Resonance Frequency Shift Research Articles

A metamaterial based microfluidic sensor for permittivity detection of liquid

The electromagnetic (EM) behavior of a microwave sensor has specific relationship with the physical properties of the materials to be detected, e.g. the concentration of solution and the permittivity of gas. The microwave sensor can detect changes of EM response in real time, and obtain the material properties with low sample consumption, high efficiency and dispersion characteristics. This work presents a microfluidic sensor using spiral resonators and plasmonic metamaterials with confined EM fields for intensive resonance. Two microfluidic chips with spiral channels engraved in polydimethylsiloxane are also adopted to enhance the interaction between the EM fields and the carried liquids at resonance frequencies. The permittivity of liquid samples can be detected through the shift of resonance frequency. A prototype of the sensor is fabricated and tested with several regular solutions and organic solvents, showing a good performance in terms of low liquid consumption (8 μl), good sensitivity (410 MHz frequency offset when ϵr changes from 1 to 36.7) and low cost.

Photothermal Responsivity of van der Waals Material-Based Nanomechanical Resonators.

Nanomechanical resonators made from van der Waals materials (vdW NMRs) provide a new tool for sensing absorbed laser power. The photothermal response of vdW NMRs, quantified from the resonant frequency shifts induced by optical absorption, is enhanced when incorporated in a Fabry–Pérot (FP) interferometer. Along with the enhancement comes the dependence of the photothermal response on NMR displacement, which lacks investigation. Here, we address the knowledge gap by studying electromotively driven niobium diselenide drumheads fabricated on highly reflective substrates. We use a FP-mediated absorptive heating model to explain the measured variations of the photothermal response. The model predicts a higher magnitude and tuning range of photothermal responses on few-layer and monolayer NbSe2 drumheads, which outperform other clamped vdW drum-type NMRs at a laser wavelength of 532 nm. Further analysis of the model shows that both the magnitude and tuning range of NbSe2 drumheads scale with thickness, establishing a displacement-based framework for building bolometers using FP-mediated vdW NMRs.

Toward In-situ Characterization of Additively Manufactured Parts Using Nonlinear Resonance Ultrasonic Spectroscopy

ABSTRACT In this study, we investigate the feasibility of using nonlinear resonance ultrasound spectroscopy (NRUS) for in-situ monitoring of additively manufactured (AM) parts i.e., while they are still on the build plate. In NRUS, the test specimen is excited around one or more of its resonance frequencies with increasing driving amplitude. The linear shift in resonance frequency with the increasing driving amplitude is a measure of the constituent material’s hysteretic nonlinearity (α), which is itself related to some degree of micro-damage in the test specimens. We conduct NRUS on test specimens glued to a thick plate. The specimens are excited using a piezoelectric transducer (PZT) adhered to the bottom of the plate. We use this setup to measure the hysteretic nonlinearity parameters ( and ) of several cylindrical AM specimens fabricated by laser powder bed fusion technique as well as a few non-AM metallic specimens. The measured nonlinearity parameters for the specimens on the build plate (process monitoring mode) are compared to those measured without the build plate (quality control mode). We observe a systematic decrease in the measured nonlinearity when the specimens are tested on the build plate. An analytical study demonstrates that we measure the weighted average nonlinearity of the specimen and build plate, which itself has a lower nonlinearity. Despite the observed difference, the measured nonlinearity parameters of the specimens with and without the build plate are highly correlated. With further investigations, the proposed test setup can potentially be used for characterization of AM parts in situ.

