This paper presents a symmetrical dual-loop antenna with ultra-wideband performance and operating in Industrial Scientific and Medical (ISM, 2.4-2.4835 GHz) band for use in wireless endoscopy applications. The antenna is composed of two identical loops located symmetrically around the center, a feeding patch at the center of the feeding loop, and a parasitic patch connected to another loop. A simulated ultra-wideband of 143%, ranging from 1.11 to 6.03 GHz, can be achieved in ISM band by adding two rectangular patches at the center of these two loops and rotating the feeding direction by 90°. Finally, the proposed antenna is measured in pork and a measurement bandwidth of 124% is obtained.

Laser-direct writing has become an alternative method to fabricate flexible electronics, whereas the resistive nature of laser-scribed conductors may distort the radio-frequency characteristics of circuits for high-frequency applications. We demonstrate that the transmission characteristics of microstrip lines are insensitive to the resistance of laser-scripted conductors when the sheet resistance is not above 0.32 Ω/□. On the other hand, the transmission and reflection characteristics of the MS lines can be simply modified through the accommodation of the resistance of the conductors, because a laser can trigger the sintering and melting of laser produced silver nanostructures. This could provide an alternative way to fabricate radio frequency (RF) resistors and promote their applications to flexible radio-frequency devices and systems.

In this paper, a conformable antenna operating at 12GHz is proposed. The antenna is composed of six Chebyshev linear array antennas (CLAAs) around the surface of cylinder. Liquid metal is used to print the antenna pattern on the flexible PDMS dielectric substrate to adapt to the cylinders with different radii. Each CLAA is connected to a radio frequency switch. The beam scanning of the antenna can be realized by controlling the on and off of each switch in turn. Single row of array antenna can achieve maximum measured gain of 14.8dBi. The performances of proposed conformable array antenna in different bending radii have also been investigated.

This paper presented a novel sensor based on a stepped impedance resonator, which can measure the permittivities of materials at different resonant frequencies simultaneously. The multiple resonant frequencies are generated by the fundamental frequency and harmonics. The sensitivity of designed sensor at different resonant frequencies is also analyzed in detail. For verifying the feasibility of the sensor, three different kinds of materials under test are measured. The experimental results demonstrated that the tested resonant frequencies show a multiplicative growth and are consistent with our theoretical analysis. Besides, the higher the tested resonant frequency, the greater the sensitivity. The permittivity of the material under test is derived from these measured resonant frequencies by simulation and calculation. The maximum relative error through simulation and calculation are 3.4% and 26.67%, respectively. Moreover, the proposed sensor also has the advantages of being simple to fabricate, inexpensive to manufacture, and compact in volume.

As an essential component for wireless power transmission and energy harvesting (EH), rectennas have received increasing attention in recent years. This article presents a flexible rectenna design based on a printed liquid metal additive manufacturing process, offering advantages, such as low cost, high reliability, repeatability, and excellent mechanical adaptability. Polydimethylsiloxane (PDMS) is used as the substrate, providing high flexibility and good conformability. The proposed rectenna consists of a Chebyshev-fed linear monopole antenna array and a compact rectifying circuit. The antenna achieves a gain exceeding 7 dBi over the 2–3-GHz frequency range, with a gain of 9.8 dBi at 2.4 GHz and radiation efficiency above 80%. It also exhibits a wide beamwidth, with a half-power beamwidth (HPBW) of 98° in the H-plane at 3 GHz, allowing for bidirectional radiation. The rectifier shows over 40% efficiency at 0-dBm input power, above 60% at 10 dBm, and retains 28% efficiency at −12 dBm. Finally, the integrated rectenna was evaluated under various conformal conditions, confirming its stable performance.