As a loudspeaker's physical size decreases, its ability to reproduce low frequencies is hindered. In this paper we propose a method of creating virtual bass using an efficient frequency tracking algorithm. The proposed algorithm has low computational complexity but excellent performance. The results of computer simulations and subjective tests are presented to validate the algorithm .

In this paper, a deep neural network (DNN) model is proposed for the behavioral modeling of nonlinear power amplifiers with supply dependency. Although the conventional nonlinear model, such as the Volterra series, has high accuracy, it is not commonly implemented because of its complexity. However, with manageable complexity, the multidimensional input parameters of the proposed model ensure the modeling of the nonlinear behavior of power amplifiers with supply voltage dependency. The proposed model is trained by multi-tone signals on a 10-W power amplifier and validated by comparing the output spectrum and the third-order intermodulation (IMD3) of the model versus the measured data. The output spectrum shows less than 0.38 dB of error over a bandwidth of 10 MHz and input power from 11 dBm to 17 dBm, and the IMD3 error is less than 0.1 dB over the output power range.

This paper presents a free-space measurement method for the dielectric properties of small biological tissues (in this study, micropig skins that are 60 mm × 60 mm in size and 1.4 mm in thickness are used) that do not meet the size requirement of conventional free-space material measurement at W-band (75–110 GHz) frequencies. The first step involved enhancing the material under test (MUT) holder of an existing free-space material measurement system to ensure the reliable measurement of small biological tissues. This enhancement was confirmed by comparing the measured dielectric properties of an air gap with its theoretical properties. The measured dielectric properties of the micropig skins were then validated through a comprehensive comparison using data based on the double Cole-Cole parametric model, which is a widely referenced model in many numerical dosimetry studies. The good agreement between the two results demonstrates the effectiveness of the proposed free-space material measurement method, as well as the reliability of the measured dielectric property of micropig skins.

In this paper, a highly efficient and compact 840 MHz class-F amplifier using E-pHEMT FET is implemented with the minimal footprints, where only the 2^nd and 3^rd harmonics is controlled to obtain the high efficiency within the harmonic control circuit. Compared to the transmission line, the discrete LC network is a more suitable solution to the small-sized implementation when it is carefully designed for the maximum performance. As such, this paper shows that the small-sized class-F PA can equally perform the ones with transmission lines for the harmonic control, and is more suitable for compact sized wireless terminal applications. The implemented power amplifiers have the peak efficiency of 81.2% with output power of 24.4 dBm.