Fabrication of frequency-selective surface by picosecond laser direct writing

In this paper, a terahertz (THz) frequency-selective surface (FSS) is fabricated through picosecond (ps) laser direct writing on the silicon-based silver film. The time-domain spectroscopy (TDS) technique is used to test its electromagnetic modulation performance. Based on the finite-difference time-domain method, CST microwave studio 2016 was used to simulate its resonance characteristic. By optimizing the process parameters, the square ring structures on the FSS with the size error below 2% are fabricated. It is found that the center frequencies of the experimental and simulated resonance peaks are nearly both at 0.293 THz, and the transmission is about 0.01%. From the simulation results, when the size error is controlled below 2 μm, the resonant frequency shift is about 2.2 GHz. Combining the simulation and experimental results, if the size error of inner square is controlled below 2%, it has little effect on the THz metasurfaces’ modulation performance. By optimizing the laser scanning strategy and processing parameters, ps laser direct writing provides a new choice for the convenient fabrication of THz metamaterials.

Dual resonance modes in two-port SAW resonator sensors: an analysis through scattering matrix approach

We report dual resonance modes occurring in two-port surface acoustic wave (SAW) resonators attached with typical sensing film and investigated the significance in sensing applications. Two-port SAW resonators operating at 303 MHz frequency were modelled using the scattering matrix approach and resonance frequency characteristics of the resonators were studied for mass loading caused by an arbitrary film attached between the interdigital transducers of the resonator. Depending on the mass loading, symmetric and antisymmetric modes occur around the near resonance frequency of the SAW device. Either a single-mode or both modes are dominant depending on the phase shift caused by the mass loading of the film. Choosing arbitrary film thickness could result in complexity to track the resonance frequency shift and degrade sensing performance. The approach used for analysis can aid to determine the optimum sensing film thickness for two port SAW resonator-based sensors that can exhibit better linearity.

Integrated thermal and magnetic susceptibility modeling for air-motion artifact correction in proton resonance frequency shift thermometry

Purpose Hyperthermia treatments are successful adjuvants to conventional cancer therapies in which the tumor is sensitized by heating. To monitor and guide the hyperthermia treatment, measuring the tumor and healthy tissue temperature is important. The typical clinical practice heavily relies on intraluminal probe measurements that are uncomfortable for the patient and only provide spatially sparse temperature information. A solution may be offered through recent advances in magnetic resonance thermometry, which allows for three-dimensional internal temperature measurements. However, these measurements are not widely used in the pelvic region due to a low signal-to-noise ratio and presence of image artifacts. Methods To advance the clinical integration of magnetic resonance-guided cancer treatments, we consider the problem of removing air-motion-induced image artifacts. Thereto, we propose a new combined thermal and magnetic susceptibility model-based temperature estimation scheme that uses temperature estimates to improve the removal of air-motion-induced image artifacts. The method is experimentally validated using a dedicated phantom that enables the controlled injection of air-motion artifacts and with in vivo thermometry from a clinical hyperthermia treatment. Results We showed, using probe measurements in a heated phantom, that our method reduced the mean absolute error (MAE) by 58% compared to the state-of-the-art near a moving air volume. Moreover, with in vivo thermometry our method obtained a MAE reduction between 17% and 95% compared to the state-of-the-art. Conclusion We expect that the combined thermal and magnetic susceptibility modeling used in model-based temperature estimation can significantly improve the monitoring in hyperthermia treatments and enable feedback strategies to further improve MR-guided hyperthermia cancer treatments.

Detection of Polystyrene Microplastic Particles in Water Using Surface-Functionalized Terahertz Microfluidic Metamaterials

We propose a novel method for detecting microplastic particles in water using terahertz metamaterials. Fluidic channels are employed to flow the water, containing polystyrene spheres, on the surface of the metamaterials. Polystyrene spheres are captured only near the gap structure of the metamaterials as the gap areas are functionalized. The resonant frequency of terahertz metamaterials increased while we circulated the microplastic solution, as polystyrene spheres in the solution are attached to the metamaterial gap areas, which saturates at a specific frequency as the gap areas are filled by the polystyrene spheres. Experimental results were revisited and supported by finite-difference time-domain simulations. We investigated how this method can be used for the detection of microplastics with various solution densities. The saturation time of the resonant frequency shift was found to decrease, while the saturated resonant frequency shift increased as the solution density increased.

