In this article, based on the electromagnetic radiation theory, the electromagnetic field characteristics of oscillating permanent magnets in both the near-field and far-field regions were derived. The factors influencing the electromagnetic field strength were analyzed, and the method for calculating the magnetic dipole moment of a rectangular permanent magnet was clarified. A three-dimensional simulation model was constructed using COMSOL Multiphysics, with an N52 neodymium-iron-boron permanent magnet oscillating at 30 Hz as the core element. Simulation results for a single magnet indicated that, at a distance of 1 m along the magnetic moment direction, the near-field magnetic flux density reached 1.16-1.52 mu T, and the field strength decreased with increasing distance. For array simulations, multiple configuration schemes were designed, including lateral arrangements (two to five rotors with 100 mm spacing), longitudinal, vertical, and planar arrays in both the XY plane (1 & times; 3, 2 & times; 3, 3 & times; 3, 2 & times; 4) and XZ plane (1 & times; 3, 2 & times; 3, 3 & times; 3). The results demonstrated that the magnetic field strength of the array increased in a nearly linear manner with the number of rotors. In particular, the radiation intensity of the lateral array increased 4.92-fold as the number of rotors grew from 1 to 5. This study provides a theoretical foundation and simulation-validated evidence for the development of compact, low-power, and highly efficient extremely low-frequency antennas.

Abstract This paper proposes a balanced filter design method based on multi-mode ring resonators. By optimizing the resonator structure, independent control of center frequencies of the dual passbands is achieved. Additionally, parallel-coupled feeding is adopted, and the external quality factor is adjusted by tuning the spacing between the feed lines and resonators, enabling independent optimization of the bandwidth for both passbands. Experimental results show that the filter achieves a return loss of less than −17 dB within the dual passbands, an inter-passband isolation exceeding −40 dB. The minimum common-mode mode (CM) suppression of the differential mode (DM) passbands are 41.9 dB and 42.2 dB. The fabricated and tested filter demonstrates good agreement between simulation and measurement results.

This paper proposes a new swinging-type extremely low frequency (ELF) permanent magnet mechanical antenna array with an innovative motion mode. The array consists of 8 permanent magnet rotors serving as electromagnetic wave transmitters, which achieve swinging motion through the cooperation of coils and 4 permanent magnet stators. The correctness of the model is verified via simulation, and a prototype is fabricated. Experimental measurements show that the array can generate a magnetic field signal of 0.14 pT in the air at a distance of 500 m, realize signal modulation and demodulation, and complete simple communication.

This paper presents a comprehensive methodology for analyzing very low frequency (VLF) magnetoelectric (ME) antennas, which integrates fully coupled multiphysics finite element simulation with a dipole equivalent radiation model. Compared to conventional approaches, the proposed method significantly improves simulation accuracy by fully accounting for nonlinear effects, magneto-mechanical-electric coupling, and the magnetoelectric effect. Based on this methodology, we designed and fabricated a prototype transverse shear mode ME antenna operating at 29.3 kHz, with physical dimensions of 5.5 × 0.7 × 0.087 cm3. By optimizing the number of Metglas-magnetostrictive layers to enhance the antenna’s radiation performance, the prototype generates a magnetic flux density of 0.476 nT at a 1-meter distance. Experimental validation confirms that the distance-dependent magnetic-field attenuation trend predicted by the analytical model agrees with the measured results within the near-field and limited measurable range. The study further investigates the antenna’s radiation mechanism, verified through near-field pattern measurements. In addition, the receiving-mode magnetic sensing performance of the ME device was evaluated at resonance, yielding a magnetic-field sensitivity of 33.1 mV/μT and an equivalent magnetic noise spectral density of 30.8pT/Hz1/2 at 29.3 kHz. Additionally, the designed PCB carrier structure and power supply method minimize external constraints on the ME antenna and provide a novel design strategy for the integration of ME antenna arrays.

In this paper, the theoretical design of switchable dual-band filter with bandpass (BP) and bandstop (BS) modes is reported. The PIN diode and SPDT switches are employed as the tuning elements to achieve BP-to-BS mode transformation. The odd-even mode analysis of method is resonant frequency adopted for the symmetrical filtering network. In addition, multiple out-of-band transmission zeros (TZs) and reflection zeros (RZs) are excited based on the virtual short mechanism and path coupling cancellation. Afterwards, different design methodologies for center frequencies (CF), fractional bandwidths (FBW) and external coupling are derived by properly adjusting microstrip electrical lengths. For demonstration, the Switchable Hybrid Integrated RF Filter (SHIRF) is designed, fabricated and measured. In the BP mode, CF of the switchable filter are 1.8 GHz and 2.48 GHz, with 3 dB FBW of 30% and 12.09%, respectively. In the BS mode, the CFs are 2.21 GHz and 2.99 GHz, with FBWs of 7.23% and 18.7%, respectively. The measured results agree well with the theoretical analysis.

