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Related Concept Videos

Passive Filters01:27

Passive Filters

Passive filters are utilized to shape the frequency spectrum of signals across a diverse array of applications. These filters, using only passive elements like resistors (R), inductors (L), and capacitors (C), are capable of selectively allowing or blocking certain frequency ranges without the need for external power sources.
Low-Pass Filters
Low-pass filters are designed to transmit signals with frequencies lower than the cutoff frequency, ωc, and attenuate those above it. The cutoff frequency...
Active Filters01:25

Active Filters

Active filters are electronic circuits that use operational amplifiers (op-amps), resistors, and capacitors to filter out unwanted frequency components from a signal. A first-order low-pass active filter is designed to pass signals with a frequency lower than a certain cutoff frequency and attenuate frequencies higher than that cutoff frequency. The transfer function for a first-order low-pass active filter is:
Parallel Resonance01:23

Parallel Resonance

The parallel RLC circuit is an arrangement where the resistor (R), inductor (L), and capacitor (C) are all connected to the same nodes and, as a result, share the same voltage across them. The parallel RLC circuit is analyzed in terms of admittance (Y), which reflects the ease with which current can flow. The admittance is given by:
Standing Waves in a Cavity01:28

Standing Waves in a Cavity

A household microwave and lasers are examples of standing electromagnetic waves in a cavity. When two conducting metal plates are placed parallel at the nodal planes, it creates a cavity where standing waves are formed. The cavity between the two planes is analogous to a stretched string held at the points x = 0 and x = L. Here, the distance 'L' between the two planes must be an integer multiple of half of the wavelength. The wavelengths that satisfy this condition are given by:
Design Example01:23

Design Example

The innovation of touch-tone telephony revolutionized the telecommunications industry by replacing the traditional rotary dial with a dual-tone multi-frequency (DTMF) signaling system. This system uses a matrix-style keypad with buttons arranged in four rows and three columns, creating 12 distinct signals each assigned to a pair of frequencies. Each button press results in a simultaneous generation of two sinusoidal tones – one from a low-frequency group (697 to 941 Hz) and one from a...
Modes of Standing Waves: II01:04

Modes of Standing Waves: II

The starting point for expressing the modes of standing waves is understanding the boundary conditions that the waves must follow. The boundary conditions are derived from the physical understanding of how the standing waves are sustained, that is, how the vibrating particles of the medium behave at the boundaries imposed on them.
For a tube open at one end and closed at the other filled with air, the modes are such that there is always an antinode at the open end and a node at the closed end.

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Related Experiment Video

Updated: May 14, 2026

Terahertz Microfluidic Sensing Using a Parallel-plate Waveguide Sensor
07:28

Terahertz Microfluidic Sensing Using a Parallel-plate Waveguide Sensor

Published on: August 30, 2012

Tunable THz notch filter with a single groove inside parallel-plate waveguides.

Eui Su Lee1, Tae-In Jeon

  • 1Division of Electrical and Electronics Engineering, Korea Maritime University, Busan 606-791, South Korea.

Optics Express
|February 8, 2013
PubMed
Summary

This study presents a tunable terahertz notch filter using a parallel-plate waveguide. Adjusting the air gap tunes the filter

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Terahertz Microfluidic Sensing Using a Parallel-plate Waveguide Sensor
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Design and Characterization Methodology for Efficient Wide Range Tunable MEMS Filters

Published on: February 4, 2018

Area of Science:

  • Terahertz (THz) photonics
  • Waveguide theory
  • Filter design

Background:

  • Parallel-plate waveguides (PPWGs) are fundamental structures in THz applications.
  • Tunable filters are crucial for flexible THz system operation.
  • Notch filters selectively remove specific frequencies.

Purpose of the Study:

  • To develop and characterize a tunable terahertz notch filter based on a single groove in a PPWG.
  • To investigate the relationship between air gap dimensions and the filter's resonant frequency.
  • To explore design parameters for enhancing THz microfluidic sensor sensitivity.

Main Methods:

  • Fabrication of a tunable notch filter using a PPWG with adjustable air gap.
  • Experimental measurement of resonant frequencies by varying the air gap (60–240 μm).
  • Finite-difference time-domain (FDTD) simulations to analyze sensor sensitivity.

Main Results:

  • The tunable notch filter demonstrated a resonant frequency shift from 1.75 to 0.62 THz with air gap changes.
  • Achieved a high tunable sensitivity of 6.28 GHz/μm for the notch filter.
  • FDTD simulations confirmed that smaller air gaps, narrower grooves, and deeper grooves enhance THz microfluidic sensor sensitivity.

Conclusions:

  • A single groove in a PPWG enables effective tuning of terahertz notch filters.
  • The air gap is a critical parameter for controlling the resonant frequency and sensitivity.
  • Optimized groove and air gap dimensions can significantly boost the performance of THz microfluidic sensors.