Heterogeneous Nanoplasmonic Amplifiers for Photocatalysis’s Application: A Theoretical Study

The higher cost of Ag and Au and their resonance frequency shift limitation opened the way to find an alternative solution by developing new nanohybrid antenna based on silicon and silicon dioxide coated with metallic nanoparticles. The latter has been recently solicited as a promising configuration for more large-scale plasmonic utilisation. This work reports a multitude of fascinating new phenomenon on LSPR on silicon antenna wires coated with core-shell nanospheres and the studying of the nanoplasmonics amplifiers to control optical and electromagnetic properties of materials. The LSPR modes and their interaction with the silicon nanowires are studied using numerical methods. The suggested configuration offers resonance covering the UV-visible and NIR regions, making them an adaptable addition to the nanoplasmonics toolbox.

ZIF-Based Metal-Organic Frameworks for Cantilever Gas Sensors

Among the different gas sensing platforms, cantilever-based sensors have attracted considerable interest in recent years thanks to their ultra-sensitivity and high-speed response. The gas sensing mechanism in a dynamic cantilever sensor is based on its resonance frequency shift upon adsorption of a gas molecule on the sensor. In order to sensitize the surface of a cantilever, a sensitive receptor material with large surface area is required. Metal-organic frameworks (MOFs) are a class of nanoporous crystalline materials composed of metal ions coordinated to organic linkers. MOFs are promising for gas sensing applications as they have large surface area, rich porosity with adjustable pore size and excellent selective adsorption capability for various gasses.[1] Zeolite imidazole frameworks (ZIFs) are a class of MOFs where metals with tetrahedral coordination (i.e. Zn, Co, Fe, Cu) are the central node and the ligands are imidazolate-based organic molecules.In this work, we developed a ZIF-based thin film for dynamic cantilever gas-sensing applications. We employed a novel atmospheric pressure spatial atomic layer deposition (AP-SALD)[2][3] technique to deposit a ZnO sacrificial layer on the silicon cantilevers. This technique allows the deposition of high-quality films at atmospheric pressure, faster than conventional ALD. The ZnO layer was then converted to a particular ZIF film with desired porosity and size, through a MOF-CVD process.[4] A gas-sensing bench setup was developed for the cantilever actuation and read-out. We present the chemical and morphological properties of the ZIF, as well as the frequency response of the sensor to various gases. The device showed reliable sensitivity to humidity, CO2 and several VOCs.

Bipolar Electrostatic Driving of Isolated Micro-Resonator for Sensing High Voltage of Battery Output with Resolution

Electrostatic Si resonator was applied to sense the voltage at the facing electrode in a highly isolated approach. The resonant frequency shifts under the effect of the electrical field from the facing electrode connected to the high voltage (corresponding to the battery). Here, two resonators are fabricated. The electrical isolation was obtained by driving the resonators to be floated electrically. The charging of the resonator causes the fluctuation of the driving performance, degrading the sensing resolution. The driving voltage was set to be bipolar to avoid the fluctuation. This novel method stabilizes the resonant frequency realizing 0.25 V accuracy against 80 V. Feasibility for measuring the voltage up to 420 V is demonstrated.

Probe temperature effect on the curling probe and its correction technique

This article introduces the effect of the probe temperature existing in a curling probe, which enables one to measure the electron density in plasma and the thickness of deposited film on the probe surface. We have recognized the effect appearing on the resonant frequency in previous reports, but we made measurement conditions where no temperature affected the frequency shift. The practical use of curling probes does not always allow one to have such an ideal condition, so it is necessary to have a good understanding of the probe temperature effect. Toward the understanding, we firstly measured the resonant frequency shift for five different operating powers with a curling probe having a heater and thermocouple attached to the probe surface. The frequency shift measurement showed consistent trends with plasma off and on. With some careful analyses, we found that the correction factor, which is necessary to compensate for the electron density measurement due to geometry reasons, etc for curling probe, had a regularity as a function of probe temperature; the inversed square of the correction factor was proportional to the degree of resonant frequency shift. Furthermore, the proportionality depended on the probe temperature with the regularity, so we finally were able to include the probe temperature effect on the correction factor, which realized the correction of the electron density even when the probe has a temperature variation. The electron density measurement with this correction technique worked well and followed the density measured with the Langmuir probe well. In particular, this research revealed that the correct technique is effective when probing temperature increases.

