SonarBell is an omni-directional,  fully passive sonar reflector that provides a strong and clear double echo return.

No batteries or electronics are used in SonarBell and therefore no maintenance is required.

SonarBell can be designed to provide a required Target Strength at the frequency band to be used.

Applications for SonarBell within the many sectors in which it could be deployed include Location Marking, Asset Marking, Testing and Sonar Performance checking.

SonarBell® is a fully passive sonar reflector used for:

  • Asset & location marking
  • Sonar testing

Advantages of SonarBell®are:

  • Clear double echo signature for identification
  • No battery or electronics
  • No maintenance
  • Use at depth
  • It is omni-directional
  • Easy to handle

In its simplest form the SonarBell consists of an outer spherical shell (made of aluminium or plastic) and an inner spherical solid core of silicone based polymer.

The SonarBell contains no power supply or electronics. It is an entirely inert and passive device and non-magnetic.

The shell has a number of tiny holes in its surface to allow water to pass into the narrow annulus between the shell and the core.

This free flooding design means that the SonarBell can be deployed at depth with any resultant change being automatically equalled.

How does the SonarBell® work?

Energy from a Sonar

The SonarBell receives and reflects an incoming sonar signal which initially reflects off the outer shell surface but then also travels around the outer shell of the SonarBell and through its inner core.

Its spherical design and the materials used in its construction control the speed of the sound waves as they pass through the SonarBell causing them to converge at the rear inner face of the outer shell in a constructive interference.

This focuses the incoming sound signal and returns it in the direction of the sonar as a strong and reliable point source acoustic signal.

The SonarBell can be used in conjunction with any sonar from the simplest echo sounder to the most sophisticated military system.

How does the SonarBell® differ from simple passive reflectors?

Resonate at Specific Frequencies

The SonarBell is manufactured to resonate at specific frequencies between 1kHz and 1.2MHz. Its design produces a single narrow band resonance peak, multiple resonance peaks or a broadband response.

The SonarBell is manufactured in different sizes and from different materials dependent upon the specific requirements of its application. Broadly speaking the larger the size of the SonarBell and the lower the frequency the further away it can be detected. The smallest SonarBell delivered to date is 50 mm in diameter and the largest 600mm in diameter. SonarBells with a size of 200mm or less will be sufficient for most non military purposes.


The SonarBell is designed to be pressure equalising and is certified to 4km depth.

The SonarBell is omnidirectional. Whatever the angle of incidence of the incoming sonar pulse on the shell of the SonarBell the incoming sound energy is captured, focused and returned in the direction of the sonar which has insonified the SonarBell.

The SonarBell has a uniquely identifiable double echo structure which does not occur naturally.

The SonarBell is made of non-magnetic materials.

Notable features of the SonarBell®

Deployed Indefinitely | Manufactured to a Specific Target Strength

The SonarBell can be deployed for an indefinite period without the need for the battery changing and maintenance which transponders require. This is a major operational/cost benefit in all situations and particularly so at depth or in hostile sea conditions. The SonarBell can be manufactured to a specific target strength.

This allows the SonarBell to be used as a reliable test target for sonars immediately post manufacture or in service including in theatre for military operations.