How can we produce ultrasonic waves

In addition, it highlights both direct and indirect applicati. Ultrasonic waves were produced by striking the surface of a metal with the focused one-joule pulse of a Q-switched ruby laser.

Rayleigh surface waves and longitudinal waves were detected with conventional transducers. Optical methods of detection were tested and developed. Rayleigh waves were produced with an oscillator and transducer.

They were optically detected on curved polished surfaces, and on unpolished surfaces. The technique uses a knife edge to detect small angle changes of the surface as the wave pulse passes the illuminated spot.

Optical flaw detection using pulse echo and attenuation is demonstrated. Improvement of solar ethanol distillation using ultrasonic waves. Directory of Open Access Journals Sweden. Full Text Available This report presents a study on the use of ultrasonic waves in solar ethanol distillation to investigate the performance of ultrasonic waves at a frequency of 30 kHz and at Watts that were installed in the inlet area of a litre distillation tank.

Based on the non-continuous distillation process batch distillation, the experiment demonstrated that using ultrasonic waves in solar ethanol distillation caused the average concentration of hourly distilled ethanol to be higher than that of a normal system solar ethanol distillation without ultrasonic wave at the same or higher distillation rate and hourly distillation volume.

The ultrasonic wave was able to enhance the separation of ethanol from the solution water-ethanol mixture through solar distillation. Furthermore, the distillation rate varied based on the solar radiation value. Ultrasonic guided wave for monitoring corrosion of steel bar. Steel corrosion of reinforced concrete structures has become a serious problem all over the word.

In this paper, the work aims at monitoring steel corrosion using ultrasonic guided wave UGW. Ultrasonic guided wave monitoring is a dynamic and non-destructive testing technology. The advantages of ultrasonic guided wave monitoring for reinforcement corrosion are real-time, online and continuous. In addition, it can judge the different stages of steel bar corrosion, which achieved non-destructive detection.

As a newly developed arc welding method, ultrasonic-wave -assisted arc welding successfully introduced power ultrasound into the arc and weld pool, during which the ultrasonic acts on the top of the arc in the coaxial alignment direction. The advanced process for molten metals can be realized by using an additional ultrasonic field. However, the stability of the metal transfer has deep influence on the welding quality equally, and the ultrasonic wave effect on the stability of the metal transfer is a phenomenon that is not completely understood.

In this article, the stabilities of the short-circuiting transfer process and globular transfer process are studied systematically, and the effect of ultrasonic wave on the metal transfer is analyzed further. Analytical results show that the additional ultrasonic wave is helpful for improving welding stability.

Absorption and dispersion of ultrasonic waves. Absorption and Dispersion of Ultrasonic Waves focuses on the influence of ultrasonics on molecular processes in liquids and gases, including hydrodynamics, energy exchange, and chemical reactions. The book first offers information on the Stokes-Navier equations of hydrodynamics, as well as equations of motion, viscosity, formal introduction of volume viscosity, and linearized wave equation for a nonviscous fluid.

The manuscript then ponders on energy exchange between internal and external degrees of freedom as relaxation phenomenon; effect of slow energy exchange on sound propagation; differe. Multipath ultrasonic gas flow-meter based on multiple reference waves. Several technologies can be used in ultrasonic gas flow-meters, such as transit-time, Doppler, cross-correlation and etc. In applications, the approach based on measuring transit-time has demonstrated its advantages and become more popular.

Among those techniques which can be applied to determine time-of-flight TOF of ultrasonic waves , including threshold detection, cross correlation algorithm and other digital signal processing algorithms, cross correlation algorithm has more advantages when the received ultrasonic signal is severely disturbed by the noise. However, the reference wave for cross correlation computation has great influence on the precise measurement of TOF.

In the applications of the multipath flow-meters, selection of the reference wave becomes even more complicated. Based on the analysis of the impact factors that will introduce noise and waveform distortion of ultrasonic waves , an averaging method is proposed to determine the reference wave in this paper.

In the multipath ultrasonic gas flow-meter, the analysis of each path of ultrasound needs its own reference wave. In case study, a six-path ultrasonic gas flow-meter has been designed and tested with air flow through the pipeline. The results demonstrate that the flow rate accuracy and the repeatability of the TOF are significantly improved by using averaging reference wave , compared with that using random reference wave.

All rights reserved. Full Text Available Ultrasonic cleaning has been used in industry for some time, but the application of ultrasonic cleaning in contaminated soil is just recently received considerable attention, it is a very new technique, especially in Indonesia.