Collisional electron paramagnetic resonance frequency shifts in Cs-Rb-Xe mixtures

We report a measurement of the ratio of dimensionless enhancement factors ${\ensuremath{\kappa}}_{0}$ for $\mathrm{Cs}\text{\ensuremath{-}}^{129}\mathrm{Xe}$ and $\mathrm{Rb}\text{\ensuremath{-}}^{129}\mathrm{Xe}$ in the temperature range 115--140 ${}^{\ensuremath{\circ}}\mathrm{C}$; both pairs are used in spin-exchange optical pumping (SEOP) to produce hyperpolarized $^{129}\mathrm{Xe}$. ${\ensuremath{\kappa}}_{0}$ characterizes the amplification of the $^{129}\mathrm{Xe}$ magnetization contribution to the alkali-metal electronic effective field, compared to the case of a uniform continuous medium in classical magnetostatics. The measurement was carried out in ``hybrid'' vapor cells containing both Rb and Cs metal in a prescribed ratio, producing approximately the same vapor density for both. Alternating measurements of the optically detected electron paramagnetic resonance (EPR) frequency shifts caused by the SEOP polarization and subsequent sudden destruction of the same quantity of $^{129}\mathrm{Xe}$ magnetization were made for $^{133}\mathrm{Cs}$ and either $^{87}\mathrm{Rb}$ or $^{85}\mathrm{Rb}$. An important source of systematic error caused by power fluctuations in the pump laser that produced variable light shifts in the EPR frequency was characterized and then mitigated by allowing sufficient warm-up time for the pump laser. We measured ${({\ensuremath{\kappa}}_{0})}_{\mathrm{CsXe}}/{({\ensuremath{\kappa}}_{0})}_{\mathrm{RbXe}}=1.215\ifmmode\pm\else\textpm\fi{}0.007$ with no apparent temperature dependence. Based on our previous measurement ${({\ensuremath{\kappa}}_{0})}_{\mathrm{RbXe}}=518\ifmmode\pm\else\textpm\fi{}8$, we determine ${({\ensuremath{\kappa}}_{0})}_{\mathrm{CsXe}}=629\ifmmode\pm\else\textpm\fi{}10$, which is more precise than, but consistent with, a previous measurement made by J. Fang et al. [Chin. Phys. B 23, 063401 (2014)].

Multifrequency Investigation of Single- and Double-Stranded DNA with Scalable Metamaterial-Based THz Biosensors.

Due to the occurrence of THz-excited vibrational modes in biomacromolecules, the THz frequency range has been identified as particularly suitable for developing and applying new bioanalytical methods. We present a scalable THz metamaterial-based biosensor being utilized for the multifrequency investigation of single- and double-stranded DNA (ssDNA and dsDNA) samples. It is demonstrated that the metamaterial resonance frequency shift by the DNA’s presence depends on frequency. Our experiments with the scalable THz biosensors demonstrate a major change in the degree of the power function for dsDNA by 1.53 ± 0.06 and, in comparison, 0.34 ± 0.11 for ssDNA as a function of metamaterial resonance frequency. Thus, there is a significant advantage for dsDNA detection that can be used for increased sensitivity of biomolecular detection at higher frequencies. This work represents a first step for application-specific biosensors with potential advantages in sensitivity, specificity, and robustness.

