Gas Detection Device Using Asymmetric AC-DC Fields
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Solution Overview
Problem
Current gas detection methods, such as classic time-of-flight IMS and DMS, face limitations including low detection efficiency, long measurement times, and inability to simultaneously detect positive and negative ions, especially for toxic chemicals like benzene, due to their complex structures and requirements for vacuum or high field strengths.
Innovation Solution
A method and device utilizing a DC voltage field superimposed with an asymmetric AC voltage field to alter the drift speed of ionized molecules, allowing for simultaneous detection of positive and negative ions and exploiting field-dependent mobility changes to characterize chemical compounds, with a simpler structure and reduced measurement time.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a classic time-of-flight IMS is used with a short start pulse to improve temporal resolution, then measurement precision is improved, but only a small part of product ions are detected resulting in low detection efficiency
Solution Approach 1:
The patent applies periodic action by using a pulsed electric field in the drift tube that periodically reverses direction. This creates alternating acceleration and deceleration phases for ions, allowing multiple detection opportunities per ion packet while maintaining temporal resolution. The periodic field reversals enable ions to be detected at multiple time points along their drift path, effectively increasing detection efficiency without sacrificing temporal precision.
2Adaptability or versatility
If the polarity of the separating tube is changed to detect both positive and negative ions, then versatility is improved, but measurement time increases
Solution Approach 1:
The patent implements continuity of useful action by using a bipolar pulsed electric field that continuously alternates between positive and negative polarities within a single measurement cycle. This allows both positive and negative ions to be detected sequentially without requiring physical reconfiguration or separate measurement runs. The field polarity switches rapidly between positive and negative phases, enabling simultaneous characterization of both ion types within one continuous measurement, thereby maintaining versatility while eliminating time loss.
3Measurement precision
If a DMS with high field strengths is used to separate ions based on mobility changes, then detection precision is improved, but device complexity and measurement time increase
Solution Approach 1:
The patent applies parameter changes by dynamically varying the electric field strength and polarity in the drift tube through pulsed voltage application. Instead of using complex multi-electrode DMS configurations, the invention achieves ion separation by changing the temporal parameters of a simpler electrode system - applying high-voltage pulses that create strong fields only during specific time windows. This reduces device complexity while maintaining the ability to separate ions based on their mobility characteristics through controlled parameter variation.
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
Enables immediate and simultaneous detection of chemical compounds with improved detection limits and resolution, characterizing ion-specific drift velocities and mobility changes, overcoming the limitations of prior art by using a DC voltage field with an asymmetric AC voltage to separate ions based on field-dependent mobility.
Implementation Method 1
The introduced product ions are constantly accelerated by the electric field and constantly decelerated by collisions with the neutral molecules in the drift gas. The electric field exerts the same tensile force on all ions with the same charge.
Implementation Method 2
The drift velocity of the product ions vd is linearly dependent on the field strength at low field strength E. At these low field strengths, the mobility K of the product ions is then independent of the field strength. However, at very high field strengths, e.g. E > 5000 V/cm, the mobility is no longer independent of the field strength.
Implementation Method 3
The target compounds are ionized continuously in an ion source either by means of radioactive radiation, photoionization or corona discharges. Radioactive sources that directly ionize air molecules are very often used.
Implementation Method 4
The target compounds are ionized continuously in an ion source either by means of radioactive radiation, photoionization or corona discharges.
Implementation Method 5
The collisions with the molecules in the ambient air result in a diffusive broadening of the admitted ions. The signal measured at the detector is accordingly in the form of a Gaussian bell curve.
Data Source
AI summary
The aim of the invention, is to develop a method of the type in question, for identification of gases and a corresponding device, which has a simple construction permitting an immediate and concurrent detection of the chemical compounds under examination and hence for identification of the material-specific mobility and at the same time the change in said mobility as a function of electrical field strength. Said aim is achieved, wherein each ionised molecule has a drift speed through the resultant electrical field, which is partly increased or reduced, the resulting electrical field being a DC field, with a superimposed asymmetrical alternating field. Said method and corresponding devices for detection and identification of gases are used for recognition and detection of chemical compounds, in particular of explosive and/or toxic materials or material compounds for detection in extremely low concentrations.