Resonance Frequency Of Sensor Research Articles

Miniaturized Antenna Design for Wireless and Powerless Surface Acoustic Wave Temperature Sensors.

This paper presents the introduction, design, and experimental validation of two small helical antennae. These antennae are a component of the surface acoustic wave (SAW) sensor interrogation system, which has been miniaturized to operate at 915 MHz and aims to improve the performance of wireless passive SAW temperature-sensing applications. The proposed antenna designs are the normal-mode cylindrical helical antenna (CHA) and the hemispherical helical antenna (HSHA); both designed structures are developed for the ISM band, which ranges from 902 MHz to 928 MHz. The antennae exhibit resonance at 915 MHz with an operational bandwidth of 30 MHz for the CHA and 22 MHz for the HSHA. A notch occurs in the operating band, caused by the characteristics of the SAW sensor. The presence of this notch is crucial for the temperature measurement by aiding in calculating the frequency shifting of that notch. The decrement in the resonance frequency of the SAW sensor is about 66.67 kHz for every 10 °C, which is obtained by conducting the temperature measurement of the system model across temperature environments ranging from 30 °C to 90 °C to validate the variation in system performance.

Chipless RFID Sensor for Measuring Time-Varying Electric Fields Using a Contactless Air-Filled Substrate-Integrated Waveguide Resonator.

This paper presents a wireless chipless resonator-based sensor for measuring the absolute value of an external time-varying electric field. The sensor is developed using contactless air-filled substrate-integrated waveguide (CLAF-SIW) technology. The sensor employs a low-impedance electromagnetic band gap structure to confine the electric field within the sensor's air cavity. The air cavity is loaded with varactor diodes whose reverse bias voltage is modified by the to-be-measured external electric field. Variation in the external electric field results in a variation of the sensor's resonant frequency. The CLAF-SIW sensor offers a high unloaded quality factor, which is required for a long-distance ringback-based interrogation system. A prototype of the proposed sensor is fabricated and tested. It can measure a time-varying external electric field up to 6.9 kV/m, has a sensitivity of 1.86 (kHz)/(V/m), and can be interrogated from a distance of 80 cm. The feasible maximum bandwidth of the external electric field is 25 kHz. The proposed sensor offers a compact planar multilayer structure that can easily be incorporated with a planar antenna and its size can be reduced by selecting a higher operating frequency without an increase in dielectric loss.

Fiber bragg grating accelerometer based on asymmetric shaped flexible hinge structure

To achieve real-time health monitoring in civil engineering, a FBG acceleration sensor with asymmetric shaped flexible hinge structure is proposed. Combined with the theoretical analysis, the expressions of resonance frequency and sensitivity are deduced, and the effects of the structural parameters of the sensor on the resonance frequency and sensitivity are analyzed and simulated. Based on the optimization results, a fiber Bragg grating acceleration sensor was designed and fabricated. The amplitude-frequency response, linear sensitivity response, and lateral anti-interference ability were tested experimentally. The experimental data shows a sensor resonance frequency of 350 Hz, a sensitivity of 90.96 pm/g, and a linear correlation of 99.59%. These results closely align with the theoretical predictions of a resonance frequency of 344 Hz, and a sensitivity of 98 pm/g, confirming the accuracy of the sensor's theoretical analysis.The transverse interference immunity of the sensor is 3.7%, and an operating frequency band of 10–250 Hz. It indicates that the sensor is promising for medium and low frequency vibration measurement.

High-sensitivity narrow‑band T-shaped cantilever Fabry-perot acoustic sensor for photoacoustic spectroscopy

Photoacoustic spectroscopy (PAS) has been rapidly developed and applied to different detection scenarios. The acoustic pressure detection is an important part in the PAS system. In this paper, an ultrahigh sensitivity Fabry-Perot acoustic sensor with a T-shaped cantilever was proposed. To achieve the best acoustic pressure effect, the dimension of the cantilever structure was designed and optimized by finite element analysis using COMSOL Multiphysics. Simulation results showed that the sensitivity of such T-shaped cantilever was 1.5 times higher than that based on a rectangular cantilever, and the resonance frequency of T-shaped cantilever were able to modulate from 800 Hz to 1500 Hz by adjusting the multi-parameter characteristics. Experimental sensing results showed that the resonance frequency of T-shaped Fabry-Perot acoustic sensor was 1080 Hz, yielding a high sensitivity of 1.428 μm/Pa, with a signal-to-noise ratio (SNR) of 84.8 dB and a detectable pressure limit of 1.9 μPa/Hz1/2@1 kHz. We successfully used such acoustic sensor to measure acetylene (C2H2) concentration in the PAS. The sensitivity of PAS for C2H2 gas was 3.22 pm/ppm with a concentration range of 50 ppm ∼100 ppm, and the minimum detection limit was 24.91ppb.

