A method of identifying articles, each of which has a data carrier that includes identifying data of the article, the data carriers having an operation frequency, provides a robust electromagnetic (EM) field within an enclosure in which the articles are stored, even when the natural resonance frequency of the enclosure differs from the operation frequency of the data carriers. In one case data carriers comprise, RFID tags. The EM energy at the operation frequency that is injected into the enclosure to form the robust EM field is injected at a selected location in the enclosure so that the reflected phase of the EM energy from enclosure walls equals the location of injection thereby producing a robust EM field to activate and/or detect data carriers. Active impedance matching is also provided.