Use of 3-D magnetic resonance electrical impedance tomography in detecting human cerebral stroke: a simulation study

We have developed a new three dimensional (3-D) conductivity imaging approach and have used it to detect human brain conductivity changes corresponding to acute cerebral stroke. The proposed Magnetic Resonance Electrical Impedance Tomography (MREIT) approach is based on the J-Substitution algorithm and is expanded to imaging 3-D subject conductivity distribution changes. Computer simulation studies have been conducted to evaluate the present MREIT imaging approach. Simulations of both types of cerebral stroke, hemorrhagic stroke and ischemic stroke, were performed on a four-sphere head model. Simulation results showed that the correlation coefficient (CC) and relative error (RE) between target and estimated conductivity distributions were 0.9245±0.0068 and 8.9997%±0.0084%, for hemorrhagic stroke, and 0.6748±0.0197 and 8.8986%±0.0089%, for ischemic stroke, when the SNR (signal-to-noise radio) of added GWN (Gaussian White Noise) was 40. The convergence characteristic was also evaluated according to the changes of CC and RE with different iteration numbers. The CC increases and RE decreases monotonously with the increasing number of iterations. The present simulation results show the feasibility of the proposed 3-D MREIT approach in hemorrhagic and ischemic stroke detection and suggest that the method may become a useful alternative in clinical diagnosis of acute cerebral stroke in humans.

Analysis and Design of Planar Tunable Inner-Coupling Step Impedance Resonator

A full planar tunable band pass resonator is introduced, which is constructed by using novel symmetric step impedance resonator （SIR） and hyperabrupt varactors for wide bandwidth tuning and size reduction. The equivalent circuit model of the proposed resonator is set up. Theoretical analysis based on transmission line as well as odd and even-mode method is completed. The attractiveness of the approach presented lies in its simplicity. Based on the detailed analysis, a 6 GHz to 10 GHz varactor tuned resonator is designed, fabricated, and measured. It shows wideband tuning ability of 37%. The experimental results of the resonator have a good agreement with the analysis results.

Tri-band bandpass filter based on coupled stepped impedance resonators

A novel tri-band bandpass filter （BPF） is proposed by using cross-coupled stepped impedance resonators （SIRs）, which can operate at 2.4 GHz, 3.5 GHz and 5.25 GHz respectively. In engineering application, it is suitable for wireless local area network （WLAN） and worldwide interoperability for microwave access （WiMAX）. In addition, the passband of this filter can be easily controlled by changing the electrical parameters of the resonators. So it is helpful to the selection of passband in engineering applications. For in-depth analysis, the equivalent circuit of the filter is also proposed. At last, it shows that the measured results agree well with the simulated results. The insertion loss of the filter within each passband is less than 1.9 dB, meanwhile two transmission zeros are obtained which can be able to meet the engineering requirements.

Compact multilayer dual-band bandpass filter design using stepped impedance resonators

Compact dual-band bandpass filter(BPF)for the 5 th generation mobile communication technology(5 G)radio frequency(RF)front-end applications was presented based on multilayer stepped impedance resonators(SIRs).The multilayer dual-band SIR BPF can achieve high selectivity and four transmission zeros(TZs)near the passband edges by the quarter-wavelength tri-section SIRs.The multilayer dual-band SIR BPF is fabricated on a 3-layer FR-4 substrate with a compact dimension of 5.5 mm×5.0 mm×1.2 mm.The measured two passbands of the multilayer dual-band SIR BPF are 3.3 GHz-3.5 GHz and 4.8 GHz-5.0 GHz with insertion loss(IL)less than 2 dB respectively.Both measured and simulated results suggest that it is a possible candidate for the application of 5 G RF front-end at sub-6 GHz frequency band.

Monitoring iodine adsorption onto zeolitic-imidazolate framework-8 film using a separated-electrode piezoelectric sensor

In this work, a separated-electrode piezoelectric sensor（SEPS）, constructed by a naked quartz crystal mounted between two electrodes, is reported for applications in a corrosive gaseous phase. The response of SEPS was measured by an impedance analysis method. It was shown that SEPS has an excellent frequency stability because its quality factor is in the order of 10^5. The SEPS can be operated even with the electrode gap in air larger than 1 cm. Compared with a conventional quartz crystal microbalance, the resonant frequency of the SEPS is independent of the mass change in the electrode. The SEPS was applied to monitor the adsorption of iodine on quartz surface and zeolitic-imidazolate framework-8（ZIF-8） film as well as in the transfer of iodine between two ZIF-8 films. The SEPS offers the advantages of easy preparation, corrosion-resistant and convenience in combination with mass and optical measurements.