The surface acoustic wave (SAW) filter is widely applied in mobile communication, and the resonator is its main component. However, the traditional simulation and design methods of resonators often require much computation because the resonator includes a multilayer structure and many interfinger pairs. In order to improve the efficiency of simulation and designing, this paper proposed a series neural network to design the structural parameters backward based on the performance indicators. We validate the method using a SAW resonator based on a 42°YX cut LiTaO3 substrate with an aluminum electrode. The device consists of an interdigital transducer and two reflector gates. The test set results from simulation data show that the trained model has a relative average error of less than 5% on the devices' structural parameters, and the coefficient of determination is more significant than 0.99. In addition, we compare the predicted and the experimental results, which show that the series neural network has excellent potential to infer the electrical response and structural parameters of SAW devices. The proposed method provides a potential solution for improving the efficiency of simulation and design of surface acoustic wave resonators.

A wideband bandpass filter (BPF) with ultrawide out-of-band rejection capability is proposed in this article. A new design concept is constructed with the employment of cascading ring resonators and a lumped element filtering network. The center frequency ( f(0) ) is located at 2.1 GHz from 0.9 to 3.4GHz with a fractional bandwidth (FBW) of 119% that can simultaneously cover the telecommunications networks of 2G, 3G, 4G, and 5G frequency bands. The 12 transmission zeros (TZs) within the 5.2f0 frequency range have been achieved due to the superposition of signals of multiple transmission paths and the virtual short effect of shorted stubs, and upper sideband rejection is up to 40 GHz ( 19f(0) ). Meanwhile, the proposed BPF realized the minimum insertion loss of 0.11 dB, the group delay in the passband within 0.6 ns, and the overall circuit only occupies 0.21 lambda g x 0.18 lambda g . The measured results match well with the simulation so as to prove the feasibility of the design method.

This paper presents a compact fully tunable wide-band bandpass filter based on the varactors loaded quadruple mode coupled resonator. Triple adaptive transmission zeros (TZs) have achieved by reasonably setting the identical shifting mechanism architecture of transmission poles and adjacent TZs, which dramatically improve the selectivity. Meanwhile, it realized the tunable center frequency (CF) with a constant absolute bandwidth, resulting in the CF tuning range of 26.7 %, 25.8 %, and 15.6 % from 1.5 to 1.95 GHz. The bandwidth tuning range of 42.7 % can be achieved from 180 to 920 MHz with a fixed CF. The test results match well with the theoretical simulation so as to successfully validate the correctness of the proposed design approach.

A compact dual-band bandpass filter (DBBPF) employing nested square ring resonator (NSSR) with abundant transmission zeros is presented in this paper. Due to the symmetrical structure, the odd - even mode analysis method and analytic solutions for the filtering network are demonstrated. Furthermore, multiple transmission zeros (TZs) based on transversal cancellation within a nested square ring resonator accompany with the virtual short mechanism of each transmission path can be excited. Afterward, suitable degrees of freedom within the dual-passbands can be obtained by properly adjusting the microstrip electrical length of the filter structure. To further investigate the proposed design methodology, a prototype DBBPF filter operating at 2.35/4.46 GHz with fractional bandwidth of 10.2% and 9.6% for 5 G applications is synthesized. The presented dual-band bandpass filter is designed, manufactured, and measured, the measured results agree well with theoretical predictions.

In this paper, the theoretical design of a compact wideband bandpass filter (BPF) with a tunable notched band is reported. We proposed a cross-shaped coupling resonator (CHCR) which resonant modes are demonstrated by employing the ABCD matrix analysis method. In addition, the independent and controllable passband characteristics can be obtained by properly adjusting the microstrip electrical length. For tunable application, the varactor diode is employed as the tuning element to achieve a notched frequency range of 8.5-10.0 GHz and the tuning rate is 16.2 %. For demonstration, the tunable circuits are designed, fabricated and measured. Simulated and measured results are matched well. The measured results agree well with theoretical predictions, which exhibit superior performance such as tunable notched band, high-selectivity, compact size, low insertion loss (IL) and ideal notched band suppression levels.

This paper proposes a compact dual-band bandpass filter (BPF) based on concepts of transversal signal interaction (TSI). The filter structure is formed by parallel coupled lines loaded with short stubs to create a T-shaped anti-coupling structure (TACS) and microstrip lines loaded with open stubs to form a multimode resonator (MMR). This configuration results in two wide passbands containing eight transmission poles (TPs). The open stubs introduce four transmission zeros (TZs) at 2.4 GHz, 2.65 GHz, 7.1 GHz, and 7.87 GHz. By leveraging TSI, the filter achieves deep rejection levels of 62 dB and 44 dB at the two stop bands, significantly improving out-of-band suppression. The filter operates at center frequencies of 0.93 GHz (f 1) and 5.25 GHz (f 2), with 3-dB fractional bandwidths of 132 % and 55.2 %, respectively. The minimum insertion losses in the passbands are 0.11 dB and 0.28 dB. The filter size is 0.06 lambda g x 0.14 lambda g, where lambda g is the guided wavelength at 0.93 GHz. Good agreement is observed between simulated and measured performances.

