Dual-frequency Operation Research Articles

Fully nonlinear three-dimensional modeling of parametric interactions in the field of a dual-frequency acoustic array.

An algorithm is developed for fully nonlinear three-dimensional (3D) simulation of a difference-frequency acoustic beam resulting from the interaction of two high-intensity pump waves. Simulations are performed in the frequency domain based on the Khokhlov-Zabolotskaya-Kuznetsov equation. A spectrum filtering method is used to enable accurate solutions for the difference-frequency fields in strongly nonlinear beams and with a high downshift frequency ratio using only dozens of spectral components retained in the algorithm. As an example, the dual-frequency operation of an underwater multi-element ellipsoidal array is considered, and numerical solutions describing parametric interactions in the array field are analyzed. It is shown that difference-frequency beams are more symmetric in transverse directions compared with the pump beams. The most efficient parametric generation of difference-frequency beams corresponded to close and beyond shock-forming conditions. Axial pressure amplitude of the difference frequency was shown to grow first quadratically with the source pressure following the quasi-linear solution and then linearly once shocks start to develop. The percentage of the total power converted to the difference frequency from pump waves increased at high power outputs without saturation. Up to twofold increase in directivity angles of difference-frequency beams under shock-forming conditions was observed compared with quasi-linear conditions.

Optimizing dual-band antenna efficiency: Ridge width parametric study of quad ridge horn antennas

The purpose of this project was to develop a quad ridged horn antenna for a GSM and mid band 5G application, capable of dual frequency range operation at 1.8 GHz and 3.5 GHz. The antenna was constructed using 3D printing technology and Polylactic Acid (PLA), a thermoplastic polymer known for its high strength and compatibility with 3D printing processes. The impact of varying ridge width dimensions on the antenna's performance was evaluated using a range of parametric techniques. Ridge widths of 10 mm, 13.5 mm, and 17 mm were analysed to assess the effects of dimension alterations. Results demonstrated that the antenna is capable of dual band frequency operation with signal reflections of -16.89 dB and -28.60 dB at 1.8 GHz and 3.5 GHz, respectively. This research contributes to the development of efficient and cost-effective antennas for wireless communication applications in the GSM and mid band 5G spectrum.

Grating magneto-optical traps with complicated level structures

We study the forces and optical pumping within grating magneto-optical traps (MOTs) operating on transitions with non-trivial level structure. In contrast to the standard six-beam MOT configuration, rate equation modeling predicts that the asymmetric laser geometry of a grating MOT will produce spin-polarized atomic samples. Furthermore, the Landé g-factors and total angular momenta of the trapping transition strongly influence both the confinement and equilibrium position of the trap. Using the intuition gained from the rate equation model, we realize a grating MOT of fermionic 87Sr and observe that it forms closer to the center of the trap’s quadrupole magnetic field than its bosonic counterpart. We also explore the application of grating MOTs to molecule laser cooling, where the rate equations suggest that dual-frequency operation is necessary, but not sufficient, for stable confinement for type-II level structures. To test our molecule laser cooling models, we create grating MOTs using the D 1 line of 7Li and see that only two of the four possible six-beam polarization configurations operate in the grating geometry. Our results will aid the development of portable atom and molecule traps for time keeping, inertial navigation, and precision measurement.

A Typical Slotted SIW Cavity-backed Antenna for Dual frequency operations in U-NII Bands

A low profile circular shaped cavity-backed substrate integrated waveguide (SIW) antenna with two-typical intersecting rectangular slots on the ground plane is designed to operate in the dominant TM010 mode at a frequency of 5.19 GHz in U-NII-1 band for wireless applications. The initially designed antenna produces a gain of 4 dBi with a narrow impedance bandwidth extending from 5.17 – 5.22 GHz. The antenna design is further modified by insertion of another shifted two-typical intersecting rectangular slots to finally resemble that of Hash shape; resulting in dual band antenna operation at 4.9 and 5.93 GHz. The gains obtained are 3.7 dBi and 1.4 dBi for 4.9 and 5.93 GHz respectively with an impedance bandwidth covering 4.88 - 4.92 GHz and 5.92 – 5.94 GHz respectively. The antenna prototype is fabricated using Arlon AD270 substrate material. Parametric studies are performed in terms of return loss and gain of the antenna. All simulations are carried out using HFSS v19.0 and show similar behavior to their experimentally measured counterparts.

