This letter presents a dual-band rectenna that can harvest ambient RF power of GSM-1800 and UMTS-2100 bands efficiently. The novel rectenna is based on a broadband 1 × 4 quasi-Yagi antenna array with bandwidth from 1.8 to 2.2 GHz and high gains of 10.9 and 13.3 dBi at 1.85 and 2.15 GHz, respectively. Also, a dual-band rectifier that can sufficiently enhance the RF-to-dc power conversion efficiency (PCE) at ambient RF power level is designed for the rectenna. Measurement results show that a PCE of 40% and an output dc voltage of 224 mV have been achieved over a 5-k Ω resistor when the dual-tone input power density is 455 μW/m ². Additionally, output dc voltage varying between 300-400 mV can be obtained by collecting the relatively low ambient RF power.

This letter presents a high-efficiency 2.45-GHz rectenna that can harvest low input RF power effectively. A new antenna with a simple structure and high gain of 8.6 dBi is proposed for the rectenna. The antenna is designed to directly match the rectifying circuit at 2.45 GHz and mismatch it at the second and third harmonics so that the use of bandpass filter between the antenna and rectifying circuit can be eliminated. The rectenna shows a maximum conversion efficiency of 83% with a load resistance of 1400 Ω. Furthermore, the overall conversion efficiency can remain 50% for the low, -17.2 dBm (corresponding power density 0.22 μW/cm ² ) input power level.

A single-fed miniaturized circularly polarized microstrip patch antenna is designed and experimentally demonstrated for industrial-scientific-medical (2.4-2.48 GHz) biomedical applications. The proposed antenna is designed by utilizing the capacitive loading on the radiator. Compared with the initial topology of the proposed antenna, the so-called square patch antenna with a center-square slot, the proposed method has the advantage of good size reduction and good polarization purity. The footprint of the proposed antenna is 10×10×1.27 mm³. The simulated impedance, axial ratio, and radiation pattern are studied and compared in two simulation models: cubic skin phantom and Gustav voxel human body. The effect of different body phantoms is discussed to evaluate the sensitivity of the proposed antenna. The effect of coaxial cable is also discussed. Two typical approaches to address the biocompatibility issue for practical applications are reported as well. The simulated and measured impedance bandwidths in cubic skin phantom are 7.7% and 10.2%, respectively. The performance of the communication link between the implanted CP antenna and the external antenna is also presented.

An implantable rectenna, which consists of a planar inverted-F antenna (PIFA) and a rectifier circuit, is proposed for far-field wireless power transfer. The PIFA has a folded ground plane to miniaturize its size. The performance of the wireless power link between the implanted antenna and an external antenna is examined. A method of adding a parasitic patch over the human body is used to enhance the wireless power link, thus to increase the received power level. Safety considerations of far-field RF powering are discussed. The RF-to-DC conversion circuit efficiency is optimized after the receiver power level of the implantable antenna is estimated based on the safety considerations. Finally, a rectifier circuit and an integrated rectenna solution are discussed.

Fast-growing flexible and stretchable electronics, such as robots, portable electronics and wearable devices, are regarded as the next-generation electronic devices. Flexible or even stretchable electromagnetic interference (EMI) shielding materials with high performance are needed to avoid the adverse effects of electromagnetic radiation produced by these devices. In this work, highly conductive and stretchable polymer films were prepared by blending a conductive polymer, poly(3,4-ethylenedioxythiophene):polystyrenesulfonate (PEDOT:PSS), with highly stretchable waterborne polyurethane (WPU). The two polymers have good miscibility at a wide range of blending ratios. The conductivity of the composite films increases while the stretchability decreases with the increase of PEDOT:PSS loading. At a 20 wt% PEDOT:PSS loading, the composite films show a conductivity of 77 S cm⁻¹ and an elongation at break of about 32.5%. More interestingly, they exhibit a high EMI shielding effectiveness (SE) of about 62 dB over the X-band frequency range at a film thickness of only 0.15 mm.

A multilayer miniaturized circularly polarized (CP) helical antenna is designed and experimentally demonstrated for industrial, scientific, and medical (ISM) (2.4-2.48 GHz) ingestible capsule endoscope systems. The proposed antenna is composed of three open loops at various layers connected by via holes to form an axial-mode helical structure to generate traveling wave radiation. A one-layer muscle phantom model is used for initial design and optimization. The footprint of the proposed antenna is π×(5.5) ² ×3.81 mm ³ . The simulated and measured impedance bandwidth is over 40% and 26% in the one-layer muscle phantom, respectively. The simulated axial ratio (AR) bandwidth is around 33.3%. The CP purity of the proposed antenna is calculated by comparing the communication link levels for two orthogonal polarizations. Additionally, electrical components are modeled inside the capsule to evaluate the effects on the antenna performance. CST voxel Gustav human body is utilized to study the design in a realistic environment. Finally, an omnidirectional CP exterior antenna is designed and the communication link is evaluated.