Low mass pass filter

FIGURE 15.8 Top, the two-step RF Cl scan function used in early ion trap Cl mode. Bottom, the SECI scan function in which the low frequency square waveform that acts as a low mass pass filter, is used to isolate Cl reagent ions. 

FIGURE 8.11 Combination of high and low mass pass filter defines the resolution of the mass analyzer. 

Figure 2.15. Schematic of a quadrupole analyzer, (a) A hyperbolic cross-section (b) cross-section of cylindrical rods (c) the operating principle of a quadrupole mass filter. The x-direction pair of rods acts like a high pass filter so ion C (with low m/z) is not allowed through, and the y-direction pair of rods acts like a low pass filter and takes care of ion A (with high m/z). Only ion B having an m/z in the stable range is allowed through the quadrupole mass filter for subsequent detection. Reprinted from A. Westman-Brinkmalm and G. Brinkmalm (2002). In Mass Spectrometry and Hyphenated Techniques in Neuropeptide Research, J. Silberring and R. Ekman (eds.) New York John Wiley Sons, 47-105. With permission of John Wiley Sons, Inc.

There are several applications of ZnO that are due to its excellent piezoelectric properties [28,164]. Examples are surface-acoustic wave (SAW) devices and piezoelectric sensors [28,165-167]. Typically, SAW devices are used as band pass filters in the tele-communications industry, primarily in mobile phones and base stations. Emerging field for SAW devices are sensors in automotive applications (torque and pressure sensors), medical applications (chemical sensors), and other industrial applications (vapor, humidity, temperature, and mass sensors). Advantages of acoustic wave sensors are low costs, ruggedness, and a high sensitivity. Some sensors can even be interrogated wirelessly, i.e., such sensors do not require a power source. 

To prevent Cs ions fi-om reaching the TOFMS a quadrupole lens acts as a high-pass filter To that effect the low mass setting is at 140 amu and there is no mass sweep. 

FIGURE 11-8 Quadfupole acts as (a) a high-pass mass filler in the ii plane, (b) a low-pass mass filter in the yr plane, and (c) a narrow-band filter when high-pass and low-pass filters are both in operation. (Reprinted with permission from P. E. Miller and M. B. Denton. J. Chem. Educ., 1986. 63.619. Figures 6. 7. and 8. Copyright 1986 Journal of Chemical Education.)... 

Tissue Vibration. Noncontact methods are preferred for measuring the surface motion of tissues. Laser vibrometers are commercially available with sufficient bandwidth and resolution for most studies. A direct mass load on the skin, together with the skin s elasticity, forms a mechanical low-pass filter (see Simple Lumped Models in Sec. 10.3.1). If a device is to be mounted directly on the skin, it must be of low weight (e.g., <3 g) and possess a comparatively large attachment area (e.g., >S cm ), in order for vibration to be recorded without attenuation of the motion at 80 Hz. An upper frequency limit of 200 Hz is theoretically achievable (—3dB) with a transducer and skin mount weighing 3 g and an attachment area of 1.8 cm. ... 

The resolution of this spectrometer is not high, but the spectrometer is of relatively low cost and fast it collects a full spectmm of the investigated substance in about 0.3 sec. In the spectrometer (also called quadrupole filter), there appears an electromagnetic field that causes the oscillation of ions. At given voltages, the oscillation amplitude of ions under a certain mass is larger than the distance between one of the pairs of electrodes such ions are thrown out of the filter. Only the ions of a determined mass pass through the filter to the detector. 

One may view the quadrupole filter s action as a combination of a low-pass and a high-pass filter for masses, i.e. a band-pass filter, as indicated in the bottom part of Figure 13.10. The transmission centre of the mass band-pass can be adjusted either by altering the modulation frequency, or by adjusting U and Vrf together, with their ratio at a constant value. 

An electrochemical probe can be used to measure the shear forces at the surface of a membrane in the presence of bubbles. The system consists of a cathode that is mounted flush to the outside of a Teflon tube as a test fiber and a reference anode. The cathode is called the shear probe and is generally made of platinum wire (0.5 mm diameter) which protrudes onto a test fiber. The electrochemical reaction between cathode and anode is provided under the influence of a constant electric potential of 250 mV. The obtained signal in voltage drop is then conditioned through an amplifier and low-pass filter. The relationship between mass transfer at the probe and the limiting diffusion current is used to convert the voltage values into shear forces [77, 78]. 

For a sinusoidal motion of arbitrary frequency / = ojI2ti, the modulus of this complex function represents the amplitude relation between the mass relative motion z t) and the ground acceleration u t), and its phase is the relative phase between them. Both are plotted in Fig. 3 as functions of frequency. The amplitude response is flat for acceleration up to the comer frequency/o and decays at higher frequencies as/ The frequencies of interest are usually in the flat zone, so the instmmental correction for amplitude is simply a constant factor. Observe, nevertheless, that the phase response deviates from flatness even for frequencies well under the natural frequency. This response function is formally like the response of a second-order low-pass filter with cutoff frequency/o = (0(J2n. 

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