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The vibration and rotation energy levels of many molecules are in the terahertz (THz) band, so THz spectroscopy can be used to qualitatively identify substances. However, the terahertz spectrum of most molecules in aqueous solution is completely different from that of solid molecules, and they have strong absorption characteristics for terahertz waves. Therefore, how to reduce the absorption of water for THz wave has become an urgent problem to be solved. Food additives are our daily necessities. They can extend the shelf life of food. In this study, a microfluidic chip with very low THz wave absorption was designed, and the THz transmission spectra of food-additive sodium hexametaphosphate solution and sodium pyrophosphate solution were measured using THz time domain spectroscopy (THz-TDS) system. The experimental results show that the THz spectral intensity of the two sodium salt solutions increases with the increase of solution concentration, which is completely contrary to the phenomenon of common sodium salts, such as sodium chloride. It shows that the process of ion hydration affects the hydrogen bond between water molecules and changes the absorption of THz waves by water. This method lays a foundation for further study of the THz characteristics of electrolyte solutions.

The bandwidth of very high gain (≥100 MV/A) transimpedance amplifiers is restricted to below 100 kHz, unless measures are employed to mitigate the effect of circuit parasitic capacitances. Current approaches involve significantly increased circuit complexity and component count. They may suffer unwanted noise pickup or destructive capacitive coupling to ground, the latter restricting the available bandwidth. We demonstrate that combining a positive feedback circuit with a low-pass filter network extends the bandwidth of a transimpedance amplifier out to the limit of gain peaking (>1 MHz) without increasing the noise signal. The circuit uses a single inverting amplifier and very large feedback-resistance to provide a canceling parasitic-capacitance positive feedback signal. This can negate both the negative feedback-resistor parasitic-capacitance and the input/output pin parasitic-capacitance of the transimpedance amplifier. The circuit solves the problem of destructive distributed-capacitive coupling to ground along the feedback resistor.

Phase-changing materials (PCMs) are widely used thermal-energy-storage substances that utilize the absorption and emission of heat during the solid–liquid–solid phase change of a substance to store and release thermal energy, which is closely related to their structural properties. This paper combines THz technology with microfluidic technology to investigate the THz spectral properties of phase-changing thermoregulated emulsions and the results show that: with the increase of the applied magnetic field strength, more molecules are magnetized and arranged with orientation, and the transmission intensity of THz increases; with the increase of the applied electric field strength, the bond length of covalent bonds becomes larger, and the transmission intensity of THz increases; during the cooling process, the free energy of molecules decreases, and the transmission intensity of THz increases. The results provide technical and data support for the in-depth study of phase-changing thermoregulated emulsions, which is important for the fine study and improvement of properties in different environments in aerospace and coating fields.