Wideband double-mode bulk acoustic wave resonator filters on lithium niobate using periodically slotted electrodes

Abstract: This paper discusses applicability of periodically slotted electrodes for realization of wideband transversely-coupled double-mode resonator filters using lithium niobate (LN) thin plate. First, two-dimensional analysis is carried out, and it is shown that the periodic structure is effective to control the frequency separation between two resonance modes, and synthesis of the fractional bandwidth larger than 24% is achievable. Next, 3D analysis is performed for suppression of spurious resonances. It is shown that the mass loading at aperture edges is effective for the piston mode operation, and transverse modes can be well suppressed. It is also pointed out that the bottom electrode should be covered only the aperture region and removed from the busbar and gap regions for suppression of unwanted resonances. With these proper edge treatments, spurious-free and wide passband can be synthesized.

APPLICATION OF ATOMIC SPECTROSCOPY TO MEASURING STRONG INHOMOGENEOUS MAGNETIC FIELDS

Using the spectrum of selective reflection (SR) of laser radiation from the boundary of the surface of the dielectric window of the spectroscopic nanocells – pairs of rubidium atoms, the value of the magnetic field applied to the nanocell is measured. A method is proposed for calculating the magnetic induction B in the range of 0.1–6.0 kG based on the ratio of the frequency intervals between atomic transitions, which greatly simplifies the determination of B, particularly, there is no need for a reference spectrum at B = 0. To implement the SR process a 300-nm column of vapors of Rb atoms is used, and atomic transitions with a sub- Doppler spectral width of 80–90 MHz are formed. This leads to frequency separation of transitions in SR spectrum that is important for the proposed method. SR spectrum can be analyzed using a specially designed computer program that accelerates the data processing. The small thickness of the vapor column allows high spatial resolution, which is important in the case of inhomogeneous magnetic fields.

Wavelet Frequency Separation Attention Network for Chest X-ray Image Super-Resolution

Medical imaging is widely used in medical diagnosis. The low-resolution image caused by high hardware cost and poor imaging technology leads to the loss of relevant features and even fine texture. Obtaining high-quality medical images plays an important role in disease diagnosis. A surge of deep learning approaches has recently demonstrated high-quality reconstruction for medical image super-resolution. In this work, we propose a light-weight wavelet frequency separation attention network for medical image super-resolution (WFSAN). WFSAN is designed with separated-path for wavelet sub-bands to predict the wavelet coefficients, considering that image data characteristics are different in the wavelet domain and spatial domain. In addition, different activation functions are selected to fit the coefficients. Inputs comprise approximate sub-bands and detail sub-bands of low-resolution wavelet coefficients. In the separated-path network, detail sub-bands, which have more sparsity, are trained to enhance high frequency information. An attention extension ghost block is designed to generate the features more efficiently. All results obtained from fusing layers are contracted to reconstruct the approximate and detail wavelet coefficients of the high-resolution image. In the end, the super-resolution results are generated by inverse wavelet transform. Experimental results show that WFSAN has competitive performance against state-of-the-art lightweight medical imaging methods in terms of quality and quantitative metrics.

Intelligent wireless theranostic contact lens for close-loop electrical sensing and regulation of glaucoma

Engineered closed-loop devices that can wirelessly track intraocular pressure (IOP) and offer feedback-medicine administrations are highly desirable for glaucoma treatments, yet remain difficult to develop. Integrated theranostic systems based on contact lens still confront several challenges, including size limits, requirements of wireless operations, and cross-coupling between multiple functional modulus. Here, for the first time to our knowledge, an integrated wireless theranostic contact lens (WTCL) for in situ electrical sensing and on-demand drug delivery of glaucoma was developed. The WTCL utilized a highly compact circuitry and structural design, which enabled high-degreed integration of IOP sensing and electrically controlled delivery modulus on the curved and limited surface of contact lens. The wireless IOP sensing modulus could ultra-sensitively detect IOP fluctuations, due to the unique cantilever configuration design of LCR circuit with ultra-soft air dielectric film sandwiched between each capacitive sensing plate. The drug delivery modulus employed a highly efficient wireless power transfer circuit, to trigger delivery of anti-glaucoma drug into aqueous chamber via iontophoresis to enhance drug permeation across cornea. The specialized design of frequency separation enabled individual operations of different modules without cross-coupling. The minimally invasive, smart, wireless and closed-loop theranostic features endowed the WTCL as a highly promising system for glaucoma treatments.

Computer Vision Technique for Blind Identification of Modal Frequency of Structures from Video Measurements

Operational modal analysis (OMA) is required for the maintenance of large-scale civil structures. This paper developed a novel methodology of non-contact-based blind identification of the modal frequency of a vibrating structure from its video measurement. There are two stages in the proposed methodology. The first stage is extracting the motion data of the vibrating structure from its video using a complex steerable pyramid. In the second stage, the principal component analysis combined with analytical mode decomposition is used for modal frequency separation from the motion data. Numerical validation of the methodology on a 10 DOF model is presented. The application of the proposed methodology on the London Millennium Bridge is also presented.