Design of Zeolitic Imidazolate Framework-8-Functionalized Capacitive Micromachined Ultrasound Transducer Gravimetric Sensors for Gas and Hydrocarbon Vapor Detection

A capacitive micromachined ultrasound transducer (CMUT) was engineered and functionalized with zeolitic imidazolate framework-8 (ZIF-8) dispersed in a photoresist AZ1512HS (AZ) matrix to function as a gravimetric gas sensor. The sensor response was recorded in the presence of nitrogen, argon, carbon dioxide, and methane gases as well as water, acetylene, a propane/butane mixture, n-hexane, gasoline, and diesel vapors. The photoresist matrix alone was found to have a negligible response to all the gases and vapors, except for water vapor. No visible difference in sensor response was detected when switching from nitrogen to methane gas. However, a strong shift in the sensor resonance frequency was observed when exposed to higher hydrocarbons, ranging from 1 kHz for acetylene to 7.5 kHz for gasoline. Even longer-chain hydrocarbons, specifically kerosene and more so diesel, had a significantly reduced sensor frequency shift compared with gasoline. Sensors functionalized with a thin film of AZ+ZIF-8 demonstrated higher sensitivity in their response to a hydrocarbon molecular mass than without functionalization.

Electro-mechanical impedance technique for concrete strength monitoring: Three-dimensional model development and experimental verification

During the application of the electro-mechanical impedance (EMI) technique for detecting the strength development of concrete, in some cases, the piezoelectric sensor is embedded in the concrete. Normally, there are two methods to embed the piezoelectric sensor: PS-EMI and CPS-EMI. For both methods, the observed resonance frequency of the piezoelectric sensor increases with the increase of the concrete strength. However, there is a contradiction in the trend of conductance amplitude at the resonance frequency, which has to an extent puzzled the researchers in this area. In this paper, we developed a three-dimensional EMI model for the embedded piezoelectric sensor. We discussed the underlying mechanism, which induces the conductance spectrum difference for the PS-EMI and CPS-EMI, and experimental verification was carried out. By plotting the evolution of the concrete strength as a function of the resonance frequency shift, it was found that both embedding methods can be used in practical applications.

Ultrasensitive miniaturized planar microwave sensor for characterization of water–alcohol mixtures

Designing a low-cost, compact, yet sensitive planar microwave sensor for complex permittivity measurement is highly desired for numerous applications though quite challenging. Here, in this research, an ultrasensitive planar microwave sensor is proposed which is based on an electric LC structure. The core sensor was fabricated on an FR-4 substrate using a simple fabrication process, then integrated within a polymethylmethacrylate microfluidic channel for straightforward liquid delivery to the sensing region. The resonance frequency of the bare sensor was designed to occur at 4.14 GHz while empty and shifted to 0.88 GHz when deionized water flows into the channel. The sensor response has been characterized for different mixture ratios of methanol and ethanol with deionized water. Next, the complex permittivity of the resulted binary mixtures has been extracted by the Debye model through a least square fitting method. The calculated average sensitivity is 1.45% which stands above most of sensors reported in the literature. Besides, the sensor has a small footprint with dimensions of 3.6 × 3.8 mm^2 making it a suitable candidate for integration with point-of-care testing devices.

Towards Monitoring and Identification of Red Palm Weevil Gender Using Microwave CSRR-Loaded TL Sensors.

This paper presents for the first time the design of a microwave sensing setup for the potential monitoring and identification of red palm weevil (RPW) gender type. The microwave sensor consists of a planar two-port transmission line (TL) with a single complementary split-ring resonant (CSRR) inclusion etched from the bottom metallic layer. The CSRR sensor is placed on top of a customized non-conductive container. The microwave sensing setup was designed, numerically demonstrated, fabricated and tested experimentally. Simulated results correlate quite well with the experimental data. Moreover, the sensitivity of the CSRR sensor when in close proximity to different RPW genders was evaluated both numerically and experimentally. Based on the measured results from 15 RPW samples with different body sizes, different RPW gender types showed unique microwave signatures. A notable shift in the sensor's resonance frequency was achieved, where on average a resonant frequency shift of 10% for adult RPWs was achieved, while a 2.4% frequency change was obtained for larvae (young) RPWs. Hence, the proposed microwave sensing setup can be adopted in field trials to examine and differentiate between various RPW genders at various developmental stages.

