Waste Water Assessment

CROSS-REFERENCE TO RELATED APPLICATIONS

p-0002This application is a filing under 35 U.S.C. 371 of International Application No. PCT/GB2011/050437 filed Mar. 7, 2011, entitled “Waste Water Assessment” claiming priority to GB Application No. 1004139.06 filed on Mar. 12, 2010, entitled “Waste Water Assessment”, which are incorporated by reference herein as if reproduced in their entirety.

FIELD

p-0003Embodiments of the present invention relate to waste water assessment. In particular, they relate to assessing waste water using microwave signals.

BACKGROUND

p-0004Private and commercial properties include waste water drainage systems for draining waste water into public sewers. The water bill received by an owner or a tenant of a property may be estimated. The estimation may depend upon the amount of water that is used by the property and the surface area of land associated with the property, rather than an accurate assessment of the amount of water that is drained away from the property.

p-0005Waste water from some properties may include more impurities than waste water from others. Waste water from some properties may include illegal discharge such as suspended metals (for example, chrome, zinc or copper) and paint. At present, many water companies are unable to assess which properties these are and consequently, the water companies are unable to take appropriate action.

BRIEF DESCRIPTION OF VARIOUS EMBODIMENTS OF THE INVENTION

p-0006According to various, but not necessarily all, embodiments of the invention there is provided waste water assessment apparatus, comprising: transceiver circuitry configured to transmit a microwave signal and to receive one or more reflections of the microwave signal; and processing circuitry configured to process the one or more reflections of the microwave signal to determine one or more characteristics of waste water flowing through a conduit.

p-0007The processing circuitry may be configured to process the one or more reflections of the microwave signal to determine the amount of waste water flowing through the conduit. The processing circuitry may be configured to determine the amount of waste water flowing through the conduit at a particular time by determining a distance between the transceiver circuitry and a surface of the waste water flowing through the conduit. The at least one property may be the amplitude of the first reflection of the microwave signal relative to the amplitude of the transmitted microwave signal.

p-0008The processing circuitry may be configured to determine the amount of waste water flowing through the conduit at a particular time by processing at least one property of a first reflection of the microwave signal. The processing circuitry may be configured to determine the amount of waste water that has flowed through the conduit over a period of time by processing at least one property of a first reflection of the microwave signal. The at least one property may be the time elapsed between the transmission of the microwave signal and the reception of the first reflection of the microwave signal.

p-0009The transceiver circuitry may be configured to transmit a microwave signal periodically over a period of time. The processing circuitry may be configured to process reflections of the periodically transmitted microwave signals to estimate the quantity of water that has flowed through the conduit over the period of time.

p-0010The processing circuitry may be configured to process the one or more reflections of the microwave signal to determine whether one or more impurities are present in the waste water.

p-0011The one or more impurities may comprise one or more hydrocarbons and/or one or more metals. The processing circuitry may be configured to determine whether one or more impurities are present in the waste water by determining at least one of: an amplitude, phase, frequency, polarization and degree of scattering of one or more reflections of the microwave signal.

p-0012The processing circuitry may be configured to process the one or more reflections of the microwave signal to determine the quantity of a particular impurity present in the waste water.

p-0013The transmitted microwave signal may be an ultra wide band microwave signal.

p-0014The waste water apparatus may further comprise a waveguide configured to guide transmitted microwave signals through a wall of the conduit.

p-0015According to various, but not necessarily all, embodiments of the invention there is provided waste water assessment apparatus, comprising: processing circuitry; and memory circuitry storing computer program instructions that, when executed by the processing circuitry, cause the processing circuitry to perform at least the following: processing one or more reflections of a microwave signal to determine one or more characteristics of waste water flowing through a conduit.

p-0016According to various, but not necessarily all, embodiments of the invention there is provided a method, comprising: transmitting a microwave signal; and processing one or more reflections of the microwave signal to determine one or more characteristics of waste water flowing through a conduit.

p-0017The method may further comprise: fitting transceiver circuitry, for transmitting the microwave signal, to a position adjacent to the conduit.

p-0018According to various, but not necessarily all, embodiments of the invention there is provided a computer program comprising computer program instructions that, when executed by processing circuitry, enable the above method to be performed.

