Frequency Shift Change Research Articles

Frequency shift of a PVDF surface acoustic wave sensor on a curved surface

Wearable sensors have generated a significant attention across various research domains, including the monitoring of human health, pressure sensing, and body health monitoring. Notably, substantial research has been focused on the utilization of piezoelectric sensors for precise pressure measurements in diverse applications, such as medical devices and structural health monitoring. This paper explains the external pressure measurement employing sensors crafted from Polyvinylidene Fluoride (PVDF), known for its remarkable ability to conform consistently to various surface shapes and curvatures. The primary objective of this study is to present an integrated experimental and numerical approach to quantifying the frequency shift of piezoelectric PVDF surface acoustic wave (SAW) sensors when deployed on curved surfaces, a crucial step in optimizing their performance for real-world applications. We aim to explain how changes in surface geometry impact frequency shifts concerning external pressure and movement. Our findings reveal a linear relationship between frequency shifts and geometric variations in a certain range, as supported by experimental data. Furthermore, it is observed that PVDF samples can be used to successfully measure the internal pressure of a canister. The consistency between experimental and numerical results underscores the validity and reliability of our approach. In summary, this paper contributes to our understanding of piezoelectric PVDF SAW sensor behavior when placed on curved surfaces. Our novel methodology combines experimental measurements and numerical simulations to quantify the impact of geometric changes on frequency shifts, providing valuable insights for future sensor applications.

Highly Sensitive Qualitative and Quantitative Identification of Cashmere and Wool Based on Terahertz Electromagnetically Induced Transparent Metasurface Biosensor.

Cashmere and wool are both natural animal fibers used in the textile industry, but cashmere is of superior quality, is rarer, and more precious. It is therefore important to distinguish the two fibers accurately and effectively. However, challenges due to their similar appearance, morphology, and physical and chemical properties remain. Herein, a terahertz electromagnetic inductive transparency (EIT) metasurface biosensor is introduced for qualitative and quantitative identification of cashmere and wool. The periodic unit structure of the metasurface consists of four rotationally symmetric resonators and two cross-arranged metal secants to form toroidal dipoles and electric dipoles, respectively, so that its effective sensing area can be greatly improved by 1075% compared to the traditional dipole mode, and the sensitivity will be up to 342 GHz/RIU. The amplitude and frequency shift changes of the terahertz transmission spectra caused by the different refractive indices of cashmere/wool can achieve highly sensitive label-free qualitative and quantitative identification of both. The experimental results show that the terahertz metasurface biosensor can work at a concentration of 0.02 mg/mL. It provides a new way to achieve high sensitivity, precision, and trace detection of cashmere/wool, and would be a valuable application for the cashmere industry.

Research on multi-dimensional micro-motion feature extraction of moving targets

The micro-Doppler effect is a physical phenomenon generated by the micro-motion of objects and their components, which have a significant influence on improving radar detection and resolution capability and also enhancing the radar imaging and target recognition performance. The extraction of micro-Doppler frequency, as a commonly used time-frequency analysis tool, is of great significance in extracting and reconstructing the signal with micro-motion targets. The micro-motion characteristics for moving targets can be verified by using simulation through combining the theory of micro-Doppler effect with the frequency domain model of electromagnetic waves. The simulation research on the micro-motion characteristics of a three-dimensional target is conducted by using the finite element method. The influences of environmental conditions such as relative humidity, visibility, and the presence or absence of turbulence on echo intensity and time-frequency relationship are investigated theoretically. The simulation results indicate that parameters such as relative humidity and visibility, which affect the atmospheric attenuation coefficient, can reduce echo intensity and the period of time-frequency curve. By triggering off beam drift in the transmission path, turbulence can lead to “frequency shift deformation” of the time-frequency curve, degrading the extraction of target motion attitude. A motion attitude classification method is proposed in order to study the micro-Doppler effect better. According to whether the frequency shift changes with time, the motion attitude can be divided into frequency shift time-invariant motion and time-variant motion. Frequency shift time-variant motion includes translation, rolling and vibration. Vibration and rolling are motions that periodically change with time, requiring the comparison of instantaneous frequency shifts at any three times within a cycle. Translation is a time-variant motion with irregular frequency shifts over time, which involves studying instantaneous frequency shifts at any three times. Transient frequency shifts should be analyzed and compared at different times for these motions. The frequency shift time-invariant motion is mainly rotation obtained experimental results indicate that the amplitude, plus-minus, and spectral width of frequency shift at different positions are aimed at inverting the target shape, attitude, direction and velocity. Demodulating one-dimensional data obtained from the FFTshift function can obtain the time-frequency-intensity relationship. This multi-parameter analysis method is a multi-dimensional processing method widely used in the fields of radar, sonar, and communication. The above research is conductive to the measurement of target macroscopic shape properties and the extraction of microscopic motion information, which lays the foundation for radar detection and recognition.

