An ultrasonic system for measuring activity
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These results led us to conclude that (i) the method is valid in that it confirmed a known cultural difference in the use of gesture; (ii) it is sensitive, as it discerned an increase in gesture during 7 min of recording when verbal expression was difficult; and (iii) it is both a reliable and practicable method, as level of gesturing was shown to be a stable characteristic of the individual.
There is quite a good definition of movement and the wavelength (8·25 mm at 40 kHz) is comparable with radio-frequency methods using 3500 MHz
More information can be extracted from an experiment by recording the system's output pulses on magnetic tape and producing, via a computer, a time-interval histogram. Using pulse duration as thex scale, the spread of amplitudes will be an indication of the amount of movement at different speeds.
KeywordsUltrasonic activity monitor
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