In this letter, a dual-band isolation enhancement technique for two closely located dual-band planar inverted-F antennas (PIFAs) is proposed using a compact planar spiral line (PSL) structure. The decoupling structure has the dimensions of less than 0.15λ × 0.1λ and can be flexibly applied to various practical multiple-input multiple-output systems. By employing this structure, two PIFAs (with port distance of 0.1λ) can achieve high isolation better than 20.3 and 26.7 dB within the lower band (2.4-2.483 GHz) and higher band (5.25-5.9 GHz), respectively. Meanwhile, the decoupling mechanism and design requirement of PSL are discussed. Influences of the proposed PSL to the efficiency, gain, and radiation pattern of PIFAs were also studied. Good agreement between the simulated results and measured results is obtained.

With the development of the Internet-of-Things, urgent market demands have also provided a huge development space for indoor pedestrian positioning systems (IPPS). Complementary filters (CF), Kalman filters and their various modifications are usually used to estimate the orientation in foot-mounted IPPS. However, the accuracy of the orientation is still low because of various types of electromagnetic interference and the diversity of pedestrians’ motion states. In this paper, an orientation estimation algorithm is proposed innovatively. First, the nine-axes inertial/magnetic sensors are calibrated using the error model of micro-electromechanical systems sensors. Then, the adaptive complementary filtering (ACF) algorithm is used to determine short- and medium-term orientation by making full use of the complementary error characteristics of the nine-axes inertial/magnetic sensors; the corridor geometry in rectangular buildings can also be regarded as prior information. Finally, the fusion of the orientation calculated by the ACF algorithm and the prior information is realized by the extended Kalman filter algorithm, which can improve the long-term accuracy of the orientation. To verify the performance of the proposed algorithm, a foot-mounted IPPS is set up based on MPU9250, and the raw data from the sensors are calibrated and imported into MATLAB for processing and analysis. The root mean square error of the orientation is less than 1.5° using the proposed method, and the results show that the proposed algorithm significantly surpasses other state-of-the-art algorithms, contributing to higher accuracy of orientation.

This letter demonstrates the dual transmission zeros (TZs) of bandpass elliptic prototype filters that can be directly implemented with two resonators in microstrip. An experimental filter based on the proposed alternate circuits is designed and fabricated. In order to improve the rejection of stopband, two additional TZs are introduced to the proposed filter. By means of directly implementing an elliptic bandpass filter in microstrip, the insertion loss of the presented filter can be less than 0.8 dB, and the Δf ₃ ^dB /Δf _{20 dB} result is better than 0.583, which means the proposed filter has a good selectivity.

In this letter, a broadband self-interference (SI) suppression structure is presented for collinear dipoles. By using this structure, an average SI improvement of 21.6 dB is realized within the frequency band of 2.2 - 2.7 GHz. It has a 14.8% operating bandwidth of transmit-receive isolation (TRI) higher than 50dB. The working mechanism and bandwidth extension are discussed. Moreover, the key parameters and influence of the proposed structure to the dipoles were also studied and presented. Measured results demonstrate that this design provides wider operating bandwidth, omnidirectional radiation patterns and ideal distribution distance. It is effective and suitable for reducing the SI between collinear dipoles.

In this paper, we propose the use of metasurfaces to enhance evanescent wave coupling to improve the wireless power transfer (WPT) efficiency of multiple receivers. A 4 × 4 negative permeability metasurface is designed and placed between the transmitter (Tx) and receiver (Rx) coils for the greatest improvement in transfer efficiency. Through the analysis of the number and position topologies of Rx coils, the efficiency can be greatly improved; the maximum efficiency at longer transmission distances is achieved through the 4 × 4 negative permeability metasurface in the multiple−receiver system. We show with simulation and measurement results that the power transfer efficiency of the system can be improved significantly by integrating metasurfaces. The maximum transfer efficiency is achieved in a multiple−receiver WPT system when the number and topology of Rx coils is case 0 of single transmitter−three receivers (STTR). The results show that the total efficiency of the multiple receivers WPT system can be as high as 97%.

With the growing elderly population, especially in urban areas, pedestrian fall detection for the elderly has become a critical global concern. Existing pedestrian fall detection systems often suffer from low accuracy and poor performance under challenging conditions such as rain, snow, nighttime, or camera obstructions. To address these issues, this paper proposes an enhanced pedestrian fall detection algorithm called Pedestrian Chain-of-Thought Prompted Adaptive Enhancer YOLO (PCE-YOLO), based on YOLOv8n. Several improvements were made to YOLOv8n, including the integration of a Chain-of-Thought Prompted Adaptive Enhancer (CPA-Enhancer) module to boost detection performance in complex environments. Additionally, the Cross Stage Partial Bottleneck with 2 Convolution Block (C2f) was optimized to reduce computational load and parameter count without compromising performance, while the Inner Extended Intersection over Union (Inner-EIoU) loss function was employed to improve bounding box regression accuracy and speed. To validate the model’s effectiveness, a dataset of 7,782 pedestrian fall images was collected, and three degraded image datasets were generated to simulate real-world conditions. PCE-YOLO improved the mean Average Precision (mAP) by 4.52% compared to YOLOv8n on both original and degraded datasets, respectively. Moreover, it achieved a frame per second (FPS) rate of 210.5, making it suitable for real-time detection applications. The results demonstrate that PCE-YOLO significantly enhances detection accuracy and speed in various challenging environments, offering a robust solution for real-time pedestrian fall detection.