The 2D focusing can drastically improve the efficiency of particle enrichment systems, but it has not been widely used due to the complexity of the required 2D focusing equipment. The conventional 2D focusing equipment includes two independent vibration systems operating at different frequencies. In contrast, a method is proposed here that can perform 2D focusing by simply exciting the PZT at dual frequencies simultaneously. This is done using a single vibration system and inputting the pre-combined signals to a high-frequency power amplifier. First, the 2D focusing of 50-µm microparticles was experimentally confirmed in a rectangular microchannel with the aspect ratio of 2. Next, the excitation signals and the vibration state in 2D focusing were analyzed in the time domain and the frequency domain. Then, a numerical simulation was done that reproduced the 2D focusing by superposition of horizontal and vertical focusing. It was also confirmed that the 2D focusing drastically improved the enrichment factor, making it equal to that of the conventional 2D focusing. Then, 2D focusing of various-sized microparticles were attempted experimentally and numerically. Finally, the 2D focusing was confirmed in the rectangular microchannels with different aspect ratios of 1.3 and 2.6. The results suggested the 2D focusing method was applicable for wide-ranging sizes of microparticles regardless of the aspect ratio. It was concluded that the method could be easily applied to most conventional acoustic systems and it was able to improve their efficiency.