Jiafeng Zhou

A High-Efficiency Broadband Rectenna for Ambient Wireless Energy Harvesting

This paper presents a novel broadband rectenna for ambient wireless energy harvesting over the frequency band from 1.8 to 2.5 GHz. First of all, the characteristics of the ambient radio-frequency energy are studied. The results are then used to aid the design of a new rectenna. A novel two-branch impedance matching circuit is introduced to enhance the performance and efficiency of the rectenna at a relatively low ambient input power level. A novel broadband dual-polarized cross-dipole antenna is proposed which has embedded harmonic rejection property and can reject the second and third harmonics to further improve the rectenna efficiency. The measured power sensitivity of this design is down to -35 dBm and the conversion efficiency reaches 55% when the input power to the rectifier is -10 dBm. It is demonstrated that the output power from the proposed rectenna is higher than the other published designs with a similar antenna size under the same ambient condition. The proposed broadband rectenna could be used to power many low-power electronic devices and sensors and found a range of potential applications.

Coplanar quarter-wavelength quasi-elliptic filters without bond-wire bridges

This paper presents the design and experimental results of two coplanar quarter-wavelength microwave filters operating at a frequency of approximately 3 GHz. Coplanar designs are of particular interest because they are less sensitive to the thickness of the dielectric substrate than other transmission-line types such as a microstrip. One of the designs has a quasi-elliptic frequency response. In addition, the design also eliminates problems with unbalancing of the ground planes normally present in coplanar structures. Bond wires between the ground planes are not required. This paper describes in detail the structure of the resonators and how they are coupled together to form a filter.

Design and High Performance of a Micromachined

This paper presents the design and performance of a low-loss rectangular air-filled coaxial cable. A high-precision micromachining technique is used to fabricate the cable. It is assembled by bonding together five layers of gold-coated SU-8 photoresist fabricated using the ultraviolet photolithographic technique. As the cable is air filled, both the dielectric and radiation losses are negligible. The cross coupling is also very weak between the cable and other parts of the circuit in a system. These advantages make the proposed cable a very good candidate for low-cost high-performance miniaturized transmission lines. The cable is designed to work in the frequency range of 14-36 GHz, which covers the whole JC-band. The size of the cable is only 8.9 mm times 8.6 mm times 1.5 mm and the measured minimum insertion loss of the as-made cable is approximately 0.6 dB. The return loss is better than 15 dB in the passband.

K

It is common practice to design multiway power dividers by interconnecting two-way power dividers. Transmission lines are used to link the two-way dividers. This paper investigates the performance of the interconnected power divider and the effects of the interconnecting transmission lines. In particular, it will be shown that the performance of multiway dividers constructed by interconnecting even-number-section two-way dividers deteriorates significantly as the number of output ports increases. The interconnecting lines can be used to improve the performance of such dividers.

-Band Rectangular Coaxial Cable

High performance narrow-band High-Temperature Superconductor (HTS) filters at 610 MHz with very sharp cut-off response and low loss are needed for improving the observation of pulsars at the Jodrell Bank Observatory, UK. An eight-pole quasi-elliptic HTS filter using compact resonators has been designed for this purpose. The measured response of filter has an insertion loss of 0.3 dB (including a 0.2 dB ripple), and a return loss of 15 dB in the passband. Two transmission zeroes are realized to improve the steepness of the cut-off. The lowest harmonic is designed to appear at 1.79 GHz, about three times the center frequency. The out-of-band rejection is better than 85 dB up to this harmonic. The filter has been tested in the observatory with excellent results.

General Design of Multiway Multisection Power Dividers by Interconnecting Two-Way Dividers

Novel resonators composed of double-spiral inductors and interdigital capacitors are developed, which not only are compact in size but also have no harmonics up to three times of the fundamental frequency. The center frequency is insensitive to the thickness of the substrate. A miniature seven-pole narrow-band HTS bandpass microstrip filter has been designed, fabricated and tested for an astronomy observation application, which requires a center frequency at 610 MHz and 0.82% fractional bandwidth. The computed and measured results are found in excellent agreement.

