A method for improving the uniformity and intensity of the electric field induced in an object to be tested illuminated by an incident electromagnetic wave, the object having a given relative permittivity, wherein the method includes: - preparation of the object to be tested, the preparation comprising: • supply of a part having a cavity to house the object and at least one extension element made of a material with a relative permittivity equal to the relative permittivity of the object within +/- 50 %, said at least one extension element partly delimiting the cavity and extending on each side of the cavity along a direction said to be the passage direction of the cavity, over a length which is, on each side of the cavity, equal to at least one third of the length of the cavity along the passage direction; and • placement of the object in the cavity such that the object is in contact with said at least one extension element along the passage direction; • placement of the part in an exposure system having a hollow electrically conducting element made of an electrically conducting material extending along a longitudinal direction and having two electrically conducting portions facing each other in a section plane along a longitudinal direction, the part being placed in the hollow element between the two electrically conducting portions of the hollow element; - application of an incident electric field on the object to be tested by illumination of the object with an incident electromagnetic wave, the direction of the incident electric field of the incident electromagnetic wave being chosen to be identical to the passage direction of the cavity. - preparation of the object to be tested, the preparation comprising: • supply of a part having a cavity to house the object and at least one extension element made of a material with a relative permittivity equal to the relative permittivity of the object within +/- 50 %, said at least one extension element partly delimiting the cavity and extending on each side of the cavity along a direction said to be the passage direction of the cavity, over a length which is, on each side of the cavity, equal to at least one third of the length of the cavity along the passage direction; and • placement of the object in the cavity such that the object is in contact with said at least one extension element along the passage direction; • placement of the part in an exposure system having a hollow electrically conducting element made of an electrically conducting material extending along a longitudinal direction and having two electrically conducting portions facing each other in a section plane along a longitudinal direction, the part being placed in the hollow element between the two electrically conducting portions of the hollow element; • supply of a part having a cavity to house the object and at least one extension element made of a material with a relative permittivity equal to the relative permittivity of the object within +/- 50 %, said at least one extension element partly delimiting the cavity and extending on each side of the cavity along a direction said to be the passage direction of the cavity, over a length which is, on each side of the cavity, equal to at least one third of the length of the cavity along the passage direction; and • placement of the object in the cavity such that the object is in contact with said at least one extension element along the passage direction; • placement of the part in an exposure system having a hollow electrically conducting element made of an electrically conducting material extending along a longitudinal direction and having two electrically conducting portions facing each other in a section plane along a longitudinal direction, the part being placed in the hollow element between the two electrically conducting portions of the hollow element; - application of an incident electric field on the object to be tested by illumination of the object with an incident electromagnetic wave, the direction of the incident electric field of the incident electromagnetic wave being chosen to be identical to the passage direction of the cavity.