Piezoelectric Pulse Sensor
Junior Engineering Clinic I, Junior Undergrad
Team members: Michael Simunek, Lauren Markey
The goal of this project was to design a wearable skin patch for pulse monitoring. The idea to use a piezoelectric device was proposed by the professor. Piezoelectric devices generate electricity when a strain is produced in the material due to deformation. These devices have garnered a lot of interest in the field of energy harvesting, however, they may be best suited for sensory application as material deformation produces large voltage spikes, but very small current output.
We began this study under the belief that the force of a pulse would be enough to trigger an electrical response in the device if placed directly on the skin.
PZT Disk
Macro Fiber Composite (MFC)
We tried both a PZT disk and a Macro Fiber Composite (MFC). The MFC is designed to be more flexible and durable than the PZT disk without sacrificing electrical output. Unfortunately, the force of a pulse was not enough to register a visible response from these devices when connected to an oscilloscope. We found that a pulse could be seen if the device was held securely on the neck or wrist in the same manner an EMT may take a patient's pulse. We found some literature claiming that the sensitivity of a piezoelectric device may be increased if it is pre-stressed, possibly by putting a small bend in the material. A wrist strap device was designed for the MFC using a 3D printed holder, a piece of Velcro, and a small piece of foam to deform the material.
This device worked well as a wearable concept, however, a pulse could still not be seen without additional pressure applied by the opposite hand. Our next step was to design a variable back pressure device. A new device was 3D printed based of the concept above. This new concept included a spring that would apply pressure to the back of the piezo device in the same manner a finger would. A screw was used to adjust tension on the spring until an optimal back pressure was reached.
Unfortunately, this design still did not produce the desired pulse signal. Literature has shown that piezoelectric devices produces the highest otuputs when actuated in a cantilever beam set-up. The next iteration of our design aimed to incorporate this fact into the previous design.
Designed and manufactured by Michael Simunek
This final device, pictured above, was successful in producing the desired pulse wave found in the wrist (pictured above right). While we were able to generate a successful prototype in course of a single semester, our prototype missed many of the desired design attributes, specifically in terms of being minimalist and non-invasive to the wearer.