In transmission mode, a short burst of electric energy generated by the ultrasound scanner (typically one to three cycles of alternating voltage for imaging) is sent to the transducer generating an ultrasound pulse of energy. COMSOL Conference, Milan 2012 . Yao Mobile：13656128000 Tel：86 +519-88671999-801 Fax：86 +519-88671999-808 Add：1-1301 Hang Seng Science Park, Tianning District, Changzhou, Jiangsu, China The impedance characteristics of the ultrasonic depth measurement transducer can be expressed as series, parallel capacitive or inductive equivalent circuits R is the series resistance, and Xs is the series impedance. Medical ultrasonic transducers (probes) come in a variety of different shapes and sizes for use in making cross-sectional images of various parts of the body. A series of powerful piezoelectric materials are available to generate ultrasound in ultrasonic probes. Changzhou Keliking Electronics Co., Ltd. Contact：Mr. In case you’re wondering, the P comes from the chemical abbreviation for lead Pb. The beam pattern of a transducer can be determined by the active transducer area and shape, the ultrasound wavelength, and the sound velocity of the propagation medium. ALUMINUM NITRIDE PIEZOELECTRIC MICROMACHINED ULTRASOUND TRANSDUCER ARRAYS Stefon Shelton 1, Andre Guedes , Richard Przybyla 2, Reut Krigel 2, Bernhard Boser , David A. Horsley 1 1Berkeley Sensor & Actuator Center, University of California, Davis, CA, USA 2 Berkeley Sensor & Actuator Center, University of California, Berkeley, CA, USA ABSTRACT Air-coupled piezoelectric micromachined ultrasound At the front of the transducer is an acoustic lens. Piezoelectric films have recently attracted considerable attention in the development of various sensor and actuator devices such as nonvolatile memories, tunable microwave circuits and ultrasound transducers. Some of the types of piezoelectric materials are: Naturally Available Ones: Quartz, Rochelle salt, Topaz, Tourmaline-group minerals, and some organic substances as silk, wood, enamel, bone, hair, rubber, dentin. For example, by measuring the time between sending a signal and receiving an echo the distance of an object can be calculated. Artificially manufactures piezoelectric materialsare Polyvinylidene difluoride, PVDF or PVF2, Barium titanate, Lead titanate, Lead zirconate titanate (PZT), Potassium niobate, Lithium niobate, Lithium tantalate, and othe… In this paper, an overview of the state of art in piezoelectric films for high frequency transducer applications is presented. Ultrasound can be used for measuring wind speed and direction (anemometer), tank or channel fluid level, and speed through air or water. The impedance of the piezoelectric vibrator is at a certain frequency point (except the resonant frequency). This is how ultrasound transducers receive the sound waves.. The active element is a piezoelectric or single crystal material which converts electrical energy to ultrasonic energy. Piezoelectric crystals have unique electromechanical properties. Applications and Uses for Electric Transducers. When an electric current is applied to a piezoelectric crystal, it starts to vibrate and these vibrations generate sound waves with frequencies between 1.5 and 8 MHz (i.e ultrasound). Passive ultrasonic sensors are basically microphones that detect ultrasonic noise that is present under certain conditions. The engineer will be involved in all stages of piezoelectric transducer development from FEM modelling, design, manufacturing and Ultrasound transducers are capable of sending an ultrasound and then the same transducer can detect the sound and convert it to an electrical signal to be diagnosed. Piezoelectric Effect (PPT, 89kb) Piezoelectric Elements (PPT, 178kb) The active element of most acoustic transducers used today is a piezoelectric ceramic, which can be cut in various ways to produce different wave modes. Ultrasound Probe (piezoelectric transducer) Human Body . An ultrasound transducer converts electrical energy into mechanical (sound) energy and back again, based on the piezoelectric effect. Moreover, the beam shape is convex (see picture below) and the transducer is good for in-depth examinations. Whilst piezoelectric hydrophones have been available for decades and have thus gained widespread acceptance in ultrasound metrology, fibre-optic hydrophones are a relatively recent development. Without this layer, the impedance difference becomes large, which causes too much of the sound waves to be reflected (leaving fewer sound waves to penetrate the tissues). A piezoelectric material is one in which an electrical potential difference appears across a certain surface of a crystal if the dimension of the crystal is changed by the application of force. These sound waves travel through the skin, chest, pericardium, myocardium, etc. It consists of five main components: Some systems use separate transmitters and receivers, while others combine both functions into a