# US 10,768,330 B2 · System and method for locating a marker using a locator with multiple transmitters

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- Number: US 10,768,330 B2
- Document ID: US10768330B2
- Status: Granted
- Kind: B2
- Application number: 15/216,503
- Filed: 2016-07-21
- Published: 2017-01-26
- Granted: 2020-09-08
- Earliest claimed: 2015-07-22
- Assignees: Metrotech Corporation
- Applicants: Metrotech Corporation
- Inventors: Stephen John Petherick
- Web page: https://patentgrep.com/patent/US10768330B2

## CPC

- G01V 3/104: {using several coupled or uncoupled coils (G01V3/101 takes precedence)}
- G01B 7/26: for measuring depth
- G01V 3/08: operating with magnetic or electric fields produced or modified by objects or geological structures or by detecting devices (with electromagnetic waves G01V3/12)
- G01V 3/12: operating with electromagnetic waves {(operating with millimetre waves G01V8/005)}
- G01V 15/00: Tags attached to, or associated with, an object, in order to enable detection of the object (record carriers for use with machines having a detectable tag or marker G06K19/00)
- G01V: GEOPHYSICS; GRAVITATIONAL MEASUREMENTS; DETECTING MASSES OR OBJECTS; TAGS (means for indicating the location of accidentally buried, e.g. snow-buried, persons A63B29/02)
- G01B: MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS

## Abstract

A system and method of for estimating the depth of a marker may include a marker locator. The marker locator may include a first transmitter that generates a first activation signal, second transmitter that generates a second activation signal, a receiver that detects first and second response signals, and a processor that determines a depth of a marker based on the first and second response signals. The first transmitter is located at a first position, and the second transmitter is located at a second position apart from the first position. The first and second response signals respectively correspond to the first and second activation signals. The processor is coupled to the receiver. According to some embodiments, the first and second activation signals and the first and second response signals may be separated by time division multiplexing.

## Claims

### Claim 1

A marker locator comprising:
a first transmitter that generates a first activation signal to activate a marker, the first transmitter being located at a first position;
a second transmitter that generates a second activation signal to activate the marker, the second transmitter being located at a second position apart from the first position;
a receiver that detects first and second response signals, the first and second response signals transmitted by the marker, the first and second response signals respectively corresponding to the first and second activation signals, wherein the receiver is located at a third position apart from the first position and the second position; and
a processor that determines a depth of the marker based on the first and second response signals, the processor being coupled to the receiver.

### Claim 2 (depends on 1)

The marker locator of claim 1, wherein at least one of the first and second transmitters includes an inductive loop.

### Claim 3 (depends on 2)

The marker locator of claim 2, wherein the inductive loop includes one or more of an air core and a ferrite core.

### Claim 4 (depends on 1)

The marker locator of claim 1, wherein the first and second activation signals and the first and second response signals are separated by time division multiplexing.

### Claim 5 (depends on 1)

The marker locator of claim 1, wherein the first and second activation signals include burst sequences, each burst in the burst sequences being at a resonant frequency of the marker.

### Claim 6 (depends on 5)

The marker locator of claim 5, wherein the resonant frequency of the marker is between 30 and 250 kHz.

### Claim 7 (depends on 5)

The marker locator of claim 5, wherein each of the burst sequences has a duty cycle of between 10% and 15%.

### Claim 8 (depends on 1)

The marker locator of claim 1, wherein the first and second response signals are characterized by an exponential decay lifetime.

### Claim 9 (depends on 1)

The marker locator of claim 1, wherein the receiver applies phase sensitive detection to the first and second response signals.

### Claim 10 (depends on 1)

The marker locator of claim 1, wherein the first and second transmitters are coupled by a rigid member.

### Claim 11 (depends on 1)

The marker locator of claim 1, wherein the processor determines the depth of the marker based on an equation:
Z
=
a
+
2
·
C
·
R
2
-
R
2
+
C
·
a
2
-
C
2
·
R
2
C
-
1
where:
Z represents the depth of the marker;
R represents a radius of the first and second transmitters;
a represents a distance between the first and second positions; and
C is given by the equation C=K2/3, where K is a ratio of a measured intensity of the first and second response signals.

### Claim 12 (depends on 1)

The marker locator of claim 1, wherein the marker includes a resonant ball marker.

### Claim 13 (depends on 1)

The marker locator of claim 1, wherein the marker locator does not move while detecting the first and second response signals.