In this paper, a novel tunable dual-band bandpass filter (BPF) with independently controlled passbands and constant absolute bandwidth (CABW) is proposed. The CABW passbands of designed dual-band BPF are obtained using manageable electric and magnetic mix coupling. Furthermore, the multiple transmission paths from the input port to the output port are extended for extra transmission zeros, which results in modified selectivity of the proposed dual-band BPF. The tunability and switchability of the developed filter can be implemented by introducing a single bias voltage of varactors for each band. For the tunable dual-band BPF, the simulated results show that the center frequency (CF) of the first passband varies from 2.38 to 2.68 GHz, and the CF of the second passband varies from 3.28 to 3.88 GHz, while 3-dB absolute bandwidths are 101 +/- 7 MHz and 98 +/- 4 MHz, respectively. Moreover, the two passbands of the filter can also be independently switched by removing the voltage imposed on the varactor CV1 and CV2. The measured results agree well with simulated results, which verify the design theory.

This paper reports a Fabry-Perot (F-P) cavity constructed of heterostructure membranes by metal-organic framework 801 (MOF-801) and graphene oxide (GO) that can achieve high-performance relative humidity (RH) sensing. The reflectance spectrum of the cavity is tuned by adjusting the concentration of MOF-801, spin coating period, and spin coating speed to achieve the optimal reflection waveform. The humidity sensing performance of the MOF-801 membrane and MOF-801/GO heterostructure membrane F-P cavities were investigated systematically. MOF-801/GO heterostructure membranes show higher humidity sensitivity (0.32 nm/% RH) and lower detection limit (0.31% RH) comparing with MOF-801 membranes because the multifunctional reactive groups of GO can interact with H2O, which enhances adsorption of H2O. The MOF-801/GO heterostructure membrane F-P cavity shows a fast optical response (400 ms), with a maximum response value of 27.9 nm (Delta lambda) at 90% RH. Moreover, the MOF-801/GO heterostructure membrane cavity exhibits excellent selectivity for H2O vapor among four interfering gases of CO2, N-2, He, and Ar. Meanwhile, the cavity keeps exceptional repeatability and reliability at different RH values. The sensitivity of the MOF-801/GO heterostructure membrane F-P cavity under mouth breathing is excellent, indicating the cavity is a promising candidate for human respiratory monitoring. The F-P cavity based on MOF-801/GO heterostructure membranes provides a path to fabricate high-performance real-time monitoring of humidity sensors.

In this paper, a novel dual-band wideband bandpass filter (BPF) based on transversal signal-interaction concepts with a wide upper stopband is proposed and investigated. The designed specification of two passbands can be managed and satisfied based on the independent controllable fractional bandwidth of the two passbands and the centered frequencies. The centered frequencies of dual-band BPF are, respectively, 0.79 GHz (f(1)) and 1.24 GHz (f(2)) with 3 dB fraction bandwidths of 26.54% and 11.3%. Two transmission paths consisting of coupled stub-loaded square ring resonators and anti-coupled shorted lines are used to realize signal cancellation of multiple transmission path signal transmission from Port 1 to Port 2. Eleven transmission zeros (TZs) modify harmonic suppression up to 10 f(1) with stopband rejection higher than 15 dB. Butterworth lumped notch network and step impedance resonator (SIR) are also utilized to improve the selectivity and harmonic suppression. A compact filter with a circuit size of 0.08 lambda g x 0.08 lambda g is implemented and tested. Good agreement between simulation and measured results verifies the reliability of the designing scheme.

In this paper, a miniaturized 5 G microstrip lumped hybrid dual-band bandpass filter (BPF) with ideal transmission response, simple structure, and compact size is proposed and characterized. The conversions from lumped elements to microstrip lines are analyzed and demonstrated by utilizing the ideal theoretical circuit model and EM field model. The center frequency of 0.57 GHz and the second passband located at 1.29 GHz are implemented by the proposed dual-band BPF with 3 dB fractional bandwidths of 59.6% and 15.5%, respectively. Additionally, five transmission zeros are strategically positioned on both sides of the passband. The prototype filter with minimized circuit size on occupies 0.05 lambda g x 0.06 lambda g is fabricated and verified that minimum insertion losses in the passbands are separately 0.83 dB and 0.52 dB. Ideal agreement between the simulated and measured results confirms the reliability of the design approach.

