Sophisticated mechanical packaging to house sensors for hospital safety systems.

Metrasens Ferroguard

The Challenge

Metrasens leads the world in the design of ferromagnetic safety systems that detect and warn staff before potentially hazardous items reach the MRI room doorway. Following the development of enhanced sensors, Metrasens approached GX for their help to design sophisticated mechanical packaging to house the sensors. The design needed to allow for the wide variation in doorway architecture encountered around the world, together with robust design-for-manufacture to maximise efficiency and reduce costs.

The Solution

MRI scanners produce a strong magnetic field that is “always on” and can result in any approaching ferrous items, such as hair pins, being pulled with great force into the magnet; the so-called “projectile effect”. Metrasens developed a new generation product that included enhanced sensors to better define movement of persons around the MRI doorway and the movement of the door itself.

The esign team at GX needed to create a solution which could be quickly and easily configured by the installer and robust enough to cope with years of life in a busy and challenging hospital environment. The design needed to be adaptable enough to overcome height variations, plus any electrical and civil engineering variations in both existing MRI suites and new build installations.


The function of the first sensor module is to detect all objects, including people, as they pass through the MRI doorway and to allow distinction between objects entering the MRI room and objects emerging from the MRI room. The Module is mounted in the majority of installations on the bottom end of one of the two Ferroguard Sensor Poles which are located either side of the MRI doorway. In some installations it is necessary to demount the Module from the Ferroguard Sensor Pole and mount it instead on the wall as a standalone unit. In others, lack of space requires the standalone module to be recessed into the wall. 

Another vital consideration for the design engineers was to incorporate a new sensor developed by Metrasens that provided real time knowledge of the door movement. The need to preserve the magnetic shielding of the door resulted in strict limitations on the way in which the technology could be deployed. The ideal locations and orientations for the doors are varied, so the design needed to cope with four classes of door opening namely:-

  • In-swing left-hinge and In-swing right-hinge
  • Out-swing left-hinge and Out-swing right-hinge

Monitoring of these sensors is undertaken in a control unit known as the “Hub” which is mounted out of the sight of staff and patients. It is made entirely of metal but designed with ease of installation, low cost manufacturing, robustness and electrical integrity in mind. Its design also follows the Ferroguard corporate product identity.

The Result

The team at GX utilised a low cost injection moulding system to produce the optical enclosure and mechanical sub-assemblies in conjunction with sheet metal parts. Many of the components are multi-functional so were designed with polarising features to ensure products could be assembled correctly. Once the components are assembled on site they must operate at extremely tight tolerances and allow no room for error, which the design achieved.

The new generation Ferroguard product is now on sale and currently being installed in hospitals across Europe, North America and Asia. The design team at GX has remained involved in the project as they manage the supply of the moulded components.