Surface-Modified Compounds Improve the Detection Sensitivity of Terahertz Metasurface Biosensors

Some trace elements in the human body, such as proteins and metabolites, are closely related to human health. Changes in the concentration of proteins can usually be used as indicators for the diagnosis of diseases. On the other side, some metabolites such as lactic acid and uric acid are closely related to human motor function. A large part of cancer markers are proteins, and their concentration changes in human serum and body fluid are usually closely related to cancer diagnosis, staging and prognosis. It has always been the goal of researchers to efficiently and sensitively detect the relevant trace elements in human body. Due to the characteristics of low energy, coherence and fingerprint, terahertz (THz) waves have been widely used in the detection of substances in recent years. Metasurface sensor is a new type of sensor with unique electromagnetic characteristics based on artificial design. The emergence of THz metasurface sensors provides a new technical means for the detection of trace elements proteins. Based on the above background, the research objects in this paper are three common protein cancer markers: carcinoembryonic antigen (CEA), neuron-specific enolase (NSE) and squamous epithelial cell carcinoma antigen (SCC), in order to study the detection performance of THz metasurface sensor and its improvement effect after modification. In the experiment, the cancer marker is dropped onto the surface of sensor, and the spectrum is detected by THz time-domain system (TDS), and the frequency shift is calculated by comparing with the resonance frequency of the blank sensor. Then the experiment was repeated by changing the concentration and class of the marker, and the sensitivity of sensors was calculated by fitting the relationship between the frequency shift and the concentration of markers. After that, two compounds (halloysite nanotube and Tungsten disulfide) were used to modify the metasurface sensor, and compared with the unmodified metasurface sensor. The experimental results show that for the detection of three markers, the metasurface sensor modified with HNT has significantly improved the detection sensitivity compared with the sensor modified with WS2 and blank sensor. This provides a new means for THz metasurface sensors in the detection of biomarkers, which is suitable for biomedicine, human health monitoring and other fields.

Wireless Human Motion Detection with a Highly Sensitive Wearable Pressure Sensing Technology

AbstractWireless flexible sensing devices using inductive‐capacitive (LC) resonator‐enabled transmission technologies are attractive in the areas of human motion detection, health inspection, and implantable medical devices. However, challenges remain in LC‐based wireless sensing devices, including low device sensitivity/resolution and slow signal readout speed based on sweeping excitation frequencies. Herein, an LC resonator‐based wireless pressure sensing technology (LC‐WPS) is proposed for flexible contact pressure measurements in a real‐time manner. It includes a fully flexible passive LC pressure sensor and a signal‐reading circuit for wireless communication with the sensor and real‐time data processing. The passive sensor detects external pressure by the changes in resonant frequency. Importantly, by optimizing the design of the LC resonator in the sensor, the LC‐WPS converts the pressure‐dependent resonant frequency into circuit output voltage to a great extent, achieving a high sensitivity (1.23 × 10−2 kPa−1) and resolution (54 Pa) within a pressure range of 0–15 kPa. In addition, the LC‐WPS utilizes a single operating frequency (i.e., 13.56 MHz) instead of sweeping the operating frequencies to identify the sensor resonant frequency, featuring fast and real‐time data analysis and processing. Real‐time monitoring of human motions, such as laryngeal movement, neck bending and wrist rotation, is demonstrated, verifying the applicability of the LC‐WPS in the fields of wearable medical care and sports biomechanics.

Frequency Sensitivity Analysis of Coil-IDE Resonance Topology Circuit and Its Humidity Sensor Applications

In this paper, the frequency sensitivity of Coil-IDE (interdigital electrode) sensor in different integrated topology is studied. In particular, the expression of resonance frequency of the Coil-IDE sensor both in series and parallel topological structure is derived. The sensitivity of frequency to IDE capacitance was analyzed, and two new results can be found: (i) Due to the existence of coil winding capacitance and grounding capacitance, Coil-IDE topology circuit has been changed which cause the Coil-IDE parallel topology structure has the higher frequency sensitivity than series; (ii) Not only the topology structure but also the parameters such as coil inductance and IDE capacitance have the regulatory effect on the frequency sensitivity. After analysis, an experiment of Coil-IDE humidity sensor was applied to verify the presented results. The parallel frequency of the Coil-IDE parallel structure has the higher sensitivity was confirmed. The error of the proposed formula predicting the regulatory effect of parameters on frequency sensitivity was discussed. The error is as low as 7.57%, which shows the beneficial to the integrated design of Coil-IDE sensor both in topological structure and parameters.

