAs) has attracted much attention in different parts of the EM spectrum, owing to their ease of fabrication and high functionality. In this thesis, the unprecedented potential of these LFMAs will be explored. This thesis explores the material and architecture requirements for the realization of a LFMA from ultraviolet (UV) to far-infrared (FIR) wavelength regimes. For this aim, we theoretically investigate the required conditions to realize an ideal perfect absorber. Then, based on the operation wavelength and application, the proper material and design architecture is defined. Later, to experimentally realize these ideal LFMAs, lithography-free large-scale compatible routes are developed to generate nanostructures in centimeter scales. Finally, the application of these LFMAs has been demonstrated in various fields including filtering, sensing, emission, photodetection, and photoelectrochemical water splitting. This thesis study demonstrates that, by the use of proper material and design configuration, it is possible to realize these LFMAs in every portion of the EM spectrum with a vast variety of potential applications. This, in turn, opens up the opportunity of the practical application of these perfect absorbers in large-scale dimensions. In the last section of the thesis, we discuss the progress, challenges, and outlook of this field to outline its future direction.
Open Access
Thermally tunable ultrasensitive infrared absorption spectroscopy platforms based on thin phase-change films
(American Chemical Society, 2016-11) Bakan, G.; Ayas S.; Ozgur E.; Celebi, K.; Dana, A.
The thermal tunability of the optical and electrical properties of phase-change materials has enabled the decades-old rewritable optical data storage and the recently commercialized phase-change memory devices. Recently, phase-change materials, in particular, Ge2Sb2Te5 (GST), have been considered for other thermally configurable photonics applications, such as active plasmonic surfaces. Here, we focus on nonplasmonic field enhancement and demonstrate the use of the phase-change materials in ultrasensitive infrared absorption spectroscopy platforms employing interference-based uniform field enhancement. The studied structures consist of patternless thin GST and metal films, enabling simple and large-area fabrication on rigid and flexible substrates. Crystallization of the as-fabricated amorphous GST layer by annealing tunes (redshifts) the field-enhancement wavelength range. The surfaces are tested with ultrathin chemical and biological probe materials. The measured absorption signals are found to be comparable or superior to the values reported for the ultrasensitive infrared absorption spectroscopy platforms based on plasmonic field-enhancement.