p-0019The above computer program may be stored by computer readable storage medium. The computer readable medium may be non-transitory.

p-0020According to various, but not necessarily all, embodiments of the invention there is provided waste water assessment apparatus, comprising: transceiver circuitry configured to transmit a microwave signal and to receive one or more reflections of the microwave signal; and processing circuitry configured to process the one or more reflections of the microwave signal, in order to quantify waste water flow through a closed conduit.

p-0021According to various, but not necessarily all, embodiments of the invention there is provided waste water assessment apparatus, comprising: processing circuitry; and memory circuitry storing computer program instructions that, when executed by the processing circuitry, cause the processing circuitry to perform at least the following: processing one or more reflections of a microwave signal, in order to quantify waste water flow through a closed conduit.

p-0022According to various, but not necessarily all, embodiments of the invention there is provided a method, comprising: transmitting a microwave signal; and processing one or more reflections of the microwave signal, in order to quantify waste water flow through a closed conduit.

BRIEF DESCRIPTION OF THE DRAWINGS

p-0023For a better understanding of various examples of embodiments of the present invention reference will now be made by way of example only to the accompanying drawings in which:

p-0024<figref idrefs="DRAWINGS">FIG. 1</figref> illustrates a first example of waste water assessment apparatus;

p-0025<figref idrefs="DRAWINGS">FIG. 2</figref> illustrates a second example of waste water assessment apparatus;

p-0026<figref idrefs="DRAWINGS">FIG. 3</figref> illustrates the waste water assessment apparatus in operation;

p-0027<figref idrefs="DRAWINGS">FIG. 4</figref> illustrates a flow diagram of a method; and

p-0028<figref idrefs="DRAWINGS">FIG. 5</figref> illustrates a graph illustrating transmitted and received microwave signals.

DETAILED DESCRIPTION

p-0029Embodiments of the invention relate to an apparatus for assessing waste water. For example, the apparatus may be used to assess the quality and/or the quantity of waste water being drained from a property.

p-0030The Figures illustrate waste water assessment apparatus <b>10</b>, comprising: transceiver circuitry <b>14</b> configured to transmit a microwave signal and to receive one or more reflections of the microwave signal; and processing circuitry <b>12</b> configured to process the one or more reflections of the microwave signal <b>70</b>, <b>75</b>, <b>80</b> to determine one or more characteristics of waste water flowing in a conduit <b>90</b>.

p-0031<figref idrefs="DRAWINGS">FIG. 1</figref> illustrates a first example of waste water assessment apparatus <b>10</b>. The waste water assessment apparatus <b>10</b> comprises transceiver circuitry <b>14</b> and processing circuitry <b>12</b>. The processing circuitry <b>12</b> is configured to provide outputs to transceiver circuitry <b>14</b> and to receive inputs from the transceiver circuitry <b>14</b>. The processing circuitry <b>12</b> may consist of a single processor, or may comprise multiple processors. In some embodiments of the invention, the processing circuitry <b>12</b> is local to the transceiver circuitry <b>14</b>. In other embodiments of the invention, at least some aspect of the processing circuitry <b>12</b> is remote from the transceiver circuitry <b>14</b>. This will be described in further detail below.

p-0032The transceiver circuitry <b>14</b> is configured to transmit and receive microwave signals. The microwave signals may, for example, have a frequency in the range 300 MHz to 300 GHz. In particular, the microwave signals may have a frequency in the range 1 GHz to 50 GHz. The microwave signals may, for example, be Ultra Wide Band (UWB) signals.

p-0033<figref idrefs="DRAWINGS">FIG. 2</figref> illustrates a second example of waste water assessment apparatus <b>10</b>. The waste water assessment apparatus <b>10</b> comprises the processing circuitry <b>12</b> and the transceiver circuitry <b>14</b> described above in relation to <figref idrefs="DRAWINGS">FIG. 1</figref>.

p-0034The waste water assessment apparatus <b>10</b> illustrated in <figref idrefs="DRAWINGS">FIG. 2</figref> further comprises a waveguide <b>11</b> and memory circuitry <b>19</b>. The waveguide <b>11</b> is optional and configured to guide microwaves transmitted by the transceiver circuitry <b>14</b> in a particular direction. The waveguide <b>11</b> is also configured to guide reflected microwave signals towards the transceiver circuitry <b>14</b>.

