Temperature noise

In order for rolling element bearings to achieve their design life and perform with no abnormal noise, temperature rise, or shaft excursions, the following precautions should be taken ... 

Amplifiers. The maser produced a new kind of amplifier, which was about a hundred times more sensitive than the amplifiers we had at the time. The maser had a so-called noise temperature of about one degree Absolute - you can get down to about that amount of noise. However, other amplifiers at that time were a hundred times more noisy. Thus the maser allowed us to measure more sensitively. 

From the last two formulas, we see the need to use a large mass of high Q and high speed of sound material, reduce its temperature as much as possible, use a high /3 transducer and an amplifier with the lowest possible noise temperature. 

L0 noise suppression Alixer noise temperature 900 K (DS8) -System noise temperature 1360 K (DSB) -Alixer conversion loss 6 dB (DSB) -20mWat 80 GHz required inW at 160 GHz generated by D162 >TF bandwidth to > 20 GHz... 

Figure 9. A 183 GHz receiver and its system noise temperature as a function of frequency [15].

Alteration of environmental factors (e.g., lighting, noise, temperature)... 

We now check whether Eq. (1), with S /3 = e2/ and modified as above to account for finite propagation time, can explain our data. The unknown parameters are the resistance Rq and the effective environment noise temperature Tq. We checked that the impedance of the samples was frequency independent up to 1.2 GHz within 5%. Fig. 2 shows the best fits to the theory, Eq. (1), for all our data. The four curves lead to Ro = 42 12, in agreement with the fact that the electromagnetic environment (amplifier, bias tee, coaxial cable, sample holder) was identical for the two samples. We have measured the impedance Zenv seen by the sample. Due to impedance mismatch between the amplifier and the cable, there are standing waves along the cable. This causes Zenv to be complex with a phase that varies with frequency. We measured that the modulus Zenv varies between 30 12 and 70 12 within the detection bandwidth, in reasonable agreement with f o = 42 12 extracted from the fits. 

Resonance-like suppression of the higher harmonics in the response spectrum of a superparamagnetic particle is investigated. Using a nonperturbative approach, we analyze the steady processes that take place under arbitrary values of the DC (bias) and AC (excitation) strengths. The results show that the suppression effect is equally achieved on varying either noise (temperature) or force (external field intensity) or by a combination of both. In the fundamental aspect, we surmise... 

The most important factors in determining the s/n ratio or sensitivity of an NMR experiment in a cryogenic NMR probe, insofar as the hardware itself is concerned, are the temperature of the coil, 7/ the resistance of the coil, Rc the temperature of the sample, Ts and the resistance added to the coil by the presence of the sample or the sample resistance, Rs. The temperature of the rf coil in a cryogenic NMR probe is typically in the range of 15-30K commercial examples of the Varian Cold-probe operate at 25 K. The preamplifier noise temperature is generally in the range of 10-15 K and the coil resistance is small compared to a conventional room temperature NMR probe. The first two terms in the expression below provide the basis for the vast improvement in the performance of a cryogenic relative to a conventional NMR probe. The sample temperature, Ts, and sample resistance, Rs,... 

The double side-band receiver noise temperature has been measured for a variety of receivers based on several mixing strategies. An InSb hot-electron bolometer operated as a mixer was found to have a double side-band receiver noise temperature = 300 K at 220 GHz (Blaney, 1980). This corresponds to an NEP = 10 W/ /Hz referred to a predetection bandwidth of 100 GHz. The single frequency performance of mixer-based receivers does not generally match this performance, however (Boucher et al., 1993). 

From Eq. (73) it is clear that there are other ways to reduce One can work at higher powers, at least until saturation occurs, or use a detector with lower noise temperature or both. Before purchasing a higher power source, one should check carefully to ensure that the detector performance is not limited by higher power levels. Schneider (1982) discusses the performance of millimeter wave diodes in detail. 

In addition to the sample concentration and specific parameters related to the pulse sequence being used, the spectral signal-to-noise ratio (SNR) depends on various components of the spectrometer hardware, in particular the sensitivity of the probe and preamplifier. The SNR can be related to the temperature of the receiver coil ( Tq), its resistance (Rc), the temperature of the sample (Tg), the resistance added to the coil by the sample (i s), and the noise temperature of the amplifier (TA) by the following equation 7... 

