A microfluidic sensor based on a microstrip line loaded with a composite resonator is reported in this paper. The composite resonator combines a shunt connected step impedance resonator (SIR) and a ...complementary split ring resonator CSRR) etched in the ground plane. By etching the CSRR beneath the patch of the SIR, the composite CSRR-loaded SIR resonator exhibits two transmission zeros and a pole in between. The operating principle of the sensor is the variation of the transmission coefficient at the pole frequency of the bare resonator, when a material or liquid under test (LUT) is in contact with the CSRR (the sensitive element). By designing the CSRR-loaded SIR resonator with closely spaced pole and transmission zeros, highly sensitive sensors are obtained. Despite the fact that the proposed sensor can also operate as a frequency variation sensor, using it as a single-frequency sensor based on the variation of the transmission coefficient (caused by the LUT) at a specific frequency reduces sensor costs. The reason is that a harmonic signal injected to the input port of the microstrip-based sensor plus a simple amplitude modulation (AM) detector (connected to the output port) suffices for measuring purposes. The proposed microfluidic sensor is applied to the characterization of volume fraction of solutions of isopropanol in deionized (DI) water. The sensor is able to resolve volume fractions as small as 5%, and the maximum measured sensitivity is as good as 4 mV/%.
Open-ended coaxial probes have been widely explored and commercialized for dielectric spectroscopy at microwave frequencies over the past decades. The working principle of the probes relies on the ...dependence of the fringing field on the complex permittivity of the material in front of the open end. In this article, inspired by the optical fiber extrinsic Fabry-Perot interferometer, we propose a novel sensing scheme based on an open-ended hollow coaxial cable resonator (OE-HCCR). The resonator is constructed using two reflectors along the coaxial line. The first reflector is a metal post at the RF input end, shorting the inner and outer conductors. The second reflector is the open end, where a metal plate is placed parallel and near the open end. The resonance frequency of the open-ended coaxial resonator depends strongly on the gap distance between the metal plate and the open end of the coaxial cable, due to the modulation of the phase of the reflection coefficient that characterizes the open end. Thus, by correlating the resonance frequency to the gap distance between the metal plate and the open end (or the movement of the metal plate), the OE-HCCR can be used as a displacement sensor device. Importantly, the displacement measurement resolution of the OE-HCCR is three orders of magnitude greater than that of the existing coaxial-cable-based displacement sensors within a certain dynamic range (~0.11 mm), affording a resolution that is comparable to fiber-optic sensors. The mathematical model of the OE-HCCR is discussed in detail, followed by a proof of concept for displacement measurements. The novel OE-HCCR device is suitable for sensing applications in harsh environments and will advance the field of physical/chemical sensing.
Electrical tuning of bandwidth is critical for microelectromechanical system (MEMS) resonator-based narrowband filters especially at ultra-high frequency ranges and beyond. The resonance frequency of ...MEMS resonators is highly susceptible to fabrication process uncertainties and very small fabrication variations could result in significant shift in their resonance frequency. Although, disk resonators are the most acceptable candidates for implementing of resonators at GHz frequencies, according to their high stiffness, electrical tuning of these resonators and consequently the resulting filters is almost impossible. This study presents a novel tuning method for low velocity through anchor coupled MEMS radial contour mode disk resonators based on the coupling beam's stiffness tuning using the piezoelectric effect. As the results of this method, high bandwidth tuning ratio as 1:1.25 is achieved due to changing the tuning DC voltage from 0 to 20 V. This impressive result for a narrowband filter with 450 kHz of bandwidth is achieved due to changing the stiffness of low stiff coupling beam which is much easier to control in comparison with extremely high stiffness disk resonators. Various simulation results, as well as analytical works, verify the proposed approach.
A new dual-fed dual-frequency antenna that integrates a microwave hollow dielectric resonator antenna (DRA) with a high-gain millimeter-wave dielectric Fabry-Perot resonator antenna (FPRA) is ...investigated. To obtain the dual-frequency operation, the dielectric and air regions of the hollow DRA are designed to satisfy the resonance condition of the FPRA. The DRA and FPRA are excited by a strip and a WR-34 waveguide, respectively. For demonstration, a prototype that covers both 2.4- and 24-GHz ISM bands was fabricated and tested. The S-parameters, radiation pattern, antenna gain, and antenna efficiency are studied, and reasonable agreement between the measured and simulated results is found.
A systematic approach to correcting electric near-field phase and magnitude over a wideband for Fabry-Perot resonator antennas (FPRAs) is presented. Unlike all other unit-cell-based near-field ...correction techniques for FPRAs, which merely focus on phase correction at a single frequency, this method delivers a compact near-field correcting structure (NFCS) with a wide operational bandwidth of 40%. In this novel approach, a time-average Poynting vector in conjunction with a phase gradient analysis is utilized to suggest the initial configuration of the NFCS for wideband performance. A simulation-driven optimization algorithm is then implemented to find the thickness of each correcting region, defined by the gradient analysis, to complete the NFCS design. According to the predicted and measured results, the phase and magnitude distributions of the electric near field have been greatly improved, resulting in a high aperture efficiency of 70%. The antenna under NFCS loading has a peak measured directivity of 21.6 dB, a 3 dB directivity bandwidth of 41% and a 10 dB return loss bandwidth of 46%, which covers the directivity bandwidth. The diameter of the proposed NFCS is <inline-formula> <tex-math notation="LaTeX">3.8\lambda _{0c} </tex-math></inline-formula>, which is around half that of all the other unit-cell-based phase-correcting structures, where <inline-formula> <tex-math notation="LaTeX">\lambda _{0c} </tex-math></inline-formula> is the free-space wavelength at the central frequency of the NFCS (13.09 GHz).
