Airborne ultrasound has many applications such as, ranging, nondestructive evaluation, gas flow measurement, and acoustic microscopy. This paper investigates the generation and detection of ultrasound in air at a few MHz. Conventional plane piston lead zirconium titanate (PZT) based transducers perform poorly for this application due to the lack of proper matching layer materials. Electrostatic, or capacitive, transducers promise higher efficiency and broader bandwidth performance. The device structure in this work consists of a capacitor where one plate is a circular silicon nitride membrane coated with gold and the other is a rigid silicon substrate. By applying a voltage between the membrane and the silicon substrate, an electrostatic force is exerted on the membrane which sets it in motion, thus generating a sound wave in air. Presented here is an electrical equivalent circuit model for electrostatic transducers which is based on the early work of Mason (1942). The electrostatic transducers were designed and constructed for operation at 1.8 and 4.6 MHz. The transducers were fabricated using standard micromachining techniques. An optical interferometer was used to measure the peak displacement of the 1.8 MHz electrostatic transducer at 230 /spl Aring//V. A transmit-receive system was built using two electrostatic transducers. The system had a signal to noise ratio of 34 dB at a transducer separation of 1 cm. Each transducer had a 3-dB bandwidth of 20%, and a one-way insertion loss of 26 dB. There is excellent agreement between the measured device performance and theoretical predictions.

A surface micromachined electrostatic ultrasonic air transducer

An ultrasonic system useful for providing imaging, therapy and temperature monitoring generally comprises an acoustic transducer assembly configured to enable the ultrasound system to perform the imaging, therapy and temperature monitoring functions. The acoustic transducer assembly comprises a single transducer that is operatively connected to an imaging subsystem, a therapy subsystem and a temperature monitoring subsystem. The ultrasound system may also include a display for imaging and temperature monitoring functions. An exemplary single transducer is configured such that when connected to the subsystems, the imaging subsystem can generate an image of a treatment region on the display, the therapy subsystem can generate high power acoustic energy to heat the treatment region, and the temperature monitoring subsystem can map and monitor the temperature of the treatment region and display the temperature on the display, all through the use of the single transducer. Additionally, the acoustic transducer assembly can be configured to provide three-dimensional imaging, temperature monitoring or therapeutic heating through the use of adaptive algorithms and/or rotational or translational movement. Moreover, a plurality of the exemplary single transducers can be provided to facilitate enhanced treatment capabilities.

Imaging, therapy, and temperature monitoring ultrasonic system

A transverse mode ultrasonic probe is provided which creates a cavitation area along its longitudinal length, increasing the working surface of the probe. Accessory sheaths are also provided for use with the probe to enable a user to select from features most suited to an individual medical procedure. The sheaths provide acoustic enhancing and aspiration enhancing properties, and/or can be used as surgical tools or as medical access devices, protecting tissue from physical contact with the probe.

Ultrasonic device for tissue ablation and sheath for use therewith

An ultrasonic medical device comprises an ultrasonic vibration generator that generates vibration along its longitudinal axis. The ultrasonic vibration is transmitted through an ultrasonic coupler and a series of transformer sections that amplify the ultrasonic vibration. A flexible member is coupled to the distal end of the transformer sections, and is thus supplied with a longitudinal vibration at its base by the transformer sections. The flexible member is designed so that it converts the longitudinal vibration into a standing wave that runs along the length of the flexible member. The standing wave produces a series of nodes and anti-nodes along the length of the flexible member. Each of the anti-nodes produces cavitation in fluids in contact with the probe. The cavitation of the fluids causes destruction of adjacent tissue. In this manner, the entire length of the flexible member becomes a working surface that may be utilized for destroying tissue.

Ultrasonic medical device operating in a transverse mode

A non-invasive visual imaging system is provided, wherein the imaging system procures an image of a transducer position during diagnostic or therapeutic treatment. In addition, the system suitably provides for the transducer to capture patient information, such as acoustic, temperature, or ultrasonic images. For example, an ultrasonic image captured by the transducer can be correlated, fused or otherwise combined with the corresponding positional transducer image, such that the corresponding images represent not only the location of the transducer with respect to the patient, but also the ultrasonic image of the region of interest being scanned. Further, a system is provided wherein the information relating to the transducer position on a single patient may be used to capture similar imaging planes on the same patient, or with subsequent patients. Moreover, the imaging information can be effectively utilized as a training tool for medical practitioners.

