A DFMD or a door frame metal detector is a security screening device which is designed to detect the presence of metallic objects on a person's body as the person passes through it. Typically spotted at airports, government buildings, courtrooms, schools and other high-security areas, DFMDs and similar screening devices reduce the risk of concealed weapons and nonpermitted metal objects entering secured zones.
What is a DFMD?
It is basically a walk-through detector system in a portal shaped like a door frame. It's used to detect metal on passengers by creating electromagnetic fields to detect and locate metal objects carried on those passing through as well.
Working Principle of DFMD: The working of DFMD is based on Electromagnetic Induction.
Core Concept: The metal in the man-made object interrupts the electromagnetic field and creates a secondary electromagnetic signal when the individual passes through the field it produces. This movement is discernible and optionally analysed by the system.
Key Components:
Transmitter Coils: Create the oscillating electromagnetic field in the detection region.
Receiver Coils: Sense changes in the magnetic field when metal objects are added or removed.
Control Unit / Signal Processor: Decodes signals from the receiver coils to determine the presence of metal objects.
Alarm System: Audio and/or visual alarm indication when metal is detected.
How DFMD Works: Step-by-Step
Field Generation: The emitter coils radiate a low frequency magnetic field into the region of passage.
Person Walks Through: As a person passes through, the magnetic field creates a signal in any metal object on the person.
Disturbance Detection: This gives rise to attainment of the metal as a new magnetic field.
Signal Analysis: These changes are detected by receiver coils, and analysed by the control unit as to whether they are indicative of metal objects.
Alarm Activation: If metal is detected above a predetermined level, an alarm is activated and it is often indicated on the system the general area in which the metal is present (in multi-zone models).
Types of DFMDs
Single-Zone DFMD: Can find metal throughout the frame. It Cannot pinpoint the exact location.
Multi-Zone DFMD: Splits the frame into several vertical zones. It Can detect where the metal is (e.g., head, torso, foot).
Advanced Digital DFMDs: Utilize microprocessors for improved sensitivity and filtering. Its Minimize false positives of benign metal objects (such as coins or belt buckles).
Technology Used
Electromagnetic Induction (main operating principle).
DSP (Digital Signal Processing): To process and analyse signals for eliminating false alarms.
Microcontrollers: System control unit and user interface.
Zone Mapping: In a multi-zone system, each receiver monitors particular zones.
Applications
Airports and Metro Stations
Courthouses and Prisons
Stadiums and Event Venues
Corporate Offices and Data Centres
Schools and Government Buildings
Advantages
Non-invasive and Safe
Quick Scanning Process
Cost-effective Security Layer
Can be used for both ferrous metal and non-ferrous metals
Limitations
Can not differentiate between metal having danger and the metal does not have danger.
Can be caused by innocuous objects (keys, watches).
Not suitable for amazingly small object or very deep object.
Necessitates calibration and periodic maintenance for accuracy.
Safety Considerations
DFMDs employ low-frequency electromagnetic fields that are safe for humans, including those who have pacemakers and pregnant people (although, as with anything you use with your body, it’s generally a good idea to consult device specs and manufacturer instructions).
Door Frame Metal Detectors (DFMDs) are an essential element of advanced security frame solutions. Because of the electromagnetic induction principle, taking place of traditional physical search, they are light and fast-especially improving the speed and efficiency of the security check. The development of digital processing and multizone technology are bringing DFMDs to a new level of accuracy and reliability, helping make public and private areas safer.