Degradation of sulfamerazine using ultrasonic horn and pilot scale US reactor in combination with different oxidation approaches

The present study aimed at utilizing ultrasonic horn (USH) and ultrasonic reactor (USR) having provision for dual frequency operation for the successful and cost-effective degradation of sulfamerazine (SMZ). USH and USR were combined with UV, persulfate (PS), peroxymonosulfate (PMS), Fenton (Fe2+/H2O2) and Fenton like (Fe3+/H2O2) process in detailed investigation to establish the optimal loading for obtaining the improved degradation of SMZ quantified in terms of the synergistic index values. A mathematical model was also developed to explain the complex SMZ degradation kinetics for all the AOPs. Significantly higher SMZ degradation (>99 %) was achieved for various combined approaches as USH/PS, USH/PMS, USH/Fe2+/H2O2, USH/Fe3+/H2O2, USH/PS/UV, USH/PMS/UV, USH/Fe2+/H2O2/UV, and USH/Fe3+/H2O2/UV, demonstrating the significant role of SO4¯ and OH radicals in intensifying the oxidation of the SMZ molecules. The pilot scale study with USR also demonstrated effective SMZ degradation using combined AOPs with maximum removal as 94.14 % for USR (22 + 44 kHz)/Fe3+/H2O2/UV. The dual frequency mode of operation was observed to be more efficient than the single frequencies. The cost estimation study based on of cavitational yield revealed that the most cost-effective system was the USR (22 + 44 kHz)/Fe3+/H2O2/UV with a degradation cost of 0.57 ₹/L (0.0069 $/L).

A compact microstrip patch antenna with DGS for WiFi/WiMAX/WLAN

In recent years, the study of microstrip patch antennas has witnessed significant advancements, offering numerous advantages and promising prospects compared with conventional antennas. These antennas are characterized by their lightweight compact size, low cost, low profile, small dimensions, and excellent conformability. Additionally, microstrip patch antennas exhibit various desirable features, such as dual and circular polarization, dual-frequency operation, broad bandwidth, flexible feedline configurations, and beam-scanning omnidirectional patterns. In this paper, a microstrip patch antenna design tailored for the 2.4 GHz frequency band is proposed, showcasing its potential for applications in wireless communication devices. The antenna is engineered to operate across multiple bands, including the wireless device band, Ultra Wide Band (UWB), and X band. It has a truncated rectangle shape with additional stubs, whereas the substrate material employed is FR4. The resulting design achieves resonance at four different frequencies, effectively covering the Microwave Access (WiMAX) band at 2.5 GHz and 4 GHz. Notably, the implementation of Digital Global Systems (DGS) plays a crucial role in reducing the antenna size while simultaneously enhancing its performance. The proposed microstrip patch antenna demonstrates great potential for meeting the increasing demand of modern wireless communication devices. Its multiband operation, compact size, and improved performance, achieved through the integration of DGS, make it a promising candidate for various wireless communication applications.

Dual-Band 28- and 39-GHz Phased Arrays for Multistandard 5G Applications

This article presents a 32-element 28/39-GHz dual-band phased array for fifth-generation (5G) communication systems. The array is based on separate sets of SiGe transmit/ receive (Tx/Rx) beamformer chips to realize independent dual-beamforming capabilities at orthogonal linear polarizations. The beamformer chips are integrated with an <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$8 \times 4$ </tex-math></inline-formula> dual-band stacked patch antenna array on a low-cost printed circuit board (PCB) and grouped together using two different Wilkinson networks to form two separate beamforming systems. The dual-band array demonstrates a measured effective isotropic radiated power (EIRP) of 40–42 dBm at the 28- and 39-GHz bands. The array is capable of scanning ±55° in the 28-GHz band and ±40° in the 39-GHz band, both in the azimuth plane. In simultaneous dual-frequency dual-beam operation with the 28-GHz band on the V-pol. and the 39-GHz band on the H-pol., spectrum measurement shows that the array has no visible intermodulation products between the 28- and 39-GHz beams. Also, complex modulation measurements with 64-QAM waveforms show < 3% error vector magnitude (EVM) at an EIRP of up to 36-dBm EIRP for both beams radiating together and without interference with each other. This work demonstrates the first millimeter-wave (mm-wave) 5G dual-band array and paves the way toward multistandard systems.

