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In this paper, three terahertz fibers based on negative curvature claddings are designed, in which the negative curvature terahertz fiber with nested triangular claddings has a minimum confinement loss of 0.005 dB/cm at 2.36 THz, and the double negative curvature terahertz fiber has a low confinement loss of $4.7 \times 10^{-4}\text{dB}/\text{cm}$ at 1.28 THz. The multimode orbital angular momentum (OAM) terahertz fiber based on double-layer elliptical cladding structure can reach the confinement loss of 10−15 dB/cm in the frequency range of 0.525 – 0.8 THz, which is beneficial to promote the application of mode division multiplexing (MDM) technology in communication systems.

Wi-Fi is the most ubiquitous wireless networking technology for loT in homes, offices, and businesses. Since the power of Wi-Fi transceivers (10s-to-100s of mW) can be prohibitively high for emerging classes of loT devices (which desire $\lt 100 \mu W$), recent work has suggested piggybacking baseband signals from the loT device directly on top of incident Wi-Fi signals generated by access points (APs) via Wi-Fi-compatible backscatter modulation [1] [2] – [4], where as low as $28 \mu W$ of active power has been demonstrated [4]. However, the major limitation of this approach is range: signals generated by the transmitting AP experience $1/d^{2}$ path loss to the backscattering tag, which has insertion loss $P_{L,ins}$ to perform single-side band (SSB) modulation, and then re-radiated modulated signals back to the receiving AP (or to another AP) experience an additional $1/d^{2}$ path loss, resulting in an overall loss $\propto 1/d^{4}+P_{L,ins}$. With no active RF amplification, the tag in [4] experienced $P_{L,ins}=15 dB$, limiting AP-to-tag-and-back-to-AP distance to $\sim 10m$, which is not sufficient in many single-AP homes.

This paper introduces the concept of self-image-guided ultrasonic (SIG-US) wireless power transmission (WPT) for robust and efficient WPT to millimeter-sized biomedical implants distributed inside the body. In SIG-US WPT, a sharp pulse is transmitted periodically by the implant to create short ringing with relatively various delays across an array of external (wearable) ultrasonic transducers. These relative delays are used to drive the external array as in phased-array beamforming, generating a highly focused ultrasound intensity at the implant’s location due to the reciprocity. Therefore, regardless of implant’s misalignment, orientation, and medium (i.e., without any prior knowledge) optimal parameters for beamforming is found by the SIG-US technique without the need for a conventional imaging system, suffering from high power consumption, size, cost, and complexity. In our proof-of-concept simulation setup with a linear transducer array (11 transducers), the SIG-US technique improved delivered power to a 1 mm3 implant with 6 mm misalignment (powering distance of 30 mm) by 95.7 times compared with conventional beamforming. In addition, for up to 6 mm implant’s misalignment, the received power with the SIG-US technique only varied by 1.2 times compared with 156.3 times variation in the received power in conventional beamforming.

The past few years have witnessed a growing demand for self-powered wearables that can enable vigilant health monitoring, with 24/7 operation. Energy harvesting from human-body motion is attractive for wearables; however, conventional unidirectional single-cantilever-beam piezoelectric energy harvesters (PEHs) [1]–[4] suffer from several body-motion harvesting challenges: such as multi-axial motion, irregular frequencies, and unpredictable amplitudes with frequent low-power levels [5]. To address these challenges, an eccentric rotor-based inertial PEH has been developed, which utilizes multiple magnetically plucked flexible thin-film $(60 \mu \mathrm {m})$ PZT-nickel-PZT beams to significantly increase the harvested energy within a small volume [5]; compared to bulk-PZT beams that are more feasible in direct-force-driven PEHs. The wrist-worn multi-beam PEH, shown in Fig. 27.4.1, converts multi-axial body motion into AC voltages with different phases and decaying amplitudes (up to several volts) within the frequency range of 90–160Hz for each beam.

This paper presents an accurate comparison between the performance of inductive and ultrasonic links for wireless power transmission (WPT) to biomedical implants with different sizes and implantation depth. These links' performances are evaluated based on the power transmission efficiency (PTE) at their optimized operation frequency (fp) to find out which WPT method is more efficient and robust. The geometry of several sets of inductive and ultrasonic links along with their fp have been optimized for different separation distances (d12) between the transmitter (Tx) and receiver (Rx) and two Rx diameters (D02) to achieve the highest PTE. The simulation results show that the ultrasonic link outperforms the inductive link when the Rx has D02 of 1.2 mm and implanted deep inside the tissue. However, for an Rx with the D02 of 5 mm and above, the inductive link achieves higher PTE, particularly at shorter d12 of 5 mm (46% vs. 40%) and 10 mm (40% vs. 28%). The simulated misalignment results show that the ultrasonic link is more prone to misalignments greater than 1 mm compared to its inductive counterpart.

This paper presents the design considerations to improve the power transfer efficiency (PTE) of ultrasonic power transmission links for wireless powering of millimeter (mm)-sized implantable microelectronic devices (IMDs). We have shown by the ultrasound theory that the diameter of the transmitter (Tx) and receiver (Rx) ultrasonic transducers, operation frequency, and powering distance have significant effect on the sound beam profile and, therefore, PTE of the link. The proposed design guideline, which has been verified by measurement results, suggests that the Rx diameter should be maximized to the extent that the application allows, and then the Tx diameter and operation frequency should be carefully chosen such that the IMD locates inside the focal zone of the Tx transducer for a given powering distance. The PTEs of ultrasonic and optimized inductive links with 2 mm Rx have also been compared that suggests the use of ultrasound when the powering distance is larger than 45 mm.