The effectiveness of ultrasonic anti-fouling

Measuring signal strength of different transducers locations on a box-cooler

Shipsonic™ has invested considerable resources in developing systems with a guaranteed, consistent effectiveness

Correct ultrasonic frequency with sufficient energy

50 Watt and 100 Watt transducer

50 Watt and 100 Watt transducer; different size, different response frequency

Our transducers are 50, 100 or 120 Watts. Their frequencies range from 20 to 40 KHz. Each transducer type has its own response frequency. That is the frequency in which the transducer functions optimally. With optimal we mean: gives the most ultrasonic sound. The transducer will also emit sound in frequencies higher or lower than its response frequency, but in these frequencies the sound pressure is considerably lower.Combining different transducers on 1 object, for example a box-cooler, will guarantee that the box-cooler will vibrate with high energy in a broad range of frequencies.

Frequency also changes depending on the structural characteristics of the object on which the transducers are installed. Hence, you can never foretell the frequencies in which an object will vibrate, even if you know the characteristics of the transducers. Combining different transducer models on 1 object optimizes the chances that the effective frequencies will occur with sufficient energy.

Correct transducer location

Prototype of the ultrasonic signal strength tester we use to optimize transducer location

Prototype of the Shipsonic ultrasonic signal strength tester

This is an acoustical problem, and acoustical problems are notoriously complex. As with all such problems, the solution is often a trial and error process.
To address this problem, Shipsonic is developing an ultrasonic signal strength measuring device. We develop this new device completely in-house. The first prototype is now ready. The signal tester will use a contact microphone to measure ultrasonic energy levels in the steel of the object to be protected, while we have a magnetic device to temporarily place transducers on the box-cooler, sea-chest or elsewhere. This way we can compare tester readings of different transducer locations and thus find the optimal locations for the transducers.

Transducer design and fixation

Comparing different transducer housings and different ways of fixation

Different transducer-housing and -fixation testing

At Shipsonic we intentionally chose a PVC transducer housing, while this is not common in shipping. However, metal housings have too much mass compared to the mass of the transducer itself. Therefor, these housings absorb more energy. This sometimes results in the housing cracking up. The mass of the metal housing also affects the resonant frequency of the transducer. Thus, the PVC housing of the transducer is not a way of cost-saving, but a conscious technical design choice. Within the PVC housing, the resonance element of the transducer can vibrate completely independent. With the water resistant model, the contact surface of the transducer is glued directly to the object to be protected, so no intermediate steel or artificial part of the housing gets in the way. This way sound reflection is avoided.

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