An ultrasonic cleaner works mostly by energy released from the collapse of millions of microscopic cavitations near the dirty surface. This paper investigates the use of ultrasonic wave to enhance remediation of diesel fuel contaminated sandy soil considering the ultrasonic power, soil particle size, soil density, water flow rate, and duration of ultrasonic waves application.

The ultrasonic guided waves are waves whose propagation characteristics depend on structural thickness and shape such as those in plates, tubes, rods, and embedded layers. If the angle of incidence or the frequency of sound is adjusted properly, the reflected and refracted energy within the structure will constructively interfere, thereby launching the guided wave. Because these waves penetrate the entire thickness of the tube and propagate parallel to the surface, a large portion of the material can be examined from a single transducer location.

The guided ultrasonic wave has various merits like above. But various kind of modes are propagating through the entire thickness, so we don't know the which mode is received. Most of applications are limited from mode selection and mode identification. So the mode identification is very important process for guided ultrasonic inspection application. In this study, various time-frequency analysis methodologies are developed and compared for mode identification tool of guided ultrasonic signal.

For this study, a high power tone-burst ultrasonic system set up for the generation and receive of guided waves. And artificial notches were fabricated on the Aluminum plate for the experiment on the mode identification. Fundamentals and applications of ultrasonic waves. A subject with applications across all the basic sciences, engineering, medicine, and oceanography, yet even the broader topic of acoustics is now rarely offered at undergraduate levels.

Ultrasonics is addressed primarily at the doctoral level, and texts appropriate for beginning graduate students or newcomers to the field are virtually nonexistent. Fundamentals and Applications of Ultrasonic Waves fills that void.

Designed specifically for senior undergraduates, beginning graduate students, and those just entering the field, it begins with the fundamentals, but goes well beyond th.

Non-contact feature detection using ultrasonic Lamb waves. Apparatus and method for non-contact ultrasonic detection of features on or within the walls of hollow pipes are described. An air-coupled, high-power ultrasonic transducer for generating guided waves in the pipe wall, and a high-sensitivity, air-coupled transducer for detecting these waves , are disposed at a distance apart and at chosen angle with respect to the surface of the pipe, either inside of or outside of the pipe.

Measurements may be made in reflection or transmission modes depending on the relative position of the transducers and the pipe. Data are taken by sweeping the frequency of the incident ultrasonic waves , using a tracking narrow-band filter to reduce detected noise, and transforming the frequency domain data into the time domain using fast Fourier transformation, if required.

Direct-current nanogenerator driven by ultrasonic waves. We have developed a nanowire nanogenerator that is driven by an ultrasonic wave to produce continuous direct-current output. The nanogenerator was fabricated with vertically aligned zinc oxide nanowire arrays that were placed beneath a zigzag metal electrode with a small gap. A piezoelectric-semiconducting coupling process converts mechanical energy into electricity.

The zigzag electrode acts as an array of parallel integrated metal tips that simultaneously and continuously create, collect, and output electricity from all of the nanowires. The approach presents an adaptable, mobile, and cost-effective technology for harvesting energy from the environment, and it offers a potential solution for powering nanodevices and nanosystems. Wireless power transmission using ultrasonic guided waves. The unavailability of suitable power supply at desired locations is currently an important obstacle in the development of distributed, wireless sensor networks for applications such as structural health monitoring of aircraft.

Proposed solutions range from improved batteries to energy harvesting from vibration, temperature gradients and other sources. A novel approach is being investigated at Cardiff University School of Engineering in cooperation with Airbus. It aims to utilise ultrasonic guided Lamb waves to transmit energy through the aircraft skin. A vibration generator is to be placed in a location where electricity supply is readily available. Ultrasonic waves generated by this device will travel through the aircraft structure to a receiver in a remote wireless sensor node.

The receiver will convert the mechanical vibration of the ultrasonic waves back to electricity, which will be used to power the sensor node. This paper describes the measurement and modelling of the interference pattern which emerges when Lamb waves are transmitted continuously as in this power transmission application.

The discovered features of the pattern, such as a large signal amplitude variation and a relatively high frequency, are presented and their importance for the development of a power transmission system is discussed. Ultrasonic guided waves have been widely employed for long range inspection of structures such as plates, rods and pipes.

