Multi-channel Signal Generator Research Articles

Photonics-enabled distributed MIMO radar for high-resolution 3D imaging

Three-dimensional (3D) imaging radar is an advanced sensor applied in space surveillance and target recognition for supplying 3D geometric features and supporting visualization. However, high 3D resolution requires both broadband operation and a large 2D aperture, which are difficult and complex for conventional radars. This paper presents a photonics-enabled distributed multiple-input and multiple-output (MIMO) radar with a centralized architecture. By use of photonic multi-dimensional multiplexing, multi-channel signal generation and reception are implemented on a shared reference signal in a central office, enabling a highly coherent network with a simple structure. Additionally, a sparse array and a synthetic aperture are combined to efficiently reduce the required transceivers, further weakening the dilemma between system complexity and angular resolution. A 4 × 4 MIMO radar is established and evaluated in field tests. A high-resolution 3D image of a non-cooperative aircraft is obtained, in which rich details are displayed. From a comparison with electronics-based radar, significant resolution improvement is observed. The results verify the superior imaging capability and practicability of the proposed radar and its great potential to outperform conventional technologies in target classification and recognition applications.

Design of A Multifunctional Micro-Magnetic Testing Instrument

Micro-magnetic testing technology is capable of non-destructively evaluating the mechanical properties and residual stress in ferromagnetic components. In the applications of micro-magnetic testing technology, several types of magnetic signals, such as magnetic Barkhausen noise, incremental permeability, tangential magnetic field and eddy current, etc., are used to characterize the target properties (mechanical properties and residual stress). In this paper, a unique framework for multifunctional micro-magnetic sensor design is proposed. Accordingly, a multifunctional micro-magnetic instrument is developed. Intermittently superimposed magnetic fields of high (several kHz) and low frequencies (several Hz) are used for material magnetization. Combined magnetic sensors are employed to measure a total of five types of signals, including the magnetic Barkhausen noise, incremental permeability, eddy currents, tangential magnetic field and main flux. Especially, twisted-pair wiring was used for winding two identical sensing coils. One of the sensing coils is used for eddy current or incremental permeability detection and the rest one acts as a compensatory coil to suppress the strong mutual induction voltage in detection coil. The entire instrument is composed of a multi-channel signal generator, a power amplifier, signal processing circuits embedded into the multifunctional sensor and a four-channel signal acquisition device. The multi-channel signal generator is constructed based on FPGA and high speed D/A converters. The direct digital synthesizer and state machine are programed in FPGA to enable the excitation of intermittently superimposed signals of high and low frequencies. Carefully experiments were performed to test the performances of the developed instrument. The results obtained from different types of steels proved that the developed instrument can acquire five types of magnetic signals with high SNR. The features of the five types of magnetic signals can used to distinguish the material and its mechanical properties such as surface hardness.

Multi-channel drive system of phased array based on DDS chips

Ultrasonic phased array focusing transducer has the advantages of adjustable focusing and achieving transcranial focusing. A multi-channel high-precision phase control drive system is one of the key technologies that determine whether it can be used in clinical practice. This paper proposes a design scheme of a phased array drive system based on direct digital synthesizer (DDS) chips. The scheme not only realizes the high-precision phase-controlled output of sine wave and square wave but also in the technical implementation, one electronic channel can be increased with only one main controller general-purpose input/output (GPIO) consumed. This means that the expansion of the number of channels much easier, solving the problem of complicated control circuit caused by the array with dense elements and large aperture. Based on the proposed scheme, a 49-channel array drive system with a phase resolution of 12-bit was fabricated using a microcontroller unit (MCU) as the main control chip. The circuit board test and ultrasonic focusing experiment results show that the phase control error of the multi-channel signal generation board is less than 0.2 degree. And the results of acoustic field distribution obtained by experimental measurement are very similar to those obtained by theoretical simulation, which indicates that the frequency and phase of the output waveform of the array drive system are stable. The design method can provide a reference value for the design of the drive system of phased array transducer with different numbers of elements.

