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Viable cell concentration (VCC) is one of the most important process attributes during mammalian cell cultivations. Current state-of-the-art measurements of VCC comprise offline methods which do not allow for continuous process data. According to the FDA’s process analytical technology initiative, process monitoring and control should be applied to gain process understanding and to ensure high product quality. In this work, the use of an inline capacitance probe to monitor online VCCs of a mammalian CHO cell culture process in small-scale bioreactors (250 mL) was investigated. Capacitance sensors using single frequency are increasingly common for biomass monitoring. However, the single-frequency signal corresponds to the cell polarization that represents the viable cell volume. Therefore single-frequency measurements are dependent on cell diameter changes. Measuring the capacitance across various frequencies (frequency scanning) can provide information about the VCC and cope with changing cell diameter. Applying multivariate data analysis on the frequency scanning data successfully enabled direct online monitoring of VCCs in this study. The multivariate model was trained with data from 5 standard cultivations. The model provided a prediction of VCCs with relative errors from 5.5 to 11%, which is a good agreement with the acceptance criterion based on the offline reference method accuracy (approximately 10% relative error) and strongly improved compared with single-frequency results (16 to 23% relative error). Furthermore, robustness trials were conducted to demonstrate the model’s predictive ability under challenging conditions. The process deviations in regard to dilution steps and feed variations were detected immediately in the online prediction of the VCC with relative errors between 6.7 and 13.2%. Thus in summary, the presented method on capacitance frequency scanning demonstrates its suitability for process monitoring and control that can save batches, time, and cost.

This paper proposes a miniaturized frequency-scanning antenna with high scanning rate. To overcome the OSB (open stopband) of traditional leaky wave antenna, CRLH-TL (Composite Right/Left-Handed-Transmission Line) is adopted. Furthermore, an antenna unit consisting of two symmetrically curved microstrip lines with two short branches is employed, whose second mode exhibits excellent transmission characteristics. The measurements demonstrate that the antenna can achieve scanning from −67.5° to 35.5° in the frequency band range of 5.65–6.5 GHz, with a scanning rate of 7.3. During scanning, the highest gain in the band is 12.3 dBi, the lowest is 10 dBi, and the gain fluctuation is within 2.3 dB, showing good scanning characteristics. Additionally, the length of the proposed antenna is approximately 3.84λ0 for a central frequency of 5.95 GHz.

Silicon (Si) and silicon carbide (SiC) are second- and third-generation semiconductor materials with excellent properties that are particularly suitable for applications in scenarios such as high temperature, high voltage, and high frequency. Si/SiC wafers face warpage and bending problems during production, which can seriously affect subsequent processing. Fast, accurate, and comprehensive detection of thickness, thickness variation, and flatness (including bow and warpage) of SiC and Si wafers is an industry-recognized challenge. Frequency scanning interferometry (FSI) can synchronize the upper and lower surfaces and thickness information of transparent parallel thin wafers, but it is still affected by multiple interfacial harmonic reflections, reflectivity asymmetry, and phase modulation uncertainty when measuring SiC thin wafers, which leads to thickness calculation errors and face reconstruction deviations. To this end, this paper proposes a high-precision facet reconstruction method for SiC/Si structures, which combines harmonic spectral domain decomposition, refractive index gradient constraints, and partitioning optimization strategy, and introduces interferometric signal “oversampling” and weighted fusion of multiple sets of data to effectively suppress higher-order harmonic interferences, and to enhance the accuracy of phase resolution. The multi-layer iterative optimization model further enhances the measurement accuracy and robustness of the system. The flatness measurement system constructed based on this method can realize the simultaneous acquisition of three-dimensional top and bottom surfaces on 6-inch Si/SiC wafers, and accurately reconstruct the key parameters, such as flatness, warpage, and thickness variation (TTV). A comparison with the Corning Tropel FlatMaster commercial system shows that this method has high consistency and good applicability.