Polarimetric Weather Radar: Overview of principles and applications

We introduce radar polarimetry, which generally is a less widely known concept of radar engineering, and explain the principles and applications of polarimetric Doppler weather radars. For example, a polarimetric radar can distinguish among precipitation particles of different shapes, compositions, and orientations. A relatively simple electromagnetic idea resulted in the 2012 upgrade of the National Weather Service (NWS) network of 160 high-resolution Doppler weather radars in the United States, with dual-polarization technology. We describe the details of the Colorado State University (CSU)–CHILL research radar, featuring exceptional polarization purity and dual-frequency operation, and its setup and role in winter field experiments in Colorado.

A Novel Design of Flat-Top Beamforming Anti-Multipath Antenna

This article discusses a novel design method of wide-beam circular polarization array antenna for satellite navigation. For special applications such as satellite navigation guiding aircraft landing, high-performance ground reference station antennas are required. In the system of satellite navigation guiding aircraft landing, the antenna of satellite navigation receiver needs to have the following radiation characteristics: the shape of antenna pattern is close to an ideal hemisphere, the upper half of space has uniform right-hand circular polarization gain, and the beam has the characteristic of sharp cutoff below 5 degrees of elevation. Whether the GNSS reference station antenna can have a wider beam circular polarization characteristic to receive more navigation satellites signal; whether it can suppress the multipath effect to a greater extent to reduce the multipath error; and whether it can work in a wider frequency band, so that several major satellite navigation systems work together, the above factors directly affect the satellite navigation and positioning accuracy of the entire system. The beam of this antenna has the following feature: sharp cutoff near the horizon for multipath mitigation at low elevation angles. Comprehensive design thereby accelerates system design. It owns wide beam, good circular polarization characteristics, low elevation angle sharp cutoff, and ultralow sidelobe radiation characteristics that achieve the purpose of receiving satellite navigation signal and multipath. The low sidelobe characteristic of the antenna is beneficial to suppress multipath effect. According to the theoretical knowledge of the symmetrical dipole and the four-arm helical antenna, the simple structure of the symmetrical element is fully utilized, and the printed balun easily realizes the dual-frequency operation of the antenna. Combined with the wide-beam circular polarization characteristic of the four-arm helical antenna structure, the shaped beam array antenna is designed. The wide-beam circularly polarized antenna unit not only covers the frequency band of the satellite navigation system but also satisfies the system performance and key feature requirements of the array antenna for the unit; that is, it satisfies the wide-beam circular polarization characteristics of the upper half space. According to the linear array basic theory and array antenna synthesis theory, Woodward Lawson sampling synthesis algorithm is used to synthesize the array amplitude and phase weights corresponding to the specific antenna pattern required for the Ground-Based Augmentation System (GBAS) engineering. The shaped beam array antenna consists of 21 units, of which 11 antenna units are directly fed, and the feeding ports of the rest are dummy ports. It is an equally spaced array antenna. The spacing between antenna units is close to half wavelength. They are fed according to the value corresponding to the excitation function. The array antenna is simulated by HFSS (High-Frequency Structure Simulator). Compared with traditional satellite navigation antennas, the antenna in this paper has excellent front-to-rear ratio and flat-top beam pattern. The results show that the wide-beam circularly polarized array antenna meets the engineering requirements of GBAS applications and lays the solid foundation for GBAS engineering applications.

