Quote:
Originally Posted by Xenon  The concept of inversing is explained here on p. 248: "The curse of periodicity", in part: "A QRD needs periodicity to form its optimum diffusion of even energy lobes, yet the periodicity lobes cause uneven scattering."
I learned that techniques of altering symmetrical periodicity in however many arrays, is called " a modulation scheme": "The modulation works best at multiples of the design frequency. Only at these frequencies do the diffuser and its inverse create exactly opposite pressures. At other frequencies, the modulation is likely to help with the scattering as it breaks up periodicity lobes, but in a more uncontrolled manner." (p. 251)
Which implies that you would want to keep the same the design frequency, whatever (inverse/flip/different N-prime) was used, but with the caveat that altering the design frequency will still be effective in the primary goal of breaking up lobes. |
That link is the best one we have for the issue of modulation. (Unfortunately for me, the Google display hides one of the pages right in the middle of the section we're interested - will have to wait for the book, which of course, is the intention of the publishing scheme, and fair enough!)
Anyway, having the same design frequency for both diffusers used in the modulation scheme is only required when the exact inverse is used.
If the second diffuser is not the inverse, but a normal panel of a different order, you will not get the advantage of exactly opposite pressure described in the bold text.
In that case, you may as well allow different frequencies into the mix, giving the ability to match the build depths.
Speaking of matching build depths.....
If you are prepared to do away with zero-depth wells, (meaning no nice half-width ends), you can often find advanced panels that have the same build depth as their inverses.
Examples are N7+4, N11+1, N11+4 (the best of the three N11's), N11+9 etc.
Because the inverses have a smaller build depth than their non-advanced counterparts, you pick up savings in well width.
I see this type of design as the main strength of QRDude.
As far as the modfusers go, I'll leave you and Terry to duke it out - my little brain is liable to explode if I stray too far from the QRD arena...