Virtual Quartz Crystal Microbalance: Bioinspired Resonant Frequency Tracking.

The reference acoustic properties of the quartz crystal used as a resonator are ensured by its high-quality factor (Q-factor). The microbalance of the quartz crystal (QCM) exploits the bulk acoustic properties of the quartz crystal. Turning a network analyzer or impedance analyzer into a QCM with a decent measurement rate is a challenge. The use of a virtual instrument to implement an impedance analyzer (VIA) provides greater flexibility to the virtual QCM. In this paper, VIA's flexibility is exploited for the experimental evaluation of conventional scanning procedures and the influence of associated parameters, in order to identify elements that can lead to a limitation of the performance of a virtual QCM. The results of the experimental investigation justify the use of an innovative and optimized bioinspired scanning procedure to effectively track the serial resonance frequency of the QCM sensor. Variable-resolution spatial sampling of the human retina and the ability of the eye to refocus on the area of interest is the source of bioinspiration for achieving an adaptive virtual QCM. The design methodology and physics are described in detail, and the experimental investigations demonstrate the effectiveness of the proposed bioinspired scanning procedure.

Acceleration sensor of medium-high frequency dual FBG based on L-shaped support sensitization structure

It is a key part for micro seismic crack detection, mechanical equipment operation state and structural health monitoring to measure high frequency vibration. A kind of FBG acceleration sensor based on flexure hinge is proposed targeting at the problem of existing medium-high-frequency FBG acceleration sensor’s low sensitivity. Two FBGs are fixed on L-shaped support in a differential arrangement to improve sensitivity of sensor and eliminate adverse effects caused by temperature changes. Matlab and ANSYS software are used to simulate, analyze and optimize sensor. According to the simulation results, the real sensor is made, and the sensor calibration experiment is carried out. Research results show that resonant frequency of sensor is about 1700 Hz and has good linearity in flat range of 50–1000 Hz. Sensitivity of sensor can reach 18.9 pm/g, while linearity is higher than 99%, and temperature sensitivity is merely 0.074 pm/°C. Research results provide reference for researching and developing the same type of sensor, and further improving optical fiber acceleration sensor sensitivity.

Characterization of Dendritic Defects of Polyethylene Insulation Materials Based on Microstrip Gap Resonator

This article attempts to reveal the detection ability of microstrip slot resonator for water and electrical tree defects in insulating samples. The characteristics of microstrip gap resonator are analyzed in high-frequency electromagnetic simulation software. A gap capacitance extraction method is proposed based on two-port transmission theory, and the gap capacitances under different dielectric constants are analyzed based on this method. The resonant frequency of sensor is found to be negatively correlated with the dielectric constant of the materials. In the experimental part, the sensor made of double-sided copper clad plate with medium FR4 was used to detect the water tree and electrical tree in low-density polyethylene (LDPE) samples, and the experiment results showed good feasibility.

Microwave Spoof Surface Plasmon Sensor for Dielectric Material Characterization

A microwave planar resonator sensor design supporting spoof surface plasmon waves is used for wafer dielectric characterization. The proposed circuit guides the microwave as a surface wave across the metal signal line, from port to port of the device. The surface wave effectively interacts with the sample being measured, placed on top of the planar sensor. The proposed planar sensor is fabricated on an RF-35 substrate, resulting in a low-cost implementation. The sensor is used to discriminate between wafers with different dielectric permittivity and thickness. Quartz, borosilicate, BK7 glass, and Silicon wafers have been characterized using the proposed sensor. The sensor resonant frequency and losses change according to the permittivity and the thickness of the samples, with an achieved sensor sensitivity of 60.22 MHz/ <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">ϵ_r</i> . Simulation and measurements demonstrate that the proposed spoof surface plasmon resonator sensor can be used to create a high sensitivity sensor for dielectric material characterization. The dielectric constant and loss tangent of the samples are inferred from a polynomial fit obtained from sample simulations and confirmed through measurements.

Encapsulated Microbubble Fiber-Tip Fabry-Perot Cavity With Tunable Bandwidth for Sensitive Acoustic Detection

A photothermally generated microbubble on a single-mode fiber tip with tunable frequency bandwidth was demonstrated for sensitive detection of acoustic waves. The microbubble with spherical gas-water interface formed a flexible Fabry-Pérot cavity at the fiber tip and detected the acoustic waves by interferometric readout of the bubble deformation. To work in different liquids besides water, the sensor was encapsulated into a water-filled tube and the effects of the encapsulation process on the optical and acoustic characteristics of the sensor were investigated. A 40 μm-diameter microbubble based sensor exhibited a noise-equivalent pressure level of ∼1.0 mPa/Hz <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1/2</sup> at the frequency of ∼100 kHz. The bubble diameter was photothermally changed from 20 μm to 60 μm, which enabled online tuning of the sensor resonant frequency from 100 kHz to 300 kHz. This tunable feature is attractive to applications that requires the detection of acoustic waves covering different frequency bands. The encapsulated microbubble sensor with advantages of high sensitivity, tunable bandwidth and low-cost would be interesting for applications in biomedical and industrial areas involving various liquid environments.

