Multiple-frequency Continuous Wave Research Articles

A Broadband MFCW Agile Radar Concept for Vital-Sign Detection Under Various Thoracic Movements

A multiple-frequency continuous-wave (MFCW) agile radar system has the ability to cope with various physiological conditions of a human subject. Following the mathematic model, a favorable carrier frequency for detection is pursued by analyzing the amplitude and composition of the baseband signal. In Experiment-1, a CMOS dual-band transceiver prototype emulate searching a subject from a distance. The frequencies of the dual-band system are 4.26–4.95 GHz and 17.06–19.79 GHz. During the experiment, the respiratory signal could be detected up to 12 m, and the heartbeat signal up to 6 m. Even with a wooden or a brick barrier in the path, the vital-sign detection remained satisfactory. Later, a concurrent MFCW detection is performed in Experiment-2 for more precise analyses. From the concurrent results, the breathing status can be inferred, and by cross-correlating the results after the ensemble empirical mode decomposition (EEMD) and principal component analysis (PCA), the nonlinear effects of respiratory harmonics or intermodulation tones are reduced, resulting in an accurate heart rate extraction. The receiver front-end and the signal source are manufactured using a 180-nm CMOS process, both packaged on an RO4003C printed-circuit board (PCB).

Phase-Extraction Method With Multiple Frequencies of FMCW Radar for Human Body Motion Tracking

A phase-extraction technique with multiple frequencies of a frequency-modulated continuous-wave (FMCW) radar is proposed, which allows the detection of target motions exactly. An FMCW chirp signal is decomposed into multiple-frequency continuous-wave (CW) signals to extract modulated phases due to target motions. The demodulated phases at multiple frequencies are summed and averaged. Since the proposed method can extract the phase without performing a fast Fourier transform (FFT), it can overcome the range migration problem, which causes an error in phase extraction using a conventional FFT-based method. Therefore, the proposed method can reduce spurious noises induced by phase errors compared with the conventional method. This was verified experimentally for both human vital sign detection and body motion tracking.

Multiple-Frequency CW Radar and the Array Structure for Uncoupled Angle-Range Indication

The frequency diverse array (FDA) radar has drawn great attention due to its range-, angle-, and time-dependent beampattern. However, the FDA radar suffers ambiguities in determining target locations, i.e., angle and range of targets are coupled. In this letter, we find that the key to decoupling the target location lies in destroying the mutual dependence of angle and range. Hence, the multiple-frequency continuous wave (MFCW) radar is proposed. The range measurement is obtained by transmitting continuous waves with multiple frequencies and separating the multiple echoes by digital mixer in the receiving end. The range information exists in the phase difference among the multiple echoes, and this process can be seen as sampling in range by multiple frequencies. Then, if a receiving array is used for spatial sampling, an angle measurement is obtained and the target location is decoupled. Four modes of the MFCW radar are derived and the reason for the uncoupled angle-range indication in the beampattern is analyzed in detail. The effectiveness of the proposed scheme is verified by simulation results.

A novel ultrasonic ranging method used for single station indoor GPS

Indoor GPS is one of the most popular positioning systems own to its high accuracy, real-time characteristics and multi-task management. In order to simplify the calibration process and extend its application, a single station model was presented recently. This paper proposes a novel ultrasonic ranging method used for the single station model. The traditional high-accuracy ultrasonic ranging method mainly uses a phase detection method by transmitting a multiple-frequency continuous wave. However, this method requires high accuracy of the phase detector and is still limited to small-scale application as a result of applying a continuous wave. Based on the constant time difference between the corresponding zero-cross points, this paper proposes a novel two-frequency pulse wave method, which can estimate the time of flight using the time differences between two received waves. Then a least squares estimation is used to eliminate random errors. Finally, an ultrasonic ranging experiment was conducted to validate its feasibility and stability.

Multiple-frequency ultrasonic distance measurement using direct digital frequency synthesizers

In this article, an improved algorithm for multiple-frequency continuous wave (MFCW) ultrasonic distance measurement is presented. Currently, MFCW method can evaluate target distance with high resolution. This method is based on phase difference detection. It therefore avoids the traditional acoustic attenuation problems that have limited time-of-flight (TOF) methods. Previous studies used divider algorithms to generate the required multiple frequencies for the MFCW method. However, divider algorithms are limited by low frequency resolution. This limitation results in the MFCW method’s restricted measurement range and frequency shift issues. This study proposes the direct digital frequency synthesizers (DDFSs) algorithm to accurately generate multiple frequencies for MFCW distance measurement. The advantages of the DDFS include fast switching times, smooth frequency transitions, and fine frequency steps. In addition, the DDFS algorithm is easily programmed into complex programmable logic devices (CPLDs) and other microprocessors. These devices are commonly used in ultrasonic distance measurements. Experimental results indicate that when measuring the range from 50 mm to 3000 mm, with temperature and humidity compensation, the combined standard uncertainty of the distance measurement is approximately 0.26 mm. Furthermore, the algorithm is simple to use and can easily be adapted for use with other microprocessors. The main advantages of this distance measurement are high accuracy, increased range and ease of implementation.

High-Resolution Estimation of Ranges Using Multiple-Frequency CW Radar

The problem of ranging multiple vehicles traveling at similar speeds using multiple-frequency continuous-wave (CW) radar is considered. A new method based on the compensation of vehicle movement and MUSIC-based time delay estimator is presented. The method is tested using a commercially available multiple-frequency CW radar sensor in real traffic situations. Test results show that the proposed method makes it possible to estimate the positions of two vehicles moving at similar speeds. Test results also demonstrate that under a given bandwidth, the multiple-frequency CW radar can provide about ten times higher resolution as compared with the coherent spread spectrum radar

X-band Gunn diode oscillator for a multiple-frequency continuous-wave radar for educational purposes

A low-cost, high-performance X-band Gunn diode oscillator for educational and research purposes has been developed. The cavities have been manufactured on a standard WR90 rectangular waveguide with UBR100 flange in order to make it compatible with the waveguide circuitry usually available in a basic microwave laboratory. The capability of sweeping the whole X band at constant output power and low phase noise, as well as the low cost of its components, make this device suitable for users at any level. As an example of its many educational applications, a multiple frequency continuous-wave (MFCW) radar has been developed, and the results of the laboratory implementation are shown.

Multiple-frequency continuous wave ultrasonic system for accurate distance measurement

A highly accurate multiple-frequency continuous wave ultrasonic range-measuring system for use in air is described. The proposed system uses a method heretofore applied to radio frequency distance measurement but not to air-based ultrasonic systems. The method presented here is based upon the comparative phase shifts generated by three continuous ultrasonic waves of different but closely spaced frequencies. In the test embodiment to confirm concept feasibility, two low cost 40 kHz ultrasonic transducers are set face to face and used to transmit and receive ultrasound. Individual frequencies are transmitted serially, each generating its own phase shift. For any given frequency, the transmitter/receiver distance modulates the phase shift between the transmitted and received signals. Comparison of the phase shifts allows a highly accurate evaluation of target distance. A single-chip microcomputer-based multiple-frequency continuous wave generator and phase detector was designed to record and compute the phase shift information and the resulting distance, which is then sent to either a LCD or a PC. The PC is necessary only for calibration of the system, which can be run independently after calibration. Experiments were conducted to test the performance of the whole system. Experimentally, ranging accuracy was found to be within ±0.05 mm, with a range of over 1.5 m. The main advantages of this ultrasonic range measurement system are high resolution, low cost, narrow bandwidth requirements, and ease of implementation.