MOF-composite sensors to eliminate the QCM positive frequency shift

In a quartz crystal microbalance (QCM) Sauerbrey equation can usually be applied in the ideal scenario and when the QCM frequency shift goes to the negative direction. In some cases, however, the requirements to achieve the ideal condition are not fulfilled and thus leading to QCM positive frequency shift phenomenon. Herein we have also observed that a porphyrin-based metal organic frameworks (MOF), namely MOF-525(Zn), QCM sensor also exhibits the positive frequency shift phenomenon when exposed to xylene isomers, which could be caused by the loose attachment of the MOF nanoparticles on the QCM surface. Therefore, in the presence of the analytes, the bonding between the MOF and the QCM surface is disturbed and higher analyte concentration also leads to the increase of the sensitive layer stiffness, resulting in higher positive frequency shift. However, such a phenomenon can be completely eliminated by simply adding polymer to MOF nanoparticle sensors to strengthen the bonding of MOF nanoparticles to the QCM surface. Through this study we have shown that adjusting the amount of polymer is very crucial to completely reverse the positive frequency response. Otherwise, it appears a critical analyte concentration of gas analytes where the QCM frequency shift changes its direction from negative to positive response. Lastly, the same strategy has also been used to other MOF-based QCM sensor systems where their sensitive layer is built from other MOFs, namely MOF-525 and NU-902, and ethanol is used as the analyte to prove the generalizability of this simple approach.

Spin-wave nonreciprocity at the spin-flop transition region in synthetic antiferromagnets

We investigate the frequency nonreciprocity in CoFeB/Ru/CoFeB synthetic antiferromagnets near the spin-flop transition region, where the magnetic moments in the two ferromagnetic layers are noncollinear. Using conventional Brillouin light scattering, we perform systematic measurements of the frequency nonreciprocity as a function of an external magnetic field. At near zero magnetic field, where the antiparallel alignment of the magnetic moments in the two layers is established, we observe a significant frequency nonreciprocity of up to a few GHz, which vanishes when the relative magnetization orientation switches into the parallel configuration at a large magnetic field. For the intermediate values of the magnetic field, where the system transitions from the antiparallel to the parallel orientation, a nonmonotonous dependence of the frequency nonreciprocity is found, with a maximum frequency shift around the spin-flop critical point. This nontrivial dependence of the nonreciprocity versus field is attributed to the nonmonotonous dependence of the dynamic dipolar interaction, which is the main factor that causes asymmetry in the dispersion relation. Furthermore, we found that the sign of the frequency shift changes even without switching the polarity of the bias field. These results show that one can precisely control the nonreciprocal propagation of spin waves via field-driven magnetization reorientation.

