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interdigitalCapacitor

Create basic interdigital capacitor

Description

Use the interdigitalCapacitor object to create an interdigital planar capacitor (IDC). IDCs are used in high frequency applications such as:

  • Receiver circuits where antenna radiators are connected to RF

  • Wireless data communications with RFID

  • Humidity and solution concentration measurements

  • Lab-on-chip devices (LOCs)

Note

This PCB object supports behavioral modeling. For more information, see Behavioral Models. To analyze the behavioral model for a interdigital capacitor, set the Behavioral property in the sparameters function to true or 1

A two-port series IDC with microstrip form feeder lines supports single and multiple dielectrics. It is a coplanar structure consisting of multiple comb electrodes or intersecting fingers with spaces between the fingers. An IDC can have identical port line lengths and widths on either sides.

Creation

Description

example

capacitor = interdigitalCapacitor creates a basic interdigital capacitor. The default property values are for an operating bandwidth of 3.6-4 GHz.

example

capacitor = interdigitalCapacitor(Name=Value) sets Properties using one or more name-value arguments. For example, interdigitalCapacitor(NumFingers=10) creates an interdigital capacitor with 10 fingers. Properties not specified retain their default values.

Properties

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Number of fingers on the capacitor, specified as a positive scalar.

Example: capacitor = interdigitalCapacitor(NumFingers=10)

Data Types: double

Length of the overlapping fingers in meters, specified as a positive scalar.

Example: capacitor = interdigitalCapacitor(FingerLength=0.0217)

Data Types: double

Width of the overlapping fingers in meters, specified as a positive scalar.

Example: capacitor = interdigitalCapacitor(FingerWidth=4.8000e-04)

Data Types: double

Distance between the fingers in meters, specified as a positive scalar.

Example: capacitor = interdigitalCapacitor(FingerSpacing=2.9000e-04)

Data Types: double

Gap between the edges of the fingers in meters, specified as a positive scalar.

Example: capacitor = interdigitalCapacitor(FingerEdgeGap=2.05000e-04)

Data Types: double

Width of the terminals in meters, specified as a positive scalar.

Example: capacitor = interdigitalCapacitor(TerminalStripWidth=4.9000e-04)

Data Types: double

Width of the ports in meters, specified as a positive scalar.

Example: capacitor = interdigitalCapacitor(PortLineWidth=0.0020)

Data Types: double

Length of the ports in meters, specified as a positive scalar.

Example: capacitor = interdigitalCapacitor(PortLineLength=0.0040)

Data Types: double

Height from the capacitor to the ground plane in meters, specified as a positive scalar.

Example: capacitor = interdigitalCapacitor(Height=6.9000e-04)

Data Types: double

Width of the ground plane in meters, specified as a positive scalar.

Example: capacitor = interdigitalCapacitor(GroundPlaneWidth=0.0040)

Example: double

Type of dielectric material used as a substrate, specified as a dielectric object. The default value is a dielectric object with these properties:

  • Name{'Roger'}

  • EpsilonR3.2

  • LossTangent0.0002

  • Thickness0.000787

Example: d = dielectric("FR4"); capacitor = interdigitalCapacitor(Substrate=d)

Data Types: string | char

Type of metal used in the conducting layers, specified as a metal object.

Example: m = metal("PEC"); capacitor =interdigitalCapacitor(Conductor=m)

Data Types: string | char

Object Functions

capacitanceCalculate capacitance
chargeCalculate and plot charge distribution
currentCalculate and plot current distribution
feedCurrentCalculate current at feed port
getZ0Calculate characteristic impedance of transmission line
layoutPlot all metal layers and board shape
meshChange and view mesh properties of metal or dielectric in PCB component
shapesExtract all metal layer shapes of PCB component
showDisplay PCB component structure or PCB shape
sparametersCalculate S-parameters for RF PCB objects

Examples

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Create and view a default interdigital capacitor.

idcapacitor = interdigitalCapacitor
idcapacitor = 
  interdigitalCapacitor with properties:

            NumFingers: 4
          FingerLength: 0.0137
           FingerWidth: 3.1600e-04
         FingerSpacing: 3.0000e-04
         FingerEdgeGap: 3.4100e-04
    TerminalStripWidth: 5.0000e-04
         PortLineWidth: 0.0019
        PortLineLength: 0.0030
                Height: 7.8700e-04
      GroundPlaneWidth: 0.0030
             Substrate: [1x1 dielectric]
             Conductor: [1x1 metal]

show(idcapacitor)

Figure contains an axes object. The axes object with title interdigitalCapacitor element contains 6 objects of type patch, surface. These objects represent Copper, feed, Roger.

Create and view a multilayer interdigital capacitor with two different dielectrics.

idcapacitor = interdigitalCapacitor;
sub = dielectric("FR4","Teflon"); 
sub.Thickness =[0.00003 0.00003];
idcapacitor.Substrate = sub;
idcapacitor.Height = 0.00003;
show(idcapacitor);

Figure contains an axes object. The axes object with title interdigitalCapacitor element contains 7 objects of type patch, surface. These objects represent Copper, feed, FR4, Teflon.

Create an interdigital capacitor using gold as the conductor.

capacitor = interdigitalCapacitor;
capacitor.Conductor = metal("Gold");
show(capacitor)

Figure contains an axes object. The axes object with title interdigitalCapacitor element contains 6 objects of type patch, surface. These objects represent Gold, feed, Roger.

Compute and plot the behavioral S-parameters of the capacitor at 3.8 GHz.

spar = sparameters(capacitor,3.8e9,Behavioral=true);
rfplot(spar)

Figure contains an axes object. The axes object contains 4 objects of type line. These objects represent dB(S_{11}), dB(S_{21}), dB(S_{12}), dB(S_{22}).

More About

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References

[1] Pozar, David M. Microwave Engineering. 4th ed. Hoboken, NJ: Wiley, 2012.

[2] Jungreuthmayer, Christian, Gerald M. Birnbaumer, Peter Ertl, and Jürgen Zanghellini. “Improving the Measurement Sensitivity of Interdigital Dielectric Capacitors (IDC) by Optimizing the Dielectric Property of the Homogeneous Passivation Layer.” Sensors and Actuators B: Chemical 162, no. 1 (February 2012): 418–24. https://doi.org/10.1016/j.snb.2011.12.009.

[3] Ruppin, R. “Surface Polaritons of a Left-Handed Material Slab.” Journal of Physics: Condensed Matter 13, no. 9 (March 5, 2001): 1811–18. https://doi.org/10.1088/0953-8984/13/9/304.

[4] Caloz, Christophe, and Tatsuo Itoh. Electromagnetic Metamaterials: Transmission Line Theory and Microwave Applications: The Engineering Approach. Hoboken, NJ, USA: John Wiley & Sons, Inc., 2005. https://doi.org/10.1002/0471754323.

Version History

Introduced in R2021b