This chip die sizes are 5 X 5 and 10 X 10 mm. The first chip (5X5 mm ) of the spectrometer, the front-end chip, has the local oscillator together with the SIS mixer and impedance matching structure for better power delivery and to time out the SIS junction capacitance. The frequency resolution of SISP determined by both the instant linewidth of the LO and its long-time stability along with the noise temperature is one of the major parameters in spectral measurements. The phase-lock loop consisted both on-chip circuitry and room-temperature electronics is employed. ... 

The resonance frequency of mixer-amplifier tank circuit is measured to be 1.5 GHz. The SQUID amplifier has the following experimentally measured parameters critical current and normal state resistance per junction of front end SQUID are Ic=40 pA and Rn=4 Q, squid inductance is 40 pH, mutual input inductance is 400 pH and input inductance is 5 nH providing the amplifier noise temperature Tn=90 K. 

Primary insomnia is considered to he an endogenous disorder due to either a neurochemical or structural disorder affecting the sleep-wake cycle. Individuals with primary insomnia may he hght sleepers who are easily aroused by noise, temperature, or anxiety. Some studies have suggested that primary insomnia is a hyperarousal state, in that insomnia patients have an increased metabohc rate compared with controls, and have longer-than-average sleep latencies in sleep studies. ... 

Due to the reduced Q factor of the quartz crystals in liquids, and therefore decreased phase slope, the requirements of the circuit with respect to phase (frequency dependence, noise, temperature dependence), to amplification linearity, and to temperature constancy are much higher. One electrode of the quartz crystal should be grounded to minimize parasitic effects and to allow operation of quartz arrays in conductive liquids. The increased damping of the oscillator should be overcome by automatic level control. The control variable in the amplitude control loop can be used as an independent measurement value. It also allows for calibration of/osc with respect to/s [36]. 

Cryogenically cooled detectors employ the low-noise GaAs Schottky barrier Mott diodes. Between 140 and 220 GHz they exhibit 400 K noise equivalent temperature at a lower limit junction temperature of 20 K, below which the performance degrades. The noise temperature is around 1000 K at 300 K junction temperature. Sensitivity of a Schottky barrier mixer diode ranges from about 2.75 VmW" to 1 VmW over the range 90-325 GHz.In comparison the helium-cooled InSb bolometer used by the present authors (Section 3.4.1) can provide double sideband noise temperatures of 200-300 K in the region 100-300 GHz and sensitivity of 5-6 VmW . ... 

When sources are progressively cooled the noise temperature approaches the actual temperature, but cannot equal it. Lesurf demonstrates that for a single sideband receiver the minimum possible noise temperature is given by... 

The significance of detector or mixer noise figure is its critical influence on the overall noise output of the spectrometer. As the first element in the amplification chain the mixer can be readily demonstrated to have the most important noise contribution of any of the stages. The noise figure and the noise temperature are equally satisfactory as figures of merit for comparing different devices. 

The simplest representation of the thermal circuit of an infrared detector is shown in Fig. 3.1. The detector is represented by a thermal mass H coupled via a conductance Gto a heat sink at a constant temperature T. In the absence of a radiation input the average temperature of the detector will also be T, although it will exhibit a fluctuation about this value. This fluctuation gives rise to a source of detector noise ( temperature noise ) which sets the ultimate limit to the minimum signal detected by a perfect thermal detector. When a radiation input is received by the detector, the rise in temperature is found by solving the equation ... 

The principal noise sources are temperature (3.9), Johnson and amplifier noise. Temperature noise sources have been discussed in detail by Logan (Logan and Moore [3.9], Logan [3.10]) who has shown that in addition to the radiative conduction, conduction and convection into the ambient gas in the encapsulation and lateral conduction into the surrounds of the element are important. With present materials, however, the Johnson noise under most circumstances is more important. If we assume that the principal contribution to r in Fig. 3.10 comes from the dielectric loss of the pyroelectric material, then the appropriate expressions for the Johnson noise limited noise equivalent power (see (3.16)) is... 

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