ВЫЯВЛЕНИЕ РАЗНОВИДНОСТЕЙ ОДНОМОДОВЫХ ОПТИЧЕСКИХ ВОЛОКОН И ОПРЕДЕЛЕНИЕ ХАРАКТЕРИСТИК ИХ ПРОДОЛЬНОГО НАТЯЖЕНИЯ

This paper presents the results of studies on the automation of the processing of measurements of Brillouin reflectograms containing various types of single-mode optical fibers. By analyzing the Mandelstam-Brillouin scattering parameters, it is possible to distinguish the varieties of optical fibers in the studied optical cables, as well as to estimate the change in Brillouin frequency shift and determine the degree of longitudinal tension. The initial values of the Brillouin frequency shift and the Mandelstam-Brillouin scattering spectrum for each type of optical fiber differ. Developed programs for processing Blilluen reflectograms are presented. Conclusions were made about the accuracy of estimates obtained according to various algorithms, based on the accumulated experience in working with the presented programs.

Disentangled structural and vibrational characteristics of methylammonium halide perovskite MAPbBr3-xClx with x = 0 [formula omitted] 3 studied by X-Ray diffraction and Raman scattering

Structural and vibrational characteristics of methylammonium(MA) halide perovskite MAPbBr3-xClx single crystals (x = 0–3) were investigated by using powder X-ray diffraction and Raman scattering experiments. The lattice constant in the cubic phase obtained from powder X-ray diffraction peaks at room temperature showed nearly a linear dependence as a function of composition. On the other hand, some of the Raman mode frequencies obtained from single crystals exhibited substantial changes in both frequency shifts and half widths over the investigated composition range. Especially, the MA torsional mode showed a significant change from 325 to 485 cm−1 and mode splitting as Cl was replaced by Br. This mode splitting was more clearly seen at low temperatures reflecting the symmetry lowering of the local structure. The contrast between the linear change in the lattice constant and the substantial change in the vibrational frequencies and half widths of the MA torsional mode in the intermediate composition range indicates the local heterogeneous environment for the MA cations caused by the substitutional disorder.

Closed-loop technique based on gain balancing for real-time Brillouin optical time-domain analysis

A closed-loop servo control based on balancing the gain of two probing frequencies is proposed for real-time Brillouin optical time-domain analysis (BOTDA) without post-processing. With the most basic BOTDA hardware setup, the system can perform measurement in 150 ms and track a sudden Brillouin frequency shift (BFS) change in excess of 300 MHz (corresponding to a temperature change of more than 250°C) over ∼5 km of fiber with a spatial resolution of 2 m. Moreover, the feedback loop is independent of the loss experienced by the probe and pump, with no requirement on the BFS uniformity along the fiber. All these advantages make the proposed system suitable for field applications in harsh environments.

Design and characterization of Screen-Printed Piezoresistive Cantilever for Gas Sensor Application

In this paper, the design, and the characterization of screen-printed cantilever-based humidity sensor are described. The project investigated in detail the sensitivity, and fabrication process of screen-printing based sensor with coated active humidity material on cantilever’s free end. The main aim of this paper is to compare the screen-printed technology with other existing technologies like micro-electro-mechanical system (MEMS), and low temperature cofired circuit (LTCC). The sensor has been simulated under different level of relative humidity with two different temperature value: 35°C, and 45°C. This paper also represents an analytical and mathematical modeling approach for frequency shift and thick film resistance change of the selected sensor. The analytical results are compared with the simulated results.

Study on the Spectral Characteristics of Plant Growth Regulators Based on the Structure Difference of Terahertz Metamaterial Sensor

In this study, in order to solve the problems of low sensitivity and complex sample pretreatment in traditional detection, a method was proposed to detect plant growth regulators using terahertz combined with metamaterial sensors. Two metamaterial sensors with different structures are designed. The differences of two kinds of metamaterial sensors for detecting plant growth regulators were analyzed from three aspects of frequency domain, time domain and absorption characteristics. It is further proved that the difference of metamaterial structure will lead to the change of frequency shift, time domain waveform and absorption characteristics of measured samples, and the influence of sample concentration on the detection characteristics of the metamaterial sensor. The results show that both metamaterial sensors can effectively detect the four plant growth regulator solutions with concentrations as low as 0.05 mg/L. In terms of detection and sensing, the frequency shift, sensitivity, figure of merit value, vibration amplitude and change rate of absorption intensity of metamaterial sensor 2 are higher than each parameter of metamaterial sensor 1, which has better detection performance. However, in terms of identification between samples, metamaterial sensor 1 is more suitable for the identification of daminozide and naphthaleneacetic acid solutions, and metamaterial sensor 2 was more suitable for the detection of glyphosine and gibberellic acid solutions. It provides a new method for multi-target fusion to detect plant growth regulators with high sensitivity and high accuracy.