p-0035The processing circuitry <b>12</b> is configured to read from and to write to the memory circuitry <b>19</b>. The memory circuitry <b>19</b> is illustrated as storing reference data <b>23</b> and a computer program <b>20</b> comprising computer program instructions <b>22</b>. The reference data <b>23</b> may be a look-up table and will be described in further detail below. The computer program instructions <b>22</b> control the operation of the processing circuitry <b>12</b>, when executed by the processing circuitry <b>12</b>.

p-0036The computer program <b>20</b> may arrive at the apparatus <b>10</b> via any suitable delivery mechanism <b>30</b>. The delivery mechanism <b>30</b> may be, for example, a non-transitory computer-readable storage medium, a computer program product, a memory device, a record medium such as a CD-ROM or DVD, or an article of manufacture that tangibly embodies the computer program <b>20</b>.

p-0037Although the memory circuitry <b>19</b> is illustrated as a single component it may be implemented as one or more separate components some or all of which may be integrated/removable and/or may provide permanent/semi-permanent/dynamic/cached storage.

p-0038The elements <b>11</b>, <b>12</b>, <b>14</b> and <b>19</b> illustrated in <figref idrefs="DRAWINGS">FIG. 2</figref> are operationally coupled and any number or combination of intervening elements can exist (including no intervening elements).

p-0039A method according to embodiments of the present invention will now be described in relation to <figref idrefs="DRAWINGS">FIGS. 3 to 5</figref>.

p-0040<figref idrefs="DRAWINGS">FIG. 3</figref> illustrates part of the waste water assessment apparatus <b>10</b> in operation. The transceiver circuitry <b>14</b> and the waveguide <b>11</b> are positioned adjacent a conduit <b>90</b>. The waveguide <b>11</b> is situated between the transceiver circuitry <b>14</b> and an outer surface of the conduit <b>90</b>. An attachment device may be provided to hold the waveguide <b>11</b> and the transceiver circuitry <b>14</b> in place adjacent the conduit <b>90</b>. The transceiver circuitry <b>14</b> and the waveguide <b>11</b> may be fitted to the conduit <b>90</b> at the time a building is being built, or they may be fitted retroactively to a conduit <b>90</b> of an old building.

p-0041The conduit <b>90</b> may, for example, be a waste water pipe of a property that channels flowing waste water <b>85</b> away from the property. For example, the waste water pipe may be made from clay or a plastics material.

p-0042The shape of the conduit <b>90</b> is defined by a continuous circumferential wall <b>83</b>. In this instance, the conduit <b>90</b> is considered to be ‘closed’ because the illustrated conduit <b>90</b> does not include an opening in its circumferential wall <b>83</b>.

p-0043In this example, the conduit <b>90</b> has a circular cross section. In other examples, the cross section of the conduit <b>90</b> may be non-circular. The illustrated conduit <b>90</b> contains waste water <b>85</b> and air <b>95</b>.

p-0044The waveguide <b>11</b> is configured to guide microwave signals transmitted by the transceiver circuitry <b>14</b> through the wall <b>83</b> of the conduit <b>90</b> and into the conduit <b>90</b>. The waveguide <b>11</b> is also configured to guide reflections of the microwave signals travelling through the wall <b>83</b> into the transceiver circuitry <b>14</b>.

p-0045In this particular example, the processing circuitry <b>12</b> and the memory circuitry <b>19</b> are remote from transceiver circuitry <b>14</b>. The processing circuitry <b>12</b> is connected to transceiver circuitry <b>14</b> by a remote communication link <b>17</b>. The remote communications link <b>17</b> may be wired and may be used to provide power to the transceiver circuitry <b>14</b>. In this example, the remote communication link <b>17</b> comprises an optical fibre. In other examples, the remote communication link <b>17</b> may, for example, be wireless.

p-0046As mentioned above, in alternative embodiments of the invention, the processing circuitry <b>12</b> and the memory circuitry <b>19</b> may be situated adjacent to the transceiver circuitry <b>14</b>. For example, the transceiver circuitry <b>14</b>, the processing circuitry <b>12</b> and the memory circuitry <b>19</b> may be located in the same housing.

