This letter presents a novel multiband rectenna for the ambient wireless energy harvesting of an autonomous internet of thing (IoT) sensor. A bow-tie antenna with slits is proposed to obtain four frequency bands at 840 MHz, 1.86, 2.1, and 2.45 GHz, respectively. Furthermore, a multiband rectifying circuit combined of four single ring-loop rectifiers is designed with high conversion efficiency. Finally, a power management circuit with storing and converting the harvested voltage is proposed for smoothing dc output voltage. The energy harvester can be used in practical wireless sensor applications.

Midfield wireless power transfer has proved its advantages in power delivery to miniature implantable medical devices located deeply in the human body, however, the delivered power level is still low. Besides, design proposals for a compact source structure concentrating the transmitter field on a miniature implant remain challenges. This letter presents a novel compact transmitting structure (TX) at the midfield band and shows the capability of focusing the magnetic field inside the human tissue. Source performance has been verified by implantable PIFA antenna with a total size of 9x13 mm² (RX) that positioned in the heart tissue layer at a 55 mm separated distance of TX and RX. In addition, the power transfer efficiency has been demonstrated by measurement setup using pork muscle, which obtained a good match of the transmission coefficient between the simulation and experiment results. Consequently, for 1W of output power from the midfield transmitter, the received energy could be achieved more than 5.6 mW via the implantable antenna at subwavelength distance.

This letter presents a novel methodology for designing high-efficiency dual-band (DB) inverse class F (class $\text{F}^{-1}$ ) rectifier for wireless power transfer (WPT) and energy harvesting (EH). Specifically, a proposed DB class $\text{F}^{-1}$ harmonic termination network is employed based on transmission lines (TLINs) which are theoretically analyzed. The closed-form design formulas are derived for providing exact class $\text{F}^{-1}$ harmonic manipulation at two arbitrary frequency bands, enabling a highly efficient DB class $\text{F}^{-1}$ operation. For validation, a Schottky diode-based rectifier is implemented at two target frequencies of 1.9 and 2.45 GHz. The experimental results show that peak power conversion efficiency (PCE) can be achieved over $76\%$ at 1.81 and 2.35 GHz with an input power of $13$ dBm. Moreover, the rectifier exhibits a $>\!\!50\%$ PCE within a wide dynamic range (DR) of $19.5$ and $17.5$ dB at 1.81 and 2.35 GHz, respectively. To the author’s best knowledge, this is the first time a DB diode-based rectifier design with the deployment of a DB harmonic termination mechanism is incorporated with a DB fundamental matching network.

In this paper, an ultra-miniaturized implantable antenna is proposed for biomedical applications, which operates in frequency of the industrial, scientific, and medical bands of 2.4 GHz. The miniaturization of the proposed antenna is obtained by using a meander line as radiating patch, introducing a $1.2~\Omega $ chip resistor, and two pairs of a rectangle slot are etched on the ground plane to expand the antenna impedance bandwidth. The antenna has an ultra-compact size with a width and length of 2.5 mm and a thickness of 0.64 mm (the total dimension of $2.5 {\mathrm {mm}} \times 2.5 {\mathrm {mm}} \times 1.28 {\mathrm {mm}}^{3}$ ). To validate the antenna structure, the optimal design is fabricated and experimentally measured. A low loss, flexible, and biocompatible PCB material, Taconic CER-10 ( $\varepsilon _{r} = 10.2, \sigma = 0.0 035$ ) is adopted as both the substrate and superstrate. The experiment results imply that the proposed antenna produces a good impedance matching at 2.4 GHz with a bandwidth of 16.6% and a maximum peak gain of −18.3 dBi. In addition, to further prove the performance of the designed biomedical implantable antenna, the effects of a coaxial cable and the simulations in the environment of the human tissue models (head, arm, and leg) are established. The antenna provides a low specific absorption rate (SAR) with the value compliance the IEEE standard safety guidelines. To the best of our knowledge, the proposed antenna is the smallest dimension (in width and length) with high performance compared to previously reported works. Thus, the antenna is a potential candidate and suitable for the biomedical applications.

This letter proposes a midfield wireless power transfer system using a bipolar spiral-shape transmitter (BPSP-Tx) for cardiac implants application. Optimal current distribution is built on BPSP-Tx surface following spiral structure to generate a focused field inside human tissue and adapt the implantable receiver (Rx) misalignments. Source performance has been verified by implantable hooked-shape Rx (HKSD-Rx) that separated at a distance of 45 mm from Tx. Measurements are conducted in minced pork for validation. Experimental results show that the transmission coefficient can achieve -20.48 dB at a distance of 45 mm and -22.15 at 60 mm. Furthermore, the Rx misalignment is verified by output power level, which shows that the proposed system can maintain high performance on a rotation range of Rx from -90 ^° to 90 ^° . Finally, the human safety regulations are verified to present a low specific absorption rate, which demonstrates the potential for cardiac implants.

Continuous blood pressure (BP) monitoring is important for patients with hypertension. However, BP measurement with a cuff may be cumbersome for the patient. To overcome this limitation, various studies have suggested cuffless BP estimation models using deep learning algorithms. A generalized model should be considered to decrease the training time, and the model reproducibility should be taken into account in multi-day scenarios. In this study, a BP estimation model with a bidirectional long short-term memory network is proposed. The features are extracted from the electrocardiogram, photoplethysmogram, and ballistocardiogram. The leave-one-subject-out (LOSO) method is incorporated to generalize the model and fine-tuning is applied. The model was evaluated using one-day and multi-day tests. The proposed model achieved a mean absolute error (MAE) of 2.56 and 2.05 mmHg for the systolic and diastolic BP (SBP and DBP), respectively, in the one-day test. Moreover, the results demonstrated that the LOSO method with fine-tuning was more compatible in the multi-day test. The MAE values of the model were 5.82 and 5.24 mmHg for the SBP and DBP, respectively.