single piezoelectric transceiver. Abstract: Much work has been published on the design of ultrasound transducers using piezoelectric ceramics, but a great deal of this work does not apply when using the piezoelectric polymers because of their unique electrical and mechanical properties. The piezoceramics are typically constructed to operate in one of two modes — … Certain single crystal materials exhibit the following phenomenon: when the crystal is mechanically strained, or when the crystal is deformed by the application of an external stress, electric charges appear on certain of the crystal surfaces; and when the direction of the strain reverses, the polarity of the electric charge is reversed. The ultrasound transducer and the piezoelectric crystals that generate and receive ultrasound waves. Size Selection Guide. Marco Cati •Which … Thus, piezoelectric crystals can convert electric currents into ultrasound waves. In these devices, audio from the transducer (microphone) is converted down to human hearing range. . A piezoelectric transducer is also used in fuel injection systems to measure manifold absolute pressure (MAP sensor) to determine engine load, and ultimately the fuel injectors milliseconds of on time. We provide ultrasound transducers and hydrophone made with high performance piezoelectric P(VDF-TrFE) copolymer film with thickness of 9 um, 12 um, 20 um, 25 um, and 40 um) with typical sizes from 3 mm to 8 mm. Piezoelectric films have recently attracted considerable attention in the development of various sensor and actuator devices such as nonvolatile memories, tunable microwave circuits and ultrasound transducers. Ultrasound . The transducer contains acoustic insulation that ensures that no other sound waves affect the transducer. The impedance characteristics of the ultrasonic depth measurement transducer can be expressed as series, parallel capacitive or inductive equivalent circuits R is the series resistance, and Xs is the series impedance. Learn how and when to remove these template messages, Learn how and when to remove this template message, 10.4233/uuid:22ccedfa-545a-4a34-bd03-64a40ede90ac, "A sensitive optical micro-machined ultrasound sensor (OMUS) based on a silicon photonic ring resonator on an acoustical membrane", "Translational and rotational resonance frequencies of a disk in a single-axis acoustic levitator". Introduction The piezoelectric transducers can be categorized into sonic, ultrasonic and megasonic Further applications include: humidifiers, sonar, medical ultrasonography, burglar alarms, non-destructive testing and wireless charging. Transmitters convert electrical signals into ultrasound, receivers convert ultrasound into electrical signals, and transceivers can both transmit and receive ultrasound. Ultrasonics, typically refers to piezoelectric transducers or capacitive transducers. The ultrasound transducer generates ultrasound (ultrasonic) waves. https://en.wikipedia.org/w/index.php?title=Ultrasonic_transducer&oldid=997202689, Articles needing additional references from July 2014, All articles needing additional references, Articles lacking in-text citations from March 2015, Articles with multiple maintenance issues, Articles with unsourced statements from November 2015, Creative Commons Attribution-ShareAlike License, Escolà, Alexandre; Planas, Santiago; Rosell, Joan Ramon; Pomar, Jesús; Camp, Ferran; Solanelles, Francesc; Gracia, Felip; Llorens, Jordi; Gil, Emilio (2011-02-28). When an electric current is applied to a piezoelectric crystal, it starts to vibrate and these vibrations generate sound waves with frequencies between 1.5 and 8 MHz (i.e ultrasound). Convex Transducers. erosive) effects. The diagrams show the sound fields of an unfocused and a focusing ultrasonic transducer in water, plainly at differing energy levels. When the reflected sound hits the piezoelectric crystals, they begin to vibrate and generate electric currents, which are transmitted to the ultrasound machine for analysis. Ultrasonic piezo sensors are used in the detection of acoustic emissions in acoustic emission testing. By utilizing this piezoelectric property an ultrasound transducer can act both as a transmitter and receiver of ultrasound. Where the black housing becomes the structure to create audible sound. High-power ultrasonic emitters are used in commercially available ultrasonic cleaning devices. A piezoelectric transducer uses a piezoelectric material as a transduction element. Ultrasonic testing is also widely used in metallurgy and engineering to evaluate corrosion, welds, and material defects using different types of scans. A piezoelectric transducer (also known as a piezoelectric sensor) is a device that uses the piezoelectric effect to measure changes in acceleration, pressure, strain, temperature or force by converting this energy into an electrical charge.. A transducer can be anything that converts one form of energy to another. ", This page was last edited on 30 December 2020, at 13:06. Ultrasonic Transducers are also used in acoustic levitation . This material provides ultrasound transducers with greatly improved performance over ones fabricated from standard commercial PZT materials. The figures of merit (FoMs) of LiNbO3 as ultrasound sensors and transducers are first studied, showing great prospective as a balanced transceiver platform. 