Terahertz polarization sensing of bovine serum albumin proteolysis on curved flexible metasurface

Proteolysis is a key research field of biochemistry and plays an important role in biomedicine, the food industry, etc. Moreover, because many molecular collective vibration and rotation energy levels containing structural information of proteins, peptides, amino acids, and other molecules are located in the terahertz (THz) band, the THz spectroscopy can perform molecular-level characterization. Here, based on the traditional time-domain spectroscopy system, we propose a reflective polarization characterization method and use the resonance enhancement effect of the flexible chiral metasurface sensor to realize the sensing of bovine serum albumin (BSA) under the proteolysis of papain. Experimental results show that under different amounts of papain proteolysis, the THz polarization characteristic spectra of the BSA solution have significant differences. Its sensitivities of frequency shift, intensity, and polarization angle changes can reach the order of 106 GHz∙mL/mol, 106 dB∙mL/mol, and 106 °∙mL/mol, respectively, and the concentration detection accuracy of papain reaches in the order of nmol/mL. This work demonstrates a new THz label-free, on-chip, wearable, and microfluidic sensing method and device for protein detection.

Single-shot chirped pulse BOTDA for static and dynamic strain sensing.

Driven by the strong need for distributed high-frequency dynamic strain sensing, ultra-fast Brillouin optical time-domain analysis is rapidly becoming a vital technique. Thus, in this Letter, we propose and demonstrate a novel method by using a chirped pulse as a pump signal to extract the relative Brillouin frequency shift (BFS) changes through the real-time delays between adjacent Brillouin traces; this enables static and dynamic strain measurement without time-consuming frequency sweeping process. Benefiting from single-shot measurement based on Brillouin traces, the system has a high acquisition rate that is only limited by the sensor length without averaging, and is immune to the polarization fading problem, thanks to electrical delay time measurement. The pump source is a 1 MHz linewidth laser without a phase-locking loop; the laser frequency drifting noise could be compensated by the signal from the non-disturbed fiber section. In the experiments, BFS measurement resolution of 0.42 MHz with 4.5 m spatial resolution is demonstrated over a 5 km non-uniform fiber.

Piezoelectric sensing of glucose oxidase activity of Aspergillus niger spores pretreated by different methods

The development of Aspergillus niger (A. niger) spores as glucose oxidase (GOD) biocatalysts to produce gluconic acid is highly anticipated in the food industry. Herein, a piezoelectric sensor (PIS) method has been developed for the detection of GOD activity and better application of rapid screening of GOD activity in A. niger spores. The GOD activity detection is based on GOD catalyzing β-d-glucose to produce gluconic acid, which results in frequency shift changes recorded by the PIS device in real-time. Using the PIS method, the kinetic parameter 6.5 mg/mL, the correlation equation υ0=31.92CGOD+1.04, the recoveries (89.4%–93.9%, and their RSDs were all within 6.1%) and the optimal GOD activity in A. niger spores under different treatment conditions was obtained. Compared with the classical methods, the proposed method is accurate, rapid, convenient and does not require additional reagents. It has a broad range of potential applications for exploring new GOD biocatalysts.

Flexible/Bendable Acoustofluidics Based on Thin-Film Surface Acoustic Waves on Thin Aluminum Sheets.

