Reciprocal invisibility cloaking with self-collimation effect of phononic crystals

In this paper, the combination of self-collimation property and the existence of band gap in two-dimensional phononic crystals are used to design the cloak and change the direction of waves for that the waves do not collide with the object. Because the waves do not hit the object, the performance of structure will not have any dependence on the shape of the hidden object. The operating fRequency for the structure is chosen as 3 kHz, which is part of the human audio frequency and can be used for sound insulation. To prove the invisibility, the pressure of the reflected waves, the waves reaching the invisibility area, and the waves reaching the back of the object are calculated. In this way, it is shown that the reflection from the structure is below 0.1 and the intensity of waves reached to the back of the structure is approximately the same as that waves reached there in the absence of the object. An obvious and important feature of this structure is that, if the hidden object is a source producing the same frequency as the external source, this invisibility coating prevents the waves from reaching the detectors. In other words, the sound waves of the person inside the invisibility area will not be detectable by detectors.