There are numerous modes with different wave velocities, and the appropriate mode selection is one of key techniques in the application of guided waves.

In the present work, phase tuning by an array transducer was applied to generate ultrasonic guided waves. Eight transducers were fabricated in order to generate guided waves by using an array transducer.

The selective tuning of wave mode can be achieved by changing the interval between elements of an array transducer. Gesturing is a natural way of communication between people and is used in our everyday conversations. Hand gesture recognition systems are used in many applications in a wide variety of fields, such as mobile phone applications, smart TVs, video gaming, etc.

With the advances in human-computer interaction technology, gesture recognition is becoming an active research area. There are two types of devices to detect gestures; contact based devices and contactless devices. Using ultrasonic waves for determining gestures is one of the ways that is employed in contactless devices. Hand gesture recognition utilizing ultrasonic waves will be the focus of this thesis work.

This thesis presents a new method for detecting and classifying a predefined set of hand gestures using a single ultrasonic transmitter and a single ultrasonic receiver. This method uses a linear frequency modulated ultrasonic signal. The ultrasonic signal is designed to meet the project requirements such as the update rate, the range of detection, etc.

Also, it needs to overcome hardware limitations such as the limited output power, transmitter, and receiver bandwidth, etc. The method can be adapted to other hardware setups. Gestures are identified based on two main features; range estimation of the moving hand and received signal strength RSS. These two factors are estimated using two simple methods; channel impulse response CIR and cross correlation CC of the reflected ultrasonic signal from the gesturing hand.

A customized simple hardware setup was used to classify a set of hand gestures with high accuracy. The detection and classification were done using methods of low computational cost. This makes the proposed method to have a great potential for the implementation in many devices including laptops and mobile phones. The predefined set of gestures can be used for many control applications. Failed fuel rod detection method by ultrasonic wave. Ultrasonic wave signals sent from an ultrasonic receiving element are supplied to an evaluation circuit by way of a gate.

A table for gate opening and closing timings at the detecting position in each of the fuel rods in a fuel assembly is stored in a memory. A fuel rod is placed between an ultrasonic transmitting element and the receiving element to determine the positions of the transmitting element and the receiving element by positional sensors. The opening and closing timings at the positions corresponding to the result of the detection are read out from the table, and the gates are opened and closed by the timing.

This can introduce the ultrasonic wave signals transmitted through a control rod always to the evaluation circuit passing through the gate. Accordingly, the state of failure of the fuel rod can be detected accurately. The ultrasonic guided waves are very promising for the long-range inspection of large structures because they can propagate a long distance along the structures such as plates, shells and pipes. The guided wave inspection could be utilized for an on-line monitoring technique when the transmitting and receiving transducers are positioned at a remote point on the structure.

The received signal has the information about the integrity of the monitoring area between the transmitting and receiving transducers. On-line monitoring of a pipe line using an ultrasonic guided wave can detect flaws such as corrosion, erosion and fatigue cracking at an early stage and collect useful information on the flaws.

However the guided wave inspection is complicated by the dispersive characteristics for guided waves. The phase and group velocities are a function of the frequency-thickness product. Therefore, the different frequency components of the guided waves will travel at different speeds and the shape of the received signal will changed as it propagates along the pipe. In this study, we analyze the propagation characteristics of guided wave modes in a small diameter pipe of nuclear power plant and select the suitable mode for a long-range inspection.

And experiments will be carried out for the practical application of a long-range inspection in a 26m long pipe by using a high-power ultrasonic inspection system. Detecting Lamb waves with broadband acousto- ultrasonic signals in composite structures. Lamb waves can be produced and detected in ceramic matrix composites CMC and metal matrix composites MMC plates using the acousto- ultrasonic configuration employing broadband transducers.

In this study a basis has been established for analyzing Lamb wave velocities for characterizing composite plates. Lamb wave disperison curves and group velocities were correlated with variations in axial stiffness and shear stiffness in MMC and CMC.

For CMCs, interfacial shear strength was also correlated with the first antisymmetric Lamb mode. In another class, structural components having shapes supporting propagation of Lamb waves monitored ultrasonically to identify signs of deterioration and impending failure.

Longitudinal ultrasonic waves dispersion in bars. The exhibition intends to review some aspects of the propagation of the longitudinal ultrasonic pulses shortly in bars of traverse section uniform.