13 Excerpt from the Proceedings of the 2012 COMSOL Conference in Milan. Introduction to echocardiography and ultraound imaging, Left ventricular systolic function and contractility, Technical aspects of the ultrasound image, Doppler effect and Doppler echocardiography, The Bernoulli principle and estimation of pressure gradients, The Continuity Equation (The Principle of Continuity), Stroke Volume, VTI (Velocity Time Integral) & Cardiac Output, Principles and Preparations for Echocardiographic Examinations, Performing Echocardiographic Examinations, Standard Transthoracic Echocardiogram: Complete Imaging Protocol, Myocardial Mechanics: Structure and Function of Myocardial Fibers, Ventricular Pressure-Volume Relationship: Preload, Afterload, Stroke Volume, Wall Stress & Frank-Starling's law, Assessing left ventricular systolic function, Ejection fraction (EF): Physiology, Measurement & Clinical Evaluation, Fractional shortening for estimation of ejection fraction, Strain, strain rate and speckle tracking: Myocardial deformation, Left Ventricular Segments for Echocardiography and Cardiac Imaging, Regional Myocardial Contractile Function: Wall Motion Abnormalities, Assessment of diastolic function by echocardiography, Heart failure: Causes, types, diagnosis, treatments & management, Echocardiography in cardiomyopathies: an overview, Hypertrophic Cardiomyopathy (HCM) & Hypertrophic Obstructive Cardiomyopathy (HOCM), Dilated Cardiomyopathy (DCM): Definition, Types, Diagnostics & Treatment, Arrhythmogenic Right Ventricular Cardiomyopathy / Dysplasia (ARVC, ARVD), Congenital heart disease & GUCH (Grown Up Congenital Heart disease), Cardiac thromboembolism: cardiac sources of embolism, Endocarditis: definitions, causes, diagnosis, echocardiography & treatment, Right ventricular strain: definition, causes, echocardiography, Constrictive pericarditis: definition, causes, diagnosis & echocardiography, The ultrasound transducer & piezoelectric crystals. A wide variety of piezoelectric transducer ultrasound options are available to you, such as ce. FEM . The role of computer aided simulation . The piezoelectric ultrasound transducer also offers the advantages of high electroacoustic efficiency while minimizing heat generation. Ultrasound is the term used when the frequency of the propagating wave exceeds 16,000 Hz, making it undetectable for the human ear. Ultrasonic sensors are widely used in cars as parking sensors to aid the driver in reversing into parking spaces. The design of transducer can vary greatly depending on its use: those used for medical diagnostic purposes, for example the range-finding applications listed above, are generally lower power than those used for the purpose of changing the properties of the liquid medium, or targets immersed in the liquid medium, through chemical, biological or physical (e.g. Piezoelectric crystals have unique electromechanical properties. Langevin transducer. The impedance of the piezoelectric vibrator is at a certain frequency point (except the resonant frequency). Systems typically use a transducer which generates sound waves in the ultrasonic range, above 18 kHz, by turning electrical energy into sound, then upon receiving the echo turn the sound waves into electrical energy which can be measured and displayed. The invention concerns an acoustic transducer for the ultrasonic range, which transducer can be used both as a transmitter and as a receiver. The latter class include ultrasonic probes and ultrasonic baths, which apply ultrasonic energy to agitate particles, clean, erode, or disrupt biological cells, in a wide range of materials; See Sonication. The frequency is 28 KHZ ~ 80KHZ. This enables the measurement resolution to far exceed the wavelength of the sound frequency generated by the transducers. Consequently, the consideration of such devices is given specific emphasis in order to shed further light on this rapidly developing field of study. It is made from aluminum alloy and titanium alloy. It is the hand-held part of the ultrasound machine that is responsible for the production and detection of ultrasound waves. PZT ceramic is the active part of the piezoelectric ultrasonic transducer used in medical ultrasound. For this therapy, high-intensity focused ultrasound (HIFU) is projected into the body with the help of piezoelectric elements. is applied to produce ultrasound waves and sent into the patient’s body; The returning ultrasound waves induce a p.d. By using a piezoceramic transducer element an extremely flexible transducer which is easy to produce, has