Theoretical Analysis of a Magnetic Shielding System Combining Active and Passive Modes.

Considering the magnetic shielding requirements of both geomagnetic field and 50 Hz power-line frequency in the complex working conditions of the power grid, an electromagnetic shielding system combining active and passive modes is proposed in this article. A three-dimensional Helmholtz coil with a magnetic shielding barrel nested inside is established by the COMSOL simulation tool, and the magnetic shielding efficiency of the system is analyzed. Comparing different materials, the simulation results indicate that permalloy alloy exhibits better shielding performance than pure iron and nickel materials. Additionally, the overall shielding efficiency of the shielding barrel increases linearly with the number of multiple layers. Under the combined active and passive electromagnetic shielding conditions, the system achieves a shielding efficiency of SE = 113.98 dB, demonstrating excellent performance in shielding both AC and DC interference magnetic fields. This study provides theoretical guidance for the construction of magnetic shielding systems in electromagnetic interference environment.

Communication-efficient federated learning with stagewise training strategy.

The efficiency of communication across workers is a significant factor that affects the performance of federated learning. Though periodic communication strategy is applied to reduce communication rounds in training, the communication cost is still high when the training data distributions are not independently and identically distributed (non-IID) which is common in federated learning. Recently, some works introduce variance reduction to eliminate the effect caused by non-IID data among workers. Nevertheless the provable optimal communication complexity O(log(ST)) and convergence rate O(1/(ST)) cannot be achieved simultaneously, where S denotes the number of sampled workers in each round and T is the number of iterations. To deal with this dilemma, we propose an optimization algorithm SQUARFA that adopts stagewise training framework coupling with variance reduction and uses a quick-start phase in each loop. Theoretical results show that SQUARFA achieves both optimal convergence rate and communication complexity for both strongly convex objectives and non-convex objectives under PL condition, thus fills the gap mentioned above. Then, a variant of SQUARFA yields the optimal theoretical results for general non-convex objectives. We further extend the technique in SQUARFA to the large batch setting and achieve optimal communication complexity. Experimental results demonstrate the superiority of the proposed algorithms.

Magnetoelectric (ME) Antenna for On-chip Implantable Energy Harvesting.

A novel magnetoelectric (ME) antenna is fabricated to be integrated to the on-chip energy harvesting circuit for brain-computer interface applications. The proposed ME antenna resonates at the frequency of 2.57 GHz while providing a bandwidth of 3.37 MHz. The proposed rectangular ME antenna wireless power transfer efficiency is 0.304 %, which is considerably higher than that of micro-coils.Clinical Relevance- This provides a suitable energy harvesting efficiency for wirelessly powering up the brain implant devices.

Ultra-compact dual-band smart NEMS magnetoelectric antennas for simultaneous wireless energy harvesting and magnetic field sensing.

Ultra-compact wireless implantable medical devices are in great demand for healthcare applications, in particular for neural recording and stimulation. Current implantable technologies based on miniaturized micro-coils suffer from low wireless power transfer efficiency (PTE) and are not always compliant with the specific absorption rate imposed by the Federal Communications Commission. Moreover, current implantable devices are reliant on differential recording of voltage or current across space and require direct contact between electrode and tissue. Here, we show an ultra-compact dual-band smart nanoelectromechanical systems magnetoelectric (ME) antenna with a size of 250 × 174 µm2 that can efficiently perform wireless energy harvesting and sense ultra-small magnetic fields. The proposed ME antenna has a wireless PTE 1-2 orders of magnitude higher than any other reported miniaturized micro-coil, allowing the wireless IMDs to be compliant with the SAR limit. Furthermore, the antenna's magnetic field detectivity of 300-500 pT allows the IMDs to record neural magnetic fields.

A Review of Thin-Film Magnetoelastic Materials for Magnetoelectric Applications.

Since the revival of multiferroic laminates with giant magnetoelectric (ME) coefficients, a variety of multifunctional ME devices, such as sensor, inductor, filter, antenna etc. have been developed. Magnetoelastic materials, which couple the magnetization and strain together, have recently attracted ever-increasing attention due to their key roles in ME applications. This review starts with a brief introduction to the early research efforts in the field of multiferroic materials and moves to the recent work on magnetoelectric coupling and their applications based on both bulk and thin-film materials. This is followed by sections summarizing historical works and solving the challenges specific to the fabrication and characterization of magnetoelastic materials with large magnetostriction constants. After presenting the magnetostrictive thin films and their static and dynamic properties, we review micro-electromechanical systems (MEMS) and bulk devices utilizing ME effect. Finally, some open questions and future application directions where the community could head for magnetoelastic materials will be discussed.

Integration of a Novel CMOS-Compatible Magnetoelectric Antenna with a Low-Noise Amplifier and a Tunable Input Matching.

A low-noise amplifier (LNA) topology with tunable input matching and noise cancellation is introduced and described in this paper, which was designed and optimized to interface with a magnetoelectric (ME) antenna in a 0.35 µm MEMS-compatible CMOS process. Compared to conventional antennas, acoustically actuated ME antennas have significantly smaller area for ease of integration. The LNA was simulated with an ME antenna model that was constructed based on antenna measurements. Input matching at the LNA-antenna interface is controlled with a circuit that varies the effective impedance of the gate inductor using a control voltage. Tunability of 455 MHz around 2.4 GHz is achieved for the optimum S11 frequency with a control voltage range of 0.3 V to 1.2 V. The proposed LNA has a noise cancelling feedback loop that improves the noise figure by 4.1 dB. The post-layout simulation results of the LNA show a 1-dB compression point of -7.4 dBm with an S21 of 17.8 dB.

