MHz Frequency Shift Research Articles

Study on Sensing Urine Concentrations in Water Using a Microwave Sensor Based on Hilbert Structure.

In this study, a two-port network-based microwave sensor for liquid characterization is presented. The suggested sensor is built as a miniature microwave resonator using the third iteration of Hilbert's fractal architecture. The suggested structure is used with the T-resonator to raise the sensor quality factor. The suggested sensor is printed on a FR4 substrate and has a footprint of 40×60×1.6mm3. Analytically, a theoretical investigation is made to clarify how the suggested sensor might function. The suggested sensor is created and put to the test in an experiment. Later, two pans to contain the urine Sample Under Test (SUT) are printed on the sensor. Before loading the SUT, it is discovered that the suggested structure's frequency resonance is 0.46 GHz. An 18 MHz frequency shift is added to the initial resonance after the pans are printed. They monitor the S-parameters in terms of S12 regarding the change in water content in the urine samples, allowing for the sensing component to be completed. As a result, 10 different samples with varying urine percentages are added to the suggested sensor to evaluate its ability to detect the presence of urine. Finally, it is discovered that the suggested process' measurements and corresponding simulated outcomes agreed quite well.

Cold and ultra-cold chain integrity monitoring via embedded resonant sensor indicators

An increasing number of products require transport at cold and ultra-cold temperatures, < 5 and −60°C respectively. Time-temperature indicators (TTIs) are used to monitor the integrity of the cold chain, however, they are frequently based on colorimetric changes that can be inaccurate for quantification and not possible to read through closed shipment materials. Here, TTIs were prototyped using microfluidic channels containing fluids (oils) that are tuned to melt above target temperatures. By coupling these TTIs to resonant sensors, the time-temperature information can be transmitted wirelessly and quantitatively by observing shifts in resonant frequency. Multiplexed TTIs containing fluids that melt at 9, 13.5, and 19.5°C are demonstrated. When coupled to the resonant sensor, the fluid flows as the temperature increases incrementally and generates a frequency shift of 3.5, 4.5, and 6 MHz at each threshold. TTI for ultra-cold environments were also designed using microfluidic channels with melt responsive fluids (ethanol). The resonant sensor coupled TTI was placed in a Styrofoam container containing dry ice, and over 1 MHz frequency shift is observed when read external to the container as the dry ice evaporates and the temperature exceeds −35°C. This augurs potential uses in inexpensive monitoring of food and pharmaceutical shipments that must remain cold for adequate quality.

Dual-band frequency reconfigurable metasurface antenna for millimeter wave joint communication and radar sensing systems

This paper introduces an innovative, compact, and high-gain metasurface antenna, covering both the 24 GHz millimeter wave (mmWave) radar band and the 5 G n257 and n258 bands. The proposed metasurface antenna consists of a wideband stacked patch antenna and a dual-layer metasurface to focus its radiation beams for multiple mmWave bands. The operating frequency can be slightly shifted by altering the distance between the feeder and the metasurface. The distribution of the metasurface unit cells is designed based on a simplified phase compensation formula. The dimension of the fabricated feeder is 6 mm × 6 mm, and the metasurface occupies a 65 mm × 65 mm radome area. Experimental results demonstrate a wide bandwidth from 23.5 GHz to 29.1 GHz for the feeder, and impressive maximum gains of 19.7 dBi and 19.5 dBi for the lower band and higher band of the metasurface antenna are achieved simultaneously. The frequency reconfiguration ability was characterized by a 750 MHz frequency shift with every 1 mm distance adjustment. The compact size and high gain performance of the proposed design underscore its potential for practical applications in millimeter wave joint communication and radar sensing systems.

An RF Ring Resonator across Fluidic Media for Dielectric Sensing and Air-bubble Detection

Design, fabrication, and characterizations of an RF ring resonator used as a dielectric sensor, air-bubble detector and droplet sizer inside fluidic media are presented. The resonator with a split in its design has been analyzed and optimized using numerical methods and design guidelines are established to select the most sensitive resonance mode. A tube with an inner diameter of 800 µm placed over the 350 µm split is used to bring liquids and test samples. Different types of liquids (Isopropyl alcohol and de-ionized water) are easily distinguished by frequency shifts in the resonance peak. For instance, a 5 MHz frequency shift between air and water is observed. Furthermore, uniform oil droplets (0.6mm and 2.8mm long) were passed through the tube and measured to demonstrate the transient response of the sensor in detecting droplet sizes.

