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1. A 100KHz-1GHz Termination-dependent Human Body Communication Channel Measurement using Miniaturized Wearable Devices

   https://doi.org/10.23919/DATE48585.2020.9116556  

   Avlani, Shitij; Nath, Mayukh; Maity, Shovan; Sen, Shreyas (March 2020, 2020 Design, Automation & Test in Europe Conference & Exhibition (DATE))

   null (Ed.)

   Human Body Communication has shown great promise to replace wireless communication for information exchange between wearable devices of a body area network. However, there are very few studies in literature, that systematically study the channel loss of capacitive HBC for wearable devices over a wide frequency range with different terminations at the receiver, partly due to the need for miniaturized wearable devices for an accurate study. This paper, for the first time, measures the channel loss of capacitive HBC from 100KHz to 1GHz for both high-impedance and 50Ω terminations using wearable, battery powered devices; which is mandatory for accurate measurement of the HBC channel-loss, due to ground coupling effects. Results show that high impedance termination leads to a significantly lower channel loss (40 dB improvement at 1MHz), as compared to 50Ω termination at low frequencies. This difference steadily decreases with increasing frequency, until they become similar near 80MHz. Beyond 100MHz inter-device coupling dominates, thereby preventing accurate measurements of channel loss of the human body. The measured results provide a consistent wearable, wide-frequency HBC channel loss data and could serve as a backbone for the emerging field of HBC by aiding in the selection of an appropriate operation frequency and termination. 

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2. Biphasic quasistatic brain communication for energy-efficient wireless neural implants

   https://doi.org/10.1038/s41928-023-01000-3  

   Chatterjee, Baibhab; Nath, Mayukh; Kumar_K, Gaurav; Xiao, Shulan; Jayant, Krishna; Sen, Shreyas (September 2023, Nature Electronics)

   Wearable devices typically use electromagnetic fields for wireless information exchange. For implanted devices, electromagnetic signals suffer from a high amount of absorption in tissue, and alternative modes of transmission (ultrasound, optical and magneto-electric) cause large transduction losses due to energy conversion. To mitigate this challenge, we report biphasic quasistatic brain communication for wireless neural implants. The approach is based on electro-quasistatic signalling that avoids transduction losses and leads to an end-to-end channel loss of only around 60 dB at a distance of 55 mm. It utilizes dipole-coupling-based signal transfer through the brain tissue via differential excitation in the transmitter (implant) and differential signal pickup at the receiver (external hub). It also employs a series capacitor before the signal electrode to block d.c. current flow through the tissue and maintain ion balance. Since the electrical signal transfer through the brain is electro-quasistatic up to the several tens of megahertz, it provides a scalable (up to 10 Mbps), low-loss and energy-efficient uplink from the implant to an external wearable. The transmit power consumption is only 0.52 μW at 1 Mbps (with 1% duty cycling)—within the range of possible energy harvesting in the downlink from a wearable hub to an implant. 

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3. Outdoor-to-Indoor 28 GHz Wireless Measurements in Manhattan: Path Loss, Environmental Effects, and 90% Coverage

   https://doi.org/10.48550/arXiv.2205.09436  

   M. Kohli, A. Adhikari (May 2022, ArXivorg)

   Outdoor-to-indoor (OtI) signal propagation further challenges the already tight link budgets at millimeter-wave (mmWave). To gain insight into OtI mmWave scenarios at 28 GHz, we conducted an extensive measurement campaign consisting of over 2,200 link measurements. In total, 43 OtI scenarios were measured in West Harlem, New York City, covering seven highly diverse buildings. The measured OtI path gain can vary by up to 40 dB for a given link distance, and the empirical path gain model for all data shows an average of 30 dB excess loss over free space at distances beyond 50 m, with an RMS fitting error of 11.7 dB. The type of glass is found to be the single dominant feature for OtI loss, with 20 dB observed difference between empirical path gain models for scenarios with low-loss and high-loss glass. The presence of scaffolding, tree foliage, or elevated subway tracks, as well as difference in floor height are each found to have an impact between 5–10 dB. We show that for urban buildings with high-loss glass, OtI coverage can support 500 Mbps for 90% of indoor user equipment (UEs) with a base station (BS) antenna placed up to 49 m away. For buildings with low-loss glass, such as our case study covering multiple classrooms of a public school, data rates over 2.5/1.2 Gbps are possible from a BS 68/175 m away from the school building, when a line-of-sight path is available. We expect these results to be useful for the deployment of mmWave networks in dense urban environments as well as the develop 