Medium and low frequency fiber Bragg grating acceleration sensor based on single-sided single-arc hinge

A medium and low frequency fiber Bragg grating (FBG) based acceleration sensor based on single-axis single-arc hinge-shaped sensitization structure is designed and experimentally demonstrated. The theoretical formula of the sensor's resonance frequency and sensitivity was given, the stress distribution, characteristic frequency and amplitude frequency characteristics of the sensor were simulated and the structural parameters of the sensor were optimized. The experimental results show that the resonance frequency of the sensor is 630 Hz, the flat frequency range is 30–300 Hz, and the acceleration sensitivity is 57.77 pm/g. The sensor has the advantages of high sensitivity, wide flat frequency range and strong transverse anti-interference ability, which can meet the requirements of acceleration detection in petroleum exploration field.

A Printed LC Resonator-Based Flexible RFID for Remote Potassium Ion Detection

This article presents a flexible printed radio-frequency identification (RFID) sensor based on a printed inductive&#x2013;capacitive (LC) resonator circuit and a potassium ion-selective electrode (ISE) for remote potassium ion sensing. The potassium ion concentration of the contact solution can be monitored by measuring the change of the resonant frequency of the RFID sensor. The resonant frequency of the sensor can be directly detected by measuring the induced change in the reflection coefficient (<inline-formula> <tex-math notation="LaTeX">$S_{11}$ </tex-math></inline-formula>) of an external interrogator coil that is inductively coupled to the RFID sensor. Results obtained for the RFID sensor exhibited a second-order exponential relationship between the resonant frequency of the sensor and the K^&#x002B; concentration of the solution over 0.001&#x2013;2 mol/L dynamic range values. Effects of varying separation distance between the sensor and the interrogator coil and the effect of temperature variations on sensor&#x2019;s measurement are shown. With less than 2-s response time and the long-term stability, the wireless passive printed sensor has potential for low-cost K^&#x002B; monitoring applications such as K^&#x002B; monitoring in food packages.

A cavity model microwave patch antenna for lubricating oil sensor applications

This paper presents a single port micro strip patch cavity antenna for identifying lubricant oil level as well as its quality. The antenna sensor has a compact structure with a ground plane of 52 mm × 45 mm and radiating patch of 40 mm × 31 mm. The substrate is made up of FR-4 (εr = 4.3) material with 1.6 mm thickness and the copper clad of 0.035 mm thickness. The cavity height is 1.5 mm and cavity is made up of FR-4 material. The parameters of the sensor are optimized using the CST-Microwave Studio tool (CST-MWS) and designed at 3.16 GHz operation, under unloaded conditions. When the cavity is filled with the fresh engine oil, then the resonance frequency reduces to 2.79 GHz. The proposed antenna provides a sensitivity of 554 MHz/ε. A prototype of the designed antenna is fabricated and its characteristics are found to match with simulation. The antenna impedance is found to increase with volume of oil, for all conditions. Moreover, the resonant frequency of sensor is gradually decrease with increase oil volume inside the cavity of antenna sensor.

Analysis of metamaterial‐inspired soil moisture microwave sensor

AbstractIn this letter, the authors propose a microwave sensor capable to detect soil moisture content parameter for use in precision agriculture and agricultural smart monitoring applications. The novel sensor is based on complementary split‐ring resonator metamaterial topology, microstrip line and was built under biodegradable dielectric substrate of polylactic acid for sustainable purposes. The sensing mechanism relates the sensor's resonant frequency to the soil moisture content changes over time. For experimental validation purposes, a compact sensor prototype (75 mm × 35 mm × 1.55 mm and 12 g) with fundamental resonant frequency at 958 MHz was built and submitted to calibration process on typically sandy and clay soils to get fitting models capable to estimate soil moisture content. Simulated and experimental results are presented together and show good agreement with each other. The calibration data for both soil types were processed using the least‐squares method and the proposed curve‐fitting models are capable to estimate soil moisture content levels from 5% to 20% for sandy soil and from 12% to 23% for clay soil with satisfactory accuracy, proving the device viability.