Microfabricated interdigital capacitive sensor and resonant sensor based on PPy/MoO3 hybrids for sensitivity-enhanced ammonia detection at room temperature

This paper proposes a microwave transduction-based gas sensor based on polypyrrole/molybdenum oxide composite (PPy/MoO3) hybrid material. Optimization of sensing material, measurement platform and fabrication techniques are carried out to achieve excellent ammonia gas real-time detection. Capacitance parameters analysis for the gas sensing response of capacitive sensor is proceeded based on PPy, MoO3, and PPy/MoO3 hybrids at room temperature. The results show that the PPy/MoO3 hybrid material exhibits a sensitivity-enhanced response to ammonia. The PPy/MoO3 capacitive sensor has good linearity (R2 =0.987), fast response, and good repeatability within 5–100 ppm ammonia concentration. Frequency parameters analysis for the gas sensing response of microwave resonator sensor is proceeded based on PPy/MoO3 hybrids in the range of 10 ppm to 100 ppm ammonia concentration at room temperature. The proposed microwave sensor has good linearity (R2 =0.991), good repeatability with 8 MHz standard deviation, high stability with gas response variation less than 2%, and anti-humidity capacity. Among 100 ppm concentration of isopropanol, acetone, ethanol, methanol and ammonia, ammonia exhibits 97.5 MHz frequency shift, which proves high sensitivity and good step toward selectivity. Therefore, this work could be regarded as a promising candidate in ammonia sensing application based on microwave solution.

Coherent OTDR with large dynamic range based on double-sideband linear frequency modulation pulse.

Rayleigh scattering-based distributed optical fiber sensors with long sensing distance and large dynamic range are highly desired for application scenarios such as vehicle tracking, structure health monitoring, and geological survey. To enlarge the dynamic range, we propose a coherent optical time domain reflectometry (COTDR) based on double-sideband linear frequency modulation (LFM) pulse. By utilizing I/Q demodulation, both the positive and negative frequency band of the Rayleigh backscattering (RBS) signal can be properly demodulated. Consequently, the dynamic range is doubled without increasing the bandwidth of signal generator, photodetector (PD), and oscilloscope. In the experiment, the chirped pulse with 10 μs pulse width and 498 MHz frequency sweeping range is launched into the sensing fiber. Single-shot strain measurement is achieved over 5 km single-mode fiber with a spatial resolution of 2.5 m and a strain sensitivity of 7.5 pε/H z. A vibration signal with 3.09 με peak-to-peak amplitude (corresponding to 461 MHz frequency shift) is successfully measured with the double-sideband spectrum, which cannot be properly recovered with the single-sideband spectrum.

Attachable DC Coil Array for Improved Functional MRI at 7T

The prefrontal cortex (PFC) has long been concerned as an important part in cognitive control of neuroscience field. Functional magnetic resonance imaging (fMRI) has been introduced as an effective neuroimaging technique to explore neural activity. However, images within PFC region are subject to susceptibility artifacts, which give rise to undesired image distortion and signal drop-out. In this work, we proposed a method of adding a static magnetic field with high-order spatial pattern for artifact correction. Based on that, a compact attachable 8-channel coil array was constructed. Two toroid chokes were optimized and connected to each coil loop to minimize radiofrequency coupling. To evaluate the array performance, bench measurements and MRI experiments over phantoms and a human subject at 7T were conducted. With the proposed array applied, only 0.3 MHz and 1 MHz frequency shift were introduced to the RF coil, and no apparent RF performance change was observed; the inhomogeneity was reduced by 15%∼24%; in fMRI images over the human subject, “notorious” artifacts within target region were relatively mitigated. The present setup offers a feasible means for practical artifact correction, which is promising for the research that focuses on PFC regions.

