Resonant Research Articles

Elastic constant estimation for low-Q materials using convolutional neural network based resonant ultrasound spectroscopy

ABSTRACT Resonant ultrasound spectroscopy (RUS) is a non-destructive technique to calculate material elastic constants from resonant frequencies. However, low quality factor (i.e., low-Q) materials experience strong energy attenuation during vibration, resulting in the overlap and partial loss of resonant peaks in experimental spectra. Consequently, extracting authentic resonant frequencies becomes challenging, making the subsequent elastic constant calculation time-intensive and necessitating expert intervention. Regarding this, a novel RUS method using convolutional neural networks (CNN) is proposed. This method circumvents the traditional frequency extraction step and enables rapid and automated estimation of elastic constants for low-Q materials directly from the experimental spectra. The CNN model was designed to take real parts of the resonant spectra and mass density as inputs, outputting the material’s independent elastic constants. Leveraging a simulation dataset for training, the model’s feasibility was demonstrated by characterizing five elastic constants of a composite material with a Q of approximately 25. The trained model performed well on both the simulated test set and three real-world samples, achieving a sample proportion of 96.5% in the test set with all relative errors of elastic constants falling within 10%. This study contributes a fresh perspective to efficiently estimating elastic constants in RUS, particularly for low-Q materials.

Electrically-Shielded Coil-Enabled Battery-Free Wireless Sensing for Underwater Environmental Monitoring.

Battery-free wireless sensing in extreme environments, such as conductive solutions, is crucial for long-term, maintenance-free monitoring, eliminating the limitations of battery power and enhancing durability in hard-to-reach areas. However, in such environments, the efficiency of wireless power transfer via radio frequecny (RF) energy harvesting is heavily compromised by signal attenuation and environmental interference, which degrade antenna quality factors and detune resonance frequencies. These limitations create substantial challenges in wirelessly powering miniaturized sensor nodes for underwater environmental monitoring. To overcome these challenges, electrically-shielded coils with coaxially aligned dual-layer conductors are introduced that confine the electric field within the coil's inner capacitance. This configuration mitigates electric field interaction with the surrounding medium, making the coils ideal for use as near-field antennas in aquatic applications. Leveraging these electrically-shielded coils, a metamaterial-enhanced reader antenna was developed and a 3-axis sensor antenna for an near-field communication (NFC)-based system. The system demonstrated improved spectral stability, preserving resonance frequency and maintaining a high-quality factor. This advancement enabled the creation of a battery-free wireless sensing platform for real-time environmental monitoring in underwater environments, even in highly conductive saltwater with salinity levels of up to 3.5%.

Effect of Primary Stability on Short vs. Conventional -Implants with Reverse Concave Neck.

The purpose of this study was to evaluate the primary stability of short implants versus conventional implants, in vitro. Two groups of implants with reverse concave neck and neck micro threads (ULT, Ditron Dental, CA) were studied; short implants (Ø 6.0mm x 7mm) and conventional implant (Ø 3.75mm x 10mm). A total of 80 implants were placed by the same calibrated clinician at 800RPM, 40 short implants and 40 conventional implants. Each implant was placed in dense (type II) and soft (type IV) bone. Implant primary stability was recorded using insertion torque (IT), Resonance Frequency Analysis (RFA), and Periotest values. Statistical comparison with Analysis of Variance were completed to compare differences between groups. The comparison of IT, RFA and Periotest of the two groups of implants showed statistical significance (P<0.0001) favoring the short implants (Ø 6.0mm x 7mm) in both the soft and dense bone qualities. Within the limitations of this study, short implants with wide diameter seem to have a higher level of implant stability compared to narrow implants with conventional length.

Measurements of Gravitational Attractions at small Accelerations

Abstract Gravitational interactions were studied by measuring the influence of small&amp;#xD;external field masses on a microwave resonator. It consisted of two spherical&amp;#xD;mirrors, which acted as independent pendulums individually suspended by strings.&amp;#xD;Two identical field masses were moved along the axis of the resonator&amp;#xD;symmetrically and periodically between a near and a far position. Their&amp;#xD;gravitational interaction altered the distance between the mirrors, changing&amp;#xD;the resonance frequency, which was measured and found consistent with Newton's&amp;#xD;law of gravity.&amp;#xD; The acceleration of a single mirror caused by the two field masses at the&amp;#xD;closest position varied from 5.4 10-12 m/s2 to 259 10-12 m/s2.&amp;#xD;

Design of a metasurface loaded with RF varactor and PIN diode integration dual-band reconfigurable antenna for bluetooth, Wi-Fi, WLAN and wireless 5G applications