Design of a Split Ring Resonator Integrated with On‐Chip Terahertz Waveguides for Colon Cancer Detection

AbstractFinite element method (FEM) simulations (employing ANSYS High Frequency Structure Simulator, HFSS) are used to investigate the response of terahertz (THz) frequency range split‐ring resonators (SRRs) integrated with on‐chip THz waveguides to cancerous tissues. Two‐port S‐parameter simulations are performed to obtain the transmission spectra (S21) of a planar Goubau line (PGL) integrated with an SRR. Permittivity and loss tangent of the colonic tissues are both taken into account in the numerical simulation. The transmission spectra of the SRR integrated PGL are obtained for cancerous and healthy tissues in close proximity to the SRR, and it is found that they can be distinguished by the resonant frequency shift of the SRR induced by dielectric loading. The electric field distribution and magnitude near the SRR for various capacitive gap widths of SRR are investigated to understand how the gap width affects the maximum electric field magnitude and the vertical extent of the electric field in the gap area. The simulated imaging of colonic tissue consisting of healthy and cancerous tissues using the SRR integrated PGL device with a protective layer on it is performed, showing how the technique could in principle be used to distinguish tumor margins with realistic THz dielectric parameters.

Glucose level detection using millimetre-wave metamaterial-inspired resonator.

Millimetre-wave frequencies are promising for sensitive detection of glucose levels in the blood, where the temperature effect is insignificant. All these features provide the feasibility of continuous, portable, and accurate monitoring of glucose levels. This paper presents a metamaterial-inspired resonator comprising five split-rings to detect glucose levels at 24.9 GHz. The plexiglass case containing blood is modelled on the sensor’s surface and the structure is simulated for the glucose levels in blood from 50 mg/dl to 120 mg/dl. The novelty of the sensor is demonstrated by the capability to sense the normal glucose levels at millimetre-wave frequencies. The dielectric characteristics of the blood are modelled by using the Debye parameters. The proposed design can detect small changes in the dielectric properties of blood caused by varying glucose levels. The variation in the transmission coefficient for each glucose level tested in this study is determined by the quality factor and resonant frequency. The sensor presented can detect the change in the quality factor of transmission response up to 2.71/mg/dl. The sensor’s performance has also been tested to detect diabetic hyperosmolar syndrome. The sensor showed a linear shift in resonant frequency with the change in glucose levels, and an R2 of 0.9976 was obtained by applying regression analysis. Thus, the sensor can be used to monitor glucose in a normal range as well as at extreme levels.

Chitosan Coating on Quartz Crystal Microbalance Gas Sensor for Isopropyl Alcohol and Acetone Detection

The development of acoustic wave sensors was driven by the presence of modern technology. Quartzcrystal microbalance (QCM) has excellent sensing capabilitiesand has wide range ofapplications. Selection of sensing layer is crucial to ensure the performance of the QCM sensor for volatile organic compound (VOC) detection. Hence, the objective of this paper is to compare the performance of chitosan coated QCM sensor for different analyte gas: isopropyl alcohol (IPA). Finite element simulation was implemented usingCOMSOL Multiphysics to study the resonance frequency shift before and after sensing. Simulation results shows IPA detection shows a higher resonance frequency shift of 62.5 Hzcompared to acetone due to higher molar mass. Experimental work is conducted to validate the simulation results where IPA analyte gas yields in 84.8 Hz which is higher than acetone analyte gas at 41.8 Hz. The functional groups for both sensing layer and analyte gas also affects the gas detection performance. IPA analyte gas possessed hydroxyl groups that favors to hydrogen bond formation with chitosan sensing layer. Thus, the QCM sensor with chitosan as the sensing layer has the potential for VOC sensing of different molar mass and functional groups.

