LDT0 Solid State Application Note 111398 Switch/Vibration Sensor 13 Nov Rev O DESCRIPTION The LDT0 is a flexible component comprising a 28 µ m thick piezoelectric PVDF polymer film with screen-printed Ag-ink electrodes, laminated to a 0.125 mm polyester substrate, and fitted with two crimped contacts. As the piezo film is displaced from the mechanical neutral axis, bending creates very high strain within the piezopolymer and therefore high voltages are generated. When the assembly is deflected by direct contact, the device acts as a flexible "switch", and the generated output is sufficient to trigger MOSFET or CMOS stages directly. If the assembly is supported by its contacts and left to vibrate "in free space" (with the inertia of the clamped/free beam creating bending stress), the device will behave as a form of accelerometer or vibration sensor. Adding mass, Part No 0-1002794-1 or altering the free length of the element by clamping, can change the resonant frequency and sensitivity of the sensor to suit specific applications. Multi-axis response can be achieved by positioning the mass off center. EXAMPLES OF PROPERTIES Four different experiments serve to illustrate the various properties of this simple but versatile component. 1) LDT0 as Vibration Sensor - with the crimped contacts pushed through a printed-circuit board, the LDT0 was soldered carefully in place to anchor the sensor. A charge amplifier was used to detect the output signal as vibration from a shaker table was applied (using a charge amplifier allows a very long measurement time constant and thus allows the "open-circuit" voltage response to be calculated). Small masses (approximately 0.26g increments) were then added to the tip of the sensor, and the measurement repeated. Results are shown in Table 1 and the overlaid plots in Fig 1. Without adding mass, the LDT0 shows a resonance around 180 Hz. Adding mass to the tip reduces the resonance frequency and increases "baseline" sensitivity. 2) LDT0 as Flexible Switch - using a charge amplifier to obtain "open-circuit" voltage sensitivity, the output was measured for controlled tip deflections applied to the sensor (supported by its crimped contacts as described above). 2 mm deflection was sufficient to generate about 7 V. Voltages above 70V could be generated by bending the tip of the sensor through 90° (see Table 2, Fig 2). 3) LDT0 Electrical Frequency Response - when the source capacitance of around 480 pF is connected to a resistive input load, a high-pass filter characteristic results. Using an electronic noise source to generate broad- band signals, the effect of various load resistances were measured and the -3 dB point of the R-C filter determined (see Table 3, Fig 3). 4) LDT0 Clamped at Different Lengths - using simple clamping fixture, the vibration sensitivity was measured (as in (1) above) as the clamp was moved to allow different "free" lengths to vibrate. The sensor may be "tuned" to suit specific frequency response requirements (see Table 3, Fig 3). Measurement Specialties Incorporated, P.O. Box 799, Valley Forge, PA 19482 610.650.1500 FAX 610.650.1509 Page 1 of 3 This document is subject to change. Application Note 111398 LDT0 Solid State Switch/Vibration Sensor TABLE I: LDT0 as Vibration Sensor (see Fig 1) Added Baseline Sensitivity Resonant +3 Db Mass Sensitivity at Resonance Frequency Frequency 0 50 mV/g 1.4 V/g 180 Hz 90 Hz 1 200 mV/g 4 V/g 90 Hz 45 Hz 2 400 mV/g 8 V/g 60 Hz 30 Hz 3 800 mV/g 16 V/g 40 Hz 20 Hz TABLE II: LDT0 as Flexible Switch (see Fig 2) Tip Charge o/c Voltage Deflection Output Output 2 mm 3.4 nC 7 V 5 mm 7.2 nC 15 V 10 mm 10 - 12 nC 20 - 25 V max (90() > 30 nC > 70 V Measurement Specialties Incorporated, P.O. Box 799, Valley Forge, PA 19482 610.650.1500 FAX 610.650.1509 Page 2 of 3 This document is subject to change. Application Note 111398 LDT0 Solid State Switch/Vibration Sensor TABLE III: LDT0 Electrical Frequency Response (see Fig 3) (480 pF source capacitance) Load -3 db Resistance Frequency 1 Megohm 330 Hz 10 Megohm 33 Hz 100 Megohm 3.3 Hz TABLE IV: LDT0 Clamped at Different Lengths (see Fig 4) Length Resonant Settling beyond Frequency Time (5 cyc) clamp 20 mm 180 Hz 28 msec (no clamp) 16 mm 250 Hz 20 msec 11 mm 500 Hz 10 msec 7 mm 1000 Hz 5 msec Measurement Specialties Incorporated, P.O. Box 799, Valley Forge, PA 19482 610.650.1500 FAX 610.650.1509 Page 3 of 3 This document is subject to change.