Piezoelectric transmitter

Sonic Methods A fixed-point level detector based on sonic-propagation characteristics is available for detection of a liquid-vapor interface. This device uses a piezoelectric transmitter and receiver, separated by a short gap. When the gap is filled with liquid, ultrasonic energy is transmitted across the gap, and the receiver actuates a relay. With a vapor filling the gap, the transmission of ultrasonic energy is insufficient to actuate the receiver. 

The piezoelectric effect was one of the crucial elements for Pierre Curie and Marie Skladowska Curie in their discovery of radioactivity. Flowever, there was no technological application for over 30 years, until it was used in radio transmitters and ultrasonics on the 1910s. Currently, the largest applica-... 

Both transducers are self-excited oscillating systems (usually piezoelectric crystals— see Section 6.3.1) which act alternately as transmitters and receivers, the receiving pulses being used to trigger the transmitted pulses in a feedback arrangement. A pulse from transmitter Tt is directed downstream over a path length Lp to transducer T2 (Fig. 6.3). The downstream elapsed time is ... 

Sensor containing piezoelectric crystal acting alternately as ultrasonic transmitter and receiver... 

The simplest SAW sensor is a two-terminal transmission (delay) line in which the acoustic (mechanical) wave is piezoelectrically launched in one oscillator, called the transmitter. It travels along the surface of the substrate and is then transformed back into an electrical signal by the reverse piezoelectric effect at the receiving oscillator (Fig. 4.18). 

PVDF is not solely of interest as a structural material. Oriented films have piezoelectric properties which are used for highly sensitive microphones, acoustic transmitters, and military applications. The piezoelectric characteristics of PVDF can be even improved by copolymerization with small quantities of other monomers which enhance its elastomeric properties. 

King (5) reported that the first crystal sorption detector was the "Martini Detector", a fun project he started in the basement of his house. He coated the crystals in his ham radio transmitter with the insect repellent (di-n-butylphthalate), and found that the frequency shifted more when the coating was exposed to alcoholic breath than to normal breath. Out of that fun project came the pioneering work of King in the development of the piezoelectric sorption detector. The high sensitivity, simplicity, and ruggedness of the piezoelectric sorption detector led to a variety of applications in air pollution research. 

Similar to the optical analogy, the problem is solved by acoustic quarterwave matching layers (Fig. 10). Silica aerogels with densities of around 300 kg/m have the ideal acoustic impedance to match a piezoelectric transducer to air [77]. In addition, they exhibit rather low attenuation, as opposed to many porous, polymer materials used for this purpose until now. An increase in sound transmittance by more than 30 dB was achieved in a relatively simple arrangement without optimization. More elaborate designs, eventually including multiple layers combining different materials, will probably result in transducer systems optimized with respect to output power, sensitivity, and bandwidth. 

Piezoelectricity links the fields of electricity and acoustics. Piezoelectric materials are key components in acoustic transducers such as microphones, loudspeakers, transmitters, burglar alarms and submarine detectors. The Curie brothers [7] in 1880 first observed the phenomenon in quartz crystals. Langevin [8] in 1916 first reported the application of piezoelectrics to acoustics. He used piezoelectric quartz crystals in an ultrasonic sending and detection system - a forerunner to present day sonar systems. Subsequently, other materials with piezoelectric properties were discovered. These included the crystal Rochelle salt [9], the ceramics lead barium titanate/zirconate (pzt) and barium titanate [10] and the polymer poly(vinylidene fluoride) [11]. Other polymers such as nylon 11 [12], poly(vinyl chloride) [13] and poly (vinyl fluoride) [14] exhibit piezoelectric behavior, but to a much smaller extent. Strain constants characterize the piezoelectric response. These relate a vector quantity, the electrical field, to a tensor quantity, the mechanical stress (or strain). In this convention, the film orientation direction is denoted by 1, the width by 2 and the thickness by 3. Thus, the piezoelectric strain constant dl3 refers to a polymer film held in the orientation direction with the electrical field applied parallel to the thickness or 3 direction. The requirements for observing piezoelectricity in materials are a non-symmetric unit cell and a net dipole movement in the structure. There are 32-point groups, but only 30 of these have non-symmetric unit cells and are therefore capable of exhibiting piezoelectricity. Further, only 10 out of these twenty point groups exhibit both piezoelectricity and pyroelectricity. The piezoelectric strain constant, d, is related to the piezoelectric stress coefficient, g, by... 

For thin shell structures, the most promising methods are those based in the analysis of the propagation of elastic waves. The wave propagation methods have often used piezoelectric wafer active sensors (PWAS) as transmitters to generate waves and simultaneously as receivers to measure the echo signals due to the defects. A time-frequency analysis allows an estimation of crack size on the basis of the relationship between new and baseline response. The sensitivity of Lamb waves to defects depends largely on the frequency, and for complex structures the dispersive Lamb waves interact with reinforcements with partial reflections and refractions. These systems have not reached the level of maturity required for industrial applications. A full discussion with alternatives is presented in the book by Giurgiutiu (2008). 

Vapor sensor based on SAW devices were first reported in 1979, most of them rely on the mass sensitivity of the detector, in conjunction with a chemically selective coating that adsorbs the vapor of interest and result in an increased mass loading of the device [5]. In its simplest form SAW sensor consists of a delay line, which consists of an IDT at each end of an appropriate piezoelectric substrate. One IDT acts as transmitter and other acts as the receiver of acoustic energy which travels along... 

Doppler Ultrasound. Doppler ultrasound has been widely used to provide quaUtative measurements of the average flow velocity in large to medium-size vessels if the vessel diameter is known. These include the extracranial circulation and peripheral limb vessels. It is also used in an assessment of mapped occlusive disease of the lower extremities. The frequency used for Doppler ultrasound is typically between 1 and 15 MHz. The basis of this method is the Doppler shift, which is the observed difference in ftequency between sound waves that are transmitted from simple piezoelectric transducers and those that are received back when both transmitter and receiver are in relative motion. The average frequency shift of the Doppler spectrum is proportional to the average particulate velocity over the cross-sectional area of the sample. When us to measure blood flow, the transducers are stationary and motion is imparted by the flowing blood cells. In this event, red cell velocity V is described by the relationship... 

Colorless amorphous (i.e., fused silica) or crystalline (i.e., quartz) material having a low thermal expansion coefficient and excellent optical transmittance in far UV. Silica is insoluble in strong mineral acids and alkalis except HE, concentrated HjPO, NH HE, concentrated alkali metal hydroxides. Owing to its good corrosion resistance to liquid metals such as Si, Ge, Sn, Pb, Ga, In, Tl, Rb, Bi, and Cd, it is used as crucible container for melting these metals, while silica is readily attacked in an inert atmosphere by molten metals such as Li, Na, K Mg, and Al. Quartz crystals are piezoelectric and pyroelectric. Maximum service temperature 1090°C... 

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