Resonator Length Research Articles

Circularly Polarized Variations of Truncated Corner Square Microstrip Antennas Employing a U-slot

Circularly polarized designs of square microstrip antennas employing U-slot are presented in a 2400 MHz frequency spectrum. Design with a U-slot employing unequal lengths or the corner truncated patch with equal length U-slot yields axial ratio bandwidths of 3.84% and 2.2%, respectively. Against the conventional offset feed patches or the truncated corner square patches, the proposed designs decrease the frequency and patch size by 10% and 22%, respectively. Reduction in the frequency and patch area, while employing the U-slot is not being discussed in the reported papers on the circularly polarized designs, and hence it is the new contribution in the present study. The U-slot cut configurations exhibit a radiation pattern in the broadside with a gain of larger than 6 dBi across the complete reflection coefficient bandwidth. To obtain a wideband and circular polarized response using a single patch, a reconfigurable design of a corner truncated square patch employed with a U-slot is presented. A design methodology is presented based on the resonant length formulation to obtain reconfigurable U-slot cut design as per specific band start frequency in wideband response or center frequency in the axial ratio bandwidth in the circular polarized antenna. This helps to design these configurations for the specific frequency band. Simulated results in the proposed design are verified using the measurements that reflect a close agreement.

Balanced tri- and quad-band BPFs based on SIR with improved passbands selectivity

Abstract In this paper, balanced tri- and quad-band bandpass filters (BPFs) with high selectivity and controllable center frequencies and bandwidths are proposed. In the tri-band BPF design, two differential-mode (DM) passbands are formed by utilizing a stub-loaded resonator (SLR) and a uniform impedance resonator (UIR). The coupling structure of the proposed BPF realizes the third DM passband. Moreover, the center frequencies and bandwidths of the three DM passbands can be controlled by the lengths of resonators and the gaps between the resonators. In order to improve the DM selectivity further, the source-load-coupled structure is introduced. In addition, common-mode (CM) suppression is achieved by using L-shaped balanced microstrip line to slotline transition structures, achieving the independence between CM responses and DM ones. Therefore, the design procedure can be simplified greatly. In order to validate the practicability, one balanced tri-band BPF operating at 2.5, 3.5 and 4.5 GHz is designed and fabricated. Moreover, by adding a short stub to the UIR located in the symmetrical plane, one flexible resonance frequency is generated, which is used to design the balanced quad-band BPF. By manufacturing and measurement, the measurement and simulation are in good agreement.

Double-tuning the inlet and outlet extension lengths of a family of straight-flow expansion chamber mufflers for broadband attenuation

This work presents a generalized end-correction expression for double-tuning the extensions of the concentric inlet and concentric/offset outlet ports of a family of straight-flow circular and elliptical expansion chamber mufflers as a function of geometrical parameters, which include the wall-thickness, ratio of chamber-to-port diameter, aspect-ratio, and the offset distance along the major-axis. To this end, first, the transmission loss (TL) performance of configurations with non-tuned extensions given by half and quarter chamber lengths at the inlet and outlet, respectively, was determined using 3-D FEA, which accounted for the multi-dimensional acoustic field at area-discontinuities. The effective lengths of the quarter-wave resonators at the inlet and outlet and the corresponding end-corrections were computed from the first and second resonance frequency peaks, respectively. The 3-D FEA showed that by considering geometric length equal to the effective inlet and outlet length, three-fourths of the troughs in the TL spectrum were nullified, thereby delivering a broadband attenuation. The 3-D effects were incorporated into the 1-D model through end-correction lengths. Parametric studies were conducted to examine the variation of end-corrections with different geometrical parameters, while the accuracy of the generalized end-correction expression was demonstrated by comparison against previous results.

A design method based on neural network to predict thermoacoustic Stirling engine parameters: Experimental and theoretical assessment

A neural network-based design method for thermoacoustic Stirling engines (TASE) is presented in this work. The main goal of the article is to predict the design parameters (Length of resonator (stub) (LR), Length of inertance tube (Lin), Mean pressure (Pm)) of the thermoacoustic Stirling engine in such a way that the dynamic instability is guaranteed. In this regard, the governing equations of the engine are presented first. Next, with the help of the data extracted from the simulation of the governing equations of the engine, a neural network with the structure of 9–35-3 is trained. The effectiveness of the artificial neural network (ANN) structure is explored via regression and MSE (mean square error) analyses. Next, in order to evaluate and validate the neural network, the experimental data of the constructed thermoacoustic Stirling engine (SUTech-SR-4) is considered. It is important to note that the SUTech-SR-4 is introduced for the first time in this work. Investigations have shown that the neural network could estimate the engine design parameters well and with an acceptable approximation in such a way that the dynamic instability of the engine is also established. Besides, the value of the estimated design parameters for the engine made by the neural network was close to the experimental values. Following, the developed engine is introduced and its performance is discussed. The developed engine has been able to produce a power equivalent to 0.346 W at a pressure of 1 bar (with air working fluid) and a working frequency of 15.9 Hz. It should be noted that the method presented in this article can be used for other types of thermoacoustic Stirling engines. Moreover, the selection of design parameters for the presented method will depend on the physics of the engine and the available facilities.

