Optimal layer sequencing of a multilayered acoustical foam is solved to maximize its sound transmission loss. A foam consisting of air and poroelastic layers can be optimized when a limited amount of a poroelastic material is allowed. By formulating the sound transmission loss maximization problem as a one-dimensional topology optimization problem, optimal layer sequencing and thickness were systematically found for several single and ranges of frequencies. For optimization, the transmission losses of air and poroelastic layers were calculated by the transfer matrix derived from Biot's theory. By interpolating five intrinsic parameters among several poroelastic material parameters, distinct air-poroelastic layer distributions were obtained; no filtering or postprocessing was necessary. The optimized foam layouts by the proposed method were shown to differ depending on the frequency bands of interest.

High-resolution compact radar in high-speed aerial vehicles can be exposed to vibration, and vibration can degrade the phase noise of crystal oscillators and other RF circuits. In this study, a laboratory experiment was conducted similar to the actual operating environment using a coherent frequency synthesizer, superheterodyne receiver realized by commercial RF circuits, an optical delay line with a maximum 20 km range delay, and a vibrator. After applying vibration to the frequency synthesizer, the phase noise was measured at each node of the receiver using a signal source analyzer. Consequently, it was confirmed that the effect of the phase noise suppression function depends on the range delay. The suppression function not only degrades the phase noise by frequency multiplication, but also degrades it by vibration. On the other hand, it has been shown theoretically and experimentally that the lower limit can be suppressed by the suppression function is determined by the higher level of the phase noise generated from the oscillator to the intermediate frequency signal or thermal noise. Finally, a transceiver architecture that has the advantage of suppressing phase noise is proposed for compact radar using high-resolution waveforms.