TDK CH101 Quick setup guide

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Chirp Microsystems reserves the right to change
specifications and information herein without notice.
InvenSense, a TDK Group Company
2560 Ninth Street, Ste 220, Berkeley, CA 94710 U.S.A
[phone]
www.chirpmicro.com
Document Number: AN-000158
Revision: 1.2
Release Date: 10/06/2021
CH101 and ICU-10201 Mechanical Integration
Guide

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1INTRODUCTION
The purpose of this document is to provide recommendations and guidance on the mechanical integration of Chirp CH101 and ICU-
10201 ultrasonic sensors in device enclosures. This document will cover the mechanical design, geometry, part and assembly
tolerances, material considerations, testing, and best practices for mechanical integration. All dimensions mentioned in this
document are in mm, unless otherwise specified.
The information in this guide only covers information related specifically to Chirp Microsystems’CH101 and ICU-10201 sensors, and
not other sensors, such as the CH201 and ICU-20201. If you are integrating other Chirp Microsystems sensors, please consult the
appropriate Mechanical Integration Guide for that product.

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2ACRONYMS AND ABBREVIATIONS
Some commonly used acronyms and abbreviations in this document are listed in Table 1.
Acronyms and Abbreviations
Definition
ASIC
Application-specific integrated circuit
FoV
Field-of-View
FPC
Flexible printed circuit
FWHM
Full-width half-maximum
IC
Integrated circuit
IR
Infrared
LSB
Least significant bits (ADC counts)
MEMS
Micro-electro-mechanical systems
PSA
Pressure-sensitive adhesive
PCB
Printed circuit board
PCBA
Printed circuit board assembly
PIF
Particle ingress filter
PMUT
Piezoelectric micromachined ultrasonic transducer
ToF
Time-of-Flight
Table 1. Acronyms and Abbreviations

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TABLE OF CONTENTS
1INTRODUCTION .........................................................................................................................................................................2
2ACRONYMS AND ABBREVIATIONS.............................................................................................................................................3
3OVERVIEW.................................................................................................................................................................................5
THEORY OF OPERATION ............................................................................................................................................................5
PACKAGE DIMENSIONS .............................................................................................................................................................5
SENSOR CONFIGURATIONS.........................................................................................................................................................6
3.3.1 Pulse-Echo...................................................................................................................................................................6
3.3.2 Pitch-Catch..................................................................................................................................................................6
4ACOUSTIC INTERFACES ..............................................................................................................................................................8
TUBES ..................................................................................................................................................................................8
HORNS .................................................................................................................................................................................8
DEFINITION OF FIELD-OF-VIEW .................................................................................................................................................10
SEPARATE VS INTEGRATED ACOUSTIC INTERFACE ...........................................................................................................................10
ANGLED/CURVED DEVICE ENCLOSURE EXTERIOR SURFACE...............................................................................................................11
MATERIALS ..........................................................................................................................................................................11
INDUSTRIAL DESIGN,TOLERANCES,AND MANUFACTURING GUIDELINES ..............................................................................................11
5PARTICLE INGRESS FILTERS ......................................................................................................................................................13
MESHES AND MEMBRANES......................................................................................................................................................13
PIF ACOUSTIC PERFORMANCE IMPACT AND INSERTION LOSSES .........................................................................................................14
PIF PLACEMENT....................................................................................................................................................................14
PIF INTEGRATION AND OPTIMIZATION ........................................................................................................................................15
6ASSEMBLY GUIDELINES, TOLERANCES AND REQUIREMENTS ...................................................................................................16
CH101 AND ICU-10201 MOUNTING........................................................................................................................................16
RECOMMENDED METHOD FOR SENSOR ASSEMBLY AND ATTACHMENT................................................................................................16
MAXIMUM RESIDUAL ASSEMBLY FORCE......................................................................................................................................16
SENSOR-TO-ACOUSTIC INTERFACE ASSEMBLY TOLERANCES ..............................................................................................................17
ACOUSTIC INTERFACE-TO-DEVICE ENCLOSURE ASSEMBLY TOLERANCES ...............................................................................................18
ASSEMBLY INSPECTION AND QUALITY CONTROL CHECKLIST ..............................................................................................................19
7SUMMARY...............................................................................................................................................................................20
DESIGN TRADEOFF CONSIDERATIONS..........................................................................................................................................20
MECHANICAL DESIGN AND INTEGRATION STEPS CHECKLIST ..............................................................................................................21
8REVISION HISTORY...................................................................................................................................................................22

