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Multi-frequency-one-time (MFOT) measurement of bioimpedance spectroscopy (BIS) can greatly reduce measurement time and grasp the transient physiological status of a living body compared with the traditional one-frequency-one-time (OFOT) measurement technology, and a wideband excitation source mixed with multiple frequencies is a crucial part of MFOT measurement of BIS. This communication describes a design of a wideband excitation source. Firstly, a multi-frequency mixed (MFM) signal containing seven primary harmonics is synthesized based on Walsh functions, which is a periodical and rectangular signal and whose 68.9% of the energy is homogeneously distributed on its seven 2nth primary harmonics. Then the MFM signal is generated by a field programmable gate array (FPGA), and a unipolar-to-bipolar convertor (UBC) is designed to convert the unipolar signal into bipolar signal. Finally, the bipolar MFM signal is driven by a voltage-controlled current source (VCCS). A 2R-1C series model is adopted as the load of the VCCS, and the simulated voltage response on the load is obtained based on the theoretical analysis. Experiments show that the practical waveform on the load matches well with the theoretical analysis, which indicates that the VCCS has a good performance on the MFM signal. The design of the wideband excitation source establishes a good foundation for fast measurement of BIS.

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Summary The new flame‐retardant plywood was manufactured by adding expanded vermiculite (EVMT) in the adhesive and by surface treatment as a flame‐retardant coating. The study discussed the effect of EVMT to the limited oxygen index values of samples. The thermal degradation process of plywood samples has been investigated by thermal analysis. The result showed that EVMT increased all the limited oxygen index values of the treated samples and decreased the thermal activation energy at a high degree of degradation. Scanning electron microscope (FEI, Holland, The Netherlands) images showed that EVMT could form a protective coating, which improved the flame retardancy of plywood. Copyright © 2015 John Wiley & Sons, Ltd.