A novel three-pole tunable bandpass filter using mixed varactor-tuned combline and split-ring resonators is proposed in this letter. A tuning range of 1.1-1.88 GHz (70.9%) with an almost constant 3 dB absolute bandwidth of MHz (7.4%-4.4% fractional bandwidth) is demonstrated. The filter shows its insertion loss varying from 6.8 dB to 4.3 dB and return loss better than 13.5 dB within the tuning range. The rejection levels at both the lower and upper stopbands are dB. The measured results show good agreement with the simulated ones.Index Terms-Combline resonators, constant absolute bandwidth (CABW), split-ring resonators, three-pole tunable filters, varactor-tuned.
The silicon microring resonator plays an important role in large-scale, high-integrability modern switching matrixes and optical networks, as silicon photonics enables ring resonators of an unprecedented compact size. But as the nature of resonators is their sensitivity to temperature, their performances are vulnerable to being affected by thermal effect. In this paper, we analyze the dominant thermal effects to the application of silicon microring optical switch. On the one hand we theoretically analyze and experimentally measure the thermal crosstalk among adjacent microring optical switches with different distances, and give possible solutions to minimize the affect of thermal crosstalk. On the other hand we analyze and measure the thermooptic dynamic response of microring switch; the experiment shows for the thermal-tuning that the rising edge is around 2 μs, and the falling edge is around 35 μs. We give the explanation of the asymmetric rise-time and fall-time.
A quartz-enhanced photoacoustic spectroscopy (QEPAS) sensor for H2S detection operating in near-infrared spectral range is reported. The optical source is an erbium-doped fiber amplified laser with watt-level optical power. The QEPAS spectrophone is composed of a quartz tuning fork with a resonance frequency of 7.2 kHz, a quality factor of 8500, and a distance between prongs of 800 µm, and two tubes with a radius of 1.3 mm and a length of 23 mm acting as an organ pipe resonator. With this spectrophone geometry, the photothermal noise contribution of the spectrophone was removed and the theoretical thermal noise level was achieved. The position of both tubes with respect to custom quartz tuning fork has been investigated as a function of signal amplitude, Q-factor, and noise of the QEPAS sensor when a high-power laser was used. Benefit from the linearity of the QEPAS signal to the excitation laser power, a detection sensitivity of 330 ppb for H2S detection was achieved at atmospheric pressure and room temperature, when the laser power was 1.6 W and the signal integration time was set to 300 ms, corresponding to a normalized noise equivalent absorption of 3.15 × 10−9 W cm−1/(Hz)1/2. The QEPAS sensor was then validated by measuring H2S in a biogas sample.
The mechanism of surface topography formation of Inconel 718 in low-speed wire electrical discharge machining was studied, and its on-line prediction based on acoustic emission detection technology is carried out. An optimized truncated cone-shaped thermal conduction model considering the scattering velocity difference between electrons and ions was put forward. Based on this model, discharge craters and temperature variation at different discharge energy conditions were systematically discussed in finite element analysis. Experimentally, five machining regimes that are reduced in accordance with the discharge energy were conducted with acoustic emission detection technology in low-speed wire electrical discharge machining. A novel denoising method has been proposed, which combines filtering analysis and Fast Fourier Transform. The experimental results indicate that acoustic emission testing technique provides great technical support in researching the discharge energy variation rule in low-speed wire electrical discharge machining. It is also concluded that the change trends of the theoretically calculated temperature in the discharge channel and acoustic emission signal root mean square and the surface roughness value and the acoustic emission signal root mean square show a similar exponential growth law. A regression equation about the arithmetic mean roughness (R a ) values and root mean square values of acoustic emission is established to predict surface roughness value R a whose error is less than 1%.
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