Aspects they are part of the denominated geometric dispersion of the pulses. This phenomenon It can present like an additional complication in the ultrasonic essay of low frequency of thin pieces in structures and machines but takes place former ex professed in some applications of the wave guides been accustomed to in the prosecution of signs. Guided- wave tomography imaging plate defects by laser-based ultrasonic techniques.

Contact-guided- wave tests are impractical for investigating specimens with limited accessibility and rough surfaces or complex geometric features. A non-contact setup with a laser- ultrasonic transmitter and receiver is quite attractive for guided- wave inspection. In the present work, we developed a non-contact guided- wave tomography technique using the laser- ultrasonic technique in a plate.

A method for Lamb- wave generation and detection in an aluminum plate with a pulsed laser- ultrasonic transmitter and Michelson-interferometer receiver was developed. The defect shape and area in the images obtained using laser scanning, showed good agreement with the actual defect. The proposed approach can be used as a non-contact online inspection and monitoring technique.

Full Text Available It has been proved that ultrasonic energy can considerably increase the amount of oil recovery in an immiscible displacement process. Although many studies have been performed on investigating the roles of ultrasonic waves , based on the best of our knowledge, little attention has been paid to evaluate wave attenuation parameter, which is an important parameter in the determination of the energy delivered to the porous medium.

In this study, free fall gravity drainage process is investigated in a glass bead porous medium. Kerosene and Dorud crude oil are used as the wetting phases and air is used as the non-wetting phase.

A piston-like displacement model with considering constant capillary pressure and applying Corey type approximation for relative permeabilities of both wetting and nonwetting phases is applied. A pressure term is considered to describe the presence of ultrasonic waves and the attenuation factor of ultrasonic waves is calculated by evaluating the value of external pressure applied to enhance the flow using the history matching of the data in the presence and absence of ultrasonic waves.

The results introduce the attenuation factor as an important parameter in the process of ultrasonic assisted gravity drainage. The results show that only a low percentage of the ultrasonic energy 5.

This proves that the ultrasonic waves , even when the contribution is not substantial, can be a significantly efficient method for flow enhancement. Selective generation of ultrasonic Lamb waves by electromagnetic acoustic transducers. In this paper, we describe a modal expansion approach for the analysis of the selective generation of ultrasonic Lamb waves by electromagnetic acoustic transducers EMATs.

The numerical simulations and experimental examinations show that the ultrasonic Lamb wave modes can be effectively regulated strengthened or restrained by choosing an appropriate driving frequency of EMAT, with the geometrical parameters given. This result provides a theoretical and experimental basis for selectively generating a single and pure Lamb wave mode with EMATs.

Full Text Available ish fillet is one of fisheries products that easily deteriorated; hence handling techniques are needed to maintain the freshness. Ultrasonic wave have been widely applied to some of food products for maintaining freshness through microbial inactivation, however the ultrasonic application to fisheries products has not been reported. The purpose of this study was to analyze the effect of ultrasonic wave on fish freshness.

The stages of the study were sample preparation, sonication, freshness parameters examination and histology observation. The sample in which the TPC value was found significantly different, were further observed after 48 and 96 hours storage. The result showed that the TPC value of sonicated sample for 9 minutes was lower to that of without sonication. Histology analysis showed, however, sonication made the structure of muscle fiber less compact and deformation of myomer was found.

Detecting Lamb waves with broad-band acousto- ultrasonic signals in composite structures. Lamb wave dispersion curves and group velocities were correlated with variations in axial stiffness and shear stiffness in MMC and CMC. For CMC, interfacial shear strength was also correlated with the first antisymmetric Lamb mode. Ultrasonic creeping wave test technique for dissimilar metal weld.

To solve the problem encountered in the defect inspection of the surface and near-surface of dissimilar metal weld effectively, a new ultrasonic creeping wave test technique is developed. In this paper, the test technique and its experimental verification are mainly described. The verification results show that linear defect, which is similar to the defect found in liquid penetrant test, on the surface and near-surface of dissimilar metal weld can be detected effectively, by using ultrasonic creeping wave test technique.

And the depth, length and height of the defect can be determined easily. The effective covering depth of ultrasonic creeping wave test technique will reach mm. Meanwhile, the planar defect, with equivalent area more than 3 mm 2 , existed in welds can be detected efficiently. So, accurate measurement, which self height dimension of planar defect is above 2 mm, will be realized. Bi-directional ultrasonic wave coupling to FBGs in continuously bonded optical fiber sensing.