A piezoelectric platform using function module actuator is presented to achieve nano-positioning and high frequency scanning in large working range. A function module actuator is designed to produce a pair of orthogonal bending deformations and a longitudinal deformation through partition exciting. The bending deformations are used to actuate the planar motion, while the longitudinal deformation is utilized to dynamically adjust the driving force and broaden the scanning frequency. The dynamic model of the platform system is developed. The open-loop performances of a prototype are first tested: a scan frequency of 308 Hz in a scanning range of 3.368 µm×3.396 µm is measured in direct actuation mode, and the displacement resolution is measured to be 16 nm; maximum speed is measured to be 3.38 mm s−1 in the inertial actuation mode. Furthermore, the closed-loop experiments are carried out and a switching strategy is proposed to obtain the switching of the inertial and direct actuation modes automatically; the platform achieves the scanning with frequency of 300 Hz at the set position.

Securing a comfortable, wearable compact frequency beam scanning antenna (FBSA) with robustness to deformation, low specific absorption rate (SAR), and good coverage of the surrounding environment for Internet of Things (IoT) applications, such as on-body navigation and wireless communication is an emerging challenge. In this work, a robust textile-based spoof plasmonic frequency scanning antenna utilizing higher-order modes is presented, which is also robust to deformation caused by the activities of the human body. The innovative design of the element ensures the high-efficiency transmission of the fundamental mode of spoof surface plasmon polaritons (SSPP) structure, providing the potential of being a multifunctional composite device in the compact on-body network. Besides, an artificial magnetic conductor (AMC) is designed underneath the SSPP structure, obtaining a low SAR value (0.113 W/kg), which ensures the safety of users. As a practical realization of this concept, a textile-based spoof plasmonic antenna was fabricated in the microwave regime and the performed experimental results show the proposed antenna has a single-beam radiation characteristic with a 70° beam scanning angle range when the frequency is 4.7–6.0 GHz with a high average realized gain of 13.15 dBi. And it still maintains a steady performance when faced with structure deformation, which proves its robustness. Wireless communication quality experiments are performed to demonstrate the proposed antenna can measure the angles of targets and realize wireless signal transmission to specific targets as the frequency varies, it may find great potential in the field of on-body IoT applications.

Retrodirectivity have several important applications in communication and in wireless power transfer. In this paper, frequency sensitive retrodirective transceiver is proposed. It receives a signal and infers its direction from its frequency spectrum, then it can transmit a new signal back to the same or other direction at the designer wish. To determine the direction of the coming signal, a 0.85-1.15GHz frequency scanning phased array antenna is used so that the received signal would have a distorted spectrum with the maximum amplitude frequency component linked to the direction of the signal. Based on the frequency scanning, the retrodirectivity system can be used for wireless power transfer or for reactive jamming. Special circuit is designed to receive the signal with strongest power and to isolate the frequency component with maximum amplitude. Phase-locked loop (PLL) circuit is used to link such frequency to specific phase shift that is introduced to the transmitter array antenna to send a new signal to the same direction of the received signal. ADS simulation is performed to demonstrate the performance of each block.

Although mid-infrared (mid-IR) spectroscopy is a mainstay of molecular fingerprinting, its sensitivity is diminished somewhat when looking at small volumes of sample. Nanophotonics provides a platform to enhance the detection capability. Tittl et al. built a mid-IR nanophotonic sensor based on reflection from an all-dielectric metasurface array of specially designed scattering elements. The scattering elements could be tuned via geometry across a broad range of wavelengths in the mid-IR. The approach successfully detected and differentiated the absorption fingerprints of various molecules. The technique offers the prospect of on-chip molecular fingerprinting without the need for spectrometry, frequency scanning, or moving mechanical parts. Science , this issue p. 1105 A pixelated dielectric metasurface is used for the mid-infrared detection of molecular fingerprints. Metasurfaces provide opportunities for wavefront control, flat optics, and subwavelength light focusing. We developed an imaging-based nanophotonic method for detecting mid-infrared molecular fingerprints and implemented it for the chemical identification and compositional analysis of surface-bound analytes. Our technique features a two-dimensional pixelated dielectric metasurface with a range of ultrasharp resonances, each tuned to a discrete frequency; this enables molecular absorption signatures to be read out at multiple spectral points, and the resulting information is then translated into a barcode-like spatial absorption map for imaging. The signatures of biological, polymer, and pesticide molecules can be detected with high sensitivity, covering applications such as biosensing and environmental monitoring. Our chemically specific technique can resolve absorption fingerprints without the need for spectrometry, frequency scanning, or moving mechanical parts, thereby paving the way toward sensitive and versatile miniaturized mid-infrared spectroscopy devices.