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3OVERVIEW
THEORY OF OPERATION
The CH101 and ICU-10201 are ultrasonic transceiver rangefinders that use a piezoelectric micromachined ultrasonic transducer
(PMUT) to send out short pulses of soundwaves into the air. Upon hitting an object, these waves reflect back towards the PMUT,
causing it to vibrate and generate an electrical signal. The time needed for the soundwaves to travel from and back to the PMUT,
known as the Time-of-Flight (ToF), is measured by the built-in application-specific integrated circuit (ASIC). Using the speed of sound
(343 m/s at room temperature), the system can determine the distance to the object.
Unlike other types of ToF rangefinders, such as infrared (IR) sensors, the CH101 and ICU-10201 sensors are not affected by the color
or transparency of objects and works in all lighting conditions. It also uses significantly less power than comparable IR sensors and
the sensor’s Field-of-View (FoV) can be customized by using different acoustic housings.
PACKAGE DIMENSIONS
Figure 1. Package dimensions of the CH101.

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Figure 2. Package dimensions of the ICU-10201.
SENSOR CONFIGURATIONS
As ultrasonic transceivers, the CH101 and ICU-10201 are capable of measuring distances to objects just by themselves. However, a
network of sensors can be used together for additional functionality such as 2D and 3D location identification. The most common
sensor configurations are detailed below.
3.3.1 Pulse-Echo
The Pulse-Echo configuration is the basic configuration for the sensor In Pulse-Echo, a single sensor both transmits and receives its
own ultrasound to perform measurements.
Figure 3. Sensor operating in Pulse-Echo configuration.
In Pulse-Echo, the sensor both transmits and receives its own ultrasound signal.
3.3.2 Pitch-Catch
In Pitch-Catch configuration, one sensor is set as the transmitter, while one or more additional sensors are acting only as receivers. A
common use case of Pitch-Catch is to have one or more sensors on separate devices. This allows for the tracking of the distance,
position, and even orientation between devices depending on how many sensors are used.

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Figure 4. Ultrasonic transceiver sensors operating in Pitch-Catch configuration. One sensor is set to transmit, with all remaining sensors set to
receive only. The transmitting sensor can still measure the ToF of its own ultrasonic signal.

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4ACOUSTIC INTERFACES
The CH101 or ICU-10201 without an Acoustic Interface has poor sound output performance. The reason for this is the large acoustic
impedance difference between the PMUT (the source) and the air (the load) resulting in the energy from the PMUT not being
transferred efficiently to the air. In this regard, acoustic impedance can be thought of as analogous to electrical impedance. To
improve the transfer of sound energy to the air, an Acoustic Interface is required in front of the sensor’s port hole to better match
the impedance. In addition, the dimensions and geometry of the Acoustic Interface dictate the FoV of the sensor. Two broad
categories of Acoustic Interface are used with the CH101 and ICU-10201: tubes and horns.
TUBES
Tubes are holes of a specific length and diameter. For the CH101, the optimal tube length is 0.475 mm with a diameter of 0.7 mm. A
straight tube is the Acoustic Interface of choice for applications that require the smallest opening possible. Straight tubes are always
omnidirectional (~180 degree FoV).
HORNS
An acoustic horn focuses the acoustic beam, making the FoV narrower. The terminology used to describe horns is shown in Figure 5.
Figure 5. Terminology for acoustic horns.
The process of calculating and determining the required dimensions for different horns is complex and beyond the scope of this
document. However, in general, the following statements hold true.
•The larger the mouth of the horn, the smaller the FoV, everything else being equal
•The longer the horn (up to a limit), the higher the output pressure, everything else being equal

