Chaoyun Song

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.

Magnetic Field Energy Harvesting Under Overhead Power Lines

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.

Matching Network Elimination in Broadband Rectennas for High-Efficiency Wireless Power Transfer and Energy Harvesting

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.

A Modified Two-Antenna Method to Measure the Radiation Efficiency of Antennas in a Reverberation Chamber

A modified two-antenna method is proposed to measure the radiation efficiency of antennas in a reverberation chamber. By combining the conventional reference antenna method and the one-antenna method, and introducing a virtual antenna, the proposed method does not need a reference antenna with known efficiency and can be applied to highly lossy antennas, which could be problematic for the existing methods. Measurements are conducted to verify the effectiveness of the proposed method. The proposed method can be regarded as a generalized form of the two-antenna method and is compared to the existing reverberation chamber methods. The advantages and limitations of the proposed approach are also discussed.

Shielding Effectiveness Measurement of an Electrically Large Enclosure Using One Antenna

A new method is proposed to measure the shielding effectiveness (SE) of an electrically large enclosure. Traditionally, the SE measurement requires at least two (in an anechoic chamber) or three antennas (in a reverberation chamber). In this paper, only one antenna is needed in the whole measurement procedure. There is no requirement to use a reference antenna. It is interesting to note that if the aperture of the enclosure under test (EUT) can be covered (by using a conductive sheet or aluminum foil), the SE can be measured quickly by comparing the Q factor or the decay time of the covered and uncovered EUT. Measurements have been conducted to evaluate and verify the proposed method. The results are compared with those obtained using the nested reverberation chamber method; limitations of the proposed method are also discussed and identified. It is found that when the EUT is well shielded, the uncertainty of the proposed method could be relatively large. Nevertheless, the proposed method does offer a new simple and efficient approach to measure the SE of an electrically large enclosure.

The Limit of the Total Scattering Cross Section of Electrically Large Stirrers in a Reverberation Chamber

The total scattering cross section (TSCS) has been proven to be an effective quantity to characterize the performance of stirrers in a reverberation chamber (RC). It is shown in this letter that the maximum TSCS is a quarter of the stirring surface area, and it is equal to the absorption cross section (ACS) of the same area with perfect radio absorbers. The mathematical proof is presented and measurements are performed to validate this limit. It is also shown that the TSCS and ACS are statistical dual quantities; related dual quantities are also given. The TSCS can be used to characterize how well a stirrer is designed or how close an RC is to a perfect RC.

Reconfigurable 3D folded monopole antenna design for DVB-H applications

A frequency tunable compact 3D folded monopole antenna designed for DVB-H applications is presented. By loading the folded monopole antenna with a variable capacitor, the operating frequency of the antenna can be continuously tuned over the frequency range of the DVB-H standard, from 470 MHz to 862 MHz. Furthermore, a water layer is loaded to reduce the dimensions of the antenna while keeping a reasonable bandwidth for DVB-H specifications. The antenna element occupies a very small volume 17.5 mm × 7 mm × 3 mm (probably the smallest reported volume for DVB-H applications), thus it is a very promising candidate for DVB-H applications.

A High-Efficiency Helical Core for Magnetic Field Energy Harvesting

Real-time data of high-voltage infrastructures collected by wireless sensors are the foundation of many smart grid applications. Energy harvesting can be an effective solution for autonomous, self-powered wireless sensors. In this paper, a coil with a novel helical core is proposed and optimized to scavenge the magnetic field energy efficiently near equipment carrying large currents. Due to the special design of the helical core, the path of the magnetic flux inside the core can be significantly increased, which leads to a reduction of the demagnetizing field. Therefore, the proposed core can generate a much higher flux density (hence more power) compared with conventional designs. The selection of the core material is studied and it is found that high permeability ferrite is the most suitable material. Experimental results show that the proposed helical coil with only 400 turns of wire can have a power density of

A broadband circularly polarized cross-dipole antenna for GNSS applications

{\rm{2.1\,\mathrm{\mu} W/ cm}}^{3}

A novel compact and frequency-tunable rectenna for wireless energy harvesting

when placed in a magnetic flux density of