This article presents a novel design for a tunable coaxial filter with the ability to switch between two resonant modes over the tuning range. The use of two resonant modes makes it possible to ...increase the tuning range while maintaining a constant absolute bandwidth. Another feature of the proposed resonator is that it is tuned using a single tuning rotating element regardless of the filter order. The cavity structure is designed such that when the coaxial resonator is tuned, it switches from a <inline-formula> <tex-math notation="LaTeX">\lambda /{4} </tex-math></inline-formula> resonator to a <inline-formula> <tex-math notation="LaTeX">\lambda /{2} </tex-math></inline-formula> resonator, as a result, the filter operates over two adjacent tuning ranges, yielding effectively a wider tuning range. To validate this concept, two prototype tunable filters, a two-pole filter, and a three-pole have been designed. The simulated tuning range of both filters spans from 1.8 to 3.8 GHz yielding a tuning range over 2:1 with less than <inline-formula> <tex-math notation="LaTeX">\pm {\%10} </tex-math></inline-formula> variation in BW and 0.05 dB for insertion loss. The two-pole filter made of aluminum housing was fabricated and measured demonstrating tunability from 1.92 to 3.78 GHz. To the best of our knowledge, this is the first design to simultaneously utilize the characteristics of a <inline-formula> <tex-math notation="LaTeX">\lambda /{4} </tex-math></inline-formula> resonator and a <inline-formula> <tex-math notation="LaTeX">\lambda /{2} </tex-math></inline-formula> resonator to achieve such a wide tuning range with almost constant absolute bandwidth.
We report, for the first time to the best of our knowledge, a technique that employs ′cross-coupling structure' in the cascaded microring resonators (MRRs) to bring new optical analogues of quantum ...coherence phenomena. The new configuration resembles a standard double resonator (SDR) but uses cross-coupled-based directional couplers (DCs) instead of the typical direct-coupled-based DCs. One of its unique features is that it does not exhibit the typical SDR's signature quantum coherence analogue effects like coupled-resonator induced transparency (CRIT) or coupled-resonator induced absorption (CRIA). On the contrary, it produces a new very narrow reflection dip positioned at single-pass phase shift θ = − π/2 which we refer to as cross-coupled resonator induced shifted absorption (CRISA). We compare extensively CRISA's characteristics with the CRIT, CRIA, and Autler-Townes splitting (ATS) found in SDR. The technique opens up new configurations with richer optical behaviours that could find potentially still unexplored applications.
This article presents a novel filter structure named by substrate-integrated suspended line (SISL) waveguide filter (SISLWF). Based on the SISL platform, by introducing the novel SISL via, both the ...magnetic-coupled air-filled waveguide resonators (AF-WRs) and the electric-coupled SISL resonators can be co-designed in the conventional SISL cavity. Magnetic-coupled TE<inline-formula> <tex-math notation="LaTeX">_{101}</tex-math> </inline-formula> mode of the AF-WR is excited by the SISL via and is utilized to design the passband. The co-designed electric-coupled SISL resonators, such as SISL open stub line (SISLOS) and a quarter of open-ended metal ring resonator (QRR), are utilized to generate transmission zeros (TZs) out of band. The SISLOS printed on G5 layer is designed as a notch filter and it is directly connected to the SISL via to generate multiple notch bands. At the end of the SISLOS, an electric-coupled QRR printed on G6 layer is also designed to generate a new TZ at higher band. Measured results show that for the proposed SISLWF, by optimizing the sizes of the SISLOS, QRR, and nonresonant SISL line, five TZs can be generated and controlled simultaneously.
•High quality factor microwave resonator sensors improve current ice and frost detection techniques.•Frost, ice, and water are detected via the S21 variation of the resonant frequency, resonant ...amplitude, and quality factor.•The real-time sensors detect frost faster and with higher sensitivity than current visual methods.•Fast and accurate detection of both the water-to-ice and ice-to-water phase transitions are demonstrated.•Sensor variation due to temperature can be compensated for to isolate the water, frost, and ice signals.
Build up of ice and snow can cause major issues in many industrial and academic endeavors if it is not properly detected and addressed. Ice detection systems are commonly based on visual detection and therefore susceptible to human error and environmental conditions. We introduce a microwave resonator sensor fabricated on a planar substrate operating between 3.5–5 GHz with resonant amplitude −14.5 dB and quality factor of 250. The resonator detects water, frost, and ice based on the measured resonant frequency, amplitude, and quality factor variation in scattering parameter, S21, of the sensor. Three situations are investigated to test the effectiveness of the sensor: first, continuous frost formation on the sensor is tracked and the phenomena of water condensation, frost formation, and subsequent frost growth are characterized. Second, a water droplet is placed on the resonator and frozen, enabling faster and more sensitive detection and representing an initial liquid impact or aggregation on a surface followed by freezing. Lastly, controlled frost formation and removal was performed to better understand the effect of substrate temperature on the sensing parameters so that it could be compensated for via calibration.
In this letter, a novel low-profile microstrip-fed compact triple band-notched ultrawideband (UWB) antenna is proposed. Notch bands around the 3.3-3.8-GHz WiMAX and 5.15-5.85-GHz WLAN frequencies are ...obtained by etching out two elliptic single complementary split-ring resonators (ESCSRRs) of different dimensions from the radiating patch of the antenna. Furthermore, by placing two rectangular split-ring resonators near the feedline-patch junction of the antenna, rejection for the 7.9-8.4-GHz X-band frequencies is achieved. Design guidelines for implementing the notch-bands at the desired frequency regions are provided. The match between the simulated and experimental results suggests that the proposed antenna can be a good candidate for application in UWB communication systems.
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