Improvement of contrast of Terahertz Images of a Terahertz Chemical Microscopy using Adaptive Digital Filter

Terahertz imaging technique for monitoring the flow of buffer solutions at different pH values through a microfluidic chip

“…For this purpose, a laser scanned area of 10 mm × 10 mm was programmed in LabVIEW ® to average the lock-in-obtained data over the total measurement time. 28) The characteristic curve indicates the peak values of the THz data, which increased monotonically with the increase in the pH concentration. The negative value of pH = 1.68 in Fig.…”

“…The output of the laser system was 790 W with a repetition rate of 82 MHz. 27,28) We set up a digital pressure machine (DPM) connected to the two inlet wells of the MC via two syringe-connected tubes to allow the flow of BSs with different pH values. The mixed pH solutions, such as pH 4, 1.68, 6.86, and 10, were flushed out naturally and sent to a beaker using another tube from the outlet well.…”

“…We used a chopper (the frequency of the chopper for our system was 2 kHz to synchronize the THz data) in the lock-in technique for reducing the noise from the THz signal data. 27,28) Further, to improve the contrast of the THz images and to sample the THz signal data in a compatible manner based on the Nyquist sampling theorem, an adaptive digital filter 28) and an analog-to-digital converter were used by applying a two-stage time delay controlling mechanism 28) in LabVIEW ® . The THz signaling system provides results in the form of a signal flow graph, as shown in Fig.…”

“…From the experimental average raw data 28) of the contour images of THz, the averaged data of the THz amplitudes as a function of the pH value are plotted in Fig. 8.…”