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09:45 Feb-28-2000
Discussion on Applications for Air Ultrasound Arrays

As we are developing a new technology for building up high efficient ultrasonic transducer arrays, we want to start a discussion with your suggestions as NDT-users on applications and specifications needed.
As a prototype we want to begin with an ultrasonic array for air ultrasound.
What applications do you think could need such arrays? What specifications should the transducer follow (frequency, bandwidth, sensitivity, number of elements, dimensions...)?
What problems could be solved with such a transducer, what could not be solved sufficiently in the past using other technologies?

02:53 Feb-28-2000
Re: Discussion on Applications for Air Ultrasound Arrays

We are interested in discussing the possibility of using your technology for 3D holographic imaging in air, using our technology,
developed for fingerprint visualisation (see: http://www.optel.com.pl/article/english/article.htm).

Important for this application are broadband air transducers.

Regards

Wielsaw Bicz

Ultrasonic holographic camera

05:21 Feb-28-2000
Re: Discussion on Applications for Air Ultrasound Arrays

Edouard G. Nesvijski

00:23 Feb-29-2000
Re: Discussion on Applications for Air Ultrasound Arrays

: Edouard G. Nesvijski

Dear Mr. Nesvijski,

your comments are very interesting for me. I would please you to describe briefly 1 example for an application, which needs such a smallband airborne transducer array. Every detail would be very welcome! How must be the specifications of such an array? What advantages would have such a solution in contrast to other methods?

Best regards,

Martin Heinz.

04:46 Feb-29-2000
Re: Discussion on Applications for Air Ultrasound Arrays

I had no contact with the group of Prof. G. Hayward. But there are different possibilities to build up ultrasonic transducers based on silicon technology. One way is followed by the company "Sensant corp. / USA", where they had built up a type of electrostatic transducer based on silicon technology. Our project focuses on other technologies. For me it is also not so important, how we will build up these structures, but what advantages could have these structures in NDT.
I`m sorry that I am not allowed to tell you something about the technology we are developing in this moment. But I will provide some technical papers, if the project is finished.

03:26 Feb-29-2000
Re: Discussion on Applications for Air Ultrasound Arrays

There may be a way to use off-the-shelf broadband transducers and "shape" their frequency spectra to create the desired narrow band transducers you discuss. The Noise Suppressor II (NSII, new product manufactured by SLX, Inc.) is a small, add-on unit that operates with any analog or digital UT instrument and is positioned between the transducer and your receiver. It has two independent manually tunable bandpass filters that can be tuned manually over the frequency range (three different models, each with a separate frequency range – 0.15 to 0.7 MHz, 0.5 to 2.5 MHz, and 1.5 to 7 MHz) and once it "locks on" to the transducer's center frequency (determined by watching your display) it has a separate bandwidth control that tunes the band width to one of three settings -- 20%, 30%, or 60% of center frequency. In other words, your receiver is now only receiving energy in a narrow band around the center frequency because all frequencies outside of this band are being attenuated. For example, a 5 MHz broadband transducer (say 100% bandwidth) can be modified to a narrow band transducer (say 20% bandwidth) simply by rotating the knobs of the NSII. Details of the NSII can be found at www.slx-inc.com or by going to the Exhibitor section here at NDTnet and scrolling down to SLX.

Tony Mucciardi

02:31 Mar-01-2000
Re: Discussion on Applications for Air Ultrasound Arrays

Liviu Singher

: Dear Mr. Nesvijski,

: There may be a way to use off-the-shelf broadband transducers and "shape" their frequency spectra to create the desired narrow band transducers you discuss. The Noise Suppressor II (NSII, new product manufactured by SLX, Inc.) is a small, add-on unit that operates with any analog or digital UT instrument and is positioned between the transducer and your receiver. It has two independent manually tunable bandpass filters that can be tuned manually over the frequency range (three different models, each with a separate frequency range – 0.15 to 0.7 MHz, 0.5 to 2.5 MHz, and 1.5 to 7 MHz) and once it "locks on" to the transducer's center frequency (determined by watching your display) it has a separate bandwidth control that tunes the band width to one of three settings -- 20%, 30%, or 60% of center frequency. In other words, your receiver is now only receiving energy in a narrow band around the center frequency because all frequencies outside of this band are being attenuated. For example, a 5 MHz broadband transducer (say 100% bandwidth) can be modified to a narrow band transducer (say 20% bandwidth) simply by rotating the knobs of the NSII. Details of the NSII can be found at www.slx-inc.com or by going to the Exhibitor section here at NDTnet and scrolling down to SLX.

: Tony Mucciardi

05:29 Mar-01-2000
Re: Discussion on Applications for Air Ultrasound Arrays

I would like to notice that originally we discussed transducers design, but now the emphasis moved to filters. Tony Macciardi presented a very interesting information of the new product that allow manual regulation of filtration in different frequency band ranges and suppress noise. Liviu Singher comments on possibility of digital filtration. I have some experience of the both approaches to filtration of acoustic signals using the FIR and IIR digital filter design. Some attempts were made to use different types of digital filters: Butterworth, Tschebyscheff Inverse, Tschebyscheff, Elliptic, Bessel, and others. Independently of digital or analog all filters introduce some frequency dependent time-phase shifts. The filters attenuate noise as well as signal changing only their ratio. Thus, we loose part of original information, and all later fine wavelet analysis becomes dependent on these transforms. For example, measurement of time of flight in this case contains time measurement error. Usage of FFT for the same income signal gives a large variation of complete or phase spectra, which also contains important data. Optimal choice of the threshold level is a complicated task in this case. Transducer itself is a primary element of the signal filtration. That is why it seems that transducer design is very important for improvement test procedures, it should be designed for a specific task, and, as a result, should not be wide-band.

Edouard G. Nesvijski