Visual imaging system for ultrasonic probe

Ultrasonic transducers comprising an ultrasonic transducer element, a pair of electrodes provided on opposite sides of the element, and an acoustic impedance-matching layer formed on an ultrasonic wave-radiating surface of the element through one electrode. The acoustic impedance-matching layer is made of a porous polymer film or a composite material comprising thermally expanded resin microspheres dispersed in a cured product of thermosetting resin and has an acoustic impedance not larger than 0.6×10 6 Ns/m 3 . Two-layer constructions may also be used as the acoustic impedance-matching layer.

Piezoelectric ultrasonic transducers having acoustic impedance-matching layers

An ultrasonic diagnostic apparatus detects variations of an acoustic characteristic to obtain the fluctuation of temperature within a body to be examined. The ultrasonic diagnostic apparatus includes an ultrasonic transducer for transmitting an ultrasonic wave and receiving the reflected ultrasonic wave which is in turn converted into an electric signal. The signal is phase-detected in accordance with a plurality of gate intervals or a plurality of window interval to detect a phase difference therebetween. The relative variation of velocity dispersion before and after heating of the body is obtained on the basis of the phase variation resulting from the variation of the ultrasonic drive frequency.

Ultrasonic temperature measurement apparatus

The design and application of high-frequency piezoelectric air transducers are described. By employing a double layer acoustic matching transformer to a ceramic thickness mode vibrator, an air transducer with low insertion loss (52 dB) and good RF pulse response (9 µs of -20 dB ring-down period) has been developed. Use of the transducer operating at 1 MHz for distance measurement in a range of 0~20 cm has revealed that the range resolution and the measurement accuracy are 1.5 mm and of the order of 0.1 mm, respectively. Other applications described here are the characterization of cloth surfaces and profile measurement of cloths.

High-Frequency Ultrasonic Transducer Operating in Air

PURPOSE:To improve the sensitivity in transmitting and receiving of the utrasonic transmilter-receiver for use in the air by utilizing a high polymer porous film provided with a laminate layer as an acoustic matching layer and thereby reducing the density of an acoustic matching layer member and decreasing the attenuation of the acoustic waves. CONSTITUTION:On the ultrasonic waves radiating surface 11 of a piezo-electric vibrator 10, the high polymer porous film 12 which is provided with laminate films 13 and 14 on either surface is provided as an acoustic matching leayer that matches the acoustic impedance with the air which is a load. These films 13 and 14 prevent liquids, etc. From intrusion to the layer 12. Additionally, because the layer 12 is the high polymer porous film, the density of the acoustic matching film as well as the attenuation of the ultrasonic waves are made small. Therefore, the sensitivity in transmitting and receiving of the ultrasonic transmitter-receiver for use in the air is improved.

Ultrasonic transmitter-receiver

PURPOSE:To obtain an ultrasonic wave transmitter-receiver with fast sound velocity, matching layer and ease of manufacture by using an epoxy resin or a silicone resin as a base material and using a composite material mixed with a thermal expansion balloon as an acoustic matching member. CONSTITUTION:The acoustic matching layer 2 is bonded to an ultrasonic wave irradiating plane 4 of a piezoelectric vibrator 11 transmitting and receiving an ultrasonic wave and a back load member 31 is bonded as required made of ferrite rubber is bonded to the back side 5. As the acoustic matching layer 2, a composite agent where the thermal expansion balloon as the 1st filler and glass balloon as the 2nd filler using silicone rubber as the base material are mixed is used. The elastic modulus of a high polymer constituting a spherical shell of the thermal expansion balloon is <=1/10 in comparison with the elastic modulus of the glass constituting the spherical shell of the glass balloon. Thus, the acoustic matching layer having fast sound velocity is obtained without reducing remarkably the sensitivity of wave transmission and reception.

Masayuki Tone

Papers

Piezoelectric ultrasonic transducers having acoustic impedance-matching layers

Ultrasonic temperature measurement apparatus

High-Frequency Ultrasonic Transducer Operating in Air

Ultrasonic transmitter-receiver

Ultrasonic wave transmitter-receiver