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Acoustic Interface Part
Number
AH101-180180
AH101-045045
AH101-045045-MR
AH101-030060
Type
Tube
Horn
Horn
Horn
Overall Length (mm)
0.475
1.85
1.5
5.3
Throat Diameter (mm)
0.7
0.7
0.75
0.7
Mouth Diameter(s) (mm)
0.7
3.0
3.0
5.0 (Horizontal)/2.0
(Vertical)
Field-of-View (Horizontal)
(Degrees)
180
45
45
30
Field-of-View (Vertical)
(Degrees)
180
45
45
60
On-Axis Pulse-Echo
Amplitude (Typ. Relative
to AH-180180)
1x
4.5x
3x
3x
Comments
Omnidirectional
Narrow FoV
Narrow FoV, Module
retrofit
Asymmetric FoV
Table 2. Summary of common CH101 and ICU-10201 Acoustic Interfaces

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DEFINITION OF FIELD-OF-VIEW
The FoV of the CH101 and ICU-10201 can be set to meet the application requirements by designing the appropriate Acoustic
Interface. It should be noted that, unlike the FoV of IR sensors, it is still possible to detect objects beyond the acoustic FoV. This is
because the acoustic FoV is defined as the full-width half-maximum (FWHM) of the round-trip beam pattern. If the reflected echo off
an object outside the FoV has an amplitude greater than the minimum amplitude threshold, it is still possible to detect such targets.
Figure 6. A beam pattern of a 45-degree FoV horn measured against a large flat target.
Note how the amplitude does not fall abruptly to zero (absolute units) and that depending on the target and the distance, it will still be possible
to detect targets outside the rated FoV.
SEPARATE VS INTEGRATED ACOUSTIC INTERFACE
The Acoustic Interface can either be a standalone, separate part or it can be integrated into the device enclosure. The choice
between a separate or integrated Acoustic Interface depends on many factors. Some major tradeoffs of each approach are
highlighted in the table below.
Figure 7. Separate Acoustic Interface (left) and integrated Acoustic Interface (right).
Separate Acoustic Interface
Integrated Acoustic Interface
Pros
•More control over critical Acoustic Interface
dimensions and surfaces, which may lead to more
consistent results
•Easier to ensure good and consistent contact with
sensor. Recommended for pitch-catch applications.
•Removes potential gaps/flushness issues caused by
assembly variation. This is especially beneficial for
wide or omnidirectional FoV Acoustic Interfaces.
Cons
•Requires at least one extra part in the BOM and extra
assembly step(s) to assemble the device
•May require tighter tolerances and/or more Design
for Assembly considerations
Table 3. Tradeoffs of separate and integrated Acoustic Interfaces.

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ANGLED/CURVED DEVICE ENCLOSURE EXTERIOR SURFACE
Chirp does not recommend having the external device enclosure be at an angle relative to the top of the sensor package. Chirp cannot
guarantee the performance of an Acoustic Interface modified to fit on an angled surface.
Figure 8. Cross-section views showing how to mount the sensor on an angled device enclosure surface.
The overall goal is to ensure that the dimension and design of the Acoustic Interface is unaltered in order to maintain acoustic performance. The
end requirement is that the top of the sensor must be parallel with the exterior device enclosure surface.
Concave exterior enclosure surfaces should generally be avoided because of the potential for ultrasound to reflect and cause signal
interference. Convex exterior enclosure surfaces are OK. However, for maximum acoustic performance, the curvature on the
exterior surface cannot “cut-off” or otherwise change the dimensions of the intended Acoustic Interface. Similar to device
enclosures with angled surfaces, the opening of the Acoustic Interface should remain parallel with the top of the sensor.
Figure 9. Types of device enclosure surface curvature. Concave surfaces should be avoided.
Convex surfaces are acceptable as long as the Acoustic Interface dimensions are not affected.
MATERIALS
Any material that does not absorb ultrasound (~175 kHz for CH101 and ICU-10201) is suitable for use as the Acoustic Interface. This
includes most plastics (PC, ABS, Delrin, etc.), metals, and composite materials. Materials NOT recommended for use include all
foams, fabrics, and textiles.
For the most consistent acoustic performance, it is also recommended to use materials that can achieve surface finish/roughness of
1.6 μm Ra or better.
INDUSTRIAL DESIGN, TOLERANCES, AND MANUFACTURING GUIDELINES
For prototyping different Acoustic Interface designs, 3D printing can be a fast and economical way to create a proof-of-concept
design. For 3D printing, the following guidelines are recommended for best performance:
•Printer type: Stereolithography (SLA)