Hierarchical model of information signals formation at the physical layer in FANET

Creation of reliable and efficient flying ad-hoc networks (FANET) requires detailed development of the model of the physical layer of data transmission, determined by the conditions of operation of the networks. The problems of well-known software simulators of communication networks are the simplified nature of the physical layer, as well as the inability to obtain specific analytical solutions in the process of simulation. The hierarchical model of formation of information signals which allows to represent various types of communication channels and the channel-forming equipment, for providing their analytical description and the further analysis is developed. The model allows to describe communication channels between UAVs and (or) ground control centers taking into account the effects of attenuation, intersymbol interference, multipath propagation of signals; schemes of terminal and intermediate network equipment with linear and nonlinear signal conversion; circuits with forward regulation, backward regulation and combined regulation; circuits with multi-channel signal generation and processing, as well as cross-links between channels. Analytical expressions of the transfer function of the generalized hierarchical model for an arbitrary number of disclosed levels of hierarchy are obtained. An example of the presentation and study of the UAV transmitter circuit on the basis of a hierarchical model of signal formation is considered.

끊김 없는 화면 전환이 가능한 UHD 다채널 신호 재생 시스템 설계 및 구현

UHD(Ultra High Definition)급 초고선명 영상을 지원하는 다중 채널 신호 재생 시스템은 다양한 콘텐츠를 다루는 방송 서비스 분야에서 필수적이다. 다중채널 신호 재생 시스템은 단순히 복수 개의 단일 신호 재생 시스템과 하나의 매트릭스 스위처를 연동하여 구성할 수 있다. 그러나 이러한 연동 시스템은 구성이 간단하다는 장점이 있지만, 신호 재생 시스템과 매트릭스 스위처 간 영상 신호 처리를 위하여 채널당 9 Gbps 이상의 데이터 전송률이 요구되어 기기간 연결 케이블 품질에 따른 화면 출력 문제를 야기할 뿐만 아니라, 비 동기적 다중 입력 신호에 대한 매트릭스 스위처 화면전환 때 불안정한 신호 출력으로 인한 화면 끊김 문제를 초래할 수 있다. 본 논문에서는 다수의 신호재생 시스템을 독립 동작이 가능 하도록 모듈화 하고, 매트릭스 스위처는 고속 비디오 처리가 가능한 FPGA(Field Programmable Gate Array) 단일 칩으로 설계 하여 이를 결합한 다중 채널 신호 재생 시스템을 구현하였다. 본 시스템은 신호재생 모듈에서 중복 컬러 데이터가 제거된 영상 데이터를 매트릭스 스위처로 전송하고 최종 화면 출력 부분에서 제거된 컬러 데이터를 추가 시켜 줌으로서 기존 시스템에 비하여 영상 데이터 전송률을 40% 줄일 수 있으며, 메모리 사용량은 25% 줄일 수 있었다. 화면 출력부분 매트릭스 스위처에서는 입력/출력 분리 설계를 통해 화면 전환 시에도 출력 신호가 끊김 없이 유지될 수 있도록 하였다. 실험을 통해 제안 시스템이 다양한 종류의 UHD 영상을 서로 다른 4개의 출력 포트로 다양하게 실시간 전송할 수 있고, 끊김 없는 (Seamless) 화면 전환이 가능함을 보았다.

Phased arrays of ultrasound emitters controlled by binary signals for acoustic levitation

A phased array of ultrasonic emitters for acoustic levitation has been developed. The array is controlled by a multichannel signal generator. The generator allows you to create 64 channels of independent signals with controlled phase. The possibility of connecting of 4 arrays of emitters, each of the 320 elements. The possibility of providing levitation of foam particles in the field of two oppositely directed arrays was experimentally shown.

