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1. A Radio Frequency Comb Filter for Sparse Fourier Transform-Based Spectrum Sensing

   https://doi.org/10.1109/ULTSYM.2018.8579645  

   Lu, Ruochen; Manzaneque, Tomas; Yang, Yansong; Zhou, Jin; Hassanieh, Haitham; Gong, Songbin (October 2018, 2018 IEEE International Ultrasonics Symposium (IUS))

   This work demonstrates a passive low-insertion-loss (IL)RF filter with periodic passbands and capable of sparsifying the spectrum from 238 to 526 MHz for sparse Fourier transform (SFT)based spectrum sensing. The demonstrated periodic filter employs LiNbO 3 lateral overtone bulk acoustic resonators (LOBARs)with high-quality factors (Qs), large electromechanical coupling (k t 2 ), and multiple equally spaced resonances in a ladder topology. The fabricated LOBARs show k t 2 larger than 1.5% and figure of merits (k 2 Q) more than 30 for over 10 tones simultaneously and are both among the highest demonstrated in overmoded resonators. The multi-band filter centered at 370 MHz have then been obtained with a passband span of 291 MHz, a spectral spacing of 22 MHz, an IL of 2 dB, FBWs around 0.6%, and a sparsification ratio between 7 and 15. An out-of-band rejection around 25 dB has also been achieved for more than 14 bands. The great performance demonstrated by the RF filter with 14 useable periodic passbands will serve to enable future sparse Fourier transform-based spectrum sensing. 

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2. Non-perturbative investigation of low-eccentricity exterior mean motion resonances

   https://doi.org/10.1093/mnras/stad483  

   Malhotra, Renu; Chen, Zherui (March 2023, Monthly Notices of the Royal Astronomical Society)

   ABSTRACT Mean motion resonances are important in the analysis and understanding of the dynamics of planetary systems. While perturbative approaches have been dominant in many previous studies, recent non-perturbative approaches have revealed novel properties in the low-eccentricity regime for interior mean motion resonances of Jupiter in the fundamental model of the circular planar restricted three-body model. Here, we extend the non-perturbative investigation to exterior mean motion resonances in the low-eccentricity regime (up to about 0.1) and for perturber mass in the range of ∼5 × 10−5 to 1 × 10−3 (in units of the central mass). Our results demonstrate that first-order exterior resonances have two branches at low eccentricity as well as low-eccentricity bridges connecting neighbouring first-order resonances. With increasing perturber mass, higher order resonances dissolve into chaos, whereas low-order resonances persist with larger widths in their radial extent but smaller azimuthal widths. For low-order resonances, we also detect secondary resonances arising from small-integer commensurabilities between resonant librations and the synodic frequency. These secondary resonances contribute significantly to generating the chaotic sea that typically occurs near mean motion resonances of higher mass perturbers. 

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3. Spin-acoustic control of silicon vacancies in 4H silicon carbide

   https://doi.org/10.1038/s41928-023-01029-4  

   Dietz, Jonathan_R; Jiang, Boyang; Day, Aaron_M; Bhave, Sunil_A; Hu, Evelyn_L (September 2023, Nature Electronics)

   Abstract Bulk acoustic resonators can be fabricated on the same substrate as other components and can operate at various frequencies with high quality factors. Mechanical dynamic metrology of these devices is challenging as the surface information available through laser Doppler vibrometry lacks information about the acoustic energy stored in the bulk of the resonator. Here we report the spin-acoustic control of naturally occurring negatively charged silicon monovacancies in a lateral overtone bulk acoustic resonator that is based on 4H silicon carbide. We show that acoustic driving can be used at room temperature to induce coherent population oscillations. Spin-acoustic resonance is shown to be useful as a frequency-tunable probe of bulk acoustic wave resonances, highlighting the dynamical strain distribution inside a bulk acoustic wave resonator at ambient operating conditions. Our approach could be applied to the characterization of other high-quality-factor microelectromechanical systems and has the potential to be used in mechanically addressable quantum memory. 

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4. Ultrafast and Wideband Microwave Photonic Frequency-Hopping Systems: A Review

   https://doi.org/10.3390/app10020521  

   Liu, Qidi; Fok, Mable P. (January 2020, Applied Sciences)

   The increasing demands to enhance information security in data transmission, providing countermeasures against jamming in military applications, as well as boosting data capacity in mobile and satellite communication, have led to a critical need for high-speed frequency-hopping systems. Conventional electronics-based frequency-hopping systems suffer from low data rate, low hopping speed, and narrow hopping-frequency bandwidth. Unfortunately, those are important aspects to facilitate frequency-hopping in emerging microwave systems. The recent advancement of microwave photonics—the use of light to process microwave signals—provides promising solutions to tackle the challenges faced by electronic frequency-hopping systems. In this paper, the challenges of achieving real-time frequency-hopping systems are examined. The operation principles and results of various microwave photonics-enabled frequency-hopping systems are comprehensively discussed, which have wide hopping-frequency bandwidth and frequency-hopping speed from nanoseconds to tens of picoseconds. Lastly, a bio-inspired jamming-avoidance system that could potentially be used for adaptive frequency-hopping is also introduced. 

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5. High-field/high-frequency electron spin resonances of Fe-doped $\beta \text{−}{\mathrm{Ga}}_2{\mathrm{O}}_3$ by terahertz generalized ellipsometry: Monoclinic symmetry effects

   https://doi.org/10.1103/PhysRevB.109.214106  

   Richter, Steffen; Knight, Sean; Bulancea-Lindvall, Oscar; Mu, Sai; Kühne, Philipp; Stokey, Megan; Ruder, Alexander; Rindert, Viktor; Ivády, Viktor; Abrikosov, Igor A; et al (June 2024, Physical Review B)

   We demonstrate detection and measurement of electron paramagnetic spin resonances (EPR) of iron defects in $\beta \text{−}{\mathrm{Ga}}_2{\mathrm{O}}_3$utilizing generalized ellipsometry at frequencies between 110 and 170 GHz. The experiments are performed on an Fe-doped single crystal in a free-beam configuration in reflection at ${45}^{\circ }$and magnetic fields between 3 and 7 T. In contrast with low-field, low-frequency EPR measurements, we observe all five transitions of the $s=5/2$high-spin state ${\mathrm{Fe}}^{3+}$simultaneously. We confirm that ferric ${\mathrm{Fe}}^{3+}$is predominantly found at octahedrally coordinated Ga sites. We obtain the full set of fourth-order monoclinic zero-field splitting parameters for both octahedrally and tetrahedrally coordinated sites by employing measurements at multiple sample azimuth rotations. The capability of high-field EPR allows us to demonstrate that simplified second-order orthorhombic spin Hamiltonians are insufficient, and fourth-order terms as well as consideration of the monoclinic symmetry are needed. These findings are supported by computational approaches based on density-functional theory for second-order and on ligand-field theory for fourth-order parameters of the spin Hamiltonian. Terahertz ellipsometry is a way to measure spin resonances in a cavity-free setup. Its possibility of varying the probe frequency arbitrarily without otherwise changing the experimental setup offers unique means of truly disentangling different components of highly anisotropic spin Hamiltonians. Published by the American Physical Society2024 

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