Piezoelectric Spheres and Hemispheres

piezoelectric sphere assembled from two hemispheres

In 2013 Sensor Technology Ltd. launched an R&D project to improve our processes for producing piezoelectric spheres and hemispheres. Now, three years later, we have reached our goals. We are CNC machining PZT spheres to the same high quality standards we impose on all of our piezoelectric ceramic components. Additionally, CNC machining has increased our throughput and decreased our production costs.

Background:

Spherical transducers offer an obvious, significant advantage over all other designs: they are inherently omnidirectional. Other common designs are omnidirectional only at lower frequencies. At higher frequencies they become increasingly directional. On the other hand, spherical devices remain omnidirectional regardless of frequency.

Spherical transducers offer other noteworthy advantages. They have good sensitivity. With the right choice of piezoelectric ceramic they make effective receivers and transmitters. They are also inherently strong.  As a result, spherical transducers generally have high depth ratings.

Sensor Technology Ltd. has been using piezoelectric spheres to build omnidirectional transducers and hydrophones for decades. Sometime around 2013 we started to see an increased demand for these omnidirectional sensors.  Interestingly, the requests didn’t come from one specific industry. Customers across several markets were asking for spherical transducers. In response, we launched an R&D project to improve our PZT sphere manufacturing processes.

Solution – CNC Machined Piezoelectric Spheres:

The crux of the project was to use as much CNC machining as possible. Precision machining would provide the same accuracy and consistency we demand of all of our other piezoelectric ceramics. At the same time we wanted to exploit one of the other advantages of CNC machining: throughput. This was not just to meet the rising demand but also to drive down production costs. Piezoelectric spheres are notoriously expensive.

Piezoelectric hemispheres made of PZT to be assembled into piezoelectric spheresTo be clear, the expense of PZT spheres is with good reason. Compared to common piezoelectric ceramic parts, such as discs and blocks, that require only a few machining steps, spheres are complicated to produce. Most notably, spheres are not machined (or molded) as a single piece. They are an assembly of two hemispheres. So, the price of a sphere reflects the price of two hemispheres.

Additionally, manufacturers create piezoelectric spheres by electrically wiring and then bonding together hemispheres. This assembly labour required to produce a sphere adds to the cost.

Finally, machining the hemispheres themselves is a complicated and time consuming process. We form the outer geometry with hundreds or even thousands of small passes. Plus, once the outer shape has been formed, we flip over the ceramic so the machining process can be repeated to hollow out the inside.

Outcome:

Sensor Technology Ltd. now CNC machines piezoelectric spheres in a wide range of sizes. We’ve made spheres as small as 0.170″ in outer diameter.  (That’s a 440 kHz resonance!)

Additionally, our process works with different materials. We can CNC machine hemispheres from any of our Navy Type PZT formulations. We can make hard PZT spheres for transmit applications and soft PZT spheres for receivers.

Ultimately, the CNC process gives us control over every detail. (For example, we can control the capacitance of a piezoelectric sphere by changing the wall thickness.) We are proud of our achievements. We can confidently state that Sensor Technology Ltd. provides industry leading piezoelectric spheres and hemispheres. Regardless, our R&D efforts are ongoing and our production of piezoelectric spheres and hemispheres continues to improve. Contact us to discuss your specific requirements.

 

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