Abstract This article presents a compact dual-band reconfigurable antenna design utilizing a metasurface integrated with an RF varactor and PIN diode for Bluetooth, Wi-Fi, WLAN, and 5G wireless applications. The results of the study show that using the metasurface reflector (MSR) structure gives a much higher gain than using a decagon antenna without a metasurface reflector. This antenna is designed and fabricated on FR4 epoxy substrate materials with a dielectric constant of 4.4 and the thickness of the substrate is 1.6 mm. The metasurface reflector (MSR) loaded antenna has a total electrical dimension of 0.51λ0 × 0.49λ0 × 0.013λ0, where λ0 represents the resonating wavelength at a 2.6 GHz center frequency. In the proposed work, the slotted decagon patch antenna consists of a complementary split-ring resonator constructed on its ground plane. Moreover, for the frequency reconfiguration, a PIN diode switch and an additional varactor diode switch are used for tuning the frequency band. Furthermore, without affecting the radiator structure, the varactor diode is placed on the upper side of the patch and the PIN diode switch is integrated into the ground plane. The proposed antenna has reconfigurable and tunable operating frequencies of 2.6 GHz and 3.4 GHz. The operational frequency of the band is switched between 2.6 GHz to 3.4 GHz. The switching operation of the dual configuration of 2.6 GHz with the PIN diode ON and 3.4 GHz with the PIN diode OFF. However, simultaneously applying a reverse bias voltage to the varactor diode from 0-10 V shifts its resonance frequency from 2640-2510 MHz and frequency tuning is done in respective bands. The proposed antenna achieved a peak gain of 7.5 dBi, and a radiation efficiency range of 72– 82% in the overall operating bands of interest. The proposed work is used for Bluetooth, Wi-Fi, WLAN, and wireless 5G applications. Performance verification is done by fabricating prototypes and verifying their performance using simulation and testing results.

Compact wide-stopband slow-wave half-mode substrate integrated waveguide filter with interdigital complementary split-ring resonator metasurface

Abstract In this work, a compact slow-wave half-mode substrate integrated waveguide (HMSIW) bandpass filter is developed by loading the proposed interdigital complementary split-ring resonator (IDCSRR) metasurface for wireless communication and sensing applications. The IDCSRR metasurface is constituted by etching interdigital slots inside the conventional CSRR, which can effectively enhance the product of the equivalent capacitance and inductance of the structure, and eventually reduces the resonant frequency. Through the evanescent-mode transmission generated in HMSIW by the negative permittivity effect of IDCSRR metasurface, miniaturized filter can be realized. Later, to further reduce the filter’s size, the capacitance-enhanced ring-mushroom units are patterned into HMSIW to generate slow-wave effect. Then, to improve the filter’s out-of-band suppression, the source-load coupling scheme is utilized to generate extra transmission zero. Meanwhile, to further widen the stopband, meander spurlines are etched on the input and output microstrip lines to suppress the higher-order harmonics with its bandgap function. To demonstrate the availability of the aforementioned concepts, a bandpass filter based on the HMSIW-IDCSRR unit cell is realized. Measurements show that the fabricated prototype exhibits an center frequency (f0) of 0.97GHz. Moreover, the out-of-band suppression can reach 30dB, with the upper stopband up to 4.31 f0. Hence, the proposed filter achieves good stopband and miniaturization performance.

Design of Piezoelectric Energy Harvester Single Cantilever Beam for IoT applications and Micro-electronic devices

A few years back the power requirement of electronic devices was very high. But with the technological developments in the field of internet-based systems, the design of low-powered microelectronic devices, WSN and IoT devices became necessary. In these systems the size and the power requirement are low and in most situations the replacement of batteries is challenging. For these microelectronic and IoT devices the abundant energy harvester is very useful. Among different abundant energy resources, vibrational energy harvesting with piezoelectric cantilever beam energy harvesters is of interest. This research work presents the design and analysis of an energy harvester (EH) which contains a single piezoelectric cantilever beam that captures the vibrational energy of the suspension bridge. This approach ties the two things together by framing piezoelectric energy harvesting as a solution to the power challenges faced by low-powered devices, making the transition feel more natural and connected. The main challenge in the design was matching the resonance frequency of the bridge with a piezo EH which is around 2.5Hz to extract maximum power. To overcome this problem Eigen frequency analysis in COMSOL Multiphysics is done. The 3D geometry of single beam piezo EH is designed and analyzed in COMSOL Multiphysics solid works. In this research work a relationship is established between the geometrical parameters of the single beam piezo EH and Eigen frequency based on the first six Eigen frequency analyses in COMSOL Multiphysics. For fi nite element analysis(FEA) a piezo single beam harvester is vibrated by application of force which is equal to the vibrational force (0.98m/s&lt;sup&gt;2&lt;/sup&gt;) in the suspension bridge. The force of (0.98 m/s²) is chosen because it avoids resonating with critical system components. The output from the harvester is achieved at a resonance frequency of 2.5Hz. The output from the piezo is very low 800 milli volts at 2.5Hz. The output results of piezo EH are also compared with a cantilever beam with a single-branch structure.