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4. Ultrafast modulation of terahertz waves using on-chip dual-layer near-field coupling

   https://doi.org/10.1364/OPTICA.469461  

   Zhang, Yaxin; Ding, Kesen; Zeng, Hongxin; Kou, Wei; Zhou, Tianchi; Zhou, Hongji; Gong, Sen; Zhang, Ting; Wang, Lan; Liang, Shixiong; et al (November 2022, Optica)

   As a key potential component of future sixth-generation (6G) communication systems, terahertz (THz) technology has received much attention in recent years. However, a lack of effective high-speed direct modulation of THz waves has limited the development of THz communication technology. Currently, most high-speed modulators are based on photonic systems that can modulate electromagnetic waves with high speed using sophisticated optoelectronic conversion techniques. Yet, they usually suffer from low conversion efficiency of light to the THz range, resulting in low output power of the modulated THz waves. Here, we describe a guided-wave modulator for THz signals whose performance nearly matches that of existing in-line fiber-optic modulators. Our results demonstrate a maximum modulation depth greater than 20 dB (99%) and a maximum sinusoidal modulation speed of more than 30 GHz, with an insertion loss around 7 dB. We demonstrate the capabilities of this modulator in a point-to-point communication link with a 25 Gbit/s modulation speed. Our modulator design, based on near-field coupling of a THz transmission line to a single resonant meta-element, represents a powerful improvement for on-chip integrated high-performance THz devices. 

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5. A Non-Reciprocal Surface Acoustic Wave Filter Based on Asymmetrical Delay Lines and Parametric Interactions

   https://doi.org/10.1109/MEMS46641.2020.9056343  

   Bahamonde, Jose A.; Kymissis, Ioannis (January 2020, 2020 IEEE 33rd International Conference on Micro Electro Mechanical Systems (MEMS))

   null (Ed.)

   Acoustic devices have played a major role in telecommunications for decades as the leading technology for filtering in RF and microwave frequencies. While filter requirements for insertion loss and bandwidth become more stringent, more functionality is desired for many applications to improve overall system level performance. For instance, a filter with non-reciprocal transmission can minimize losses due to mismatch and protect the source from reflections while also performing its filtering duties. A device such as this one was originally researched by scientists decades ago. These devices were based on the acoustoelectric effect where surface acoustic waves (SAW) traveling in the same direction are as drift carriers in a nearby semiconductor are amplified. While several experiments were successfully demonstrated in [1], [2], [3]. these devices suffered from extremely high operating electric fields and noise figure [4], [5]. In the past few years, new techniques have been developed for implementing non-reciprocal devices such as isolators and circulators without utilizing magnetic materials [6], [7], [8], [9]. The most popular technique has been spatio-temporal modulation (STM) where commutated clock signals synchronized with delay elements result in non-reciprocal transmission through the network. STM has also been adapted by researchers to create non-reciprocal filters. The work in [10] utilizes 4 clocks signals to obtain a non-reciprocal filter with an insertion loss of -6.6 dB an isolation of 25.4 dB. Another filter demonstrated in [11] utilizes 6 synchronized clock signals to obtain a non-reciprocal filter with an insertion loss of -5.6 dB and an Isolation of 20 dB. In this work, a novel non-reciprocal topology is explored with the use of only one modulation signal. The design is based on asymmetrical SAW delay lines with a parametric amplifier. The device can operate in two different modes: phase coherent mode and phase incoherent mode. In phase coherent mode, the device is capable of over +12 dB of gain and 20.2 dB of isolation. A unique feature of this mode is that the phase of the pump signal can be utilized to tune the frequency response of the filter. Under the phase-incoherent mode, the pump frequency remains constant and the device behaves as a normal filter with non-reciprocal transmission exhibiting over +7 dB of gain and 17.33 dB of isolation. While the tuning capability is lost in this mode, phase-coherence is no longer necessary so the device can be utilized in most filtering applications. 

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