In this paper, we explore the acoustofluidic performance of zinc oxide (ZnO) thin-film surface acoustic wave (SAW) devices fabricated on flexible and bendable thin aluminum (Al) foils/sheets with thicknesses from 50 to 1500 μm. Directional transport of fluids along these flexible/bendable surfaces offers potential applications for the next generation of microfluidic systems, wearable biosensors and soft robotic control. Theoretical calculations indicate that bending under strain levels up to 3000 με causes a small frequency shift and amplitude change (<0.3%) without degrading the acoustofluidic performance. Through systematic investigation of the effects of the Al sheet thickness on the microfluidic actuation performance for the bent devices, we identify the optimum thickness range to both maintain efficient microfluidic actuation and enable significant deformation of the substrate, providing a guide to design such devices. Finally, we demonstrate efficient liquid transportation across a wide range of substrate geometries including inclined, curved, vertical, inverted, and lateral positioned surfaces using a 200 μm thick Al sheet SAW device.

Asymmetric complementary split ring resonator for identification of materials

In this paper, a new microwave sensor for identification of materials is presented. The sensor is composed of an asymmetric complementary split ring resonator etched on the ground side of the microstrip line. The sensor is designed using low cost FR4 substrate. The S21 simulation result shows the unloaded resonator operates at 6.45 GHz. The overall size of the sensor is 100mm×50mm×0.8mm. When the sensor is loaded with sample material, the resonant frequency shift is noticed. This change in frequency shift is used to identify the material type and also the thickness of the material under test. The sensor is tested for different test samples placed on the ground and is correctly able to identify the material under test and its thickness by its resonant frequency variations.

Учет фазовых искажений, вызванных движением геостационарных ретрансляторов, при местоопределении наземных источников радиоизлучения

Currently, there are often cases of illegal use of the resource of relay satellites located in geostationary orbit, and the creation of unintentional and deliberate interference with legal users of satellite communication systems, for example due to non-compliance with the power standards of radio transmitting devices and antenna radiation patterns, as well as the rules for the frequency spectrum regulating. One of the possible stages of the response by the radio frequency service and satellite systems operators to such situations may be an operational assessment of locating of the interference ground radio emission sources that violate the established requirements. The existing methods for estimating the coordinates of radio emission sources operating through geostationary satellites-repeaters involve calculating the Cross-Ambiguity Function (CAF) of signals received from several satellites that relay the signals of the main and side lobes of the antenna pattern of the geolocated source. In the case of a low received signals SNR, it is required to record signals for a long time, and in such cases, to achieve a sufficient SNR at the correlator output, it is necessary to take into account not only the Doppler frequency shift between the signals, but also the change in the frequency shift caused by the change in the velocity vectors of the repeater satellites. The aim of this work is to study the recording duration, at which it is required to take into account phase distortions caused by a change in the speed of the repeater satellite and their effect on the SNR at the correlator output, as well as to develop a method for accounting for such distortions. The theory of digital signal processing and the method of simulation were used as research methods. As a result of the study, an assessment was made of the duration of the signal recording, at which the Doppler frequency shift can be considered constant; introduced the concept of a modified CAF, which takes into account the change in the Doppler frequency shift due to its approximation by a linear function; the maximum duration of signal recording was estimated, at which the proposed linear approximation is valid. It is concluded that in the case of using the modified CAF, the minimum duration of signal recording, at which the absence of correlator output SNR degradation will be guaranteed, is 8.1 times greater than when using the traditional CAF.

Ultra-high resolution strain sensor network assisted with an LS-SVM based hysteresis model