Coherent harmonic generation of magnons in spin textures

Harmonic generation, a notable non-linear phenomenon, has promising applications in information processing. For spin-waves in ferromagnetic materials, great progress has been made in the generation higher harmonics, however probing the coherence of these higher harmonics is challenging. Here, using in-situ diamond sensors, we study the coherent harmonic generation of spin waves in a soft ferromagnet. High-order resonance lines are generated via a microwave input and detected by nitrogen-vacancy (NV) centers in nanodiamonds. The phase coherence of the harmonic spin waves is verified by the Rabi oscillations of the NV electron spins. Numerical simulations indicate that the harmonic generation by microwaves below the ferromagnetic resonance frequency is associated with the nonlinear mixing of spin waves by magnetization structures at the film edge. Our finding of geometry-induced magnon harmonic generation constitutes a new way to generate magnon combs with coherent high-order harmonics and may pave the way for magnon-based information processing and quantum sensing applications.

Optimized Design of a Triangular Shear Piezoelectric Sensor Using Non-Dominated Sorting Genetic Algorithm-II(NSGA-II)

A new piezoelectric sensor with a triangular shear structure was designed to conduct the deformation monitoring of geotechnical bodies in mining airspace. Firstly, a three-dimensional sensor model was developed to analyze the impact of structural parameters on resonant frequency and voltage, utilizing both finite element and experimental methods. Secondly, the NSGA-II genetic algorithm was employed to optimize the sensor’s structural parameters, focusing on resonant frequency and voltage, resulting in a Pareto optimal solution set. For the first time, the optimal parameter combination was selected by minimizing the difference method (the height of the mass block was 10.6 mm, the thickness of the piezoelectric plate was 3.29 mm, the height of the piezoelectric plate was 8.1 mm, and the height of the central column was 19 mm). The optimized sensor exhibited a 4.14% increase in resonant frequency and a 9.11% increase in voltage. Finally, the prototype was fabricated, and the effectiveness and feasibility of the design were verified through experiments. The findings indicate the sensor’s promising potential for monitoring geotechnical deformation in mining airspace regions.

Optically levitated nanoparticles as receiving antennas for low frequency wireless communication

Low-frequency (LF) wireless communications play a crucial role in ensuring anti-interference, long-range, and efficient communication across various environments. However, in conventional LF communication systems, their antenna size is required to be inversely proportional to the frequency, so that their mobility and flexibility are greatly limited. Here we introduce a novel prototype of LF receiving antennas based on optically levitated nanoparticles, which overcomes the size-frequency limitation to reduce the antenna size to the hundred-nanometer scale. These charged particles are extremely sensitive to external electric field as mechanical resonators, and their resonant frequencies are adjustable. The effectiveness of these antennas was experimentally demonstrated by using the frequency shift keying (2FSK) modulation scheme. The experimental results indicate a correlation between error rate and factors such as transmission rate, signal strength, and vacuum degree with a signal strength of approximately 0.1V/m and a bit error rate below 0.1%. We extend the application of levitated particle mechanical resonators as an entirely new type of compact LF antennas, which may be utilized in long-distance communications in extreme environments.

Selective passive tuning of cavity resonance by mode index engineering of the partial length of a cavity

Cavities in large-scale photonic integrated circuits (PICs) often suffer from a wider distribution of resonance frequencies due to fabrication errors. It is crucial to adjust the resonances of cavities using post-processing methods to minimize the frequency distribution. We have developed a concept of passive tuning by manipulating the mode index of a portion of a microring cavity, which we named mode index engineering (MIE). Through analytical studies and numerical experiments, we have found that depositing a thin film of dielectric material on top of the cavity or etching the material enables us to fine-tune the resonances and minimize the frequency distribution. This versatile method allows for the selective tuning of each cavity’s resonance in a large set of cavities in a post-fabrication step, providing robust passive tuning in large-scale PICs. We show that the proposed method achieves a tuning resolution below 1/Q and a range of up to 103/Q for visible to near-infrared wavelengths. Furthermore, this method can be applied and explored in various integrated photonic cavities and material configurations.

