Wearable Radar System Design on Semi-Flexible PCB for Visually Impaired People

This paper presents a compact and wearable frequency-modulated continuous-wave (FMCW) radar on a semi-flexible printed circuit board (PCB) for an anti-collision system. This can enable visually impaired people to perceive their environment better and more safely in their everyday lives. In the proposed design, a multiple-input multiple-output (MIMO) antenna array with four receivers (RXs) and three transmitters (TXs) has been designed to achieve obstacle-detection ability in both horizontal and vertical planes through a specific geometrical configuration. Operating at 76–81 GHz, an aperture coupled wide-beam patch antenna with two parasitic patches is proposed for each channel of RXs and TXs. The fast Fourier transform (FFT) algorithm has been implemented in the radar chip AWR1843 for intermediate frequency (IF) signals to generate a range-Doppler map and search precise target angles in high sensitivity. The complete system, which includes both the MIMO antenna array and the radar chip circuit, is utilized on a six-layer semi-flexible PCB to ensure compactness and ease in wearability. Field testing of the complete system has been performed, and an obstacle-detection range of 7 m (for humans) and 19 m (for larger objects) has been obtained. A wide angular detection range of 64-degree broadside view (±32°) has also been achieved. A voice module has also been integrated to deliver the obstacle’s range and angle information to visually impaired persons.

Reliability Analysis of Solder Joints on Rigid-Flexible PCB for MEMS Pressure Sensors Under Combined Temperature Cycle and Vibration Loads with Continuously Monitored Electrical Signals

The reliability of lead-free solder joints on flexible PCB has created significant new challenges in the industry, especially in automotive electronics, and possibly for future wearable electronics.In this paper, the submodeling technique was used to construct the finite element model of the rigid-flexible printed circuit board (rigid-flexible PCB) for a MEMS pressure sensor subjected to combined temperature cycle and random vibration loadings. During all the experiments, the electrical signals of each specimen were continuously monitored using an event detector. One advantage of this method is that any individual soldering interconnect failure will result in the diagnostic signal of the circuit, which could be detected in real time. The influence of vibration frequency and acceleration on the vibration fatigue life of solid joints was investigated.The research results are helpful to effectively characterize the performance of the MEMS sensors under combine thermal cycling test and vibration test. Two kinds of land shapes and two kinds of PCB assemblies were selected. The solder joint is sliced and the crack on the cross section of solder joint was observed. Results of finite element modeling analysis were consistent with the experimental results. Two design parameters have been identified in our research as being important to soldering usage in automotive environments: pad type (teardrop vs. non-teardrop) and pad size (big vs. small, matching size for Cu-wire and pad). Experimental results also showed that the solder joint with big land shape presented a relatively good thermal fatigue resistance.