SOUND WAVE AND MICROWAVE SPAC£ PATTERNS 



569 



strate refraction in its simplest form. One sees, along with the downward 

 beam tilt, a dissymmetry of the minor lobe structure, the upper lobe being 

 quite pronounced. 



Addition or Phase 



From this point on, the portrayal of phase will be added to most of the 

 photographs. This is accomplished by combining, with the signal picked up 

 by the probe microphone, a constant-phase constant-amplitude signal from 

 the oscillator feeding the source loud speaker. As the probe moves away 



Fig. 7 — Increasing the sound intensity in Fig. 6 brings 

 out the details of the minor lobes. / = 9 KC. 



from the loud speaker and lens combination, the phase of the microphone 

 signal varies with respect to the constant signal from the oscillator. Con- 

 structive and destructive interference results and pictures such as shown in 

 Fig. 6 are obtained. This is a pattern for a progressive sound wave (not a 

 standing wave) emerging from the strip lens; it is, in fact, the same pattern 

 as that of Fig. 3 except that phase has been added and the signal intensity 

 reduced somewhat. The curved wave fronts converging towards the brighter 

 focal spot are evident and as the sound energ>' progresses through the focal 

 point the wave fronts become concave outward. Figure 7 shows a similar 

 pattern but with the intensity of the signal increased. This procedure brings 

 up the intensity of the weaker field and shows more clearly the minor lobe 



