Spectrum analyzer

About: Spectrum analyzer is a research topic. Over the lifetime, 12217 publications have been published within this topic receiving 101851 citations.

Stabilized Optical System for Flow Cytometry

Abstract: A particle analyzer that includes optical waveguides, a support, and a detector. The optical waveguides direct spatially separated beams from a source of radiation to produce measuring beams in a sample flow measuring area. The support maintains each of the optical waveguides in a fixed relative position with respect to each other and maintains the positioning of the measuring beams within the measuring area. The detector senses light produced from the measuring beams interacting with a particle flowing through the measuring area. At least one of the support and the detector can be coupled to the core stream sample system. The coupling can use an optical waveguide device configured to convey optical radiation arising from sample interaction to the detector. In another example, a particle analyzer comprises an optical system configured to be fixedly coupled to a sample system and configured to direct beams along independent beam paths from a source of radiation to produce measuring beam spots in a sample flow measuring area of the sample system and a detection system configured to sense radiation delivered from the sample flow measuring area.

A review of experimental transverse Doppler studies

Abstract: The possibility of detecting useful Doppler information when the ultrasound beam is transversely oriented to the flow, has so far been studied by several authors. A new theory, in particular, has demonstrated that the focusing properties of piezoelectric transducers involve a Doppler signal bandwidth proportional to the transverse velocity component. The key element to perform reliable "transverse" Doppler experimental studies is thus an efficient spectrum analyzer, capable of performing accurate and repeatable bandwidth measurements. The authors review here experimental tests of the new theory, independently done in several laboratories by means of a specially developed computerized spectrum analyzer. The results of these tests include the demonstration that the "transverse" Doppler bandwidth is invariant with the range of cell depth and dimensions. It is also discussed how the basic transverse Doppler technique can be conveniently extended to allow the two- and three-dimensional estimation of the flow vector. Experimental evidence about the possibility of using the new theory to give a correct interpretation of in vivo transverse spectrograms is also presented. >

Phase sensitivity of gain-unbalanced nonlinear interferometers

Abstract: The phase uncertainty of an unseeded nonlinear interferometer, where the output of one nonlinear crystal is transmitted to the input of a second crystal that analyzes it, is commonly said to be below the shot-noise level but highly dependent on detection and internal loss. Unbalancing the gains of the first (source) and second (analyzer) crystals leads to a configuration that is tolerant against detection loss. However, in terms of sensitivity, there is no advantage in choosing a stronger analyzer over a stronger source, and hence the comparison to a shot-noise level is not straightforward. Internal loss breaks this symmetry and shows that it is crucial whether the source or analyzer is dominating. Based on these results, claiming a Heisenberg scaling of the sensitivity is more subtle than in a balanced setup.

Online Frequency Response Analysis: A Powerful Plug-in Tool for Compensation Design and Health Assessment of Digitally Controlled Power Converters

Abstract: This paper presents a cycle efficient software frequency response analyzer (SFRA), which is integrated into the firmware of the digitally controller power converter to measure the frequency response of the plant and the open-loop gain of the closed-loop system. The algorithm uses the readily available measurements taken for the power stage control and does not require additional hardware. This enables periodic measurement of the frequency response which can be used to monitor changes in the power converter. The proposed technique can run on a conventional microcontroller without any host intervention, and adds no cost to the system, which is important for the cost-sensitive power converters. Both floating point and fixed point implementation are compared enabling widespread applicability of the technique. In order to validate the efficacy of the analyzer, a synchronous buck power converter is designed and its control transfer function is compared with the measured online frequency response. An algorithm is outlined to fit the measured SFRA data to a pole–zero format through intelligent cost function estimation. The correlation of zeros and poles identified using this method with the modeled plant transfer function is analyzed. A dual core approach is discussed to run SFRA on a high-switching-frequency converter, thus showing applicability of the technique in high-switching-frequency converters.

Ultrafast Sweep-Tuned Spectrum Analyzer with Temporal Resolution Based on a Spin-Torque Nano-Oscillator.

Abstract: We demonstrate that a spin-torque nano-oscillator (STNO) rapidly sweep-tuned by a bias voltage can be used to perform an ultrafast time-resolved spectral analysis of frequency-manipulated microwave signals. The critical reduction in the time of the spectral analysis comes from the naturally small-time constants of a nanosized STNO (1-100 ns). The demonstration is performed on a vortex-state STNO generating in a frequency range around 300 MHz, when frequency down-conversion and matched filtering is used for signal processing. It is shown that this STNO-based spectrum analyzer can perform analysis of frequency-agile signals, having multiple rapidly changing frequency components with temporal resolution in a μs time scale and frequency resolution limited only by the "bandwidth" theorem. Our calculations show that using uniform magnetization state STNOs it would be possible to increase the operating frequency of a spectrum analyzer to tens of GHz.