Enhanced Half-Mode SIW Loaded With Interdigital Capacitor for Permittivity Measurements

This paper presents a novel sensor topology employing an Interdigital Capacitor (IDC) integrated in Half Mode Substrate Integrated Waveguide (HMSIW) for permittivity measurement of solid materials. HMSIW with around 50% smaller size compared with SIW offers a compact solution for hosting the sensing section. Capacitive-like characteristic of IDC further improves the size reduction up to 71.6%. In addition, IDC with enhancing the electric field concentration is exploited for sensing section. Design details of the hosting section and the sensing section are provided along with extraction and analysis of the equivalent circuit model of the sensor. Design and simulations are carried out by means of design tools, and the proposed sensor is fabricated on a 50×24×1.6 mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> printed circuit board (PCB). Measurements demonstrates that the fabricated sensor prototype shows 113 MHz frequency shift per unit permittivity change around 3.5 GHz, and it has a normalized sensitivity of 3.16% within a wide range of permittivity values, which is relatively better than similar sensors in the literature.

A New Microwave Sensor Based on the Moore Fractal Structure to Detect Water Content in Crude Oil.

This paper presents a microwave sensor based on a two-ports network for liquid characterizations. The proposed sensor is constructed as a miniaturized microwave resonator based on Moore fractal geometry of the 4th iteration. The T-resonator is combined with the proposed structure to increase the sensor quality factor. The proposed sensor occupies an area of 50 × 50 × 1.6 mm3 printed on an FR4 substrate. Analytically, a theoretical study is conducted to explain the proposed sensor operation. The proposed sensor was fabricated and experimentally tested for validation. Later, two pans were printed on the sensor to hold the Sample Under Test (SUT) of crude oil. The frequency resonance of the proposed structure before loading SUT was found to be 0.8 GHz. After printing the pans, a 150 MHz frequency shift was accrued to the first resonance. The sensing part was accomplished by monitoring the S-parameters in terms of S12 regarding the water concentration change in the crude oil samples. Therefore, 10 different samples with different water percentages were introduced to the proposed sensor to be tested for detecting the water content. Finally, the measurements of the proposed process were found to agree very well with their relative simulated results.

High Sensitive Metamaterial Sensor for Water Treatment Centres

In this study, a high sensitive metamaterial sensor has been designed to detect quality of water for water treatment centre. The water samples have been obtained and electrical properties have been measured in microwave range to design the proposed sensor. These electrical properties have been assigned in microwave simulator. Water quality has been investigated by using parametric study and genetic algorithm approach to realize high sensitivity in terms of resonance frequency shift. Around 130 MHz frequency shift has been observed between the water samples. This shift is sufficient to detect instantaneously to the quality of water. This is the first study that metamaterial approach has been used to detect water quality in literature.

Mass sensing by quantum criticality.

Mass sensing connects mass variation to a frequency shift of a mechanical oscillator, whose limitation is determined by its mechanical frequency resolution. Here we propose a method to enlarge a minute mechanical frequency shift, which is smaller than the linewidth of the mechanical oscillator, into a huge frequency shift of the normal mode. Explicitly, a frequency shift of about 20Hz of the mechanical oscillator would be magnified to be a 1MHz frequency shift in the normal mode, which increases it by 5 orders of magnitude. This enhancement relies on the sensitivity appearing near the quantum critical point of the electromechanical system. We show that a mechanical frequency shift of 1Hz could be resolved with a mechanical resonance frequency ωb=11×2π MHz. Namely, an ultrasensitive mechanical mass sensor of the resolution Δm/m∼2Δωb/ωb∼10-8 could be achieved. Our method has potential application in mass sensing and other techniques based on the frequency shift of a mechanical oscillator.

High-Performance Wireless Ammonia Gas Sensors Based on Reduced Graphene Oxide and Nano-Silver Ink Hybrid Material Loaded on a Patch Antenna.

Reduced graphene oxide (rGO) has been studied as a resistive ammonia gas sensor at room temperature. The sensitive hybrid material composed of rGO and nano-silver ink (Ag-ink) was loaded on a microstrip patch antenna to realize high-performance wireless ammonia sensors. The material was investigated using scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS). Firstly, interdigital electrodes (IDEs) printed on the polyethylene terephthalate (PET) by direct printing were employed to measure the variation of resistance of the sensitive material with the ammonia concentration. The results indicated the response of sensor varied from 4.25% to 14.7% under 15–200 ppm ammonia concentrations. Furthermore, the hybrid material was loaded on a microstrip patch antenna fabricated by a conventional printed circuit board (PCB) process, and a 10 MHz frequency shift of the sensor antenna could be observed for 200 ppm ammonia gas. Finally, the wireless sensing property of the sensor antenna was successfully tested using the same emitted antenna outside the gas chamber with a high gain of 5.48 dBi, and an increased reflection magnitude of the emitted antenna due to the frequency mismatch of the sensor antenna was observed. Therefore, wireless ammonia gas sensors loaded on a patch antenna have significant application prospects in the field of Internet of Things (IoTs).

