The unit of sensitivity is usually V/Pa or mV/Pa (V: Receiving voltage, Pa: Pascal). However, for the convenience of expressing the performance of transducers, the sensitivity is used to express the reception intensity. Generally, Pref is defined as 0.0002 ubar (derived from the human hearing threshold). Where P is the sound pressure, Pref is the standard reference sound pressure. SPL = 20*log(P/Pref) the unit of measurement is dB SPL is the effective sound pressure measured by a logarithmic scale relative to a reference value, defined as: Major characteristics of an ultrasonic transducer include sensitivity, directivity and blind zone, explained below:īefore understanding the sensitivity, it is necessary to introduce the Sound Pressure Level (SPL). How to Choose The Appropriate Ultrasonic Transducer? Generally, a damping layer is used to let the ultrasonic transducer quickly return to its static state to reduce its ringing. When people design ultrasonic transducers for proximity measurement, the ringing limits the minimum detection distance. It should be noted that ultrasonic transducers have ringing characteristics, inherently. Depending on applications, ultrasonic transducers can be used in either a pitch-catch mode or a pitch-echo mode. At present, the commonly used material for acoustic matching layers is a kind of composite material made of polymer matrix and hollow powder to achieve lower acoustic impedance with reasonable reliability. The ideal value of acoustic impedance for the matching layer of an ultrasonic air transducer is Rayl, which is about 0.122 MRayl, but it is difficult to find materials with acoustic impedance lower than 1 MRayl and durable in nature. Therefore, the acoustic matching layer becomes a necessary part of the ultrasonic transducer, which is placed between the piezoelectric ceramic and air, so that the acoustic impedance of the two can be matched and the ultrasonic energy can be effectively transmitted into air. The sound velocity and acoustic impedance characteristics of common substances are as follows: substanceįor the example of an ultrasonic air transducer, the acoustic impedance of piezoelectric ceramics is about 35 MRayl (106 kg/m2∙s), while the acoustic impedance of air is as low as around 414 Rayl (kg/m2∙s). However, in order to make the generated ultrasonic waves be transmitted efficiently from the piezoelectric ceramic to the object or fluid (e.g., in air or water), the acoustic impedance between the piezoelectric ceramic and the object or fluid must be matched through acoustic matching layers. 5 Schematic diagram of the transceiver design
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