Home > ANSYS Q3D 教學 > Fingerprint Recognition Simulation

 

The article is intended to introduce the simulation for fingerprint recognition with Q3D 2015. I believe this is the first one to use 3D EM extractor and MATLAB post-process to demonstrate how to simulate fingerprint recognition.  --2015.01.01

1. Introduction

2. Model Structure

3. C Matrix of 12x12 Array

4. C Matrix of 16x16 Array

5. Add a Mesh Plane for ESD Protection

6. 問題討論(Q&A)

   6.1 Is there any precision\resolution limit of Q3D solver?

   6.2 How to set grounding\floating property for plane in step5?

   6.3 Why to add a conductive ring to enclose the sensing array? (important)

   6.4 How to plot field with different parametric variables as step3?

   6.5 What points should be noted for in-cell and fingerprint, these kinds of simulation with Q3D?

7. Reference

1. Introduction [1][2] 

2. Model Structure 

0.4mm pitch, 0.1mm depth for fingerprint pattern\stripe

藍寶石(Sapphire, Al₂O₃), Dk=9.3, thickness=0.43mm for cover glass [3]

3. C Matrix of 12x12 Array 

12x12 pixels for 1.42x1.42mm²

The capacitor distribution (C induced between sensing array and fingerprint)

下圖右請以IE瀏覽器檢視

The outer array is a little lighter, and it is because of fringe effect.

4. C Matrix of 16x16 Array 

Increase the pixel resolution (from 12x12 to 16x16 for 1.42x1.42mm² area), and decrease the thickness of cover glass from 0.43 to 0.35mm.

500dpi is recommended for fingerprint recognition [5], and 500 dot per inch => 500x500 per 25.5mm² => 25x25 per 1.25mm²

下圖右請以IE瀏覽器檢視

5. Add a Mesh Plane for ESD Protection 

This is a 16x16 array and insert a grounding mesh plane between finger and sensing array.

The "grounding" mesh plane inserted between array and finger will reduce a lot of induced capacitor. (decrease about 40% for this case)

If the mesh plane is "floating", it reduces less as below. (decrease about 25% for this case)

6. 問題討論(Q&A)

6.1 Is there any precision\resolution limit of Q3D solver? 

Ans：No limit. The more mesh, the higher precision. For this case, Q3D can get the C matrix result with 0.01fF precision.

6.2 How to set grounding\floating property for plane in step5? 

Ans：To set by reduce matrix (post-process), or by assigning net directly.

6.3 Why to add a conductive ring to enclose the sensing array? 

Ans：It is a tip to implement a finite array with minimized fringe effect on boundary edges.

6.4 How to plot field with different parametric variables as step3? 

Ans：Check the term of [Save Fields And Mesh] in Parametric Setup

      Analyze all, and plot Q field.

      [Q3D Extractor] \ [Fields] \ [Edit Source] to define the excitation voltage sources

      RMB (Right-Mouse-Button) on field term, then run [Animate]

　

6.5 What points should be noted for in-cell and fingerprint, these kinds of simulation with Q3D? 

Ans：

6.5.1 Set smaller [Percent Error], (for example,  change from 1 by default to 0.05~0.01) to get great precision.

6.5.2 Use [Thin conductor] boundary in Q3D, if the capacitive effect of sides can be ignored.

6.5.3 Use [Class mesh], and add [Mesh Operations] based on max. length of elements, then it will converge very well.

6.5.4 Using MATLAB for post-process can get very useful information\indications. [6][7][8]

7. Reference 

[1] 淺談指紋辨識原理

[2] iPhone 5S指紋辨識技術

[3] 藍寶石工藝  p.18
[4] Sapphire Glass v.s Gorilla Glass
     Sapphire glass thickness 70~140um for fingerprint recognition

[5] 10TopTenReview -- Fingerprint Scanner
     Handbook of Fingerprint Recognition, p.83

[6] Fingerprint Recognition, MATLAB source code1

[7] Fingerprint Recognition, MATLAB source code2

[8] Fingerprint Recognition, MATLAB source code3

[9] Fingerprint Sensing Techniques 

[10] Fingerprint Sensing Techniques