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•Layer thickness of 0.025 mm (0.001”)
For critical dimensions, the tolerance of printed samples should be within 0.1 mm of nominal. Chirp DOES NOT recommend using
FDM (filament based) 3D printers for making horn Acoustic Interfaces. FDM 3D printing does not have the required resolution,
accuracy, and surface finish to produce Acoustic Interfaces with good acoustic performance.
For mass production, Chirp has the following recommendations for the tooling of Acoustic Interfaces:
•Unless specified otherwise, the tolerance of critical dimensions should be ± 0.05 mm or better. Critical dimensions include
the internal geometry of the Acoustic Interface and the alignment features that will align it to the sensor’s port hole. For
non-critical dimensions, a tolerance of ± 0.1 mm is acceptable.
•The sensor-contacting surface of the Acoustic Interface should be flat to 0.025 mm or better.
•The minimum surface finish for all critical Acoustic Interface surfaces (sensor contact surface, tube/horn internal profile
surface, exterior top surface) should be equivalent to SPI-B2 or better, with SPI-A3 or better recommended.
Figure 10. Critical surfaces on Acoustic Interfaces are highlighted in red.
The inside pocket surface of the Acoustic Interface needs to be smooth to ensure good and gapless contact with the sensor. The highlighted
exterior-facing surfaces (in red) interact with the ultrasound wave. To minimize unwanted interference (constructive or destructive), these
surfaces should also be tightly controlled to ensure a smooth finish.
•For straight tubes, the tube interior edges must be as sharp as possible for optimal acoustic performance. The maximum
allowable edge fillet radius is 0.025 mm.
Figure 11. The exterior edge of a tube Acoustic Interface (highlighted blue) should be as sharp as possible to maintain a wide FoV.

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5PARTICLE INGRESS FILTERS
Using a protective covering or Particle Ingress Filter (PIF) over the sensor is recommended if dust, liquid or other contaminants are
present in the application environment. For the CH101 and ICU-10201, the currently supported PIF material is SAATI Acoustex
B042HY. The B042HY has been tested by Chirp to provide a dust protection rating of IP5X. Due to the small size of the sensor, it is
not feasible to test for IP6X, because negative pressure cannot be applied to the part. Should the customer require certification for
IP6X, they must run that test independently on their device with the sensor(s)installed.
MESHES AND MEMBRANES
There are two broad categories of PIF materials: meshes and membranes. Meshes are primarily woven material (like fabric), and
thus its structure is 2-dimensional and very regular throughout the material. On the other hand, membranes are often nonwoven
material, so they inherently have a randomness in their structure. An example of a nonwoven membrane material would be
expanded PTFE. Membranes can also be solid, thin barriers, like polyester or mylar films.
Figure 12. Representative close-up images of the structure of woven meshes (left) and nonwoven membranes (right).
A natural consequence of the difference in meshes vs membranes is that meshes generally have a smaller acoustic performance
impact and reduced ingress protection capability compared to membranes.
Mesh
Membrane
•Often woven, fabric-like material with a grid-like, regular,
“2D” structure.
•Simpler, more predictable structure generally allows for
better airflow, sound transmission and less acoustic
performance impact
•Good for IP5X and brief liquid splash or shallow
submersion when coated with a hydrophobic coating
•Dust protection is dictated by mesh opening size. Liquid
protection is dependent on acoustic path geometry and
design.
•Either nonwoven, random structure or a thin solid film
•The random structure or solid film aspects of membranes
generally result in higher acoustic performance impact
•Materials rated up to IP68 and generally independent of the
Acoustic Interface design and placement of the membrane.
Table 4. Summary table of properties of meshes and membranes.

