Measurement Transducer Impulse Response Using an Exponential Sine Sweep Method

: The impulse response of a piezoelectric transducer can be calculated using the electrical equivalent circuit model with the Manson method for bandwidth transducers. Nevertheless, these approaches are not sufficiently precise because the importance of the homogeneous structure medium where the transducer emits the signal in part determines the bandwidth in which it acts due to the medium interactions with the environment. This paper describes preliminary research results on piezoelectric impulse response measurements in a small space, making use of the procedure presented by Angelo Farina for transducers emitting in reverberant spaces. Combining the basics of the exponential sine sweep (ESS) method, techniques of arrival detection, and signal processing it is possible to obtain the impulse response in a piezoelectric transducer emitting in a homogeneous medium.

The impulse method, which is based on recording measuring signal, can be used to obtaining transfer function of common electroacoustic systems and their impedance.Also, physical phenomena occurring in the ultrasonic transducers can be observed and diagnosed in detail when the impulse method in association with digital processing of the signal.
One of these methods with sweep sinus requires an anechoic chamber in order to delete the influence of the room and get a good signal-to-noise ratio.On the other hand, using a quasi-anechoic chamber give the possibility of the measurement in a small room.
In this paper, the method proposed by A. Farina to get the impulse response in rooms is implemented in electromechanical transducers and an ultrasonic transducer through exponential sweeps.For several reasons, sweeps are a far better choice for transfer-function measurements than noise sequences MLS.

II. Method
In order to test the method in twice sorts of transducers, an anechoic chamber was used to reduce the number of reflections in the walls, floor, and cell in the case of electromechanical loudspeaker transducer.In the second case with piezoelectric ceramic PZT a sweep sinus was emitted in a water medium.In both cases, to avoid reflections from surfaces the signal has been cut before the first reflection according to the size of each room.Also, in both cases, the same method to obtain the impulse response was used.
The signal emitted depends on the frequency response of the transducer evaluated whereby an exponential sine sweep is generated in a width band suitable . / * 0 12 3 4 3 5 − 1 Where 8 9 and 8 : are the initial and end frequencies of the signal respectively and ; represent the time.

II. Method
Once the signal has been emitted by the device under test (DUT) and record in digital system acquisition (DAQ), the spectrums of the record and the inverse signal emitted are multiplied to get the impulse response.
Jorge Otero and Ivan Felis.
Finally, an IFFT brings back the inverse filter to time domain.

III. Electromechanical transducer measurement
A sweep sinus measurement with a single microphone was performed.A loudspeaker Genelec 8010A was set up over a flat surface separated from floor 1.6 meters.A receiver is a Behringer ECM 8000 microphone separated 1 meter of the source • Sample rate: 48kS/s.
• M-Audio sound card.
• Signal calibrated to 91dB with white noise The instantaneous sweep power should be controllable according to the frequency just being swept through.With this, it avoids the saturation on the sound card.

IV. Underwater transducer measurement
The process of impulse measurement was assessed in a couple of RESON TC 4034 transducers.The experimental environment is a water tank with a water volume of 0.64 m & .Both similar sensors are separated 30cm each other and a national instrument DAQ acquisition system was used with a sample rate of 10 ⁄ +, ,.
Jorge Otero and Ivan Felis.
This sweep was recorded for -../0 and in order to suppress all reflections a time window of 12./0 was used to extricate the direct signal from the file before the first scatter appear and delete the electromagnetic signal from the electric components.
The exponential sweep signal emitted has a duration of 200us.