All pyroelectric materials are, by their very nature, also piezoelectric. This means that a detector’s pyroelectric chip reacts not only to changes in radiation (the pyroelectric signal) but also to structure-borne and airborne sound, like a microphone or an accelerometer (the piezoelectric signal). This phenomenon is known as vibration sensitivity or the microphonic effect.
The interference caused by piezoelectrically generated signals, which is unavoidable in pyroelectric detectors, cannot be reduced by the choice of operating mode, but only through mechanical countermeasures. In InfraTec detectors, the patented mounting of the pyroelectric chip ensures that the microphonic effect is minimized.
Causes of the Microphonic Effect
When external forces act on a pyroelectric material due to shock or vibration, its crystal lattice deforms. If this causes the charge centers in the crystal to shift perpendicular to the material’s metallized surface, surface charges are generated.
In this process, surface charges generated by the pyroelectric effect due to temperature changes overlap with parasitic mechanically induced charges arising from the piezoelectric effect (vibration sensitivity).
Minimizing the Microphonic Effect
For pyroelectric detectors, the crystal orientation is selected such that the pyroelectric effect is maximized. The resulting sensitivity to acceleration is minimal but unavoidable. Its influence on the pyroelectric detector’s measurement signal can be minimized by mechanically decoupling the detector from its surroundings as much as possible or by effectively damping vibrations. Special measures can also be taken within the detector itself to ensure that critical vibration modes are strongly damped, thereby limiting their contribution to the signal.
Based on simulations using the finite element method (FEM), InfraTec has developed a special chip holder (see figure) and successfully implemented it in series production. The patented suspension of the pyroelectric chip significantly reduces its deformation, as well as vibrations at the typical modulation frequencies of the pyroelectric detector of approximately 10 Hz. This reduces the interference signal generated by mechanical influences by 95% compared to the interference signal in a conventional pyroelectric detector.
Detectors with reduced microphony are identified by the letter M in the middle of the detector designation (LME or LMM).
Detector Search
InfraTec offers different product groups including approximately 50 standard pyroelectric detectors. Detectors with reduced microphone technology and integrated operational amplifier as well as digital detectors are part of our product range.
Choose your suitable infrared detectors with the help of our detailed detector search.