Fiber Bragg grating FBG sensors are typically spot-bonded onto the surface of a structure to detect ultrasonic waves in laboratory demonstrations. However, to protect the rest of the optical fiber from any environmental damage during real applications, bonding the entire length of fiber, called continuous bonding, is commonly done.

In this paper, we investigate the impact of continuously bonding FBGs on the measured Lamb wave signal. In theory, the ultrasonic wave signal can bi-directionally transfer between the optical fiber and the plate at any adhered location, which could potentially produce output signal distortion for the continuous bonding case. Therefore, an experiment is performed to investigate the plate-to-fiber and fiber-to-plate signal transfer, from which the signal coupling coefficient of each case is theoretically estimated based on the experimental data.

Finally, the signal waveform and arrival time of the output FBG responses are compared between the continuous and spot bonding cases. The results indicate that the resulting Lamb wave signal output is only that directly detected at the FBG location; however, a slight difference in signal waveform is observed between the two bonding configurations.

This paper demonstrates the practicality of using continuously bonded FBGs for ultrasonic wave detection in structural health monitoring SHM applications.

Structural damage detection using deep learning of ultrasonic guided waves. Structural health monitoring using ultrasonic guided waves relies on accurate interpretation of guided wave propagation to distinguish damage state indicators.

However, traditional physics based models do not provide an accurate representation, and classic data driven techniques, such as a support vector machine, are too simplistic to capture the complex nature of ultrasonic guide waves. To address this challenge, this paper uses a deep learning interpretation of ultrasonic guided waves to achieve fast, accurate, and automated structural damaged detection. To achieve this, full wavefield scans of thin metal plates are used, half from the undamaged state and half from the damaged state.

This data is used to train our deep network to predict the damage state of a plate with The goal of this ongoing work is to optimize experimental variables for a guided wave scanning method to obtain the most revealing and accurate images of defect conditions in composite materials.

This study focuses on signal processing effects involved in forming guided wave scan images. Signal processing is involved at two basic levels for deriving ultrasonic guided wave scan images.

At the primary level, NASA GRC has developed algorithms to extract over 30 parameters from the multimode signal and its power spectral density. At the secondary level, there are many variables for which values must be chosen that affect actual computation of these parameters.

In this study, a ceramic matrix composite sample having a delamination is characterized using the ultrasonic guided wave scan method. Energy balance and decay rate parameters of the guided wave at each scan location are calculated to form images.

These images are compared with ultrasonic c-scan and thermography images. The effect of the time portion of the waveform processed on image quality is assessed by comparing with images formed using the total waveform acquired. Full Text Available Introduction: Increase of world population, lack of food sources, and need for food security, protection of agricultural products against losses, drought, pests, and diseases, all seems to be necessary more than ever.

During the years, grains have been the main food of humans, especially wheat, barley, rice, and corn. So production and storage of these products is important for societies. One of the main problems in this field is protecting the grains in stores until consuming or planting them again.

Annually, over hundreds of millions tons of grains are lost by pests present in stores and not observing the scientific principles of storing. Control of insects and pests during storage as a destructive factor of stored products by harmless methods is necessary.

There are restrictions in use of chemically control methods against pests in stores. Therefore in recent decades, physically control methods have attracted a lot of attentions. The purpose of using physically control methods is eliminating pests with minimum destructive effect on the environment.

These methods directly affect on pests or change their living situations and create an unsafe environment for them. One of the tools that indirectly affect pests is ultrasonic waves. Ultrasonic waves are mechanical waves which can properly penetrate in air and porous areas.

These waves are completely safe for the environment and cause no damage to the environment. Ultrasonic waves as new safe strategy in insect control can prepare unsafe areas for annoying insects and agricultural pests.

The main characteristics of ultrasonic waves are safe for humans and environment. Materials and Methods: In this study, experiments were carried out to assess the repellent impact of ultrasonic waves on one important storage pest, red flour beetle Tribolium castaneum Herbs. The system, which produces ultrasonic waves , includes distributor of ultrasonic waves , power supply, central processor, oscillator, display. Process monitoring using optical ultrasonic wave detection. Optical ultrasonic wave detection techniques are being developed for process monitoring.

An important limitation on optical techniques is that the material surface, in materials processing applications, is usually not a specular reflector and in many cases is totally diffusely reflecting. This severely degrades the light collected by the detection optics, greatly reducing the intensity and randomly scattering the phase of the reflected light. A confocal Fabry-Perot interferometer, which is sensitive to the Doppler frequency shift resulting from the surface motion and not to the phase of the collected light, is well suited to detecting ultrasonic waves in diffusely reflecting materials.

