A method for testing a structure, the method comprising: detecting a plurality of waves propagating in the structure at a number of transducers operatively coupled to the structure, each transducer unit in the number of transducers comprising a first segment configured to generate a first electrical signal in response to detecting the plurality of waves and a second segment configured to generate a second electrical signal in response to detecting the plurality of waves propagating in the structure, wherein the first segment has a center and is symmetric about two axes in a direction of wave propagation, and the second segment has the center and is symmetric about the two axes in the direction of the wave propagation; and processing the first electrical signal and the second electrical signal to form a result, wherein said step of processing comprises: forming a measured signal matrix using the first electrical signal and the second electrical signal; forming a scaling factor matrix, wherein the scaling factor matrix comprises a number of scaling factor values; and identifying a common factor matrix by pre-multiplying a pseudo-inverse of the scaling factor matrix with the measured signal matrix; wherein the plurality of waves is a first plurality of waves, wherein the first plurality of waves is propagated in the structure when the number of transducers is a first distance apart, wherein the number of scaling factor values is obtained using a second plurality of waves, wherein the second plurality of waves is detected when the number of transducers is at a second distance apart, wherein the plurality of waves comprises a plurality of modes, and wherein the common factor matrix comprises a number of Lamb modes in the plurality of modes. detecting a plurality of waves propagating in the structure at a number of transducers operatively coupled to the structure, each transducer unit in the number of transducers comprising a first segment configured to generate a first electrical signal in response to detecting the plurality of waves and a second segment configured to generate a second electrical signal in response to detecting the plurality of waves propagating in the structure, wherein the first segment has a center and is symmetric about two axes in a direction of wave propagation, and the second segment has the center and is symmetric about the two axes in the direction of the wave propagation; and processing the first electrical signal and the second electrical signal to form a result, wherein said step of processing comprises: forming a measured signal matrix using the first electrical signal and the second electrical signal; forming a scaling factor matrix, wherein the scaling factor matrix comprises a number of scaling factor values; and identifying a common factor matrix by pre-multiplying a pseudo-inverse of the scaling factor matrix with the measured signal matrix; forming a measured signal matrix using the first electrical signal and the second electrical signal; forming a scaling factor matrix, wherein the scaling factor matrix comprises a number of scaling factor values; and identifying a common factor matrix by pre-multiplying a pseudo-inverse of the scaling factor matrix with the measured signal matrix; wherein the plurality of waves is a first plurality of waves, wherein the first plurality of waves is propagated in the structure when the number of transducers is a first distance apart, wherein the number of scaling factor values is obtained using a second plurality of waves, wherein the second plurality of waves is detected when the number of transducers is at a second distance apart, wherein the plurality of waves comprises a plurality of modes, and wherein the common factor matrix comprises a number of Lamb modes in the plurality of modes. <EOS>