Theoretical design of high-performance guiding and filtering devices using photonic comb-like waveguides with defective resonators

This paper uses the Transfer Matrix Method (TMM) to investigate the transmission rate and the photonic band structure of one-dimensional photonic comb-like waveguides (CWGs) system. This study is crucial as it provides valuable insights into the properties of photonic waveguides, which can be leveraged to design high-performance guiding, filtering and multiplexing devices. The primary objective of our study is to comprehend the impact of defects on the transmission and band structure of CWGs. Specifically, how changes the geometrical and material properties of defective resonators affect defect modes in photonic band gaps. By modifying the relative permittivity and length of these defective resonators, we observed a shift of defect modes to lower frequencies. This work shows, for the first time, the influence of these defects on defect modes and their potential applications in the development of high-performance guidance and electromagnetic filtering devices.

Anneal-free ultra-low loss silicon nitride integrated photonics

Heterogeneous and monolithic integration of the versatile low-loss silicon nitride platform with low-temperature materials such as silicon electronics and photonics, III–V compound semiconductors, lithium niobate, organics, and glasses has been inhibited by the need for high-temperature annealing as well as the need for different process flows for thin and thick waveguides. New techniques are needed to maintain the state-of-the-art losses, nonlinear properties, and CMOS-compatible processes while enabling this next generation of 3D silicon nitride integration. We report a significant advance in silicon nitride integrated photonics, demonstrating the lowest losses to date for an anneal-free process at a maximum temperature 250 °C, with the same deuterated silane based fabrication flow, for nitride and oxide, for an order of magnitude range in nitride thickness without requiring stress mitigation or polishing. We report record low anneal-free losses for both nitride core and oxide cladding, enabling 1.77 dB m-1 loss and 14.9 million Q for 80 nm nitride core waveguides, more than half an order magnitude lower loss than previously reported sub 300 °C process. For 800 nm-thick nitride, we achieve as good as 8.66 dB m−1 loss and 4.03 million Q, the highest reported Q for a low temperature processed resonator with equivalent device area, with a median of loss and Q of 13.9 dB m−1 and 2.59 million each respectively. We demonstrate laser stabilization with over 4 orders of magnitude frequency noise reduction using a thin nitride reference cavity, and using a thick nitride micro-resonator we demonstrate OPO, over two octave supercontinuum generation, and four-wave mixing and parametric gain with the lowest reported optical parametric oscillation threshold per unit resonator length. These results represent a significant step towards a uniform ultra-low loss silicon nitride homogeneous and heterogeneous platform for both thin and thick waveguides capable of linear and nonlinear photonic circuits and integration with low-temperature materials and processes.

Classical guitar intonation and compensation: The well-tempered guitar.

An intuitive model of classical guitar intonation is presented that includes the effects of the resonant length of the fretted string, linear mass density, tension, and bending stiffness. An expression is derived for the vibration frequencies of a stiff string using asymmetric boundary conditions at the saddle and the fret. Based on logarithmic frequency differences ("cents") that decouple these physical effects, Taylor series expansions are introduced that exhibit clearly the origins of frequency deviations of fretted notes from the corresponding 12-tone equal temperament (12-TET) values. A simple in situ technique is demonstrated for measurement of the changes in frequency of open strings arising from small adjustments in length, and a simple procedure is proposed that any interested guitarist can use to estimate the corresponding frequency shifts due to tension and bending stiffness for their own guitars and string sets. Based on these results, a least-squares fit method is employed to select values of saddle and nut setbacks that map fretted frequencies-for a particular string set and guitar-almost perfectly onto their 12-TET targets. A general approach to tempering an "off-the-shelf" guitar is shown to further reduce the tonal errors inherent in any fretted musical instrument.

