Noise microphonic

CUORICINO has 24 cold electronics acquisition channels and 38 channels with room temperature amplifiers. The formers are realized by JFET pairs working in the cryostat at 120K [104], The differential configuration and their position close to the detectors (between 1.5 K and 600 mK stages) have minimized interferences and microphonic noise from the detector wires. 

In powder samples with broad EPR lines, large Zeeman modulation amplitudes have to be applied to improve the sensitivity. Such amplitudes often produce microphonic noise in the cavity and cause an uncertainty in the orientation selection in single crystal-like ENDOR spectra (Sect. 4.1). A modulation technique which avoids these problems in powder ENDOR studies has been proposed by Hyde et al.32). In this scheme the Zeeman modulation is replaced by a 180° modulation of the phase of the microwave signal. 

The electrical connection between detector and transistor was approximately 3 cm., the short lead distance is important in reducing stray electrical capacitance and microphonic noise owing to mechanical vibration. The circuit is a modified version of that of Bradley (3), with transistor types 2N4861 or 2N3823. 

Schwander and Levitt, 1987] Schwander, T. and Levitt, H. (1987). Effect of two-microphone noise reduction on speech recognition by normal-hearing listeners. J. Rehab. Res. andDevel., 24 87-92. 

The Faraday plate detectors, the mainstay of detector technology in IMS from its inception as a modern analytical method, are seen as robust and effective for field instruments and relatively small ions. Nonetheless, the poor gain and susceptibility to microphonic noise can also be seen as disadvantages. Probably, these worries and wishes are small compared to the fundamental barrier to improved resolving power, which is established with the ion shutter. The Bradbury-Neilson (BN) or Tyndall-Powell (TP) shutters have and will certainly be the method of choice into the foreseeable future for IMS analyzers. The constraint is ambient pressure based. The limitation induced with fleld-mobility-based injections are large, yet no improved solution has been demonstrated. 

An alternative source of microphonic noise is said to be ice inside the Dewar. Two mechanisms have been suggested ... 

Piezoelectric properties. At first sight it seems surprising that piezoelectric properties are important in pyroelectric devices. However, all pyroelectric detectors used in a high-vibration or acoustically noisy environment will produce a piezoelectric microphonic noise signal, mostly through flexure, which can be very significant if steps are not taken to suppress it. 

The presence of carbon dioxide is usually not quite as detrimental as water vapor because CO2 absorbs in less important spectral regions for most applications. Nonetheless, the best spectra are acquired by purging the instrument with C02-free air. Some regenerating driers produce C02-free air. The flow rate of the purge gas through the spectrometer should be enough to reduce the level of H2O and CO2 to an acceptably low level within about a minute after the sample has been loaded into the spectrometer. However, the flow rate should not be too high, because microphonic noise can be introduced into the spectrum. 

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