The CAST-CAPP axion haloscope, operating at CERN inside the CAST dipole magnet, has searched for axions in the 19.74  μ eV to 22.47  μ eV mass range. The detection concept follows the Sikivie haloscope principle, where Dark Matter axions convert into photons within a resonator immersed in a magnetic field. The CAST-CAPP resonator is an array of four individual rectangular cavities inserted in a strong dipole magnet, phase-matched to maximize the detection sensitivity. Here we report on the data acquired for 4124 h from 2019 to 2021. Each cavity is equipped with a fast frequency tuning mechanism of 10 MHz/ min between 4.774 GHz and 5.434 GHz. In the present work, we exclude axion-photon couplings for virialized galactic axions down to g a γ γ  = 8 × 10 −14 GeV −1 at the 90% confidence level. The here implemented phase-matching technique also allows for future large-scale upgrades. Haloscopes aim at detecting axions by converting them into photons using high-quality resonant cavities, where the cavity resonance should be tuned with the unknown axion mass. Here, the authors improve exclusion limits using four phase-matched resonant cavities and a fast frequency scanning technique.

Parity-time (PT) symmetry is an active research area that provides a variety of new opportunities for different systems with novel functionalities. For instance, PT symmetry has been used in lasers and optoelectronic oscillators to achieve single-frequency lasing or oscillation. A single-frequency system is essentially a static PT-symmetric system, whose frequency is time-invariant. Here we investigate time-variant PT symmetry in frequency-scanning systems. Time-variant PT symmetry equations and eigenfrequencies for frequency-scanning systems are developed. We show that time-variant PT symmetry can dynamically narrow the instantaneous linewidth of frequency-scanning systems. The instantaneous linewidth of a produced frequency-modulated continuous-wave (FMCW) waveform is narrowed by a factor of 14 in the experiment. De-chirping and radar imaging results also show that the time-variant PT-symmetric system outperforms a conventional frequency-scanning one. Our study paves the way for a new class of time-variant PT-symmetric systems and shows great promise for applications including FMCW radar and lidar systems. Frequency-scanning systems with narrow instantaneous linewidth hold promise for various fields. Here, the authors report the use of time-variant parity-time symmetry to dynamically narrow the instantaneous linewidth of frequency-scanning systems.

High-index dielectric resonators support different types of resonant modes. However, it is challenging to achieve a high-Q factor in a single dielectric nanocavity due to the non-Hermitian property of the open system. We present a universal approach of finding out a series of high-Q resonant modes in a single nonspherical dielectric cavity with a rectangular cross section by exploring the quasi bound-state-in-the-continuum (QBIC). Unlike conventional methods relying on heavy brutal force computations (i.e., frequency scanning by the finite difference time domain method), our approach is built upon Mie mode engineering, through which many high-Q modes can be easily achieved by constructing avoid-crossing (or crossing) of the eigenvalue for pair-leaky modes. The calculated Q-factor of mode TE(5,7) can be up to Qtheory  =  2.3  ×  104 for a freestanding square nanowire (NW) (n  =  4), which is 64 times larger than the highest Q-factor (Qtheory  ≈  360) reported so far in a single Si disk. Such high-Q modes can be attributed to suppressed radiation in the corresponding eigenchannels and simultaneously quenched electric (magnetic) field at momentum space. As a proof of concept, we experimentally demonstrate the emergence of the high-Q resonant modes [Q  ≈  211 for mode TE(3,4), Q  ≈  380 for mode TE(3,5), and Q  ≈  294 for mode TM(3,5)] in the scattering spectrum of a single silicon NW.