Ultrasonic measurement technology
An essential competence in working with ultrasound is the availability of and experience in dealing with acoustic measurement technology. Here, inoson GmbH has been able to gather experience over many years, which has resulted in specific measurement technology, be it procedures or devices. As the procedures and in particular the analysis and evaluation of their results often require specialised knowledge and experience, we also offer this as a service. As a result, we always provide meaningful documentation and discuss the results with the client.
The methods can be roughly described as follows.
The complex, frequency-dependent electrical impedance of an ultrasonic transducer contains a lot of information about this ultrasonic transducer and its transfer function. This is due to the piezoelectric coupling in the resonator, which connects the mechanical and electrical worlds. Using knowledge of the electromechanical equivalent models, far-reaching statements can be made regarding the resonance behaviour. We measure the complex, frequency-dependent impedance under different load conditions and, of course, as a function of temperature.
These analyses are required for tolerance tests, optimisation procedures and fault analysis, among other things.
The spatial sound pressure distribution or the surface movement of an ultrasonic transducer is an important transmission characteristic in addition to the temporal transmission behaviour. Focussing and direction of the sound on the area of interest increases efficiency and reduces disturbance variables. Damage to an ultrasonic transducer can also be detected.
Of course, we can also verify whether the ultrasound arrives at the expected position, e.g. in flow measurement sections.
Such an analysis is carried out using a scanning system, whereby we use hydrophones or microphones as sensors or directly scan the surface movement using dynamic laser interferometry.
The temporal transmission behaviour of an ultrasonic transducer describes the electrical wave train that the ultrasonic transducer makes available for signal processing. The analysis of the behaviour of this transfer function with regard to the measurement task but also disturbance variables (such as temperature) is an essential prerequisite for sensor optimisation. We use special laboratory equipment to take the signal generation into account and operate the transducer at the correct operating point. Of course, we have countless tools at our disposal for evaluating and characterising the transmission behaviour.
The results are often used in the specification of ultrasonic transducers to describe the transmission behaviour of an ultrasonic transducer.
There are ultrasonic applications where the requirements are exceptional. This applies to flow measurement, for example, where differences in the sound transit time in the picosecond range must be reliably determined. Here, linearity and the quality of reciprocal operation, which is essential for the process, play an important role. Structure-borne noise also has a significant influence here. We have developed measurement methods with which we can qualitatively and quantitatively assess these special properties.
Within an ultrasonic sensor system, many materials are often used to fulfil acoustic tasks. These can be waveguides, matching layers, lenses, damping or housing parts. In most cases, the acoustic properties of such materials are not defined in the data sheet. The temperature dependence of these properties is also almost always unknown. This is a challenge when designing, as the wavelength and acoustic transmission behaviour are not known. It is also difficult to guarantee an initial test of such materials that reflects the acoustic functionality.
In addition to piezoelectric resonators, we also characterise passive materials in terms of temperature-dependent sound velocity and frequency-dependent attenuation. Different wave types such as longitudinal and transverse waves or guided waves can be specified.
A common problem with ultrasonic systems is the inadequate description of the transducer properties. An available transducer is used, at least as long as it is still available. Replacement is not possible due to the lack of standardisation of ultrasonic transducers. In addition, a transducer does not have fixed transmission characteristics, but these are determined by the electrical operating parameters.
We offer a comprehensive application-oriented characterisation and description of ultrasonic transducers. The results are summarised in a report. One of the main areas of application for this service is the characterisation of ultrasonic transducers for flow measurement. Here, based on our experience, we have a standardised procedure so that different ultrasonic transducers can be compared with each other in terms of their suitability in a measuring section. The results of such a "fingerprint" are always discussed in detail with the client.
