Inductive Security Sensor Immune to Magnetic Tampering
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Proximity-based security systems using mechanical reed switch sensors are vulnerable to tampering through the use of tamper-magnets that mimic the magnetic field of the magnet-target, allowing unauthorized access by masquerading as the legitimate target.
Innovation Solution
An inductive security sensor system featuring an inductive sensor assembly with an inductor coil and a conductive proximity target, coupled with an inductance-to-data conversion unit that drives the coil with an excitation signal to project a time-varying magnetic field, making it immune to external magnetic fields and false conductive targets by detecting changes in coil inductance and resonance state.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a mechanical reed switch sensor with magnet target is used for proximity detection, then the security system can detect unauthorized movement, but the system becomes susceptible to magnetic tampering with false targets
Solution Approach 1:
The patent replaces the mechanical reed switch sensor system with an inductive sensor system that uses electromagnetic induction principles. The inductive sensor detects changes in inductance caused by the proximity of a conductive target, eliminating vulnerability to magnetic tampering while maintaining security detection functionality. This substitution of mechanical/magnetic field detection with electromagnetic induction detection resolves the contradiction between reliability and tampering susceptibility.
Solution Approach 2:
The patent changes the detection parameter from magnetic field presence (in reed switches) to inductance changes (in inductive sensors). By measuring inductance variations rather than magnetic field strength, the system can distinguish between legitimate target proximity and false magnetic targets, as false targets do not produce the same inductance changes. This parameter transformation resolves the vulnerability to magnetic tampering.
2Object-affected harmful factors
If an inductive sensor with time-varying magnetic field is used, then the system becomes immune to external DC magnetic fields, but the device complexity increases
Solution Approach 1:
The inductive sensor system uses periodic excitation signals to generate time-varying magnetic fields at specific frequencies. This periodic action creates a dynamic detection field that is inherently resistant to static DC magnetic interference, as the sensor detects changes rather than static field presence. The periodic modulation allows the system to distinguish between legitimate targets and false magnetic targets while managing complexity through frequency-based detection.
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
The system effectively prevents magnetic tampering and false target interference, ensuring reliable detection of displacement and tamper conditions without being susceptible to external DC magnetic fields or conductive false targets, enhancing security and accuracy over traditional mechanical designs.
Implementation Method 1
The IDC unit drives the inductor coil with an excitation signal to project a time-varying magnetic field for magnetic coupling to the proximity target
Implementation Method 2
measuring changes in sensor resonator losses as representing eddy current losses in the proximity target
Implementation Method 3
The IDC unit is configured to drive the sensor resonator with an excitation signal to establish a resonant state of the sensor resonator, at a sensor resonator frequency
Data Source
AI summary
An inductive security sensor system is not susceptible to magnetic tampering (such as by using an external magnet or false target). A sensor assembly includes an inductive sensor (inductor coil), mounted in a relatively secure location, and a conductive proximity target incorporated with an object (such as a window or door, or an object/asset). An alarm condition can be detected as either a displacement condition in which the proximity target is displaced relative to the inductive sensor, or a tamper condition in which magnetic coupling between the proximity target and the inductive sensor is interfered with (such as by introducing a false conductive target) An inductance-to-data converter drives the inductor coil with an excitation signal to project a time-varying magnetic field for magnetically coupling to the proximity target. The IDC acquires sensor measurements (such as coil inductance), which are converted into corresponding sensor data representing alarm conditions (displacement or tamper).