Resonant fiber optic gyroscope driven by a broadband light source based on an over-coupled state fiber ring resonator

The resonant fiber optic gyroscope (RFOG) driven by a broadband light source has advantages over conventional RFOGs in terms of structure, solution, etc., and provides new ideas for the commercialization of RFOGs. In this paper, the basic working principle of RFOG driven by a broadband light source is introduced. The optimal modulation coefficients are provided for sinusoidal wave modulation. The influence of the length of the fiber-optic ring resonator (FRR) and the coupling coefficient of the fiber coupler on the sensitivity is analyzed. The FRR is constructed in the over-coupled state to improve the utilization of optical power, and thus significantly increase the system sensitivity. In experiments, an RFOG prototype with a diameter of 13 cm, a height of 7 cm, and a fiber ring length of 210 m is produced. A bias instability (BI) of 0.06°/h and an angular random walk (ARW) of 0.01∘/h are obtained.

Modeling and measurement of lead tip heating and resonant length for implanted, insulated wires.

To study implant lead tip heating because of the RF power deposition by developing mathematical models and comparing them with measurements acquired at 1.5 T and 3 T, especially to predict resonant length. A simple exponential model and an adapted transmission line model for the electric field transfer function were developed. A set of wavenumbers, including that calculated from insulated antenna theory (King wavenumber) and that of the embedding medium were considered. Experiments on insulated, capped wires of varying lengths were performed to determine maximum temperature rise under RF exposure. The results are compared with model predictions from analytical expressions derived under the assumption of a constant electric field, and with those numerically calculated from spatially varying, simulated electric fields from body coil transmission. Simple expressions for the resonant length bounded between one-quarter and one-half wavelength are developed based on the roots of transcendental equations. The King wavenumber for both models more closely matched the experimental data with a maximum root mean square error of 9.81°C at 1.5 T and 5.71°C at 3 T compared to other wavenumbers with a maximum root mean square error of 27.52°C at 1.5 T and 22.01°C for 3 T. Resonant length was more accurately predicted compared to values solely based on the embedding medium. Analytical expressions were developed for implanted lead heating and resonant lengths under specific assumptions. The value of the wavenumber has a strong effect on the model predictions. Our work could be used to better manage implanted device lead tip heating.

Low-frequency broadband valley transport for acoustic topology based on extended resonance

This paper proposes an extended resonant structure to solve the problem that topological acoustic waveguides have a narrow bandwidth at low frequencies. This acoustic structure consists of a two-dimensional structure and a resonant cavity in the three-dimensional direction, and its essence is to extend the resonant cavity in the two-dimensional structure to the three-dimensional direction. The problem that the size of the resonant cavity is limited by the size of the two-dimensional structure can be solved by this special extension. At the same time, the resonant cavity can be maximized in the three-dimensional direction. The topological properties of the original structure are not affected as long as the radius of the resonant cavity is widened without changing the symmetry of the overall composite structure. The rotating scatterer remains a reliable method for realizing topological phase transitions. The effect of the resonant cavity length on the band position is obtained using the finite element method, and it is demonstrated that the topological acoustic waveguide has a wide operating band at low frequencies. Simulation results show that this structure still has a bandgap width of 100 Hz at a low frequency of 350 Hz. The topological acoustic waveguide structure proposed in this paper can provide a new idea for the study of low-frequency broadband acoustic topology, which promotes the control of low-frequency acoustic waves by the topological acoustic waveguide.

Influence of resonator length and temperature configuration on the performance of a supercritical CO2 thermoacoustic engine

The peculiar properties of CO2 at supercritical pressures and transcritical temperature conditions are favorable for thermoacoustic devices. The printed circuit heat exchanger has been employed to fabricate a standing-wave thermoacoustic engine that works under these conditions. Experiments performed in this paper are devoted to exploring the influences of resonator length and temperature configuration on its performance. Results demonstrate that the oscillation frequency drops when the resonator is elongated, while the pressure amplitude is strengthened. To generalize the experimental data, the power-law relation for pressure amplitude and the bilinear law of frequency are extended to include resonator length as an independent variable, serving as the basis for tuning performance through resonator length. The best temperature configuration is to put the pseudo-critical temperature at the midpoint of heating and cooling temperatures to induce the pressure oscillation at maximum amplitude. Guided by the above results, experiments are performed to explore the extremum of low onset temperature difference. The current record is finally identified as 8.6 °C, close to the literature record of 7.0 °C. This paper elucidates the effects of resonator length and temperature configuration. Conclusions drawn in this paper can guide the design and operation of thermoacoustic devices working with supercritical CO2.