Optimization and validation of an inverse method for elastic constant estimation in resonant ultrasound spectroscopy

This article introduces an inverse method using a particle swarm optimization algorithm enhanced by fuzzy logic to determine elastic constants in resonant ultrasound spectroscopy. The method adaptively adjusts algorithm parameters and incorporates frequency pairings into the error function, effectively addressing the issue of missing frequencies. Notably, it achieves precise mode matching with a fitting error of 0.163%, even when up to 50% of the first 30 eigenfrequencies are absent in polycrystalline Ti-6Al-4V studies. Under the assumption of Ti-6Al-4V orthotropic symmetry, the method iterates over grouped sets of the nine independent elastic constants, reducing the fitting error to 41.7% compared to the isotropic assumption. When applied to cortical bone with one-third of measured frequencies missing, the algorithm successfully obtained both frequency pairings and transverse isotropic elastic constants. This approach is anticipated to overcome limitations on the number of measured resonant frequencies, expanding the applicability of the method to low-symmetry materials.

Transient Response Characterization of Wind Turbine Structure–Extended Foundation Under Wind Loading

To study the transient response characteristics of wind turbine structures–extended foundations under wind loads in mountainous areas, this paper develops a simplified analytical model based on soil–structure interaction theory. It explores the effects of constraint conditions, wind speed, and foundation shear wave speed on the transient response behavior. By analyzing the time–domain and frequency–domain trends of tower top displacement, foundation horizontal displacement, and foundation rotation angle, the relationship between foundation shear wave speed and the safe wind speed of the wind turbine is clarified. The results indicate that different constraint conditions lead to variations in the calculated resonance frequency, maximum tower top displacement, and acceleration response spectrum. Furthermore, based on the analysis of the tower top acceleration response curve, the influence interval of frequency can be categorized into three distinct ranges: stable range, small influence range, and large influence range. Wind speed primarily influences the vibration amplitudes of the three displacement components, while the overall trend of the time-displacement waveform remains unchanged. The foundation shear wave speed primarily affects the displacement of the foundation itself, exerting a smaller influence on the displacements of the wind turbine structure. Notably, the total displacement at the tower top decreases as the shear wave speed increases. Moreover, the safe wind speed of the wind turbine shows a positive correlation with the foundation shear wave speed, indicating a linear relationship between the two variables.

Evaluation of Impact of Soil on Performance of Monopole Antenna for IoT Applications in Urban Agriculture

Built indoor IoT-based urban farms successfully combine the cultivation of fresh vegetables with attractive architectural designs. Moreover, implementing IoT-driven urban agriculture requires installing multiple IoT devices containing sensors, controllers, transceivers, and antennas for real-time data transmission. In this context, several factors, including the height of the IoT device above the soil level and the water content in the soil, can affect antenna performance and, consequently, the propagation of radio waves. This paper presents the results from numerical and experimental studies that evaluate the impact of soil on the performance of a monopole antenna for three different antenna positions relative to the soil in a pot and two soil water contents, presented by twelve scenarios. The results show that the antenna has a stable performance in six of the twelve scenarios, with a minimal shift in the resonant frequency of 3% and a narrowing of the frequency bandwidth by 2% compared to the antenna in free space. In the worst-case scenario, the antennas demonstrate a reduction in radiation efficiency of 44%, with the frequency bandwidth narrowing by up to 14% for the antenna fabricated on a PLA substrate and up to 17% for the one built on a foam board substrate.

Elastomer-assisted graphene transfer technique for enhanced resonance characteristics in chemisorption-based graphene resonant mass sensors.

A process technology was developed for transferring strained graphene sheets using an elastomer nanosheet to enhance the resonance characteristics of a graphene resonator. The strain-induced graphene resonator demonstrated a 1.80-fold improvement in the product of resonant frequency and Q-factor compared to the unstrained resonator. The system exhibited a frequency change in response to single inactivated SARS-CoV-2 whole virus by functionalizing the surface of the strained suspended graphene with a DNA aptamer, indicating a mass sensitivity of 0.99 zg Hz-1, which is 3.5 × 106 times greater than conventional chemisorption-based resonant mass sensors.

Investigation of the Impact of Thionine Functionalization on Magnetoelastic Sensor Performance.

This study investigates the functionalization of gold-coated magnetoelastic sensors with thionine molecules, focusing on resonance frequency shifts. The functionalization process was characterized by using Raman spectroscopy and analyzed via scanning electron microscopy and atomic force microscopy, revealing the progressive formation of molecular clusters over time. Our results demonstrate that longer functionalization time leads to saturation of surface coverage and cluster formation, impacting the sensor's resonance frequency shifts. Such modifications offer insights into the adsorption process of these molecules on the sensor's gold surface, as well as its performance.

