Sensitive plane

As McDonald has pointed out, one-dimensional STRAFI images can be obtained using a standard broadband NMR spectrometer and rapid data capture system. The most important technical obstacle to be overcome in configuring a conventional spectrometer for use as a STRAFI system lies in determining the optimum position for imaging. It is necessary to locate a sensitive plane of uniform gradient in the axial (z) direction (parallel to Bq) and uniform field in the orthogonal (xy) plane. The location of the optimum plane is that at which the condition... 

Fig. 5.4. Sketch of the STRAFI principle. The sample is mechanically (arrows) stepped through a sensitive plane perpendicular to the stray field gradient along the z-direction (left). The signal intensity from each consecutive slice forms a projection of the sample (right).

Vollmeke, PreuB, and Steinke 2010). This ensures that the sensitive plane of the sensor also can really rest on the specimen. The metallization (2 //m to 20 fjxa track spacing depending on sensor) consists of MoSi and is covered by a planarized passivation of SiO and SiNy... 

When converted into decibel, the sensitivity of elements should rather stand in the range of +/-3 dB. The time of flight should show very smooth variations corresponding to a mispositioning of the probe or of the active surface, if any. Acceptance criteria depends on the shape of the probe let us just say that for plane probes expected variations should be below... 

This corresponds to the physician s stethoscope case mentioned above, and has been realized [208] by bringing one leg of a resonatmg 33 kHz quartz tiinmg fork close to the surface of a sample, which is being rastered in the x-y plane. As the fork-leg nears the sample, the fork s resonant frequency and therefore its amplitude is changed by interaction with the surface. Since the behaviour of the system appears to be dependent on the gas pressure, it may be assumed that the coupling is due to hydrodynamic mteractions within the fork-air-sample gap. Since the fork tip-sample distance is approximately 200 pm -1.120), tire teclmique is sensitive to the near-field component of the scattered acoustic signal. 1 pm lateral and 10 mn vertical resolutions have been obtained by the SNAM. 

From the early 1980s to present, infrared sensitive two dimensional arrays were mated to integrated circuits for signal processing and sensitivity to better than 0.03 K (see Photodetectors). These focal plane arrays of some 500 by 500 elements eliminate the need for scanning and provide good spatial resolution. Some versions have no special cooling requirements. The development trend is to increase the number of pixels to improve resolution, increase the field of view and keep the size and cost of the optics within acceptable bounds. 

Fig. 7. Fluorescence polarization (FP). (a) The formation of the large FITC—protein A—IgG complex which leads to a net increase in plane polarized light transmitted from the solution. Molecular weights of the protein A-FITC, IgG, and complex are ca 43,000, 150,000, and 343,000, respectively, (b) Detection of IgG by fluorescence polarization immunoassay using A, a laboratory fluorimeter where (O) represents AP = change in polarization, and B, a portable detection unit where (D) is —fiV = change in voltage (27). The field detector proved to be more sensitive than the fluorimeter.

AlGaAs quantum well infrared photodetector (QWIP) focal planes have achieved sufficient sensitivity out to 10-p.m wavelength to result in scene temperature sensitivity of ca 0.2°C when the focal plane is cooled to 77 K. Spectral sensitivity is shown in Eigure 9c and array information is given in Table 1. The supedattice, a newer tool for achieving controlled activation energy, should present many alternative infrared detection techniques. 

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