High frequency power supply to improve operation stability of linear electron accelerator

The use of linear electron accelerators in medicine and industry is explained by the simplicity of the input and output of accelerated electrons and adjusting the energy and dose rate, as well as the high dose rate of bremsstrahlung. The purpose of this work is to increase the stability of their work. A standing wave accelerator containing a high-frequency generator, a phase shifter, a waveguide bridge, a high-frequency load, and an accelerating system of two accelerating sections is equipped with two waveguide tees. Their inputs are connected to the output arms of the waveguide bridge, and the first and second output arms of each tee are connected to the first and last accelerating cells of each section, respectively. In this system, due to the introduction of several elements that do not require large costs for manufacturing and tuning, a significantly greater frequency separation of the operating mode of oscillations from neighboring ones is ensured, or even a single-frequency excitation mode is implemented, which makes it possible to significantly increase the stability of the accelerator operation. This technique can be used to increase the stability of operation in the design and calculation of linear accelerators of electrons with a standing wave.

Design of sliding mode flight control system for a flexible aircraft

The evolution of large transport aircraft is characterized by longer fuselages and larger wingspans, while efforts to decrease the structural weight reduce the structural stiffness. Both effects lead to more flexible aircraft structures with significant aeroelastic coupling between flight mechanics and structural dynamics, especially at high speed, high altitude cruise. The lesser frequency separation between rigid body and flexible modes of flexible aircraft results in a stronger interaction between the flight control system and its structural modes, with higher flexibility effects on aircraft dynamics. Therefore, the design of a flight control law based on the assumption that the aircraft dynamics are rigid is no longer valid for the flexible aircraft. This paper focuses on the design of a flight control system for flexible aircraft described in terms of a rigid body mode and four flexible body modes and whose parameters are assumed to be varying. In this paper, a conditional integral based sliding mode control (SMC) is used for robust tracking control of the pitch angle of the flexible aircraft. The performance of the proposed nonlinear flight control system has been shown through the numerical simulations of the flexible aircraft. Good transient and steady-state performance of a control system are also ensured without suffering from the drawback of control chattering in SMC.

Tuned vibration modes in a miniature hearing organ: Insights from the bushcricket

Bushcrickets (katydids) rely on only 20 to 120 sensory units located in their forelegs to sense sound. Situated in tiny hearing organs less than 1 mm long (40× shorter than the human cochlea), they cover a wide frequency range from 1 kHz up to ultrasounds, in tonotopic order. The underlying mechanisms of this miniaturized frequency-place map are unknown. Sensory dendrites in the hearing organ (crista acustica [CA]) are hypothesized to stretch, thereby driving mechanostransduction and frequency tuning. However, this has not been experimentally confirmed. Using optical coherence tomography (OCT) vibrometry, we measured the relative motion of structures within and adjacent to the CA of the bushcricket Mecopoda elongata. We found different modes of nanovibration in the CA that have not been previously described. The two tympana and the adjacent septum of the foreleg that enclose the CA were recorded simultaneously, revealing an antiphasic lever motion strikingly reminiscent of vertebrate middle ears. Over the entire length of the CA, we were able to separate and compare vibrations of the top (cap cells) and base (dorsal wall) of the sensory tissue. The tuning of these two structures, only 15 to 60 μm (micrometer) apart, differed systematically in sharpness and best frequency, revealing a tuned periodic deformation of the CA. The relative motion of the two structures, a potential drive of transduction, demonstrated sharper tuning than either of them. The micromechanical complexity indicates that the bushcricket ear invokes multiple degrees of freedom to achieve frequency separation with a limited number of sensory cells.

A Multi-Frequency Galileo PPP-RTK Convergence Analysis with an Emphasis on the Role of Frequency Spacing

The single-receiver integer ambiguity resolution-enabled variant of precise point positioning (PPP), namely PPP-RTK, has proven to be crucial in reducing the long convergence time of PPP solutions through the recovery of the integerness of the user-ambiguities. The proliferation of global navigation satellite systems (GNSS) supports various improvements in this regard through the availability of more satellites and frequencies. The increased availability of the Galileo E6 signal from GNSS receivers paves the way for speeding up integer ambiguity resolution, as more frequencies provide for a stronger model. In this contribution, the Galileo-based PPP-RTK ambiguity resolution and positioning convergence capabilities are studied and numerically demonstrated as a function of the number and spacing of frequencies, aiming to shed light on which frequencies should be used to obtain optimal performance. Through a formal analysis, we provide insight into the pivotal role of frequency separation in ambiguity resolution. Using real Galileo data on up to five frequencies and our estimated PPP-RTK corrections, representative kinematic user convergence results with partial ambiguity resolution are presented and discussed. Compared to the achieved performance of dual-frequency fixed solutions, it is found that the contribution of multi-frequency observations is significant and largely driven by frequency separation. When using all five available frequencies, it is shown that the kinematic user can achieve a sub-decimeter level convergence in 15.0 min (90% percentile). In our analysis, we also show to what extent the provision of the estimable satellite code biases as standard PPP-RTK corrections accelerates convergence. Finally, we numerically demonstrate that, when integrated with GPS, the kinematic user solution achieves convergence in 3.0 and 5.0 min on average and at 90%, respectively, in the presence of ionospheric delays, thereby indicating the single-receiver user’s fast-convergence capabilities.