Huygens’ metasurface: From anomalous refraction to reflection

Huygens' metasurfaces (HMS) without any reflection or transmission are widely studied due to the high-efficiency manipulation of electromagnetic waves. In this work, three-layered metallic Huygens' metasurfaces are proposed and the geometry-dependences of anomalous refraction and reflection are investigated. The surface impedance and admittance are independently tailored by changing the length of metallic resonators, which is dictated by the introduction of the intermediate layer. Huygens’ metasurfaces can be geometrically engineered to realize anomalous refraction with an efficiency of 62% and anomalous reflection with an efficiency of 60%, respectively. It is anticipated that the proposed metasurface with tunable materials could achieve reconfigurable terahertz devices.

High-average-power single-frequency pulse optical parametric oscillator based on pulse-integrated seed-injection automatic locking.

Near-infrared nanosecond (ns) single-longitudinal-mode (SLM) pulse light generated from an optical parametric oscillator (OPO) is an important source in nonlinear optics and high-precision spectral analysis. In this Letter, a stable SLM near-infrared ns pulse light source generated from the OPO is presented, which is achieved by developing a seed-injection automatic locking technique based on a pulse-integrated photodetector (PIPD). Depending on the PIPD, the peak power of the pulse light detected by the photodiode is converted to the average power by integrating several pulses. As a result, the detector saturation is thoroughly eliminated, and the interference signal including the resonance point between seed and pulse lights can easily be attained by scanning the resonator length. On this basis, a microcontroller unit (MCU) is employed to realize automatic locking by looking for the minimum value of the interference signal. Finally, a SLM 824 nm pulse light source with an output power of 20.5 W and a linewidth of 51.42 MHz is obtained. The presented method can pave the way to implement a low-cost and compact high-average-power SLM pulse OPO.

High-efficiency and high-brightness broad area laser diodes with buried implantation current blocking

Buried-regrown-implant-structure (BRIS) technology combines two-step epitaxial regrowth with an intermediate ion implantation step in order to realise a buried current aperture close to the active region of a laser diode. In this paper we carry out a systematic performance comparison demonstrating the benefit of BRIS technology in single emitter broad-area lasers (BALs). We investigate stripe width W = 100 μ m and resonator length L = 4 mm single emitter lasers emitting at wavelength λ = 915 nm, comparing the performance of BRIS devices with different implantation depths with reference devices with only contact layer implantation. We show that using BRIS technology we achieve a continuous wave output power of 20 W at 57% efficiency, with a peak efficiency of 68%, and maintain a lateral brightness of 3.4 mm · mrad up to 19 W, improved over the reference devices due to reduced lateral current spreading in the BRIS devices. Further, we show results of ongoing aging experiments, which has shown no device degradation up to 5000 hours from BRIS devices.

A compact continuous-wave intracavity frequency doubling Pr:YLF ultraviolet laser at 360 nm

We demonstrate a continuous-wave (CW) ultraviolet (UV) laser operating at 360 nm, achieved through intracavity frequency doubling of a Pr:YLF laser. This UV laser is more compact and simpler compared to previously reported designs, due to the adoption of a straight cavity. The total length of the laser system measures 75 mm, with a resonant cavity length of only 25 mm. By utilizing an InGaN laser diode (LD) emitting at 444 nm with a maximum incident power of 3.1 W, we were able to achieve a CW UV laser with an output power of 252 mW. The optical to optical conversion efficiency reached up to 8.1%, and the output power stability remained within ±1.9% over a period of two hours. This innovative UV laser has potential applications in various fields such as spectral analysis, material analysis, bioengineering, optoelectronic detection, and medical treatment.

Fiber-Optic Photoacoustic CO Sensor for Gas Insulation Equipment Monitoring Based on Cantilever Differential Lock-In Amplification and Optical Excitation Enhancement.

A fiber-optic photoacoustic CO sensor for gas insulation equipment is proposed, which relies on F-P interferometric cantilever-based differential lock-in amplification and optical multipass excitation enhancement. The sensor has excellent characteristics of high sensitivity, antielectromagnetic interference, fast response, and long-distance detection. The photoacoustic pressure waves in the two resonators of the differential photoacoustic cell (DPAC) are simultaneously detected by two fiber-optic interferometric cantilevers and processed differentially; thereby, the gas flow noise is effectively suppressed. Based on the comprehensive analysis of the superposition of photoacoustic excitation and multipass absorption, the diameter of the resonator is determined to be 6 mm. The optical power emitted by the 1566.6 nm distributed feedback laser is increased to 500 mW by an erbium-doped fiber amplifier. The near-infrared light is reflected 30 times in the multipass cell, which improves the order of magnitude of optical effective excitation. Due to the low sound velocity of SF6 gas, the resonant frequency of the DPAC with a resonator length of 80 mm is 760 Hz. The response time to CO/SF6 gas is 93 s with a flow rate of 500 sccm. The detection limit of the CO sensor is 53 ppb, which realizes the accurate and timely perception of the SF6 decomposition derivative CO and provides technical support for trouble-free operation of gas insulation equipment.