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PIF ACOUSTIC PERFORMANCE IMPACT AND INSERTION LOSSES
The SAATI Acoustex B042HY has one-way insertion loss of 3 dB. This implies a 6 dB total insertion loss in use with the sensor,
because the insertion loss applies during both transmit and receive.
PIF Material
IP Rating
Insertion Loss (Round-trip)
SAATI Acoustex B042HY
IP5X
6 dB
Table 5. Acoustic insertion loss of PIF materials on sensor.
PIF PLACEMENT
For the CH101 and ICU-10201, the PIF must be placed in a specific position in the acoustic path between the sensor PMUT and the
air. Chirp’s testing has shown that PIFs placed directly on top of the sensor package and right over the port hole generally
significantly decrease acoustic performance. Placing the PIF for the sensor at the top of the Acoustic Interface is recommended.
Chirp has validated this placement for the SAATI Acoustex B042HY. The optimal PIF placement for any other PIF other than the SAATI
Acoustex B042HY is not guaranteed. Please contact Chirp for more information.
Figure 13. Examples of bad vs good PIF placement.
Bad PIF placement (left) is when the PIF is placed directly on top of the sensor package. Good PIF placement involves placing it on top of the
Acoustic Interface. This applies for both tubes (middle) and horns (right).

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In some instances when using a straight tube Acoustic Interface, designers may want to have the PIF invisible for industrial design
reasons. In this case, the PIF can be obscured by placing an additional straight tube on top of the inner tube Acoustic Interface. The
outermost tube will need to have a 0.9 mm diameter and 0.9 mm thickness. This outermost tube only has a minor effect on the
acoustic performance of the sensor, as the performance is primarily dictated by the inner tube. This PIF placement also works
because the PIF is on top of the first inner tube Acoustic Interface, and not directly on top of the sensor.
Figure 14. How to integrate a PIF without it being visible on the exterior (tube interfaces only, does not apply to horns).
The solution is to put another tube on top of the inner Acoustic Interface tube.
PIF INTEGRATION AND OPTIMIZATION
The addition of a PIF can potentially change the acoustic properties of the Acoustic Interface and is likely to negatively impact
acoustic performance. The severity of the change will vary from material to material, with membranes generally having a larger
negative impact than meshes. Some of this performance impact can be mitigated by changing the dimensions of the Acoustic
Interface to accommodate the addition of the PIF.
For tube Acoustic Interfaces, adding a PIF often changes its resonance characteristics. To get optimal acoustic performance with a
given PIF, the length/thickness of the tube may need to be changed to re-optimize it for the PIF.
For horn Acoustic Interfaces, the approach is not as predictable. Though in general, horns are less sensitive to the impact from small
dimension changes caused by the addition of a PIF and the performance may be acceptable without modifications.
If you are having issues with integrating PIFs in your design, please contact Chirp for assistance.

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6ASSEMBLY GUIDELINES, TOLERANCES AND REQUIREMENTS
CH101 AND ICU-10201 MOUNTING
The recommended method of placing the CH101 or ICU-10201 in a device is to mount and solder it on its own PCB (FPC, rigid flex or
rigid PCB). This PCBA makes it much easier to control the mounting and assembly of the sensor onto the Acoustic Interface, thereby
decreasing the chances of poor assembly accuracy and reduced acoustic performance.
RECOMMENDED METHOD FOR SENSOR ASSEMBLY AND ATTACHMENT
The assembly method recommended by Chirp for securing the sensor PCBA to the Acoustic Interface is to use liquid adhesive (glue),
because liquid adhesive does not impart additional stress onto the sensor. For all other assembly methods, it is important to verify
that the maximum assembly force is not exceeded post-assembly. For example, while gluing the sensor PCBA to the Acoustic
Interface, an operator may temporarily exceed the maximum assembly force, but before the adhesive finishes curing, this excess
force must be removed. This can be checked by testing the sensor’s operating frequency before and after assembly. The sensor’s
post-assembly operating frequency should not shift beyond a given amount compared to the pre-assembly operating frequency (see
Table 66).
The following is a list of adhesives recommended by Chirp for assembling the PCBA onto the Acoustic Interface:
•Dymax 9-911 REV A Ultra-light Weld (UV Cure)
For designs using an Acoustic Interface that is separate from the device enclosure, it is also recommended to use glue to assemble
the Acoustic Interface and sensor PCBA subassembly to the device enclosure, because the maximum assembly force requirement
still applies. This method avoids assembly force/stress that can be transferred from the Acoustic Interface and onto the sensor
package.
During the assembly gluing process, care should be taken to dispense adhesive in such a way that the adhesive does not flow or wick
into the port hole of the sensor. Therefore, it is recommended to apply the adhesive between the Acoustic Interface and the PCB
(not between the Acoustic Interface and the sensor). A post-cure visual inspection should be conducted to verify that no adhesive
has flowed or wicked into the sensor port hole.
Figure 15. Cross-sectional picture showing where glue should be dispensed for attaching the Acoustic Interface.
The glue should be dispensed between the Acoustic Interface and the PCB and not between the Acoustic Interface and sensor.
MAXIMUM RESIDUAL ASSEMBLY FORCE
To effectively radiate ultrasound into the air, the CH101 and ICU-10201 are manufactured in such a way that the PMUT is not
completely stress-isolated from the package. One integration requirement arising from this feature is that there is a limit to the
amount of residual force that can be applied to the sensor before it results in excessive change in the PMUT’s acoustic
characteristics. For sensor configurations that are sensitive to operating frequency, such as in Pitch-Catch, the maximum allowed
residual force during operation is 50 grams-force. For all other sensor configurations where the operating frequency is not critical,
the maximum allowable residual force during operation is 150 grams-force. It is acceptable to temporarily exceed these values when
the sensor is not in operation, such as during assembly, as long as the excess force is reduced or removed afterwards (i.e. there are
no excess residual stresses/forces on the sensor after assembly). It is critical that there is no excess residual assembly force above
the maximum allowable value on the sensor once assembly is complete.

