Subjecting transducers to high input powers can generate significant temperature rises within the device. The resultant temperature depends on the thermal properties of the materials used, efficiency of the transducer and the operating environment. OnScale separates the design problem into an acoustic simulation to calculate losses which can be input into a thermal model to solve for the temperature gradients.

1. Transducer Heating
CONFIDENTIAL

2. Introduction
o When subjected to high input power, ultrasonic transducers can
experience significant internal temperature rises
o The temperature reach depends on the thermal properties of the
material used, the efficiency of the transducer, and the environment in
which the transducer is operating
o OnScale can be used to the thermal behaviour of transducers, and its
effect on their performance

3. Effects of Increased
Temperature
o Increased temperature can have a number of disruptive effects on
performance:
o Reduction in efficiency due to softening of transducer materials,
particularly polymers
o Mechanical distortion of the transducer:
o Loss of front face flatness causes wavefront distortion
o Internal stresses can damage bondlines and materials

4. Thermal Modelling Approach
o Acoustic and thermal timescales often differ by 6 orders of magnitude
o Microseconds vs seconds
o This makes it useful to decouple the acoustic and thermal simulations
o Acoustic simulation is used to calculate the heat generated due to
losses in the device
o This can be applied to a thermal model which runs over a much
longer timescales (minutes or hours)

5. Piezocomposite Example
o Consider the 2-2 piezocomposite device shown below:
PZT Pillars
Polymer filler
Matching
layer
Water load
Backing
Electrodes
Absorbing boundaries on all sides

6. Acoustic Simulation
o An acoustic model is run to calculate loss per cycle:
o Mechanical Loss
o Dielectric Loss
Acoustic model Loss

7. Thermal Simulation
o Loss is then included as the input to a thermal model which
can be run over a much longer timescale:
o minutes vs milliseconds
Thermal map Temperature at device centre

8. Thermo-Mechanical
Simulation
o The temperature map can be used to perform thermo-
mechanical analysis:
o Displacements
o Stresses
Resultant displacement at maximum temperature

9. Thermal Analysis Overview
1. Acoustic model generates loss
array data
2. Loss array is input into a thermal
model
3. Thermal array used to calculate
thermo-mechanical deformation
Acoustic model
Loss Data
Thermal model
Max Temp.
Thermo-mechanical model

10. Simulation Metrics
Model
Acoustic/Thermal/
Mechanical
Elements 9200
Total Runtime* 25s
Memory (RAM) 27 MB
* Run on Dell Precision Tower 7810