Index of content:
Volume 78, Issue 7, July 2007
- ELECTRONICS; ELECTROMAGNETIC TECHNOLOGY; MICROWAVES
78(2007); http://dx.doi.org/10.1063/1.2751399View Description Hide Description
We present the results of combining a hardware implementation of an analog comb filter with an ultralow noiseelectromagneticsensor. The comb filter is designed to attenuate mains related interference, at either 50 or , and related harmonics. The sensor chosen for this work is an induction magnetometer, but the method is applicable to any low noise high dynamic range sensor. The resultant system, in this case, uses only a single coil, not a gradiometric configuration, thus providing a magnetometer capable of sensing field as opposed to field gradient. This combination of filter and sensor allows additional gain to be added and the full sensitivity of the system to be achieved, previously only realized in an electromagnetically screened room. At the same time, the high dynamic range, low noise performance, and original bandwidth of the sensor are maintained. The technique is illustrated by using the system in an urban environment to observe Schumann resonance phenomena. This approach to acquiring small signals in a noisy environment is compared with conventional analog filter and digital signal processing techniques.
78(2007); http://dx.doi.org/10.1063/1.2757135View Description Hide Description
We described the properties of microstrip band gap filter with elliptic-fractal pattern from . It used the characteristic of the fractal and elliptic pattern to improve the performance of microstrip band gap filter. The center frequencies of gaps of the filter were about 5.5 and , and the band stop bandwidth of the filter can be increased by increasing the numbers of the cell of elliptic-fractal pattern. To verify the characteristic of dual-mode band gap filter, we simulated the above microstrip filter with the finite differential time-domain method. The simulation results were in good agreement with the experimental results.
78(2007); http://dx.doi.org/10.1063/1.2753833View Description Hide Description
Recent analysis and experiments have demonstrated the potential for transmission line transformers to be employed as compact, high-frequency, high-power, pulsed oscillators with variable rise time, high output impedance, and high operating efficiency. A prototype system was fabricated and tested that generates a damped sinusoidal wave form at a center frequency of into a load, with operating efficiency above 90% and peak power on the order of . The initial rise time of the pulse is variable and two experiments were conducted to demonstrate initial rise times of 12 and , corresponding to a spectral content from and from , respectively. A SPICE model has been developed to accurately predict the circuit behavior and scaling laws have been identified to allow for circuit design at higher frequencies and higher peak power. The applications, circuit analysis, test stand, experimental results, circuit modeling, and design of future systems are all discussed.