Recently, Li and Xia proposed a physical-layer security design to guarantee a low probability of interception (LPI) for asynchronous cooperative systems without relying on upper-layer data encryption. The proposed scheme utilizes diagonal unitary codes to perform different encoding in the frequency domain over subcarriers within each OFDM block to randomize the transmitted signals. To build on their idea, in this letter, a subcarrier-reference (SR) transmission scheme is proposed with deliberate signal randomization to achieve LPI in multiuser MISO-OFDMA systems. For each user, one of the allocated subcarriers is chosen by the transmitter to send reference signals, and others are chosen to send the user's information symbols. By some deliberate signal randomization, the eavesdropper cannot detect the transmitted symbols, while the authorized users can operate the system successfully without knowledge of the channels by subcarrier-reference demodulation. Extensive simulations are conducted to demonstrate the scheme's effectiveness.

A high energy-efficiency and area-reduction switching scheme for a low-power successive approximation register (SAR) analog-to-digital converter (ADC) is presented. Based on the sequence initialization, monotonic capacitor switching procedure and multiple reference voltages, the average switching energy and total capacitance of the proposed scheme are reduced by 99.4% and 87.5% respectively, compared to the conventional architecture.

According to a new kind of permanent contactor, this paper analyses the dynamic behavior of the contactor with and without current-feedback system. And it presents a method to obtain the dynamic characteristics of the contactor with current-feedback system. The experiments prove that the method is correct. Then, it compares the contactor without current-feedback system with the one with current-feedback system. The result shows that the contactor with current-feedback system can avoid this flaw of the contactor without current-feedback system.

This paper simulates the dynamic behavior of the operating mechanism of ACB, and analyzes factors influencing the mechanism's operating time. First, it builds a dynamic model for the mechanism with virtual prototype technology. Experiment validation is carried out to prove the correctness of the model. Based on this model, it puts emphasis on analyzing the influence of electro-dynamic repulsion force on the operating time of the mechanism. Simulation and experimental results show that after adding electric repulsion force to the model, the operating time is shortened about 1.1 ms. Besides the repulsion force, other influencing factors including the stiffness of opening spring, locations of every key axis, mass and centroidal coordinates of every mechanical part are analyzed as well. Finally, it makes an optimum design for the mechanism. After optimization, the velocity of operating mechanism is improved about 6.7%.

Similarities and differences of the thermal analysis issues between the intelligent and general AC contactors are analyzed. Heat source model of the magnet system is established according to the unique control mode of the intelligent AC contactor. Linking with the features common of the two kinds of contactors, the extension of the thermal analysis method of the general AC contactor to the intelligent AC contactor is demonstrated. Consequently, a comprehensive thermal analysis model considering heat sources of both main circuit and magnet system is constructed for the intelligent AC contactor. With this model, the steady-state temperature rise of the intelligent AC contactor is calculated and compared with the measurements of an actual intelligent AC contactor.

In the optimum design of AC contactors, it is important to analyze the dynamic behavior. Moreover, movable contact and core bounces have remarkable effect on the lifetime of contactors. According to a new kind of contactor with feedback controlled magnet system, this paper builds two different sets of periodically inter-transferred equations to obtain the dynamic characteristics of the contactor. The equations describe the coupling of the electric circuit, electromagnetic field and mechanical system taking account of the influence of friction. Then, the paper gives an optimum design to the dimension and the duty ratio of the contactor' pulse modulated wave (PWM) under different exciting, and proves, by experiment and simulation, that the bounce time of the contactor working in the optimized duty ratio is much less than that of the general AC contactors.