28.02 W LD side-pumped CW laser operated at 2.8 µm in YSGG/Er:YSGG/YSGG crystal.

We demonstrated a 978 nm laser diode (LD) side-pumped YSGG/Er:YSGG/YSGG composite crystal with a size of Ф 3 mm × 65 mm and continuous-wave (CW) mode. By optimizing resonator length and output mirror transmittance, a maximum output power of 28.02W is generated, corresponding to slope efficiency of 17.55% and optical-optical efficiency of 12.29%, respectively. The thermal focal lengths are obtained by resonator stability condition. The laser wavelength is centered near 2.8 µm. Moreover, the beam quality factors M x2/M y2 are fitted to be 8.14 and 7.35, respectively. The above results indicate that a high-performance 2.8µm CW laser can be achieved by LD side-pumped YSGG/Er:YSGG/YSGG composite crystal with excellent heat dissipation ability, which promotes effectively the development and applications of the mid-infrared solid-state lasers.

Compact 3D monolithic microwave integrated circuit bandpass filter based on meander resonator for 5G millimeter-wave

Bandpass filters for millimeter-wave band applications are typically designed using resonators. However, the design of a multilayer coplanar waveguide (CPW) monolithic microwave integrated circuit (MMIC) bandpass filter for 5G millimeter-wave band, n257 with operating frequencies from 26.5 to 29.5 GHz is still not available. Therefore, in this work, a compact bandpass filter for 5G millimeter-wave application was designed with multilayer CPW MMIC bandpass filter based on a meander resonator. The meander resonator of the bandpass filter was designed using low-loss multilayer CPW lines. In designing the bandpass filter, the resonator length and perturbation was utilized to optimize the resonance and bandwidth, and meander resonator was used to miniaturize the bandpass filter. As result, a compact bandpass filter with size of 0.75×0.75 mm<sup>2</sup> for 5G millimeter-wave band n257 was achieved. It has bandwidth of 3 GHz, an insertion loss of -2.87 dB and a return loss of -11.1 dB at frequency 28 GHz.

Commonality and difference in the eigenfunctions of various types of acoustic trapped modes

We investigate and compare various types of acoustic trapped modes (TMs) in resonator–waveguide systems. The goal is to understand the commonality and difference between the mechanisms of common (symmetry protected, invisibility protected and symmetry–periodicity protected) and accidental TMs, occurring continuously and discretely in the resonator length–frequency two-parameter space. The latter type cannot yet be explained via an operator decomposition. Here, all TMs are explained in the same way by analysing why and how the propagating-wave loops in the eigenfunctions can satisfy the eigenmode condition (loop magnitude and phase constraints for closure) and the wave-trapping condition (loop zero-radiation condition) simultaneously. Firstly, the unified analysis reveals the commonality that one or multiple coupled propagating-wave loops satisfy TM conditions, and the difference. In common TMs, the loop zero radiation is independent of the single loop phase constraint that selects the TM frequency as a continuous function of resonator length. On the other hand, loop zero radiation in accidental TMs depends on the loop phase constraints and there are two phase constraints. Only at the crossing points of the two phase constraints can zero-radiation loops be ensured. Secondly, in contrast to previous studies, it suggests that modal degeneracy, avoided crossing and resonance-width bifurcation are not the mechanisms of accidental TMs.

A Method for Low Sidelobe Substrate-Integrated Waveguide Slot Antenna Design Applied for Millimeter-Wave Radars

With the development of millimeter-wave radar systems, substrate-integrated waveguide (SIW) slot antennas have been widely used. This paper presents a computational approach for calculating the equivalent normalized admittance of slot in low sidelobe SIW longitudinal slot antennas. In contrast to the existing methods, this method takes into account the impact of the N-slots coupling on the admittance. Through this method, fitting functions for resonant length and conductance are obtained, which describe the relationship between the resonant length, resonant conductance, and offset of slots. Moreover, based on the two fitting functions, a low sidelobe SIW longitudinal slot linear antenna is designed for millimeter-wave radar applications at 77 GHz. This antenna consists of a transition from the standard WR-12 waveguide to the SIW and a set of radiating slots. The simulation results indicate an impedance bandwidth of 4.8% and a gain of 13.2 dBi. The sidelobe level in the H-plane is below −28 dB, which meets the desired specifications and confirms the accuracy of the presented method.