Distance estimation method measurable from 0m based on standing wave using band-limited sound with uniform amplitude and random phase

In many engineering fields, distance to target is very important information. Typical distance measurement methods use time delay between transmitted and reflected waves, but it is difficult to estimate short distance. On the other hand, a method for measuring short distances using standing wave, which is generated by phase interference of transmitted and reflected waves, is known in the field of microwave radar. We have applied this method to the distance estimation using audible sound and shown the validity in our previous studies. However, the minimum measurable distance depends on the bandwidth of transmitted wave. The shorter distance measurement requires the wider bandwidth of the transmitted wave. In this research, we expand the distance estimation method so as to be able to measure a distance close to 0m without changing the bandwidth of the transmitted wave. We adopt the band-limited noise with uniform amplitude and random phase from 0 to 2π as a transmitted wave, and examine the validity and effectiveness of our method by applying it to an actual sound field.