Current-induced modulation of backward spin-waves in metallic microstructures

We performed a propagating spin-wave spectroscopy for backward spin-waves in ferromagnetic metallic microstructures in the presence of electric-current. Even with the smaller current injection of A m−2 into ferromagnetic microwires, the backward spin-waves exhibit a gigantic 200 MHz frequency shift and a 15% amplitude change, showing 60 times larger modulation compared to previous reports. Systematic experiments by measuring dependences on a film thickness of mirowire, on the wave-vector of spin-wave, and on the magnitude of bias field, we revealed that for the backward spin-waves a distribution of internal magnetic field generated by electric-current efficiently modulates the frequency and amplitude of spin-waves. The gigantic frequency and amplitude changes were reproduced by a micromagnetics simulation, predicting that the current-injection of A m−2 allows 3 GHz frequency shift. The effective coupling between electric-current and backward spin-waves has a potential to build up a logic control method which encodes signals into the phase and amplitude of spin-waves. The metallic magnonics cooperating with electronics could suggest highly integrated magnonic circuits both in Boolean and non-Boolean principles.

K-band MEMS-based frequency adjustable waveguide filters for mobile back-hauling

This paper presents the first experimental results of a novel MEMS-based waveguide filter for mobile back-hauling at K-band with adjustable center frequency. The tuning concept employs commercial packaged RF MEMS switches, wire-bonded within a rectangular cavity. The switches are used to perturb the current distribution of the TE101 mode so as to tune the resonant frequency of the cavity. A tuning range up to 2% with unloaded Qs of the order of 1000 in K-band can be obtained. A second-order filter prototype employing commercially available MEMS on silicon substrate has been tested. Measurements show a 160 MHz frequency shift (0.7%) and Qs up to 1000 using only one MEMS per resonator. New higher-order prototypes using low-loss substrate MEMS (e.g. quartz) will be fabricated in order to get higher Qs. The concept here present leads to a very simple structure. The number of MEMS per resonator is, in fact, minimized (we use only one MEMS) and the design is simple. On the other hand, the achievable tuning range is lower (&lt;2%) than the other concepts. Higher tuning ranges are achievable using more MEMS, but at the expense of lower Qs of the resonators.

RF-MEMS load sensors with enhanced Q-factor and sensitivity in a suspended architecture

In this paper, we present and demonstrate RF-MEMS load sensors designed and fabricated in a suspended architecture that increases their quality-factor (Q-factor), accompanied with an increased resonance frequency shift under load. The suspended architecture is obtained by removing silicon under the sensor. We compare two sensors that consist of 195μm×195μm resonators, where all of the resonator features are of equal dimensions, but one’s substrate is partially removed (suspended architecture) and the other’s is not (planar architecture). The single suspended device has a resonance of 15.18GHz with 102.06 Q-factor whereas the single planar device has the resonance at 15.01GHz and an associated Q-factor of 93.81. For the single planar device, we measured a resonance frequency shift of 430MHz with 3920N of applied load, while we achieved a 780MHz frequency shift in the single suspended device. In the planar triplet configuration (with three devices placed side by side on the same chip, with the two outmost ones serving as the receiver and the transmitter), we observed a 220MHz frequency shift with 3920N of applied load while we obtained a 340MHz frequency shift in the suspended triplet device with 3920N load applied. Thus, the single planar device exhibited a sensitivity level of 0.1097MHz/N while the single suspended device led to an improved sensitivity of 0.1990MHz/N. Similarly, with the planar triplet device having a sensitivity of 0.0561MHz/N, the suspended triplet device yielded an enhanced sensitivity of 0.0867MHz/N.

