Acoustic wave manipulation by means of a time delay array

A method of designing or configuring a device for manipulating acoustic waves comprising a plurality of unit cells arranged into one or more layers in which each layer comprises an array of unit cells, at least some unit cells of said plurality of unit cells being configured to introduce time delays to an incident acoustic wave at respective positions of the unit cells within the arrays of unit cells, such that said plurality of unit cells define an array of time delays to thereby define a spatial delay distribution for manipulating an incident acoustic wave to generate an acoustic output, the method comprising:

• determining a quantised delay distribution of a desired analogue acoustic field containing a set of discrete pairs of time delay values and spatial positions representing the distribution of time delays required in the device for generating the desired analogue acoustic field;
• mapping the quantised delay distribution of said desired analogue acoustic field to the positions and time delay values of the unit cells within the device;
• and
• selecting the time delays for the unit cells within the device based on said mapping,
• the method further comprising a step of:
• compressing the quantised delay distribution in the spatial and/or delay domains in order to generate a compressed delay distribution, wherein a resolution of the compressed delay distribution in the spatial and/or delay domains is such that the compressed delay distribution may be mapped directly to the positions and time delays of the unit cells for the device,
• wherein the step of compressing the quantised delay distribution in the spatial and/or delay domains in order to generate the compressed delay distribution comprises decomposing the quantised delay distribution into a sum of two or more terms such that each term of the two or more terms of the decomposed delay distribution may be mapped respectively to two or more layers of unit cells of the device.