Optical fiber sensor network has attracted considerable research interests for geoscience applications. However, the sensor capacity and ultra-low frequency noise limits the sensing performance for geoscience data acquisition. To achieve a high-resolution and lager sensing capacity, a strain sensor network is proposed based on phase-sensitive optical time domain reflectometer (φ-OTDR) technology and special packaged fiber with scatter enhanced points (SEPs) array. Specifically, an extra identical fiber with SEPs array which is free of strain is used as the reference fiber, for compensating the ultra-low frequency noise in the φ-OTDR system induced by laser source frequency shift and environment temperature change. Moreover, a hysteresis operator based least square support vector machine (LS-SVM) model is introduced to reduce the compensation residual error generated from the thermal hysteresis nonlinearity between the sensing fiber and reference fiber. In the experiment, the strain sensor network possesses a sensing capacity with 55 sensor elements. The phase bias drift with frequency below 0.1 Hz is effectively compensated by LS-SVM based hysteresis model, and the signal to noise ratio (SNR) of a strain vibration at 0.01 Hz greatly increases by 24 dB compared to that of the sensing fiber for direct compensation. The proposed strain sensor network proves a high dynamic resolution of 10.5 pε·Hz^-1/2 above 10 Hz, and ultra-low frequency sensing resolution of 166 pε at 0.001 Hz. It is the first reported a large sensing capacity strain sensor network with sub-nε sensing resolution in mHz frequency range, to the best of our knowledge.

Fast Acquirable Brillouin Optical Time-Domain Reflectometry Based on Bipolar-Chirped Pulse Pair

In this article, fast measurement of Brillouin optical time-domain reflectometry (BOTDR) based on a linearly frequency modulated (LFM) pulse and a digital matched filter is studied theoretically and demonstrated experimentally. The Brillouin frequency shift (BFS) change is detected by measuring the time shift of the Brillouin gain spectrum (BGS) along the time axis instead of the frequency shift, as in traditional BOTDR. In the experiment, we propose to use a positive- and negative-swept pulse, named bipolar-chirped pulse pair (BPP), to determine the BFS change with high accuracy. A BGS acquisition of up to 320 Hz is obtained for a fiber length of 2 km with a strain measurement accuracy of ±8 ${\rm{\mu \varepsilon }}$ . Strain measurements in a range of up to 10000 ${\rm{\mu \varepsilon }}$ are conducted, and the resulting strain coefficient is equal to 0.048 MHz/ ${\rm{MHz}}/{\rm{\mu \varepsilon }}$ , which matches that of standard single-mode fibers. The BPP-BOTDR technique is an intrinsic one-end-injection truly distributed system that exhibits high measurement speed and high accuracy, which may pave the way for various BOTDR applications.

Discrete Lissajous and Recton Functions: A New Method for Frequency Response Measurements

An innovative and completely new technique so called discrete Lissajous functions and recton functions for signal analysis and measurement is explained. The contribution of the study is that it is a new digital method of obtaining information on frequency, change of frequency, phase and phase shift as well as auto-correlation, cross-correlation and energy functions of signals in digital form on-line that may be difficult to be provided in analog form and available for measurement and control applications at each sampling instance directly. The discrete Lissajous figures and recton functions can also be sketched in digital image form for further analysis of signals and systems. They are based on an algorithm utilizing discrete convolutions of discrete time signals. They can be depicted in 3D form. They give more information than classical analog Lissajous figures obtained on an oscilloscope screen. They can be used for several applications from chaotic systems to biomedical applications requiring to finding correlations, energies as well as frequency and phase information of the signals and controlling such systems. In this study, the application of them to systems steady-state, mainly frequency response analysis is explained after giving basic definitions.

A 28-/60-GHz Band-Switchable Bidirectional Amplifier for Reconfigurable mm-Wave Transceivers

Performance limits and design techniques for millimeter-wave amplifiers employing switches for multiband operation are presented in this article. A bidirectional dual-band amplifier is designed in a 130-nm silicon-germanium (SiGe) process. The amplifier can shift its operational frequency between 28 or 60 GHz and can operate in low-noise receive or high-power transmit mode. The frequency shift and transmit-receive (T/R) mode change has been realized using shunt switches based on SiGe HBTs. The switches are co-optimized and integrated with amplifiers to reduce the die area and improve performance. An analysis of switch loss reduction and associated tradeoffs is provided. The designed shunt switch, for band-switching operation, achieves the simulated ON-loss of as low as 1 dB at 60 GHz and OFF-loss of 0.7 dB at 28 GHz. By using these low-loss switches and a codesign approach, the proposed T/R amplifier surpasses the state-of-the-art performance in terms of mm-wave multiband amplifiers.