SEN-09196 SparkFun

LDT with Crimps Vibration Sensor/Switch Piezo Film Sensors High Sensativity AC Coupled Laminated Robust The LDT0-028K is a flexible component comprising a 28 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 dimensions is deflected by direct contact, the device acts as a flexibleswitc, and the generated output is sufficient to trigger MOSFET or CMOS stages directly. If the assembly is supported by its contacts and left to vibratein free spac (with the inertia of the clamped/free beam creating bending stress), the device will behave as an accelerometer or vibration sensor. Adding mass, 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. The LDTM-028K is a vibration sensor where the sensing element comprises a cantilever beam loaded by an additional mass to offer high sensitivity at low frequencies. FEATURES Solder Tab Connection Both No Mass & With Mass Version Withstands High Impact Operating Temperature: 0C to 85C Storage Temperature: -40C to 85 C Higher Temperature Version up to 125 C available on a Custom Basis APPLICATIONS Vibration Sensing in Washing Machine Low Power Wakeup Switch Low Cost Vibration Sensing Car Alarms Body Movement Security Systems LDT0-028K Piezo Vibration Rev 1 www.meas-spec.com 10/13/2008 1of 4 LDT with Crimps Vibration Sensor/Switch examples of properties Four different experiments serve to illustrate the various properties of this simple but versatile component. Experiment 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 theopen-circui 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 increasesbaselin sensitivity. TABLE 1: LDT0 as Vibration Sensor (see Fig 1) Added Mass Baseline Sensitivity at Resonant +3 Db Sensitivity 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 Experiment 2 LDT0 as Flexible Switch - using a charge amplifier to obtainopen-circui 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). LDT0-028K Piezo Vibration Rev 1 www.meas-spec.com 10/13/2008 2 of 4