Sweep-frequency resonance method

This method has the advantage of producing a quantitative estimate of bond strength in metal-to-metal and metal-to-core structures, as well as 

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One of the oldest and best known ultrasonic testing systems for NDT is the Fokker Bond Tester. This method uses a sweep frequency resonance method of ultrasonic inspection. Some degree of quantitative analysis is claimed with the Fokker Bond Tester in the aircraft industry. 

An alternative method of running an nmr spectrometer is to hold the magnetic field constant and to sweep the transmitter frequency through the resonances. This mode of operation is more like other forms of spectroscopy and gives the same line shapes as sweeping the field (Figure 9-25). 

The diagrams in Fig. 1 lb can be obtained by the so-called frequency-sweep method, where the lateral position and the distance Zc are fixed, while the frequency is varied around (O0. The Zc value corresponds to a given set-point ratio of the amplitude in contact to the free amplitude, rsp=Asp/Af. Depending on the tip-sample interaction, both the amplitude and the phase curve shifts in a certain direction. When the overall force is repulsive, the resonance frequency moves to higher values and results in a positive phase shift A(p=90 °-(p>0, where the phase shift of 90 ° corresponds to the free cantilever oscillations at ks=0 in Eq. 12. When the force is attractive the resonance frequency decreases compared to the free cantilever and Acp becomes negative. The situation in Fig. lib corre-... 

All of the experiments described above were performed by the field-sweep method, in which the radiofrequencies i and a>2 are passed through the spectrum by changing the magnetic field. This method has serious disadvantages when removal of large couplings is required, and, under these conditions, recourse should be had to frequency-sweep experiments. It is also possible to introduce more than one decoupling field and, hence, to effect triple-resonance experiments. 

Nuclear spins with different electronic environments may be brought into resonance by either one of two techniques. In the frequency-sweep method, the spectrum is recorded by sweeping the applied radiation frequency. In the transient-response method, the transient signal for its component frequencies is sorted/transformed after an induction (by pulse(s) of an applied field in terms of angles, e.g. 90° or 180°) of transient response in the system. The transient signal is changed into a normal spectrum by Fourier transformation in the transient-response method, which is used by most modem NMR spectrometers. There are four parameters that define the NMR spectrum ... 

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