p-0047<figref idrefs="DRAWINGS">FIG. 4</figref> illustrates a flow chart of a method. At block <b>100</b> of <figref idrefs="DRAWINGS">FIG. 4</figref>, the transceiver circuitry <b>14</b> transmits a microwave signal <b>50</b> at a time t₁. For example, the microwave signal <b>50</b> may be a UWB pulse signal spanning a wide frequency band. <figref idrefs="DRAWINGS">FIG. 3</figref> illustrates the microwave signal <b>50</b> travelling through the wall <b>83</b> of the conduit <b>90</b>.

p-0048<figref idrefs="DRAWINGS">FIG. 5</figref> illustrates an amplitude-time graph <b>40</b> illustrating transmitted and received microwave signals. <figref idrefs="DRAWINGS">FIG. 5</figref> illustrates the microwave signal <b>50</b> being transmitted at a time t₁.

p-0049The interaction between microwaves and their medium of propagation depends upon the permittivity of the medium. An interface between different propagation mediums will result in a microwave being strongly reflected if the contrast in the permittivity of the mediums is large.

p-0050In this example, the permittivity of the air <b>95</b> is much lower than the permittivity of the waste water <b>85</b>. Thus, when the microwave signal <b>50</b> meets the surface <b>82</b> of the waste water <b>85</b>, a portion of the microwave signal <b>50</b> is reflected and the remainder propagates into the waste water <b>85</b>.

p-0051The dotted arrow <b>70</b> indicates a reflected portion of the microwave signal <b>50</b> travelling back towards the transceiver circuitry <b>14</b>. This first reflection <b>70</b> of the microwave signal <b>50</b> is received by the transceiver circuitry <b>14</b> at a time t₂.

p-0052As the remaining portion of the microwave signal <b>50</b> propagates through the waste water <b>85</b>, it is reflected almost continuously by the waste water <b>85</b> and the impurities contained within it. The nature of this second reflection <b>75</b> depends upon the content of the waste water <b>85</b>. That is, a particular material contained in the waste water <b>85</b> may cause a reflection that to occur that has one or more properties which are characteristic of that material. For example, the second reflected signal <b>75</b> may have an amplitude, phase, frequency, polarization and/or degree of scattering that indicates that a particular material is present in the waste water <b>85</b>.

p-0053The second reflected signal <b>75</b> is received over between the times indicated as t₃and t₄in <figref idrefs="DRAWINGS">FIG. 5</figref>. It will be appreciated by those skilled in the art the second reflected signal <b>75</b> contains very fine detail that is not shown in <figref idrefs="DRAWINGS">FIG. 5</figref> for clarity purposes.

p-0054<figref idrefs="DRAWINGS">FIG. 3</figref> illustrates a portion <b>60</b> of the microwave signal <b>50</b> reaching the inner surface <b>84</b> of the wall <b>83</b> of the conduit <b>90</b>. When the portion <b>60</b> reaches the interface between the waste water <b>85</b> and the inner surface <b>84</b> of the wall <b>83</b>, the large contrast in permittivity of the interface causes a further portion of the microwave signal <b>50</b> to be reflected. This third reflection <b>80</b> reaches the transceiver circuitry <b>14</b> at a time t₅. The amplitude of the third reflection <b>80</b> is typically smaller than the first reflection <b>70</b>, as illustrated in <figref idrefs="DRAWINGS">FIG. 5</figref>.

p-0055It will be appreciated by those skilled in the art that further reflections of the microwave signal <b>50</b> may occur which are not illustrated in <figref idrefs="DRAWINGS">FIG. 5</figref> for clarity purposes. For example, a further reflection may occur when the when the third reflected signal <b>80</b> crosses the interface between the waste waster <b>85</b> and the air <b>95</b>.

p-0056The transceiver circuitry <b>14</b> may be configured to determine the times t₂, t₃, t₅that the first, second and third reflections <b>70</b>, <b>75</b>, <b>80</b> are received, relative to the time at which the microwave signal <b>50</b> is transmitted. This information, along with one or more of the reflected signals <b>70</b>, <b>75</b> and <b>80</b>, may be provided to the processing circuitry <b>12</b> via the communication link <b>17</b>.

