Enhanced electromagnetic pressure in a sandwiched reflection grating

We suggest that strongly enhanced electromagnetic pressure can be induced at the boundary of a sandwiched reflection grating due to a special kind of deep subwavelength Fabry-Perot (FP)-like resonance. A theoretical formula will be derived and employed to study this effect at both the infrared and microwave regimes. The magnitude or sign of the electromagnetic force can be tuned by adjusting the system parameters, which in turn adjust the balance between the electric and magnetic energies stored in the system. In the infrared regime, a strong attractive pressure was found, which is controllable by the FP cavity length. In the microwave band, a repulsive pressure can be realized in most situations. What is rather amazing is that a strong attractive electromagnetic pressure, which has not been found previously, can also be demonstrated in some geometries in the microwave regime.