Dual-Frequency Microstrip Leaky-Wave Antenna for High-Gain Broadside Radiation

This article presents a resonator-fed dual-frequency dual-mode bidirectional leaky-wave antenna to provide attractive high-gain broadside radiation at dual desired frequencies. First, by analyzing the dispersion diagrams of the first (EH <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1</sub> ) and third (EH <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> ) higher order modes of a microstrip line, it is theoretically verified that these two modes can both be suitably employed for bidirectional leaky-wave antenna design. In addition, it is also determined that the ratio between these two operation frequencies can be handily controlled by appropriately loading periodical shorting pins along the nodal lines of the EH <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> modal field. As such, the dual-frequency operation principle is thoroughly investigated and determined. Afterward, to effectively excite the desired modes and suppress any unwanted modes of the microstrip line, a dual-frequency resonant-fed strategy is adopted. More specifically, the introduced feeding resonator is first fed by a pair of differential probes, and then, the microstrip EH <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1</sub> and EH <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> modes are excited through the coupling gap. In this way, the desired pure EH <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1</sub> and EH <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> modes are successfully excited. As an example, a dual-frequency bidirectional microstrip leaky-wave antenna is designed to work at 3.6 and 4.9 GHz, and its prototype is simulated, fabricated, and tested. The obtained far-field radiation patterns from simulations and measurements show a reasonable agreement, and the concerned high-gain radiation at the broadside is well achieved at both frequencies.

Performance Analysis of Wearable Dual-Band Patch Antenna Based on EBG and SRR Surfaces.

This paper presents the performance comparison of a dual-band conventional antenna with a split-ring resonator (SRR)- and electromagnetic bandgap (EBG)-based dual-band design operating at 2.4 GHz and 5.4 GHz. The compactness and dual-frequency operation in the legacy Wi-Fi range of this design make it highly favorable for wearable sensor network-based Internet of Things (IoT) applications. Considering the current need for wearable antennas, wash cotton (with a relative permittivity of 1.51) is used as a substrate material for both conventional and metamaterial-based antennas. The radiation characteristics of the conventional antenna are compared with the EBG and SRR ground planes-based antennas in terms of return loss, gain, and efficiency. It is found that the SRR-based antenna is more efficient in terms of gain and surface wave suppression as well as more compact in comparison with its two counterparts. The compared results are found to be based on two distinct frequency ranges, namely, 2.4 GHz and 5.4 GHz. The suggested SRR-based antenna exhibits improved performance at 5.4 GHz, with gains of 7.39 dbi, bandwidths of 374 MHz, total efficiencies of 64.7%, and HPBWs of 43.2 degrees. The measurements made in bent condition are 6.22 db, 313 MHz, 52.45%, and 22.3 degrees, respectively. The three considered antennas (conventional, EBG-based, and SRR-based) are designed with a compact size to be well-suited for biomedical sensors, and specific absorption rate (SAR) analysis is performed to ensure user safety. In addition, the performance of the proposed antenna under bending conditions is also considered to present a realistic approach for a practical antenna design.

Analysis and Characterization of Optimized Dual-Frequency Vibration Energy Harvesters for Low-Power Industrial Applications.

We present a multiresonant vibration energy harvester designed for ultra-low-power applications in industrial environments together with an optimized harvester design. The proposed device features dual-frequency operation, enabling the harvesting of energy over a wider operational frequency range. It has been designed such that its harvesting bandwidth range is [50, 100] Hz, which is a typical frequency range for vibrations found in industrial applications. At an excitation level of 0.5 g, a maximum mean power output of 6 mW and 9 mW can be expected at the resonance frequencies of 63.3 and 76.4 Hz, respectively. The harvester delivers a power density of 492 µW/cm2. Design optimization led to improved harvester geometries yielding up to 2.6 times closer resonance frequencies, resulting in a wider harvesting bandwidth and a significantly higher power output.

Gradient-index phononic crystal and Helmholtz resonator coupled structure for high-performance acoustic energy harvesting

Acoustic energy harvesting (AEH) has emerged as a promising powering process for the sustainable self-powered operation of wireless sensors in wearable, biomedical, and industrial applications. However, despite the abundance of sound sources in the environment, intrinsically low acoustic energy density still poses a critical challenge; therefore, the development of various sound amplification structures, such as Helmholtz resonators (HRs), phononic crystals, and acoustic metamaterials is required. In this study, we combined two distinct sound amplification mechanisms, Helmholtz resonance and omnidirectional acoustic wave focusing, to generate a sufficiently high power output within an ambient sound environment at practically low frequencies (< 1 kHz). A two-degree-of-freedom model was developed to systematically design a HR integrated with a piezoelectric device (HR-PEH). Subsequently, the HR-PEH was incorporated with a circularly symmetric gradient index phononic crystal (GRIN PnC) structure that enabled omnidirectional sound focusing. Finally, we constructed a coupled acoustic system GRIN-HR-PEH. Analytical modeling and experimental characterization revealed the existence of two distinct dual operating frequencies for power maximization: mechanical and acoustic resonances, which offers design flexibility in coupled AEH systems. As a result, the coupled GRIN-HR-PEH system yielded an output power of up to 4.1 mW under an ambient incident sound pressure of 47 dB, satisfying the power requirements of practical applications.

