We have been working on air-coupled ultrasonic transducers for more than 20 years. The main result is a robust, efficient and flexible technology able to produce different transducers in terms of centre frequency, sensitivity, bandwidth and field geometry that can be adapted to different applciations that include NDT, materials characterization, surface metrology, etc.
We started by making transducers for our own research. Now we make transducers for academic collaborations or for industrial partners under contract.
We have tested our technology for different applications, different clients and in different industrial enviroments, including food, agriculture, aeronautical, farma, building, and energy industries, with industrial partners that include: ACCIONA, AIRBUS, Oi2GO, Qi2, SIRO, TECNATOM, TETRAPAK, etc.
Our air-coupled transducers are the result of research in five main areas:
Figure 1. Fields involved in the desing, optimization and fabrication of air-coupled piezoelectric transducers.
This permit us to produce efficient air-coupled transducers. Three main standard designs are available:
One of the main characteristics of these transducers is that they can be used with any comercial ultrasonic electronic equipment currently available (probably for NDT purposes of for water inmerison or for medical applications) for both trasmission and reception stages. We currently use Krautkramer, Olympus and DASEL pulser/receivers. But any other more general equipment can also be used. For example, excellent results are also obtained in the transmission stage by using a conventional function generator (e.g. Agilent) that can be supported by a power amplifier (e. Falco). The same for the reception stages where standalone amplifiers or preamplifiers can also be used (Olympus, DASEL, Phoenix, etc.)
These flat transducers are designed to optimize both sensitivity and bandwith. The standard desing (with a BNC back connector) is illustrated in Fig. 2. Hosing is cylindrical and made of aluminum, with a front ring.
Figure 2. Schematic representation of the flat general-purpose transducers.
Available frequency range and main transducer characteristics are shown in table I
These transducers are characterized as illustrated in figure 3.
Figure 3. Transducer characterization set-up
As an example, figure 4 and 5 shows impulse response (excitation 100 V, one semicycle of square wave with a Olympus 5077 PR and reception directly into a Tektronix digital oscilloscope, 1 Mohm).
Figure 4. 2 MHz air-coupled trasnducer. Impulse response and sensitivity frequency band.
Figure 5. 0.25 MHz air-coupled trasnducer. Impulse response and sensitivity frequency band