a broad band width and ensures technological repeatability can be provided. Piezoelectric materials for sensors, actuators and ultrasound transducers Piezo-materials offer a direct coupling between electrical signals and mechanical movements. Thus, the principle of ultrasound imaging is simple: sound waves are sent into the tissue and the reflected waves are used to create an image of the tissue (Figure 1). Thousands of piezoelectric crystals are attached to the front of the transducer (Figure 2). Capacitive transducers use electrostatic fields between a conductive diaphragm and a backing plate. It expands and contracts rapidly when subjected to any voltage. These devices are fabricated using silicon micro-machining technology (MEMS technology), which is particularly useful for the fabrication of transducer arrays. 1 Horn-Type Piezoelectric Ultrasonic Transducer: Modelling and Applications Tao Li 1*, Jan Ma 1 and Adrian F. Low 2* 1School of Materials Science and Engin eering, Nanyang Technological University 2National University Heart Centre; Na tional University Health System, Singapore 1. such as magnetostriction. Transducer Construction . Ultrasonics are a great solution for clear object detection and for liquid level measurement, applications that photoelectrics struggle with because of target translucence. A capacitor ("condenser") microphone has a thin diaphragm that responds to ultrasound waves. This is how ultrasound transducers receive the sound waves.. Piezoelectricity is the electric charge that accumulates in certain solid materials (such as crystals, certain ceramics, and biological matter such as bone, DNA and various proteins) in response to applied mechanical stress.The word piezoelectricity means electricity resulting from pressure and latent heat. By analyzing the reflected sound waves, the ultrasound machine creates an image of the tissues. Join our newsletter and get our free ECG Pocket Guide! In the transition between each medium (tissue, blood, etc. The same effect can be used in reverse – inverse piezoelectric effect – whereby the application of an electric field to a crystal causes realignment of the internal dipole structure. Almost all piezoelectric transducers for power ultrasonics are of the Langevin type — i.e., one or more piezoceramics that are mechanically compressed (prestressed) between a front driver and a back driver. They are being tested for a number of other automotive uses including ultrasonic people detection and assisting in autonomous UAV navigation. Electric signal Pressure wave . For coupling a transducer crystal to a sample various materials can be used, such as: conductive and nonconductive epoxy, ceramic cement, and cyanoacrylate glue. The same effect can be used in reverse – inverse piezoelectric effect – whereby the application of an electric field to a crystal causes realignment of the internal dipole structure. An ultrasonic transducer is affixed to a stainless steel pan which is filled with a solvent (frequently water or isopropanol). This is the hard rubber that focuses the ultrasound waves, which results in less scatter of the waves and thus increase the resolution of the image. An introduction to piezoelectric transducer crystals, and suggested reading. One of which that is gaining a decent amount of traction in the past decade is ultrasonic gun cleaning. In a piezoelectric transducer, an alternating p.d. By utilizing this piezoelectric property an ultrasound transducer can act both as a transmitter and receiver of ultrasound. The crystals are supported by a backing layer that suppresses the vibrations of the crystals, allowing sound waves to be sent out in shorter pulses and this improves resolution (discussed below). Ultrasound waves are emitted rapidly from the transducer. A large piezoelectric ceramic element can be seen in the image of a sectioned low frequency transducer. This method can be very precise in terms of temporal and spatial resolution because the time-of-flight measurement can be derived from tracking the same incident (received) waveform either by reference level or zero crossing. As can be seen from Figure 2, the ultrasound transducer contains several components. Bulk piezoelectric transducers, in which a plate of lead zirconate titanate (PZT) piezoelectric ceramic is mechani-cally diced and backﬁlled with a polymer ﬁller to form a one- or two-dimensional array of elements, have dominated ultrasonic transducer technology for a long time.1 Micro electromechanical system (MEMS) based ultrasound trans- The crystals can also do the opposite; when the crystals are hit by reflected ultrasound waves, they begin to vibrate and these mechanical vibrations are converted into electric current that is sent back to the ultrasound machine, where the electrical signal is interpreted and translated into an image (Figure 3). Electric signal Pressure wave . An ultrasonic transducer itself is a device that is capable of generating