Galfenol Slotted Cylinder Transducer

ETREMA Products, Inc. (EPI), in conjunction with an STTR partner, developed a design and the manufacturing methods for a Galfenol-based low frequency, split ring (slotted cylinder) transducer. The design is targeted for high acoustic performance with reduced production costs, improved reliability, and improved robustness. Performance attributes include:

• Operating frequency < 1 kHz
• Source levels > 210 dB
• Bandwidth at least 200 Hz
• Q factor ≤ 7

For a slotted cylinder transducer in the first resonance mode, the two sides of the split move in opposite directions, so that the entire shell opens and closes in the manner of a clam shell. The size of the split ring transducer is much smaller than a wavelength at its operating frequency. Typical slotted cylinder transducers have a high Q resonance and narrow operating bandwidth. In an attempt to maximize the bandwidth, the shell is made from a low mass material such as fiberglass or carbon fiber composite. Conventionally made units still have a Q of 7 or more.

 

Conventional split ring transducers are expensive assemblies. The outer shell is a graphite fiber composite of tapered thickness. The piezoceramic drivers on the inside of the ring are also tapered. This requires the individual piezoceramic bars to be a trapezoid with different heights and different base angles. Each must be ground to a different shape specification, greatly increasing the cost of the purchased piezoelectric material. The complexity of the assembly also adds to the cost as each piezoceramic bar must be electrically connected together. These electrical connections are common points-of-failure in the design.

In order to improve upon the design from a cost and reliability standpoint an innovative solution utilizing Galfenol as the active material was conceived. Exploiting the toughness and robustness that Galfenol alloys exhibit, horseshoe shaped active elements were designed to be integrated into existing graphite composite shells. The use of Galfenol as the active component simplifies the design by reducing the number of parts and electrical connections that must exist. In addition, forging of the horseshoe shape can be accomplished using low cost manufacturing techniques reducing the overall cost of the device.