# US 11,906,427 B2 · Method and apparatus for determining a reflectivity value indicating a reflectivity of an object

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- Number: US 11,906,427 B2
- Document ID: US11906427B2
- Status: Granted
- Kind: B2
- Application number: 17/466,231
- Filed: 2021-09-03
- Published: 2022-03-10
- Granted: 2024-02-20
- Earliest claimed: 2020-09-07
- Assignees: Infineon Technologies AG
- Applicants: Infineon Technologies AG
- Inventors: Armin Josef Schoenlieb; Caterina Nahler; Hannes Plank
- Web page: https://patentgrep.com/patent/US11906427B2

## CPC

- G01N 21/55: Specular reflectivity
- G01S 17/894: Three-dimensional [3D] imaging with simultaneous measurement of time-of-flight at a two-dimensional [2D] array of receiver pixels, e.g. time-of-flight cameras or flash lidar
- G01S 7/4802: {using analysis of echo signal for target characterisation; Target signature; Target cross-section}
- G01S 7/497: Means for monitoring or calibrating
- G01S 17/32: using transmission of continuous waves, whether amplitude-, frequency-, or phase-modulated, or unmodulated
- G01S 17/36: with phase comparison between the received signal and the contemporaneously transmitted signal
- G01N 2021/558: {Measuring reflectivity and transmission}
- G01N: INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES (measuring or testing apparatus or processes other than immunoassay, involving enzymes or microorganisms C12M, C12Q)
- G01S: RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES

## Abstract

A method for determining a reflectivity value indicating a reflectivity of an object is provided. The method includes performing a Time-of-Flight (ToF) measurement using a ToF sensor. A correlation function of the ToF measurement increases over distance within a measurement range of the ToF sensor such that an output value of the ToF sensor for the ToF measurement is independent of the distance between the ToF sensor and the object. The method further includes determining the reflectivity value based on the output value of the ToF sensor for the ToF measurement.

## Claims

### Claim 1

A method for determining a reflectivity value indicating a reflectivity of an object, the method comprising:
performing a Time-of-Flight (ToF) measurement using a ToF sensor, wherein a correlation function of the ToF measurement increases over distance within a measurement range of the ToF sensor such that an output value of the ToF sensor for the ToF measurement is independent of the distance between the ToF sensor and the object; and
determining the reflectivity value based on the output value of the ToF sensor for the ToF measurement.

### Claim 2 (depends on 1)

The method of claim 1, wherein the correlation function represents an expected distance-dependent output of the ToF sensor for the ToF measurement assuming that a light strength of light received at the ToF sensor during the ToF measurement is constant over distance within the measurement range of the ToF sensor.

### Claim 3 (depends on 1)

The method of claim 1, wherein determining the reflectivity value comprises applying at least one correction to the output value of the ToF sensor for the ToF measurement.

### Claim 4 (depends on 1)

The method of claim 1, wherein performing the ToF measurement comprises:
illuminating a scene comprising the object with modulated light based on an illumination signal;
driving a light capturing element of the ToF sensor based on a reference signal; and
varying at least one of the illumination signal, the reference signal and a time offset between the illumination signal and the reference signal during the ToF measurement.

### Claim 5 (depends on 4)

The method of claim 4, wherein each of the illumination signal and the reference signal exhibits a respective alternating series of high and low pulses of equal duration, and wherein the time offset between the illumination signal and the reference signal is varied during the ToF measurement.

### Claim 6 (depends on 4)

The method of claim 4, wherein at least one of the illumination signal and the reference signal exhibits a respective alternating series of high and low pulses of varying duration, and wherein the respective alternating series of high and low pulses is varied for at least one of the illumination signal and the reference signal during the ToF measurement.

### Claim 7 (depends on 6)

The method of claim 6, wherein the respective alternating series of high and low pulses is varied with increasing variation rate for at least one of the illumination signal and the reference signal during the ToF measurement.

### Claim 8 (depends on 6)

The method of claim 6, wherein the time offset between the illumination signal and the reference signal is varied during the ToF measurement.

### Claim 9 (depends on 4)

The method of claim 4, wherein the ToF sensor temporarily exhibits a respective auxiliary correlation function for each variation of the illumination signal, the reference signal and the time offset between the illumination signal and the reference signal used during the ToF measurement, wherein the correlation function of the ToF measurement is a combination of the auxiliary correlation functions, and wherein the at least one of the illumination signal, the reference signal and the time offset between the illumination signal and the reference signal is varied such that the auxiliary correlation functions are shifted with respect to each other within the measurement range of the ToF sensor.

### Claim 10 (depends on 4)

The method of claim 4, wherein the modulated light is emitted by an illumination element of the ToF sensor, and the method further comprising:
measuring a temperature at the illumination element; and/or
measuring a light strength and/or a rise time of the modulated light emitted by the illumination element; and
varying the at least one of the illumination signal, the reference signal and the time offset between the illumination signal and the reference signal based on at least one of the measured temperature at the illumination element and the measured light strength and/or rise time of the modulated light emitted by the illumination element.

### Claim 11 (depends on 1)

The method of claim 1, wherein a course of the correlation function of the ToF measurement over distance depends on an estimated course of an actual light strength of light received at the ToF sensor over distance within the measurement range.

### Claim 12 (depends on 1)

The method of claim 1, wherein the correlation function of the ToF measurement is predetermined in a factory calibration.

### Claim 13 (depends on 1)

The method of claim 1, further comprising:
performing a plurality of ToF calibration measurements for obtaining calibration data indicating the actual light strength of light received at the ToF sensor for different distances between the ToF sensor and a reference object; and
adapting the correlation function of the ToF measurement based on the calibration data.

### Claim 14 (depends on 1)

The method of claim 1, further comprising:
performing one or more further ToF measurements using the ToF sensor;
determining a distance value indicating a distance to the object based on an output of the ToF sensor for the one or more further ToF measurements; and
outputting data indicating the reflectivity value and the distance value.

### Claim 15

An apparatus for determining a value indicating a reflectivity of an object, the apparatus comprising:
a Time-of-Flight (ToF) sensor configured to perform a ToF measurement, wherein a correlation function of the ToF measurement increases over distance within a measurement range of the ToF sensor such that an output value of the ToF sensor for the ToF measurement is independent of the distance between the ToF sensor and the object; and
a processing circuit configured to determine the reflectivity value based on the output value of the ToF sensor for the ToF measurement.