A cold preamplifier based on superconducting quantum interference devices (SQUIDs) is currently the preferred readout technology for the low-noise transition edge sensor (TES). In this work, we have designed and fabricated a series SQUID array (SSA) amplifier for the TES detector readout circuit. In this SSA amplifier, each SQUID cell is composed of a first-order gradiometer formed using two equally large square washers, and an on-chip low pass filter (LPF) as a radio-frequency (RF) choke has been developed to reduce the Josephson oscillation interference between individual SQUID cells. In addition, a highly symmetric layout has been designed carefully to provide a fully consistent embedded electromagnetic environment and achieve coherent flux operation. The measured results show smooth V–Φ characteristics and a swing voltage that increases linearly with increasing SQUID cell number N. A white flux noise level as low as 0.28 μ Φ 0/Hz1/2 is achieved at 0.1 K, corresponding to a low current noise level of 7 pA/Hz1/2. We analyze the measured noise contribution at mK-scale temperatures and find that the dominant noise derives from a combination of the SSA intrinsic noise and the equivalent current noise of the room temperature electronics.
This paper presents experimental validation of an alternate integral-formulation method (AIM) for predicting acoustic radiation from an arbitrary structure based on the particle velocities specified on a hypothetical surface enclosing the target source. Both the normal and tangential components of the particle velocity on this hypothetical surface are measured and taken as the input to AIM codes to predict the acoustic pressures in both exterior and interior regions. The results obtained are compared with the benchmark values measured by microphones at the same locations. To gain some insight into practical applications of AIM, laser Doppler anemometer (LDA) and double hotwire sensor (DHS) are used as measurement devices to collect the particle velocities in the air. Measurement limitations of using LDA and DHS are discussed.
It has been shown [Wu and Hu, J. Acoust. Soc. Am. 103, 1763–1774 (1998)] that acoustic radiation from a vibrating object can be calculated directly by an Alternate Integral-formulation Method (AIM), once the particle velocity distribution over a hypothetical surface enclosing this object is specified. This concept is extended here to prediction of aerodynamically generated sound. The particle velocity distribution on a hypothetical enclosure is measured by a fully integrated sound pressure-velocity (p-u) probe. This novel p-u sensor combines a MEMS particle velocity sensor and miniature pressure transducer, which allows for measurements of the acoustic pressure and particle velocity at a single point simultaneously. It is simple and easy to use and is suitable for both narrow and broadband sound measurements. This p-u probe is employed to measure the particle velocity field generated by a typical hairdryer. Measurements thus obtained are taken as input to AIM to predict the radiated acoustic pressure field. Experiments are conducted inside an anechoic chamber at the Acoustics, Vibration, and Noise Control Laboratory at Wayne State Uni- versity. The predicted acoustic pressures are then compared with those measured at the same locations by microphones. Satisfactory agreements are obtained at all frequencies.
The optical properties have been numerically investigated in crystalline silicon nanoholes array for various structural parameters. We have demonstrated that the light absorption can be greatly enhanced in silicon nanoholes array especially for long wavelength absorption compared with single diameter nanoholes array. We have also obtained the optimal parameters for absorption wavelength control, at which the photocurrent enhancement factors have been achieved to be 14.43% compared to silicon thin film. Furthermore, the underlying mechanism of the absorption enhancement in dual-diameter nanoholes array has been discussed.
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