Ultrasonic sensors typically have a piezoelectric ceramic transducer that converts an excitation electrical signal into ultrasonic energy bursts. The energy bursts travel from the ultrasonic sensor, bounce off objects, and are returned toward the sensor as echoes. Transducers are devices that convert electrical energy to mechanical energy, or vice versa. The transducer converts received echoes into analog electrical signals that are output from the transducer. Ultrasonic transducers operate to radiate ultrasonic waves through a medium such as air. Transducers generally create ultrasonic vibrations through the use of piezoelectric materials such as certain forms of crystals or ceramic polymers. Piezoelectric materials vibrate in response to alternating voltages of certain frequencies applied across the material. Piezoelectric elements are similar to common analog capacitors in that piezo elements generally include two electrodes separated by a piezoelectric material that functions as a dielectric. The overall capacitance of a transducer is dependent upon the area and the thickness of the piezo material. Ultrasonic transducers are available in various technical forms. Ultrasonic transducers are typically formed of either piezoelectric elements or of micro-machined ultrasonic transducer (MUT) elements. For industrial use, solid-state transducers are usually used, because of their robustness. They basically include a piezoceramic device as an element for converting between electric signals and acoustic signals and a resonant adapter layer, with which the transfer of sound to the air is optimized. The piezoelectric elements typically are made of a piezoelectric ceramic such as lead-zirconate-titanate (PZT), with a plurality of elements being arranged to form a transducer. Piezoceramic ultrasonic transducers are the transducers of choice for rugged, industrial applications because they are efficient and environmentally robust. These sensors have been used in industry for numerous applications; however have not been capable of short range object detection until recently. A micro-machined ultrasonic transducer (MUT) is formed using known semiconductor manufacturing techniques resulting in a capacitive ultrasonic transducer cell that comprises a flexible membrane supported around its edges over a silicon substrate. The membrane is supported by the substrate and forms a cavity. The MUT may be electrically energized to produce an appropriate ultrasonic wave. Similarly, when electrically biased, the membrane of the MUT may be used to receive ultrasonic signals by capturing reflected ultrasonic energy and transforming that energy into movement of the electrically biased membrane, which then generates a receive signal. Capacitive micromachined ultrasonic transducers (cMUTs) are tiny diaphragm-like devices with electrodes that convert the sound vibration of a received ultrasound signal into a modulated capacitance. For transmission the capacitive charge is modulated to vibrate the diaphragm of the device and thereby transmit a sound wave. In general, ultrasonic transducers are constructed by incorporating one or more piezoelectric vibrators which are electrically connected to pulsing-receiving system.

Ultrasonic sensing techniques have earned a pre-eminent position in a variety of fields including medicine, nondestructive testing and process monitoring, geophysics, and sonar surveillance. Ultrasonic flow sensors have been employed for a number of years for performing intraoperative or extracorporeal blood flow measurements. Intraoperative flow measurements are typically conducted to monitor blood flow in various vessels during vascular, cardiac, transplant, plastic and reconstructive surgery. Transit-time ultrasonic flow sensors detect the acoustic propagation time difference between the upstream and downstream ultrasonic transmissions in a moving fluid and process this information to derive a fluid flow rate. Ultrasonic array transducers rely on wave interference for their beam forming effects, and typically include a plurality of individual transducer elements organized as either a one-dimensional (linear) array or a two-dimensional array. Ultrasound is used as a non-invasive technique for obtaining image information about the structure of an object which is hidden from view, and is widely known as a medical diagnostic tool as well as a tool for non-destructive testing and analysis in the technical arts. Ultrasound diagnostic imaging systems are in widespread use for performing ultrasonic imaging and measurements. Ultrasonic imaging sensors act as both transmitters and receivers of ultrasonic energy. The sensor first acts as a transmitter; emitting ultrasonic energy in a train of high frequency pulses, typically in the range of 2 to 10 Mhz. Then the transmitter is turned off and the sensor acts as a receiver, which listens for returned echoes at the transmitted frequency. Ultrasonic sensors are used to make remote distance measurements. One particular use of ultrasonic sensors is within a vehicle occupant protection system within a vehicle. Ultrasonic range finders typically use ultrasonic frequencies which are inaudible to the human ear. These high frequencies have inherently shorter wavelengths, which lead to greater positional accuracy than audible frequencies. Parking aid systems of today usually consist of an electronic control unit and several ultrasonic sensors. Each ultrasonic sensor possesses a separate data line, since, in order to improve evaluation, echo information from several ultrasonic sensors is required at a certain instant. Thus, the evaluation of several ULS on the basis of one transmitted sound wave permits more precise conclusions to be made about the position of and the range of the obstacle. Ultrasonic sensors are equipped in robots and used for detecting objects positioned along a robot travel path. Such ultrasonic sensors are adapted to convert a pulse signal into an ultrasonic wave energy which is, in turn, radiated at a search area.