and receiving ultrasonic vibrations. Piezoelectric transducers can be used for numerous applications that use electric power for industrial, environmental and personal use. To produce an ultrasound, a piezoelectric crystal has an alternating current applied across it. Omega introduces OPT5400 a new lead zirconate titanate (PZT) piezoelectric ceramic for use in medical ultrasound transducers. The role of computer aided simulation . Changes in the electric field between the diaphragm and a closely spaced backing plate convert sound signals to electric currents, which can be amplified. This is called the direct piezoelectric effect, and the crystals that exhibit it are classed as piezoelectric cry… They have 100 nm thick gold electrode and they are in stock. Ultrasonic transducer is the core device that converts electrical energy into mechanical energy (ultrasonic), the piezoelectric ceramic chip adopts imported parts, and can give a strong and stable output. Materials with this property change size slightly when exposed to a magnetic field, and make practical transducers. Ultrasonic technology has been used for multiple cleaning purposes. Ultrasound Transducer Hydrophone; Ultrasound Transducer Hydrophone. This technique is known as Sonomicrometry where the transit-time of the ultrasound signal is measured electronically (ie digitally) and converted mathematically to the distance between transducers assuming the speed of sound of the medium between the transducers is known. The convex ultrasound transducer (such as GE C1-6) type is also called the curved transducer because the piezoelectric crystal arrangement is curvilinear.. The transducer is held with one hand and its position and angle are adjusted to send ultrasound waves through structures to be visualized. They can be divided into three broad categories: transmitters, receivers and transceivers. Ultrasonic transducers and ultrasonic sensors are devices that generate or sense ultrasound energy. A series of powerful piezoelectric materials are available to generate ultrasound in ultrasonic probes. PZT ceramic is the active part of the piezoelectric ultrasonic transducer used in medical ultrasound. Ultrasound cleaning utilizing piezoelectric transducers functions by rapidly vibrating when operating at the appropriate ultrasonic frequencies. Marco Cati •Which … Piezoelectric Transducer: Above is a cheap three terminal piezoelectric transducer used in 12V Piezo Buzzer that produces sound with the below circuit arrangement. Almost all piezoelectric transducers for power ultrasonics are of the Langevin type — i.e., one or more piezoceramics that are mechanically compressed (prestressed) between a front driver and a back driver. It is typically used in a vacuum cleaner. Even though the image resolution decreases when the depth increases. To obtain ultrasound on the scale of millions of cycles per second, most medical applications of ultrasound use lead zirconate titanate ceramics, also known as PZT. Ultrasound transducers are designed for optimal transmission and reception of sound waves ( Figure 3.1 ).An electrical shield lines the transducer case to prevent external electrical interference from distorting sound wave transmission.A thin acoustic insulator dampens vibrations from the case to piezoelectric elements and prevents transmission of spurious … In doing so, the complex structure of a piezoelectric ultrasonic transducer is reduced to an active surface, which can generate and receive sound pressure waves. The piezoelectric effect converts kinetic or mechanical energy, due to crystal deformation, into electrical energy. The piezoelectric ultrasound transducer also offers the advantages of high electroacoustic efficiency while minimizing heat generation. A composite ultrasound transducer (array) contains piezoelectric ceramic transducer elements which radiate substantially in the longitudinal direction, and are embedded in a polymer matrix. An ultrasonic transducer is made up of an active element, a backing, and wearplate. Ultrasonic transducers convert AC into ultrasound, as well as the reverse. Used to work in a team, versatile and with global vision. An ultrasound transducer, comprising a substrate (10) which forms a backing medium, a layer of piezoelectric material (20), and one or more matching layers (30, 40) whose acoustic impedance has a value between that of the piezoelectric material and that of a foremost, propagation medium (50). Piezoelectric crystals change size and shape when a voltage is applied; AC voltage makes them oscillate at the same frequency and produce ultrasonic sound. Piezoelectric transducers can be used for numerous applications that use electric power for industrial, environmental and personal use. 13 Excerpt from the Proceedings of the 2012 COMSOL Conference in Milan. These materials differ in their physical properties. The reflected sound waves will have the same speed as the emitted sound waves, but