Plasmonic mass and Johnson–Nyquist noise

The study of rock fabric through the anisotropy of magnetic susceptibility requires instruments capable of high-precision measurement of weakly magnetic sedimentary rocks. The magnetometer here described is such an instrument. The rock specimen spins on a shaft in an air-gap in a closed magnetic circuit of permalloy with barium ferrite permanent magnets. The air-gap is designed to apply to the rotating specimen a very uniform flux density with a value of 0.115 tesla when the magnets are saturated. Magnetizing coils integral to the transducer are used to magnetize or demagnetize the permanent magnets. Coils in the specimen gap detect specimen magnetization parallel and perpendicular to the applied field. The magnetic circuit forms a balanced bridge and allows alternative modes of transduction. The design is such that Nyquist noise is the largest noise contributed by the magnetic circuit and is smaller than the Johnson noise from the detector coils. Measured noise from the completed transducer is only 4.7 dB above the Johnson noise. The limiting sensitivity is, however, set by the time variation of anisotropy signal from the shaft and empty specimen holder. This limit is at 1.5 × 10−9 mksu (1.2 × 10−10 emu/cm3), so that relative anisotropy of 0.01% can be detected in a weakly magnetic sandstone of bulk susceptibility 1.5 × 10−5 mksu. Calibration is discussed and sample measurements are presented. Construction of the transducer required solution of many technological problems, of which the greatest was encapsulation to suppress all vibration of parts without strain-induced loss of permeability of the permalloy. The more important of the solutions found are outlined briefly.

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Effect of transverse electric field on nyquist noise

Solid-State Electronics ◽

10.1016/0038-1101(81)90110-6 ◽

1981 ◽

Vol 24 (10) ◽

pp. 905-906 ◽

Cited By ~ 2

Author(s):

R.P. Jindal ◽

A. van der Ziel

Keyword(s):

Electric Field ◽

Transverse Electric ◽

Transverse Electric Field ◽

Nyquist Noise

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Joint Effect of Heterogeneous Intrinsic Noise Sources on Instability of MEMS Resonators

Electronics ETF ◽

10.7251/els1519059j ◽

2016 ◽

Vol 19 (2) ◽

pp. 59

Author(s):

Olga Jakšić ◽

Ivana Jokić ◽

Miloš Frantlović ◽

Danijela Randjelović ◽

Dragan Tanasković ◽

...

Keyword(s):

Phase Noise ◽

Noise Analysis ◽

Intrinsic Noise ◽

Noise Spectrum ◽

Joint Effect ◽

Noise Sources ◽

Mems Resonators ◽

Micro Resonator ◽

Micro Cantilever ◽

Nyquist Noise

This article's focus is on the numerical estimation of the overall instability of microelectromechanical-system-based (MEMS) resonators, caused by intrinsic noise mechanisms that are different in nature (electrical, mechanical or chemical). Heterogeneous intrinsic noise sources in MEMS resonators that have been addressed here are Johnson–Nyquist noise, 1/f noise, noise caused by temperature fluctuations and adsorptiondesorption induced noise. Their models are given first (based on analytical modeling or based on empirical expressions with experimentally obtained parameters). Then it is shown how each one contributes to the phase noise, a unique figure of merit of resonators instability. Material dependent constants  and knee position in noise spectrum, needed for empirical formulae referring to 1/f noise, have been obtained experimentally, by measurements of noise of MEMS components produced in the Centre of Microelectronic Technologies of the Institute of Chemistry, Technology and Metallurgy in Belgrade. According to these measurements,  varies in the range from 0.776.10-4 to 2.26.10-4 and cut off frequency for 1/f noise varies from 147 Hz to 1 kHz. The determined values are then used for the modeling of micro-resonator phase noise with electrical origin and overall phase noise of a micro-resonator. Numerical example for calculation of overall phase noise is given for a micro-cantilever, produced by the same technology as measured components. The outlined noise analysis can be easily extended and applied to noise analysis of MEMS resonator of an arbitrary shape.

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