Mapping of cavitation intensity in a novel dual-frequency ultrasonic reactor of capacity 10 L

Mapping of a dual-frequency ultrasonic reactor was performed based on measurements of local cavitation intensity at various horizontal and vertical planes in the reactor for single frequency operation (22 kHz or 44 kHz) and dual-frequency operation (22 + 44 kHz) at varying input power of 250 and 450 W. The average cavitation intensity ranged between 73.6 and 86.7 W/cm2, 38.75 and 64.4 W/cm2, 86.7 and 100.6 W/cm2 for the operating frequencies of 22, 44 and 22 + 44 kHz respectively at maximum input power of 450 W depending on the location. Bubble dynamics simulations at various frequencies were also performed using the Keller-Miksis equation and the trends of bubble radius, collapse temperature and pressure were found to effectively match the experimental findings for cavitation intensity. The work has clearly elucidated the dependency of the cavitational activity on location, power dissipation and operating frequency mode with dual-frequency operating showing higher cavitation intensity.

A Dual-Frequency Terahertz Metasurface Capable of Distinguishing the Handedness of Circularly Polarized Light

Circularly polarized light can present more optical properties of chiral materials and is widely used to analyze and detect biomolecules. In this paper, a dual-frequency terahertz circular polarization detection structure, which is based on multilayer metamaterials, is proposed. The proposed structure consists of a dual-frequency quarter-wave plate, a polyimide spacer, and a filter. The simulation results show that the structure can distinguish the handedness of circularly polarized light by filtering. The extinction ratios are 4 dB and 5.26 dB at 0.952 THz and 1.03 THz, respectively, and the maximum transmittance efficiency reaches 40%. Given the advantages of easy integration and dual-frequency operation, our design is bound to facilitate the development of multi-frequency detection in biomedical imaging devices.

A resonator-based dual-frequency driven atmospheric pressure plasma jet

An atmospheric-pressure argon plasma jet featuring a novel integrated resonator-based multi-frequency impedance matching is presented and briefly characterized. Two narrow RF frequency bands can be chosen for operation or used simultaneously. This includes a mode with the higher frequency value being exactly five times the lower one. Phase-resolved optical emission spectroscopy measurements show a distinct influence of the input frequency combination on the discharge dynamics. Measurements of the dissipated electrical power and the emission spectrum for each operating mode complete the basic characterization of the device. Although it is constructively much simpler and more compact than dual-frequency discharges using a conventional impedance matching system, the presented device shows an excellent performance in dual-frequency operation.

Enhancing cavitation dynamics and its mechanical effects with dual-frequency ultrasound

Objective. Acoustic cavitation and its mechanical effects (e.g. stress and strain) play a primary role in ultrasound applications. Introducing encapsulated microbubbles as cavitation nuclei and utilizing dual-frequency ultrasound excitation are highly effective approaches to reduce cavitation thresholds and enhance cavitation effects. However, the cavitation dynamics of encapsulated microbubbles and the resultant stress/strain in viscoelastic tissues under dual-frequency excitation are poorly understood, especially for the enhancement effects caused by a dual-frequency approach. The goal of this study was to numerically investigate the dynamics of a lipid-coated microbubble and the spatiotemporal distributions of the stress and strain under dual-frequency excitation. Approach. The Gilmore–Zener bubble model was coupled with a shell model for the nonlinear changes of both shell elasticity and viscosity to accurately simulate the cavitation dynamics of lipid-coated microbubbles in viscoelastic tissues. Then, the spatiotemporal evolutions of the cavitation-induced stress and strain in the surrounding tissues were characterized quantitatively. Finally, the influences of some paramount parameters were examined to optimize the outcomes. Main results. We demonstrated that the cavitation dynamics and associated stress/strain were prominently enhanced by a dual-frequency excitation, highlighting positive correlations between the maximum bubble expansion and the maximum stress/strain. Moreover, the results showed that the dual-frequency ultrasound with smaller differences in its frequencies and pressure amplitudes could enhance the bubble oscillations and stress/strain more efficiently, whereas the phase difference manifested small influences under these conditions. Additionally, the dual-frequency approach seemed to show a stronger enhancement effect with the shell/tissue viscoelasticity increasing to a certain extent. Significance. This study might contribute to optimizing the dual-frequency operation in terms of cavitation dynamics and its mechanical effects for high-efficient ultrasound applications.

