Electric Potential Sensor for Non-Contact Charge Density Imaging
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Solution Overview
Problem
Current methods for measuring charge density distribution in fingerprints are limited by restricted scan areas, slow scan speeds, and difficulty in determining the time elapsed since deposition due to environmental and subject factors, leading to cumbersome technology and inaccurate measurements.
Innovation Solution
An electric field microscopy system using a high spatial resolution raster scanning microscope with an electric potential sensor for non-contact, weak capacitive coupling to measure surface charge density, allowing for flexible resolution and non-destructive imaging of fingerprints on insulating surfaces.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If atomic force microscopy is used to image fingerprint residue, then measurement precision is improved, but scan area is restricted to 40 μm×40 μm which is insufficient to image a whole fingerprint
Solution Approach 1:
The patent replaces mechanical contact-based imaging (atomic force microscopy) with non-contact electric field-based imaging. The electric potential sensor detects surface charge distribution through capacitive coupling without physical contact, enabling large scan areas while maintaining high measurement precision for fingerprint residue detection.
2Area of stationary object
If scanning electrochemical microscopy is used, then scan area is increased to 5 mm×3 mm, but scan time increases to 5 hours and significant sample preparation is required
Solution Approach 1:
The patent replaces electrochemical measurement methods with direct electric field sensing. The electric potential sensor measures surface charge distribution through capacitive coupling, eliminating the need for complex sample preparation and reducing scan time significantly while maintaining the ability to image large areas.
Solution Approach 2:
The patent changes the measurement parameter from electrochemical signals to electric potential/charge density. This parameter change simplifies the measurement process, eliminates the need for sample preparation, and reduces scan time while maintaining comprehensive coverage of the scan area.
3Reliability
If scanning Kelvin probe microscopy is used for latent fingerprint imaging, then non-destructive measurement is achieved, but scan time is relatively long, between 6 and 30 hours
Solution Approach 1:
The patent replaces Kelvin probe microscopy with a simplified electric field sensing system. The electric potential sensor uses direct capacitive coupling to detect surface charge, reducing scan time from 6-30 hours to significantly shorter durations while maintaining non-destructive measurement and preserving DNA material.
4Measurement precision
If conventional techniques are used to determine time elapsed since deposition, then measurement is possible, but the technology becomes cumbersome and measurements are inaccurate due to multiple environmental and subject factors
Solution Approach 1:
The patent replaces complex multi-factor analysis methods with direct electric field measurement. By measuring surface charge density distribution, the system provides a simpler, more direct approach to determining time elapsed since deposition, reducing technological complexity while improving measurement accuracy by focusing on a single measurable parameter.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This method provides high spatial resolution images of fingerprints, enabling accurate identification and estimating the time elapsed since deposition by measuring the decay of surface charge, which is independent of subject and transfer methods, and can be repeated without degrading the sample.
Implementation Method 1
the electrical potential sensor comprises a probe for capacitively coupling the electric potential sensor to the surface of a material sample
Implementation Method 2
using an electric field microscopy system to image electrical charge deposited due to a finger touching a thin insulating surface
Data Source
AI summary
The invention provides a method and apparatus for the detection of charge density distribution at the surface of a material sample. The apparatus comprises an electric potential sensor for measuring surface charge on a material sample, wherein the electrical potential sensor includes a probe for capacitively coupling the electric potential sensor to the surface of the material sample, an amplifier for generating a measurement output, the probe being connected to an input of the amplifier and the measurement output being supplied at an output of the amplifier, and a feedback arrangement driven from the output of the amplifier for enhancing the input impedance of the amplifier. A positioning system mounts the probe of the electric potential sensor above the material sample and moves the probe at a constant height over a surface of the said sample, and a processing system receives and processes the measurement output of the electric potential sensor for generating a digital record of the charge density distribution at the surface of the material sample.