When poled, PVDF is a ferroelectric polymer, exhibiting efficient piezoelectric and pyroelectric properties. Ink jet printers operating on the Piezoelectric transducer principle also use valveless pumping. It is a ferroelectric ceramic material that exhibits the photorefractive effect and piezoelectric properties. The vibration is typically created by a motor or a piezoelectric actuator. Second generation devices used piezoelectric or electromagnetic generators. This can be done using piezoelectric transducers. Piezoelectric, or piezo, pickups represent another class of pickup. Electroacoustic resonators based on piezoelectric materials can be used for filters. These sensors are piezoelectric and EMAT sensors. These include spectroscopic, piezoelectric, electrochemical and fluorescent detectors. They can be either electric, pneumatic, hydraulic, piezoelectric or ultrasonic. Tactile sensors may be of different types including piezoresistive, piezoelectric, capacitive and elastoresistive sensors. Magnetostrictive transducers were pursued after World War II as an alternative to piezoelectric ones. Electric violins may use magnetic, piezoelectric, or electrodynamic pickups. There are two types of ultrasonic scalers; piezoelectric and magnetostrictive.