Development of High-Speed Mechanical Tuning System for HTS Filters

We developed a high-speed ( ~1 second) mechanical tuning system for HTS microstrip line (MSL) filters using a dielectric tuning plate, dielectric trimming rods, and conducting trimming rods. The tuning plate has windows through which the dielectric and conducting trimming rods pass. It was designed for a 3-pole filter with 5 GHz center frequency (fc) and 100 MHz bandwidth (BW) using a 3-dimensional electromagnetic simulator. The simulation of 500 MHz frequency shift induced by dielectric tuning plate was done and, in addition, by using both kinds of trimming rods an improvement of insertion loss (IL), pass-band ripples reduction and increase of bandwidth was achieved. In the experiment, the positions of the plate and the rods above the filter were adjusted by using high-resolution operating at room temperature step motors. The minimum step of moving the plate and the rods was 0.001 mm. We found that the fc was shifted by 500 MHz while retaining the IL, pass-band ripple, and BW by experimental evaluation. The time taken by the 500 MHz tuning was less than 1 second. These results indicate that our method and system will be useful for the next generation of wireless communication systems.

Low Spurious, Broadband Frequency Translator Using Left-Handed Nonlinear Transmission Line

In this letter, we present a frequency translator based on a left-handed nonlinear transmission line (LH NLTL). The proposed LH NLTL can achieve a very linear phase variation as a function of applied dc bias for a broadband frequency that facilitates a low spurious, broadband frequency translation. Our experiment demonstrates that the LH NLTL enables frequency shift with 30 dB maximum spurious suppression. For any frequency between 3 and 3.8 GHz, it was possible to achieve 100 KHz-1 MHz frequency shift while the range of spurious suppression is between 21 and 30 dB. Because of its compactness and possibility of low-cost monolithic fabrication, this circuit will be very useful for microwave instrumentation, or a coherent communication system where single sideband modulation is required.

A Wireless Implantable Passive Microdosimeter for Radiation Oncology

Wireless measurement of ionizing radiation in close proximity or/and within an irradiated solid tumor is extremely valuable for dose verification and quality control in radiation oncology. For such applications, it is preferable to manufacture such sensors using passive components since high levels of ionizing radiation can damage active electronics. In addition, passive implementation can reduce the cost associated with fabrication and assembly. This paper reports on the development of an implantable micro-machined passive LC transponder for in situ radiation measurement. Dose measurement is performed by monitoring the resonance frequency change associated with the decay of surface change of an electret upon exposure to radiation. This is achieved through a micromachned capacitor with a movable plate that is partially filled with a Teflon electret and connected in parallel with an inductor, thus forming a passive LC tank circuit. For an implantable prototype encapsulated in a glass capsule (2.5 mm in diameter, 2.8 cm in length), test results show that a dose of 30 Gy (from a Co60 source) can produce 1.46 MHz frequency shift resulting in a sensitivity of 49 kHz/Gy.

Intra-body data transmission for the personal area network

Intra-body communication is a wireless means of exchanging information within a personal area network (PAN) between wearable electronic sensors and devices. The feasibility of intra-body communication is confirmed through several experiments on signal propagation within the human body, and a human phantom is designed and used to obtain reproducible results over repeated experiments. Based on the results of these experiments, a prototype transmission system is constructed using aluminum electrodes powered by 3 V DC and operating in the 10.7 MHz frequency modulation (FM) band. This prototype is demonstrated to be capable of transmitting analog signals through the human subjects in the presence of external noise. Digital data transmission at 9600 bps is also achieved using newly fabricated 10.7 MHz frequency shift keying (FSK) transmitter and receiver devices. The carrier frequency of 10.7 MHz is the intermediate frequency of FM radio receivers, meaning that the proposed system can make use of a wide selection of inexpensive, commercial radio frequency devices.

Properties of Dielectric Ring Resonator and Application to Moisture Measurement

This paper presents properties of a dielectric ring resonator and its application to measurement of material moisture. Theoretical analysis has been done to select better resonant modes in the resonator with higher sensitivity and wider moisture content measurable range than the formerly often used TE011 mode by some researchers. Experiments have also been done to verify the theoretical results. The HE212 mode in the resonator has the highest sensitivity of 1.0 MHz frequency shift corresponding to change of 1.0% moisture content. The measurable range of moisture content is up to 12% at dry basis. The mode of HE211 has a wide measurable range approximately between 3% and 75% and its corresponding frequency shift is 12 MHz.