In noise control, the identification of source velocity field remains an important and open problem. In this way, methods such as Nearfield Acoustical Holography (NAH), Principal Source Projection (PSP), inverse Frequency Response Function method (iFRF) or hybrid NAH have been developed. However, these methods require free field conditions that are often difficult to achieve in practice. In this article, an alternative method, developed in the SILENCE European project framework and called inverse Patch Transfer Functions, is presented to identify source velocities. This method is based on the definition of a virtual cavity, the double measurement of the pressure and particle velocity fields on aperture surfaces of this volume, divided into elementary areas called patches and the inversion of impedances matrices, numerically computed from a modal basis obtained by FEM. Theoretically, the method is applicable to sources with complex 3D geometries and measurements can be carried out in a non-anechoic environment even in the presence of other stationary sources outside the virtual cavity. In the present paper, theoretical background of the iPTF method is exposed and results (numerical and experimental) on a source with simple geometry (two baffled pistons driven in antiphase) are presented and discussed.