the amplitude, frequency and angle of incidence may differ from the emitted sound waves. COMSOL Conference, Milan 2012 . A linear piezoelectric micromachined ultrasound transducer (PMUT) array was fabricated and integrated into a device for photoacoustic imaging (PAI) of tissue phantoms. As well, target color or reflectivity do not affect ultrasonic sensors, which can operate reliably in high-glare environments. The ultrasound waves are generated by ceramic crystals exhibiting piezoelectric properties (i.e piezoelectric crystals). The appeal of pMUTs is based on several key advantages In PLUS, the waves generated in a material from a piezoelectric transducer with a single element are received by a laser Doppler vibrometer, which moves around the material's surface to … ), a significant portion of all sound waves will be reflected back to the transducer. ... Piezoelectric ceramics are the best basis for generating and detecting ultrasonic waves. Section 7.1 deals with a semi-analytical approach to calculate sound fields and electrical transducer outputs for common transducer shapes, e.g., piston-type transducers. PVDF-TrFE Copolymer piezoelectric film ultrasound transducer with gold electrode, 3 um to 100 um, 100 x 100 mm; PVDF-TrFE Copolymer piezoelectric film ultrasound transducer with gold electrode, 3 um to 100 um, 100 x 100 mm. What is Piezoelectric Transducer. These materials differ in their physical properties. PVDF-TrFE Copolymer piezoelectric film ultrasound transducer with gold electrode, 9~100 um, high coupling factor. The diaphragm (or membrane) principle is also used in the relatively new micro-machined ultrasonic transducers (MUTs). To obtain ultrasound on the scale of millions of cycles per second, most medical applications of ultrasound use lead zirconate titanate ceramics, also known as PZT. The most important and common type of piezoelectric transducer elements used in ultrasonic broadband applications is a thin piezoelectric plate, with lateral dimensions much greater than the thickness, driven in a simple thickness extensional mode of vibration. Ultrasonics, typically refers to piezoelectric transducers or capacitive transducers. Ultrasound transmitters can also use non-piezoelectric principles. An electrical square wave feeds the transducer, creating sound in the solvent strong enough to cause cavitation. Ultrasound Probe (piezoelectric transducer) Human Body . From the transducer, ultrasound waves are sent out in pulses. With a piezo transducer in cleaning fluid, the rapid expansion and contraction from the vibrations exerts enough force to clean. In this paper, an overview of the state of art in piezoelectric films for high frequency transducer applications is presented. In case you’re wondering, the P comes from the chemical abbreviation for lead Pb. In a similar way to radar and sonar, ultrasonic transducers are used in systems which evaluate targets by interpreting the reflected signals. They can sense the edge of material as part of a web guiding system. An ultrasonic transducer is made up of an active element, a backing, and wearplate. In transmission mode, a short burst of electric energy generated by the ultrasound scanner (typically one to three cycles of alternating voltage for imaging) is sent to the transducer generating an ultrasound pulse of energy. They usually operate in the frequency range 0.5-15 MHz. The active element is a piezoelectric or single crystal material which … An ultrasonic transducer itself is a device that is capable of generating and receiving ultrasonic vibrations. The PMUT contained 65 array elements, with each element having 60 diaphragms of 60μm diameter and 75μm pitch. Since piezoelectric materials generate a voltage when force is applied to them, they can also work as ultrasonic detectors. Piezoelectric micromachined ultrasound transducer (pMUT) two-dimensional (2D) arrays have been proposed as an alternative to conventional bulk-PZT thickness-mode transducers for high frequency, forward-looking, catheter-based ultrasound imaging of the cardiovascular system. FEM . The overview is about piezoelectric single crystal properties and it's limitation for high frequency applications, and commercialization status of medical ultrasound transducer using single crystal and the next step of single crystal transducer. Ultrasound cleaning utilizing piezoelectric transducers functions by rapidly vibrating when operating at the appropriate ultrasonic frequencies. Ultrasonic transducers convert AC into ultrasound, as well as the reverse. Applications and Uses for Electric Transducers. Table 2. It produces frequencies that are far above that which can be heard by the human ear. Ultrasonic sensors can detect movement of targets and measure the distance to them in many automated factories and process plants. Passive ultrasonic sensors may be used to detect high-pressure gas or liquid leaks, or other hazardous conditions that generate ultrasonic sound.