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Sensor Configuration
Max Assembly Force (grams-force)
Max Allowable Frequency Shift Due to
Assembly (Hz)
Pulse-Catch
50
750
Pitch-Echo
150
1500
Table 6. Summary of maximum allowable residual assembly force.
The easiest way to detect when this force is exceeded is to measure the frequency shift from before and after assembly.
One method of holding the module against the device enclosure while avoiding applying excessive force on the module is to use a
backplate to transfer the force applied to the module to the Acoustic Interface instead of the sensor (see Figure 16).
Figure 16. Example of a backplate-based module design to avoid applying excessive force on the sensor.
SENSOR-TO-ACOUSTIC INTERFACE ASSEMBLY TOLERANCES
When assembling the sensor and Acoustic Interface together, Chirp recommends the sensor port hole be concentrically aligned to
Acoustic Interface to within 0.1 mm or better. The sensor port should not be blocked or occluded by the Acoustic Interface (see
Figure 17).
For the Z-dimension assembly tolerance, the only requirement is that there is no gap between the sensor and the Acoustic Interface
and that their mating surfaces are parallel (see Figure 18). Any gap between the sensor and Acoustic Interface will result in
unpredictable acoustic performance. In addition, while ensuring no gap between the sensor and Acoustic Interface, the assembly
force must be below the maximum force limit as discussed in Section 6.3.
Figure 17. Examples of various degrees of sensor port alignment with the Acoustic Interface, from perfect concentric alignment (left), maximum
acceptable limit tangent alignment (middle), to bad occluded alignment (right).

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Figure 18. Examples of what good and bad assembly of the Acoustic Interface look like.
There must be no gap between the Acoustic Interface and the sensor for optimal acoustic performance.
ACOUSTIC INTERFACE-TO-DEVICE ENCLOSURE ASSEMBLY TOLERANCES
For applications using a separate Acoustic Interface from the overall device enclosure, there are additional considerations for the
assembly and associated tolerances of the Acoustic Interface to the device enclosure. They primarily address the potential impact to
the beam pattern caused by obstructions and reflections from undesired features, such as edges and gaps (see Figure 19 and Figure
20 ). Because of this, wider FoV Acoustic Interfaces are more susceptible to these effects and steps should be taken during assembly
to ensure a good beam pattern and overall acoustic performance.
Figure 19. Bad assemblies create edges for ultrasound to reflect off from and affect the beam pattern. A good assembly has no gaps/steps,
resulting in a smooth, consistent beam pattern.
Figure 20. Effect of edges on the beam pattern.
Edges created from gaps or steps in the assembly process reflect ultrasound, causing interference (red dashed lines) and results in inconsistent
beam patterns.
Ideally, the Acoustic Interface is mounted flush to the device enclosure. In general, Chirp recommends the Acoustic Interface be
mounted flush to the device enclosure to within 0.2 mm.