Ultrasensitive detection of low-dose gamma radiation using polymeric thin films on microelectromechanical system-based sensors

ABSTRACT A polymer-coated microelectromechanical system (MEMS) sensor was used in this study to detect electromagnetic nuclear radiation (gamma radiation) with high sensitivity. The resonance frequencies shift (RFS) resulting from the effect of gamma irradiation on the MEMS sensors coated with two polymeric thin films (polyacrylic acid [PAA] and polystyrene [PS]) were measured. The mechanical and optical properties of the coated polymer layers on Si wafers were evaluated before and after irradiation using atomic force microscopy (AFM) and ultraviolet–visible spectrophotometry. Further, surface roughness and reflectivity of the PS polymer thin film were found to be linear as a function of the gamma irradiation time. However, there was no noticeable change in the RFS, surface roughness, or reflectivity of the PAA polymer thin film. These results were confirmed using spectroscopic ellipsometry measurements which showed that the surface roughness increased linearly as a function of the gamma irradiation time. Based on these findings, the interaction between gamma radiation and PS polymer revealed that the MEMS coated with PS produced a linear response that could be used to develop radiation sensors for low gamma doses. Although many techniques exist for detecting nuclear radiation, the sensor proposed has ultrasensitivity, high measurement accuracy, and low cost.

Study on a terahertz biosensor based on graphene-metamaterial

The interaction between the terahertz wave propagating in free space and the sample is weak, which leads to the weak signal of the sample, which cannot meet the detection needs of trace samples. In order to meet the detection of trace samples, a kind of metamaterial absorber (the basic unit of the absorber is composed of gold-high resistance silicon-aluminum three-layer structure) is designed, and the monolayer graphene is transferred on the surface of the metamaterial absorber to construct the graphene-metamaterial absorber heterostructure. The transmission spectrum of the resonant cavity is simulated and measured by terahertz time domain spectroscopy system, and the obvious resonance frequency shift is observed. The results show that the graphene-metamaterial absorber heterostructure can detect josamycin antibiotic solution with concentration of 0.02 mg/L (the mass of josamycin is 0.2 ng). Compared with using the same structure metamaterial absorber to detect josamycin antibiotics, the sensitivity is increased by an order of magnitude. Using graphene-metamaterial heterostructure to detect the relative change of heterostructure reflectivity caused by josamycin antibiotics can reach 40%. The research in this paper provides a new technical means for accurate and rapid detection in terahertz band.

Highly Sensitive Hydrogen Sensor Based on an Optical Driven Nanofilm Resonator.

Nanofilm resonators combine ultracompact and highly mechanically sensitive properties, making them intriguing devices for sensing applications. For trace hydrogen detection, we demonstrate an optomechanical nanofilm resonator by employing a Pd- and Au-decorated graphene onto a fiber end facet. The Pd layer is a sensitive layer for selective absorption of hydrogen. Hydrogen sensing is achieved by all-optical measuring of the resonant frequencies shift of the optomechanical nanofilm resonator induced by hydrogen-related mechanical stress change. Using the approach, we realize highly sensitive hydrogen sensing at room temperature with a low detection limit, challenging the state-of-the-art. When the measured hydrogen concentration increases from 0 to 1000 ppm (v/v), the mechanical resonance frequencies of the sensor at 511.7 kHz, 1253.4 kHz, and 2231.7 kHz blue-shift by 100.4 kHz, 257.5 kHz, and 400.6 kHz, respectively. The response and recovery time are 120.3 and 91.3 s at a 1000 ppm hydrogen concentration. Such a sensor exhibits a low detection limit of 741 ppb and good repeatability in the measurement process, which makes the practical application of the sensor possible.

Quantitative capacitance measurements in frequency modulation electrostatic force microscopy

We have proposed a method for quantitative capacitance measurements using frequency modulation electrostatic force microscopy (EFM) with a dual bias modulation method and demonstrated it on n- and p-type Si samples. First, we theoretically derived a conversion formula from a frequency shift of cantilever resonance in EFM into a capacitance value based on the parallel plate capacitor model, by which a pair of an EFM tip and a semiconductor sample is expected to be equivalently represented. Then the capacitance measurements were experimentally conducted on the n- and p-type Si substrates, and the acquired capacitance–voltage curves indicated that the obtained capacitance values were consistent with the expected ones and that the carrier densities evaluated from the depletion capacitances were also in good agreement with those evaluated by the conventional Hall effect measurements. From those results, the validity of our quantitative evaluation method has been well confirmed.