High Q GaN/SiC-Based SAW Resonators for Humidity Sensor Applications

This paper presents the simulation and experimental results for high-frequency surface acoustic wave (SAW) sensors for humidity detection. The SAW structures with a wavelength of 680 nm are fabricated on GaN/SiC and presented two resonance frequencies: ~6.66 GHz for the Rayleigh propagation mode and ~8 GHz for the Sezawa mode. A SiO2 thin layer (~50 nm thick) was employed for the functionalization of the SAW. Relative humidity characterization was performed in the range of 20–90%. The SAW sensors achieved high values of humidity sensitivity for both adsorption and desorption. The Sezawa mode showed about 2.5 times higher humidity sensitivity than the Rayleigh mode: 17.2 KHz/%RH versus 6.17 KHz/%RH for adsorption and 8.88 KHz/%RH versus 3.79 KHz/%RH for desorption.

Large-Area Conductor-Loaded PDMS Flexible Composites for Wireless and Chipless Electromagnetic Multiplexed Temperature Sensors.

Capacitive dielectric temperature sensors based on polydimethylsiloxane (PDMS) loaded with 10vol% of inexpensive, commercially-available conductive fillers including copper, graphite, and milled carbon fiber (PDMS-CF) powders are reported. The sensors are tested in the range of 20-110°C and from 0.5 to 200MHz, with enhanced sensitivity from 20 to 60°C, and a relative response of 85.5% at 200MHz for PDMS-CF capacitors. PDMS-CF capacitors are interrogated as a sensing element in wirelessly coupled chipless resonant coils tuned to 6.78MHz with a response in the resonant frequency (fr) of the sensor, demonstrating an average sensitivity of 0.38%°C-1, a 40x improvement over a pristine PDMS capacitive sensor and outperforms state-of-the-art frequency-domain radio frequency temperature sensors. Exploiting its high sensitivity, the wireless sensing platform is interrogated using a low-cost, portable, and open-source NanoVNA demonstrating a relative response in fr of 48.5%, good agreement with instrumentation-grade vector network analyzers (VNAs) and negligible change in performance at a range of reading distances and humidities. Finally, a wireless tag is demonstrated with rapid, reversible dynamic response to changes in temperature, as well as the in the first scalable, multiplexed array of chipless sensors for spatial temperature detection.

A Versatile Electronic Dimer Exhibiting PT and Anti-PT Symmetry

We propose a versatile electronic dimer cooperatively coupled by means of mutual induction, capacitance, and resistance. In a lot of related works, the electronic dimer is inductively coupled, with one resonator characterized by positive resistance (dissipation) and the other by negative resistance (amplification). We go beyond this picture by considering capacitive and resistive coupling, and by exploring cases where both resistances are positive, as well as a case where the resonant frequencies of the individual resonators are different. Based on analytical derivation and numerical calculations, we obtain and observe the properties of parity-time (PT), quasi-PT (QPT) and quasi-anti-PT (QAPT) symmetry by adjusting the constitutive parameters of the system. This study provides a versatile and feasible platform for observing PT/anti-PT (APT) symmetry-based phenomena and provides a foundation for further studies on finding PT/APT symmetry in more sophisticated circuits.

Hybrid Acoustic Metamaterial Based on Absorption Accumulation Peaks for a Broad Sound Energy Control

Controlling sound energy over a wide spectrum of frequencies through structures with a subwavelength scale is a challenge in acoustics. In this sense, a hybrid acoustic metamaterial model (HAMM) that acts over a wide frequency spectrum is presented. The structure consists of a combination of a porous layer and an acoustic metamaterial (AMM). Two samples are evaluated to establish effective control of sound energy () between 450 and 6400 Hz with the structure reaching a maximum ratio of . Furthermore, the behavior of sound waves in the structure is explored through analysis of the sound pressure field, instantaneous particle velocity, and thermoviscous dissipation. One of the highlights of the HAMM is that it is composed of an AMM that has a low phase velocity. Thus, the ultra‐slow sound in part of the structure allows the low‐frequency resonance frequency to be shifted to lower frequencies. Another characteristic is that because of the accumulation of absorption peaks below the bandgap of the AMM, a low‐frequency broadband absorption is guaranteed. Therefore, this work contributes substantially to advances in the area of sound energy control over a wide spectrum of frequencies through the use of different combined acoustic materials.