Head of Group: Professor Suleiman Sharkh
The research interests of the Electro-Mechanical Research Group (EMRG) cover the application of transducers, measurement systems and control systems to a broad range of activities.
Thick Film Unit
The term "thick film" refers to the fact that these sensors are fabricated using screen printing techniques that were originally developed for the production of thick film hybrid circuits that employed screen printed interconnections and passive components (such as resistors and capacitors) with surface mounted integrated circuits (chips).
The devices are typically built up in layers by printing the active materials of the sensors onto a variety of different support media (substrates). Most commonly ceramic but increasingly steel, plastics and other materials are used.
The screen printing process forces ink (or paste) through a pre-patterned mesh or stencil (the screen) onto the substrate. The thickness of the deposited layer is controlled by the printer and the properties of the ink define the function of the layer
Thick film hybrid circuits
These devices are made here in the Thick Film Unit and are 4 to 20 mA transmitters incorporating an instrumentation amplifier. They are typically used in instrumentation applications in the process industries where low level sensor signals are converted to a current for transmission to a control centre. A current of 4 mA corresponds to the sensor minimum value and 20 mA to the sensor maximum output value.
These miniature pressure sensors are designed to fit inside the automatic gearbox of a car. It consists of 4 interconnected thick film strain gauges printed onto a steel pressure sensing diaphragm that screws onto a threaded pipe. The device is extremely rugged, as it does not use any adhesive or wires to connect the strain gauges to the diaphragm. By measuring the pressure of the hydraulic fluid inside the gearbox, the car's on-board computer system can decide when best to change gear.
Thick film technology is a particularly good medium for fabricating arrays of sensors on a common substrate. For example, a water quality sensor can consist of 13 thick film layers that make up 5 separate solid state sensors for detecting the dissolved oxygen concentration, temperature, pH, redox potential (a measure of ionic activity) and conductivity of the water. The complete array is only 35mm in diameter and would easily fit into a matchbox.
Using thick film chemical sensor technology the group developed a series of rugged miniaturized pH sensors for use in controlling the viscosity of printing ink. They were funded as part of a European Commission project aimed at producing disposable sensors that would survive in the harsh environment of a printing works. Modern printing inks are water based, as opposed to solvent based, and have to have ammonia added to them to keep them workable. The thick film pH sensors were developed to enable the dosing of the ink to be controlled more precisely. Thick film is an excellent means for mass producing disposable sensors as many such devices can be printed at the same time making them very cost effective to manufacture.