This paper describes the application of this detector to the real-time monitoring of the sintering of ceramic materials. Guided- wave tomographic imaging of plate defects by laser-based ultrasonic techniques. Numerical simulation of ultrasonic wave propagation in elastically anisotropic media. The ultrasonic non-destructive testing of components may encounter considerable difficulties to interpret some inspections results mainly in anisotropic crystalline structures.

A numerical method for the simulation of elastic wave propagation in homogeneous elastically anisotropic media, based on the general finite element approach, is used to help this interpretation. The successful modeling of elastic field associated with NDE is based on the generation of a realistic pulsed ultrasonic wave , which is launched from a piezoelectric transducer into the material under inspection.

The aim of this work is the comparison between the results of numerical solution of an ultrasonic wave , which is obtained from transient excitation pulse that can be specified by either force or displacement variation across the aperture of the transducer, and the results obtained from a experiment that was realized in an aluminum block in the IEN Ultrasonic Laboratory. The wave propagation can be simulated using all the characteristics of the material used in the experiment valuation associated to boundary conditions and from these results, the comparison can be made.

Fatigue crack growth monitoring in multi-layered structures using guided ultrasonic waves. This contribution investigates the application of low frequency guided ultrasonic waves for monitoring fatigue crack growth at fastener holes in the 2nd layer of multi-layered plate structures, a common problem in aerospace industry.

The model multi-layered structure investigated consists of two aluminum plate-strips adhesively bonded using a structural paste adhesive. Guided ultrasonic waves were excited using multiple piezoelectric discs bonded to the surface of the multi-layered structure.

The wave propagation in the tensile specimen was measured using a laser interferometer and compared to numerical simulations. Experiments and 3D Finite Element FE simulations show a change in the scattered field around fastener holes caused by a defect in the 2nd layer. The amplitude of the guided ultrasonic wave was monitored during fatigue experiments at a single point.

The measured changes in the amplitude of the ultrasonic signal due to fatigue crack growth agree well with FE simulations. Decrease of Salmonella typhimurium in skim milk and egg by heat and ultrasonic wave treatment. Ultrasonic waves induce cavitation which is lethal for many bacteria.

When Salmonella typhimurium was suspended in skim milk or brain heart infusion broth and placed in an ultrasonicating water bath, the number of bacteria decreased by 2 to 3 log CFU in a time dependent manner. The killing by ultrasonic waves was enhanced if the menstruum was simultaneously maintained at 50 degrees C. Ultrasonic reduction in S. The results indicate that indirect ultrasonic wave treatment is effective in killing Salmonella in some foods.

Depending on which way the crystal is cut, the waves can be focused along the direction of ultrasound propagation or at right angles to the direction of propagation. Waves that travel along the direction of propagation are called longitudinal waves; as noted above, these waves travel in the direction in which molecules in the surrounding medium move back and forth. Waves that travel at right angles to the propagation direction are called transverse waves; the molecules in the surrounding medium move up and down with respect to the direction that the waves propagate.

Ultrasound waves can also propagate as surface waves; in this case, molecules in the surrounding medium experience up-and-down motion as well as expanding and contracting motion. In most applications, ultrasonic waves are generated by a transducer that includes a piezoelectric crystal that converts electrical energy electric current to mechanical energy sound waves.

Sound waves of frequency more than 20,Hz are called Ultrasonics. These frequencies are beyond the audible limit. Their wavelength are small. Production of Ultrasonic waves. Principle: When a rod of ferromagnetic material like nickel is magnetized. Longitudinally, it undergoes a very small change in length. This is called Magnetostriction effect. The circuit diagram of magnetostriction ultrasonic generator is as shown in the figure1. A short permanently magnetized nickel rod is clamped in the middle between two knife edges.

A coil L 1 is wound on the right hand portion of the rod. C is a variable capacitor. L 1 and C 1 form the resonant circuit of the collector-tuned oscillator. Coil L 2 wound on the LHS of the rod is connected in the base circuit. The coil L 2 is used as a feed back loop. When the battery is switched on, the resonant circuit L 1 C 1 sets up an alternating current o frequency. This current lowing round the coil L1 produces an alternating magnetic iels of frequency f along the length of the nickel rod.