p-0057At block <b>101</b> of <figref idrefs="DRAWINGS">FIG. 4</figref>, one or more of the reflections <b>70</b>, <b>75</b> and <b>80</b> of the transmitted microwave signal <b>50</b> are processed by the processing circuitry <b>12</b> to determine one or more characteristics of the waste water <b>85</b> flowing through the conduit <b>90</b>. Determining one or more characteristics of the waste water <b>85</b> may include one or more of the following: quantifying the waste water flow through the conduit <b>90</b>, determining which impurities are present in the waste water <b>85</b>, and determining the quantity of a particular impurity that is present in the waste water <b>85</b>.

p-0058Quantifying the waste water flow through the conduit <b>90</b> may involve determining the amount of waste water that is present in the conduit <b>90</b> at a particular instance in time, and/or determining the amount of waste water <b>85</b> that has flowed (or is flowing) through the conduit <b>90</b> over a period of time.

p-0059In order to determine the amount of waste water <b>85</b> contained in the conduit <b>90</b> at a particular time. For example, the processing circuitry <b>12</b> may determine the distance between the transceiver circuitry <b>14</b> and the surface <b>82</b> of the waste water <b>85</b>. The processing circuitry <b>12</b> may determine this distance by processing at least one property of the first reflection <b>70</b> of the transmitted microwave signal <b>50</b>. In this example, the at least one property is the time that elapsed between the transmission of the microwave signal <b>50</b> and the reception of the first reflection <b>70</b> of the microwave signal <b>50</b> (t₂-t₁). Alternatively, the at least one property may be the amplitude of the first reflection <b>70</b>, relative to the amplitude of the transmitted microwave signal <b>50</b>.

p-0060If the distance d between the transceiver circuitry <b>14</b> and the surface <b>82</b> of the waste water <b>85</b> is known, and the dimensions of the conduit <b>90</b> and the waveguide <b>11</b> are known, the height h of the waste water <b>85</b> can be found.

p-0061If the dimensions of the conduit <b>90</b> are not known, the diameter of the conduit <b>90</b> can be estimated by determining the time that elapsed between the transmission of the microwave signal <b>50</b> and the reception of the third reflection <b>80</b> (t₅-t₁).

p-0062Once the height h of the waste water <b>85</b> is known and the dimensions of the conduit <b>90</b> are also known, the hydraulic radius R_hcan be calculated using the following equation:

p-0063<maths id="MATH-US-00001" num="00001"><math overflow="scroll"><mrow><msub><mi>R</mi><mi>h</mi></msub><mo>=</mo><mfrac><mi>A</mi><mi>P</mi></mfrac></mrow></math></maths>

p-0064where: A=the cross sectional area of flow of the waste water <b>85</b> and P=the wetted perimeter of the conduit <b>90</b>.

p-0065The cross sectional area of flow A indicates the amount of waste water <b>85</b> flowing through the conduit <b>90</b> at a particular time.

p-0066The average cross-sectional velocity or flow of the waste water <b>85</b> in the conduit <b>90</b> can be calculated using the Manning equation (also known as the Gauckler-Manning equation and the Gauckler-Manning-Strickler equation):

p-0067<maths id="MATH-US-00002" num="00002"><math overflow="scroll"><mrow><mi>V</mi><mo>=</mo><mrow><mfrac><mi>k</mi><mi>n</mi></mfrac><mo></mo><msubsup><mi>R</mi><mi>h</mi><mrow><mn>2</mn><mo>/</mo><mn>3</mn></mrow></msubsup><mo></mo><msup><mi>S</mi><mrow><mn>1</mn><mo>/</mo><mn>2</mn></mrow></msup></mrow></mrow></math></maths>

p-0068where: V=average cross-sectional velocity of the waste water <b>85</b>, k=a conversion constant equal to 1 for SI units, n is the Gauckler-Manning co-efficient, R_his the hydraulic radius and S is the slope of the waste water surface.

p-0069The Gauckler-Manning co-efficient depends upon the material that the conduit <b>90</b> is made from. The slope of the waste water surface may be estimated to be the same as the slope of the conduit <b>90</b>, which can be measured readily. Alternatively, the slope of the conduit <b>90</b> can be estimated by timing two different amounts of water travelling through the conduit <b>90</b>, and solving the relevant simultaneous equation.