A quad-band microstrip bandpass filter (BPF) based on a 13-mode resonator is proposed in this article with compact size, high band-to-band isolation, and multiple transmission zeros (TZs). The proposed filter is constructed by two transmission paths from the input to the output port, which employs the transversal cancellation mechanism of two transition paths to introduce extra nine TZs. Therefore, a total of 12 TZs are located at 0.2, 1.8, 2, 3.88, 4.61, 5.24, 5.9, 9.26, 9.51, 12.32, 12.75, and 13.27 GHz, respectively, realizing high selectivity. Moreover, the designed filter can achieve quad passbands with centered frequency at 0.95, 2.78, 7.32, and 10.63 GHz for the requirement of multi-service in modern communication systems, with wide bandwidth of 235, 790, 2200, and 1540 MHz, respectively. The measured results agree well with the simulation results, which proves the feasibility of the design method.

Recently, lithium niobate thin film laterally excited bulk wave resonators (XBARs) have attracted much attention because of their advantage of high frequency and outstanding electromechanical coupling factor (K2) enabling wide filter bandwidths. These can satisfy the increasing 5G communication demand. However, their large temperature coefficient limits their development to some extent. To improve their temperature stability with little K2 reduction, this paper has proposed a sandwiched structure for temperature compensated XBARs (TC XBARs). This structure includes the top silicon dioxide (SiO2) layer and the bottom SiO2 layer. One layer can improve temperature stability, and the other layer can increase K2. The optimized XBARs have a temperature coefficient of frequency (TCF) of −90.77 ppm⁄°C. The common two-layer TC XBARs can achieve a TCF of −22 ppm⁄°C sacrificing K2 to 8%. However, the proposed sandwiched TC XBARs can achieve a K2 of 12.15 and a TCF of −28.94 ppm⁄°C simultaneously, with a large FoM. Meanwhile, spurious modes can be suppressed in the sandwiched structure. Thus, this sandwiched structure can provide a good solution for the high performance of XBARs.

Surface acoustic wave (SAW) gas sensors based on the acoustoelectric effect exhibit wide application prospects for in situ gas detection. However, establishing accurate models for calculating the scattering parameters of SAW gas sensors remains a challenge. Here, we present a coupling of modes (COM) model that includes the acoustoelectric effect and specifically explains the nonmonotonic variation in the center frequency with respect to the sensing film’s sheet conductivity. Several sensing parameters of the gas sensors, including the center frequency, insertion loss, and phase, were experimentally compared for accuracy and practicality. Finally, the frequency of the phase extremum (FPE) shift was determined to vary monotonically, and the range of selectable test points was wide, making the FPE an appropriate response parameter for leveraging in SAW gas sensors. The simulation results of the COM model were highly consistent with the experimental results. Our study is proposed to provide theoretical guidance for the future development of gas SAW sensors.

GaN high electron mobility transistors (HEMTs) with a 120-nm T-shape gate on a silicon substrate were fabricated. The fabricated devices had a maximum drain current (I-DMAX) of 1.7 A/mm, a low on-resistance (R-ON) of 1.3 Omega center dot mm, a low current collapse ratio of 12% and a minimum noise figure (NFmin) of 1.45 dB with an associated gain (Ga) of 4.7 dB at 30 GHz. A cut-off frequency (fT) of 106 GHz, and a maximum oscillation frequency (f(max)) of 139 GHz were measured, resulting in f(T) x L-G = 12.72 GHz center dot mu m and f(max) x LG = 16.68 GHz center dot mu m. At 28GHz, an output power (Pout) of 0.39 W/mm with an associated 43.4% PAE was obtained at V-DS of 3V.

In this manuscript, a miniature high-temperature superconductor (HTS) bandpass filter (BPF) with multi-transmission zeros (TZs), high selectivity, and great attenuation of stopband is presented. A couple of dual-mode resonator (DMR) is employed to achieve the proposed BPF, which can be characterized by using the classical even-odd mode analysis technique. The presented cascaded DMR can excite four resonant modes, which can be individually managed. Plus, a pair of intrinsic transmission zeros can be yielded at both the lower and upper edges of the passband, which results in sharp shirt performance. As an example, the HTS BPF is designed, fabricated, and tested, in which the center frequency is centred at 3.95 GHz and the 3-dB fractional bandwidth (FBW) is 2.5%. The proposed HTS BPF is implemented by using Tl2Ba2CaCu2O8 (Tl-2212) thin films which are fabricated by two-step processing and the superconducting critical temperatures (Tc) of the HTS films can reach 103 K. The design methodology is confirmed since the experimental results are in good agreement with theoretical results, showing desired bandpass characteristics, high selectivity, and the attenuation of lower and upper stopbands above -50 dB. Further, the circuit size is only 0.4 cm2.