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In this work, some analyses of a generalized expression of the thermo-acoustic (TA) emission are carried out. The results of the study clearly show that a wideband flat amplitude-frequency response mostly in ultrasonic region exists for TA emission from not only porous silicon (PS) but any solid, and the fully thermal-mechanical coupling and effective thermal-wave penetration depth should be taken into account for the calculation of its signal magnitude and frequency range. Problems occurring in Nature paper on the thermally induced ultrasonic emission from PS are also pointed out and discussed. Besides, the performance evaluation techniques for both TA material and its backing are presented.