Ferro-electret sensors for OEM customers

Quasi-piezoelectric sheet, band and cable sensors

Emfit sensors convert mechanical force into proportional electrical energy. In contrast to the crystalline structure of PZT or PVDF piezo-sensors, EMFIT sensor is based on a permanent electric charge inside the cellular structure of the sensor core.

Operating in a reciprocal fashion, changes in thickness to Emfit sensor generate a corresponding charge and hence, voltageto appear on the electrodes. Since the transducer behaves like an “active” capacitor, consequently, the loading of the signal by the input impedance of the measuring device must be considered. 

Due to the thinness of the films, the associated capacitance can be sufficient to give adequate low frequencyresponse into standard 1 MΩ load but the use of an X10 probe will extend the low frequencyrange by a decade. For extremely low force change levels, some buffering may be desirable. For the majority of analysis work, this is unnecessary and the film can feed directly to the instrument. Again, the low mass contributed by the transducer is of major importance,and its non-resonate behaviour. Frequency response is inherently flat to over 20 KHz with only the R-C roll off at low frequencies distorting the profile. 

Though EMFIT sensor is responding to thickness change rather than strain, low signal levels may be generated by low frequencyflexing, so a distinction must be made between the frequency response of the film for changes in its primary parameter (i.e. thickness) and its relative behaviourcompared with, say piezoelectric sensors. The sensor has a flat response over a very wide frequency range, with resonant frequency points well above 20 KHz.