Mechanical-Resonance-Enhanced Thin-Film Magnetoelectric Heterostructures for Magnetometers, Mechanical Antennas, Tunable RF Inductors, and Filters.

The strong strain-mediated magnetoelectric (ME) coupling found in thin-film ME heterostructures has attracted an ever-increasing interest and enables realization of a great number of integrated multiferroic devices, such as magnetometers, mechanical antennas, RF tunable inductors and filters. This paper first reviews the thin-film characterization techniques for both piezoelectric and magnetostrictive thin films, which are crucial in determining the strength of the ME coupling. After that, the most recent progress on various integrated multiferroic devices based on thin-film ME heterostructures are presented. In particular, rapid development of thin-film ME magnetometers has been seen over the past few years. These ultra-sensitive magnetometers exhibit extremely low limit of detection (sub-pT/Hz1/2) for low-frequency AC magnetic fields, making them potential candidates for applications of medical diagnostics. Other devices reviewed in this paper include acoustically actuated nanomechanical ME antennas with miniaturized size by 1-2 orders compared to the conventional antenna; integrated RF tunable inductors with a wide operation frequency range; integrated RF tunable bandpass filter with dual H- and E-field tunability. All these integrated multiferroic devices are compact, lightweight, power-efficient, and potentially integrable with current complementary metal oxide semiconductor (CMOS) technology, showing great promise for applications in future biomedical, wireless communication, and reconfigurable electronic systems.

Multi-vinyl linked benzothiadiazole conjugated polymers: high performance, low crystalline material for transistors.

In this work, we proposed a multi-vinyl linker fusing strategy for designing low crystallinity, high performance materials for organic field effect transistors. A corresponding conjugated polymer, PTBTV, base was synthesized, exhibiting an impressive hole mobility of up to 3.2 cm2 V-1 s-1, yet grazing incidence X-ray diffraction revealed a relatively weak crystallinity in the thin film.

Poly(naphthalene diimide) vinylene: solid state red emission and semiconducting properties for transistors.

In this work, a conjugated polymer PNV is developed, linking naphthalene diimide with a vinyl linkage. Owing to the C-HO hydrogen bond between the carbonyl and the vinyl, PNV exhibits a high red emission with a quantum yield of 33.4% in the solid state while it shows n-type properties with an electron mobility up to 1.5 × 10-3 cm2 V-1 s-1 in organic field effect transistors, simultaneously.

Highly Sensitive Flexible Magnetic Sensor Based on Anisotropic Magnetoresistance Effect.

A highly sensitive flexible magnetic sensor based on the anisotropic magnetoresistance effect is fabricated. A limit of detection of 150 nT is observed and excellent deformation stability is achieved after wrapping of the flexible sensor, with bending radii down to 5 mm. The flexible AMR sensor is used to read a magnetic pattern with a thickness of 10 µm that is formed by ferrite magnetic inks.

Aggregation-Induced Emission and Aggregation-Promoted Photo-oxidation in Thiophene-Substituted Tetraphenylethylene Derivative.

Aggregation-induced emission combined with aggregation-promoted photo-oxidation has been reported only in two works quite recently. In fact, this phenomenon is not commonly observed for AIE-active molecules. In this work, a new tetraphenylethylene derivative (TPE-4T) with aggregation-induced emission (AIE) and aggregation-promoted photo-oxidation was synthesized and investigated. The pristine TPE-4T film exhibits strong bluish-green emission, which turns to quite weak yellow emission after UV irradiation. Interestingly, after solvent treatment, the weakly fluorescent intermediate will become bright-yellow emitting. Moreover, the morphology of the TPE-4T film could be regulated by UV irradiation. The wettability of the TPE-4T microcrystalline surface is drastically changed from hydrophobic to hydrophilic. This work contributes a new member to the aggregation induced photo-oxidation family and enriches the photo-oxidation study of tetraphenylethylene derivatives.

Thieno[3,4-c]Pyrrole-4,6-Dione and Dithiophene-Based Conjugated Polymer for Organic Field Effect Transistors: High Mobility Induced by Synergic Effect of H-Bond and Vinyl Linkage.

Here, a conjugated polymer VTTPD based on thieno[3,4-c]pyrrole-4,6-dione (TPD) and dithiophene with vinyl as linker is synthesized and characterized. Electrochemical and optical studies indicate the LUMO and HOMO energies of the polymer are -3.70 and -5.39 eV. Theoretical calculation with density functional theory suggests that H-bonds are formed between the TPD carbonyl (O) and its neighboring vinyl (H) which benefit the planarity and π-conjugation of the polymer backbone. Bottom contact bottom gate organic field effect transistor devices based on VTTPD are fabricated and examined in air. After annealing at 160 °C, the devices exhibit excellent performance of µh = 0.4 cm(2) V(-1) s(-1) , Ion/off = 10(6) , Vth within -10 V to -5 V. Thin film morphologies before and after the annealing process are also investigated with XRD and AFM.