A Link-Independent Hybrid Inductive and Capacitive Wireless Power Transfer System for Autonomous Mobility

A link-independent hybrid wireless power transfer system (HPT) that uses both capacitive and inductive action for autonomous vehicle charging application is presented in this article. A three-leg inverter topology is utilized here. Two legs of the inverter, switched at 85 kHz, are used for inductive wireless power transfer (IPT) and the third leg, switched at 1 MHz, is used for capacitive wireless power transfer (CPT). The three-leg inverter module is realized using SiC and GaN switches. The dual switching frequency operation of the converter enables independent compensation techniques to be adopted for IPT and CPT, bringing the modularity feature in the HPT. The circular inductive-link outer diameter is 460 mm and the parallel plate capacitive-link dimension is 600 mm × 600 mm. The power transfer distance or air gap is 100 mm between both links. The output power ratio of IPT to CPT is 2:1. The effectiveness of the proposed topology is validated experimentally. The advantages of this HPT system are modular-link architecture, improved misalignment performance, and distinct frequency of operation for each link that allows the inductive link to meet the SAEJ2954 standard frequency limits compared with the existing HPT systems proposed for electric vehicle charging to support autonomous mobility.

Compact Leaky-Wave SIW Antenna With Broadside Radiation and Dual-Band Operation for CubeSats

This letter presents a substrate-integrated waveguide (SIW) antenna for CubeSat applications. The compact structure utilizes middle-point feeding and shorting walls to achieve broadside radiation in the far-field at two distinct frequencies. In particular, this dual-frequency behavior is related to the transition from a dominant leaky wave (LW) on the aperture at lower frequencies to more hybrid radiation (at higher frequencies) due to LW fields and structure resonance due to truncation. This response is generated by the shorting vias at the lateral ends of the SIW antenna. Given these conditions, the developed leaky-wave antenna (LWA) prototype is well matched ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$|S_{11}|$</tex-math></inline-formula> <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\leq$</tex-math></inline-formula> −10 dB) from 23.2 to 23.5 GHz and 24.8 to 25.2 GHz with realized gains of 8 and 6 dBi, respectively. Maximum efficiency (including the connector) is around 87%. Such dual-frequency operation could enable up-link and down-link operation in the K-band. Overall dimensions of the antenna are 2 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\lambda _0$</tex-math></inline-formula> × 2.6 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\lambda _0$</tex-math></inline-formula> (at the lower frequency). Possible placement on CubeSats can be underneath solar panels, thus increasing the available surface area for solar power harvesting. Also, to the best knowledge of the authors, no similar dual-frequency SIW-LWA has been previously reported.

The enhanced effect of collapse strength of a dual-frequency driven bubble in 2-dimensional space

The bubble-collapse strength is closely related to the ultrasonic cavitation effect. The enhanced effect of collapse strength of a dual-frequency driven bubble is one of the mechanismsunderlying the synergistic effect of dual-frequency excitation. In this paper, the growth rate of bubble-collapse strength is defined as:G=(Rmax,d′-Rmax,s′)/Rmax,s′, where Rmax,s′and Rmax,d′are the bubble maximum oscillation radius under single- and dual-frequency exciting, respectively. The enhanced region I (below the main resonances line), II (above the main resonances line) and III (around the diagonal line) concerning to the bubble-collapse strength in f1-f2 plane are analyzed. The results show that the enhanced effect of bubble-collapse strength is implicated in the acoustic pressure, bubble equilibriumradius and pressure amplitude ratio. This paper could be helpful for optimizing the dual-frequency operation from the perspective of bubble radial dynamics.