Photonics-based MIMO radar with high-resolution and fast detection capability

A photonics-based multiple-input-multiple-output (MIMO) radar is proposed and demonstrated based on wavelength-division-multiplexed broadband microwave photonic signal generation and processing. The proposed radar has a large operation bandwidth, which helps to achieve an ultra-high range resolution. Compared with a monostatic radar, improved radar performance and extended radar applications originated from the MIMO architecture can be achieved. In addition, low-speed electronics with real-time signal processing capability is feasible. A photonics-based 2 × 2 MIMO radar is established with a 4-GHz bandwidth in each transmitter and a sampling rate of 100 MSa/s in the receiver. Performance of the photonics-based multi-channel signal generation and processing is evaluated, and an experiment for direction of arrival (DOA) estimation and target positioning is demonstrated, through which the feasibility of the proposed radar system can be verified.

The effect of alternating current stimulation on the esophageal motility of rabbits

Objective To observe the effect of electrical stimulation on the movement of rabbits esophagus, and to promote effective esophageal peristalsis and determine the best electrical pacing parameters. Methods After anesthesia, 24 healthy rabbits underwent open surgery and the lower esophagus was exposed. The esophagus was stimulated with the multi-channel signal generator, and the changes of esophagus pressure and the length of esophageal contraction with high resolution manometry were recorded.(1) The effects on contraction pressure of esophagus body and lower esophageal sphincter (LES) after single site electrical stimulation under different parameters were observed.The stimulation modes utilized were electric current 3 mA, 5 mA and 8 mA, frequency 5 Hz, 10 Hz and 20 Hz, pulsewidth 0.25 ms, 25 ms and 50 ms, waveform of single phase and double phase.(2)The esophagus was sequentially stimulated. The stimulation mode utilized was electric current 5 mA, frequency 20 Hz, pulsewidth 25 ms, stimulation duration 3 s, single phase square wave. Results At electrical stimulation on the esophagus body and LES, contraction delay was 13.00±1.54 ms and 12.00±0.73 ms respectively. The contraction pressure of esophageal body was significantly positively related tothe electric current (R=0.968, P<0.01), the pulse width(R=0.971, P<0.01), and the frequency (R=0.947, P<0.01). The length of contraction in 10 Hz group was shorter than that of the 20 Hz group(1.33±0.06 cm VS 1.80±0.00 cm, P<0.05). The contraction pressure of LES was also significantly positively related to the electric current(R=0.965, P<0.01), the pulse width (R=0.973, P<0.01), and the frequency (R=0.842, P<0.01). The pressure of lower esophageal sphincter of single phase square wave was greater than that of the double phase square group (P<0.05). Under the same parameters, the contraction pressure of LES group was lower than that of the esophageal body group (27.33±1.15 mmHg VS 104.00±6.00 mmHg, P<0.05). Esophageal sequential contraction was induced by multi-points sequential electrical stimulation. Conclusion Single point electric stimulation can cause esophageal contraction immediately without obvious delay. Within a certain range, the esophageal contraction pressure is positively correlated with electric current, frequency and pulse width. The contraction pressure of single square phase wave is greater than that of the double square phase wave. The contraction pressure of esophageal body is greater than that of LES after electric stimulation. Multi-points sequential electrical stimulation can promote sequential movement of esophagus. Key words: Electrostimulation; Achalasia; Gastroesophageal reflux; High resolution manometry; Low esophageal sphincter

Real-Time Simulation of VLF Atmospheric Noise for Use in the Calibration and Characterization of LORAN-C Receivers for Aircraft Navigation

This paper describes a real-time simulation technique for generating realistic VLF band atmospheric noise. Noise in this band consists of a background Gaussian component plus a non-stationary impulsive component. The simulator implements as a real time simulation the theoretical model described in Feldman[1]. Stored channel simulation using a high performance personal computer (PC ) drives an off the shelf multi-channel signal generator, providing a high degree of sophistication at low cost. The simulator developed at the Volpe National Transportation Center has been used to characterize Loran-C receivers for use in aircraft navigation. Examples of use of the new simulator in the characteriza tion of Loran-C receivers are presented.