A simple wireless strain sensor using a frequency modulation technique is presented. The sensor employs a piezoelectric transducer that produces electric voltage as it is mechanically strained. When the piezoelectric sensor is connected to a single-transistor frequency modulation circuit, the sensor output voltage causes the modulation circuit frequency to shift. This modulated signal is then wirelessly transmitted to a remote station, where a demodulation circuit retrieves the buried strain measurement data in real time. Using this technique, a dynamic strain measurement is possible without any wire connection between the sensing point and the monitoring station. In order to demonstrate the performance of the wireless strain sensor and the measurement system, a wireless measurement of a vibrating cantilevered beam is experimentally conducted. This type of sensor has numerous applications in the strain or vibration measurement of moving or rotating structures such as turbo machinery.

ObjectivesPotential environmental risks caused by chemicals that could be released from a recycled plastic product were assessed using a screening risk assessment procedure for chemicals in recycled products.MethodsPlastic slope protection blocks manufactured from recycled plastics were chosen as model recycled products. Ecological risks caused by four model chemicals -di-(2-ethylhexyl) phthalate (DEHP), diisononyl phthalate (DINP), cadmium (Cd), and lead (Pb)- were assessed. Two exposure models were built for soil below the block and a hypothetic stream receiving runoff water. Based on the predicted no-effect concentrations for the selected chemicals and exposure scenarios, the allowable leaching rates from and the allowable contents in the recycled plastic blocks were also derived.ResultsEnvironmental risks posed by slope protection blocks were much higher in the soil compartment than in the hypothetic stream. The allowable concentrations in leachate were 1.0×10-4, 1.2×10-5, 9.5×10-3, and 5.3×10-3 mg/L for DEHP, DINP, Cd, and Pb, respectively. The allowable contents in the recycled products were 5.2×10-3, 6.0×10-4, 5.0×10-1, and 2.7×10-1 mg/kg for DEHP, DINP, Cd, and Pb, respectively.ConclusionsA systematic ecological risk assessment approach for slope protection blocks would be useful for regulatory decisions for setting the allowable emission rates of chemical contaminants, although the method needs refinement.