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.