HTS narrow band filters at UHF band for radio astronomy applications

This letter presents the design of six-resonator multiple-coupled microstrip filter. A low-pass prototype of six-resonator multiple-coupled filter is developed first based on the conventional Chebyshev filter. The characteristics of attenuation poles located on both sides of the frequency response are described. According to the low-pass prototype, the design of a six-resonator multiple-coupled microstrip hairpin filter at 6 GHz is completed with the aid of EM simulation. The experimental results are demonstrated and discussed.

Superconducting microstrip filters using compact resonators with double-spiral inductors and interdigital capacitors

Condition monitoring for overhead power lines is critical for power transmission networks to improve their reliability, detect potential problems in the early stage, and ensure the utilization of the transmitting full capacity. Energy harvesting can be an effective solution for autonomous self-powered wireless sensors. In this paper, a novel bow-tie-shaped coil is proposed, which is placed directly under overhead power lines to scavenge the magnetic field energy. Compared to the conventional method by mounting the energy harvester on the power lines, this approach provides more flexibility and space to power bigger sensors such as the weather station. As the harvesting coil cannot entirely enclose the power lines, the demagnetization factor that is closely related to the core geometry should be considered and optimized. Thus a new bow-tie-shape core is designed to produce a much lower demagnetization factor (hence more power) than that of the conventional solenoid. The selection of core material is studied and found that Mn-Zn ferrite is the most suitable core material because it greatly reduces the eddy current losses and also has high permeability. Experiment results show that the bow-tie coil could have a power density of 1.86 μW/cm3 when placed in a magnetic flux density of 7 μTrms. This value is 15 times greater than the reported results under the same condition. If a longer bow-tie coil with more turns is placed in a magnetic flux density of 11μTrms, the produced power density is 103.5 μW/cm3, which is comparable to a solar panel working during a cloudy day. Thus, the proposed solution is a very efficient and attractive method for harvesting the magnetic field energy for a range of monitoring applications.

Multiple-coupled microstrip hairpin-resonator filter

The design and experimental results of a four-pole coplanar waveguide (CPW) quasi-elliptic filter using high-temperature superconductor (HTS) films are presented. Quarter-wavelength meander-line resonators are used in the filter topology. Although the resonators are aligned in two lines, no bond-wire bridges are required to balance the ground planes in the design and measurement. The slot-line mode of the filter was shifted to be higher than its third harmonic. The filter is highly miniaturized and the performance is significantly improved by the use of superconductors. The main circuit of the filter only has an area of about 6.6 mm /spl times/ 2.4 mm on a magnesium oxide substrate, coated with 600-nm-thick YBCO HTS thin film on single side of the substrate. The 3-dB bandwidth is about 1.6% centered at 2.95 GHz. The performance measured at 30 K, without any tuning, gives an insertion loss of better than 0.4 dB and a return loss of about 12 dB in the passband. The first spurious mode is about triple the center frequency.

Magnetic Field Energy Harvesting Under Overhead Power Lines

Impedance matching networks for nonlinear devices such as amplifiers and rectifiers are normally very challenging to design, particularly for broadband and multiband devices. A novel design concept for a broadband high-efficiency rectenna without using matching networks is presented in this paper for the first time. An off-center-fed dipole antenna with relatively high input impedance over a wide frequency band is proposed. The antenna impedance can be tuned to the desired value and directly provides a complex conjugate match to the impedance of a rectifier. The received RF power by the antenna can be delivered to the rectifier efficiently without using impedance matching networks; thus, the proposed rectenna is of a simple structure, low cost, and compact size. In addition, the rectenna can work well under different operating conditions and using different types of rectifying diodes. A rectenna has been designed and made based on this concept. The measured results show that the rectenna is of high power conversion efficiency (more than 60%) in two wide bands, which are 0.9–1.1 and 1.8–2.5 GHz, for mobile, Wi-Fi, and ISM bands. Moreover, by using different diodes, the rectenna can maintain its wide bandwidth and high efficiency over a wide range of input power levels (from 0 to 23 dBm) and load values (from 200 to 2000 Ω). It is, therefore, suitable for high-efficiency wireless power transfer or energy harvesting applications. The proposed rectenna is general and simple in structure without the need for a matching network hence is of great significance for many applications.