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Figure 21. The Acoustic Interface should be mounted flush to the device enclosure to within 0.2 mm.
There should also be minimal diametrical/clearance gap between the Acoustic Interface and the device enclosure. Chirp recommends
no more than 0.1 mm clearance gap between the device enclosure and Acoustic interface.
Figure 22. The clearance gap between the device enclosure and Acoustic Interface should be 0.1 mm or less.
ASSEMBLY INSPECTION AND QUALITY CONTROL CHECKLIST
The following is a list of items to check to ensure that the sensor is correctly assembled and integrated into the overall device:
1. Sensor port is not blocked or occluded. If the sensor port is blocked or occluded, whether by the Acoustic Interface, glue or
foreign contaminants, the acoustic performance will be negatively affected. One simple method for checking that the sensor
port is not blocked or occluded is to visually inspect that the annular gold plating on the port hole is visible and is not “cut
off”(see Figure 17).
2. The assembly process does not impart excessive residual stress on the sensor. This can be verified by checking the sensor’s
frequency before the sensor is securely attached to the Acoustic Interface (e.g. Acoustic Interface sits on top of the sensor
with only gravity) and after the sensor is fixed to the Acoustic Interface (such as with glue). Residual stress on the sensor will
shift its operating frequency.
3. No gap between Acoustic Interface and top of the sensor. Gaps between the Acoustic Interface and sensor will reduce
performance. This can be (indirectly) checked by measuring the gap between the bottom of the Acoustic Interface and the
PCB or measuring the top of the Acoustic Interface to the top of the PCB. It is also important to check that the Acoustic
Interface is not mounted crooked or at an angle by checking that the Acoustic Interface top/bottom is parallel to the PCB (see
Figure 18).
4. If a separate Acoustic Interface is being used, check that it meets the assembly requirements highlighted in Figure 21 and
Figure 22.

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7SUMMARY
DESIGN TRADEOFF CONSIDERATIONS
As with any engineering design, there are always design tradeoffs. When integrating the CH101 or ICU-10201, the top tradeoff
considerations are:
•FoV vs max range: The amount of energy being emitted from the PMUT is finite. To focus the ultrasound beam in a narrow
FoV requires taking energy from the sides of the beam pattern. Conversely, to make a wide FoV beam, the sound energy
cannot be focused and must be spread out more equally in all directions. Consequently, narrow FoV designs have longer
maximum operating range.
•Horn size vs performance: If the application requires a horn (e.g. for increased maximum range or a narrower FoV), the
overall acoustic performance can be improved or limited by the size of the horn. In particular, the larger the size of the horn
mouth, the smaller the FoV. Generally, a longer horn has more sound output (up to a limit).
•Level of ingress protection vs acoustic performance impact: The more demanding an application’s ingress protection
requirement, the more an appropriate PIF material will restrict airflow. The more restrictive material will necessarily reduce
the amount of sound output into the air, thus reducing maximum range.
•Assembly tolerance vs acoustic performance consistency: The acoustic performance is the highest when the alignment of
all parts in the acoustic path are perfectly concentric with the sensor port hole. The more the assembly deviates from this
ideal alignment, the more the acoustic performance is impacted.
•Separate vs integrated Acoustic Interface: A separate Acoustic Interface will make tighter tolerances possible on critical
dimensions, everything else being equal. However, this will result in an additional part in the BOM and assembly and
introduce another contribution towards the overall tolerance stack-up. In comparison, an integrated Acoustic Interface has
the opposite characteristics and may require tighter tolerances and/or additional Design for Assembly considerations to
stay below the allowable maximum residual assembly force.
When working through these considerations for mechanical integration design, keep in mind the overall requirements of the
application and device. Depending on the application, one or possibly even all the negative performance tradeoffs may ultimately be
inconsequential, because the sensor still performs sufficiently for the application’s needs. As a result, it is worthwhile to test the
“worst-case” design and to see how far off it is from meeting the application’s performance requirements.