Conventional dielectric solid materials, both natural and artificial, lack electromagnetic self-duality and thus require additional coatings to achieve impedance matching with free space. Here, we present a class of dielectric metamaterials that are effectively self-dual and vacuum-like, thereby exhibiting full-polarization omnidirectional impedance matching as an unusual Brewster effect extended across all incident angles and polarizations. With both birefringence and reflection eliminated regardless of wavefront and polarization, such anisotropic metamaterials could establish the electromagnetic equivalence with “stretched free space” in transformation optics, as substantiated through full-wave simulations and microwave experiments. Our findings open a practical pathway for realizing unprecedented polarization-independence and omnidirectional impedance-matching characteristics in pure dielectric solids.

传统的介电固体材料，无论是天然的还是人造的，都缺乏电磁自对偶性，因此需要额外的涂层来实现与自由空间的阻抗匹配。在这里，我们提出了一类介电超材料，它们实际上是自对偶和类真空的，从而表现出全偏振全向阻抗匹配，作为一种不寻常的布鲁斯特效应延伸到所有入射角和偏振。无论波前和偏振如何，双折射和反射都被消除，这种各向异性超材料可以与变换光学中的“拉伸自由空间”建立电磁等效，正如全波模拟和微波实验所证实的那样。我们的研究结果为在纯介电固体中实现前所未有的偏振无关和全向阻抗匹配特性开辟了一条实用途径。