p-0070When the average cross sectional velocity V has been calculated, it can be used to determine the amount of waste water (for example, the volume of waste water) that has flowed through the conduit <b>90</b> over a period of time.

p-0071In some embodiments of the invention, the transceiver circuitry <b>14</b> may be configured to transmit microwave signals 50 periodically. In these embodiments of the invention, the first reflection <b>70</b> of each microwave signal <b>50</b> may be used to estimate the quantity of waste water (for example, the volume of waste water) that is flowing or that has flowed through the conduit <b>90</b> over a period of time.

p-0072The waste water assessment apparatus <b>10</b> may be calibrated to ensure that reliable results are being provided. The apparatus <b>10</b> may, for example, be calibrated by sending a known amount of water through the conduit <b>90</b> and comparing the known amount with the amount estimated by the processing circuitry <b>12</b>.

p-0073The processing circuitry <b>12</b> may be configured to determine the nature of the flow of waste water <b>85</b> through the conduit. For example, the processing circuitry <b>12</b> may be configured to determine whether the flow of the waste water <b>85</b> is steady or turbulent. A steady flow of waste water <b>85</b> may, for example, have a reasonably constant height h within the conduit <b>90</b>. A turbulent flow of waste water <b>85</b> may have a highly variable height h.

p-0074The Manning formula described above is particularly applicable to circumstances in which the waste water <b>85</b> has a steady flow. It will be appreciated by those skilled in the art that other techniques may be used to determine the average cross sectional velocity V of the waste water <b>85</b> if the flow is considered to be turbulent.

p-0075If the processing circuitry <b>12</b> determines that the height h of the waste water <b>85</b> has been constant for longer than a threshold period of time (for example, a number of hours or longer), it may determine that the conduit <b>90</b> is at least partially blocked. The waste water assessment apparatus <b>10</b> may have an alerting device (for example, a light source such as a light emitting diode and/or an audible alarm) that alerts a user to the presence of such a blockage.

p-0076The processing circuitry <b>12</b> may also be configured to determine whether one or more impurities are present in the water. As mentioned above, when the microwave signal <b>50</b> travels through the waste water <b>85</b>, it is reflected by the impurities contained within the waste water <b>85</b>. The second reflection <b>75</b> of the transmitted microwave signal <b>50</b> has one or more properties that indicate that one or more impurities are present in the waste water <b>85</b>.

p-0077The processing circuitry <b>12</b> may be configured to process the second reflected signal <b>75</b> to determine whether it has one or more properties that are characteristic of the presence of a particular impurity or impurities. For example, the processing circuitry <b>12</b> may process the second reflected signal <b>75</b> to determine whether it has an amplitude, phase, frequency, polarization and/or degree of scattering that indicates that a particular material is present in the waste water <b>85</b>, and to determine the quantity of that material that is present in the waste water <b>85</b>. The processing circuitry <b>12</b> may be configured to perform an Inverse Fast Fourier Transform (IFFT) on the second reflected signal <b>75</b> in order to analyse it in the frequency domain. Tomographic techniques may be used to analyse the second reflected signal <b>75</b>.

p-0078The second reflected signal <b>75</b> may be processed by the processing circuitry <b>12</b> in conjunction with the reference data <b>23</b> stored in the memory circuitry <b>19</b>. For example, the reference data <b>23</b> may be a look-up table that comprises data identifying the reflected signal properties (such as amplitude, phase, frequency, polarization and/or degree of scattering) that are associated with the presence of a particular impurity in the waste water. For instance, the reference data <b>23</b> may include such reflected signal properties for a number of impurities.

p-0079When a set of properties from a particular second reflected signal <b>75</b> have been determined, the processing circuitry <b>12</b> may compare them with the properties stored in the reference data <b>23</b> to determine whether a particular impurity is present in the waste water <b>85</b> (such as hydrocarbons or metals) and also to determine how much of that impurity that is present in the waste water <b>85</b>.

p-0080In summary, embodiments of the invention enable the quantity of waste water <b>85</b> being drained from a particular property to be accurately estimated. This may advantageously enable water companies to levy more accurate charges to customers.

p-0081Embodiments of the invention also enable the quality of waste water <b>85</b> being drained from a particular property to be accurately estimated. For example, embodiments of the invention may be used to estimate which impurities are present in the waste water and the quantities that are present. This potentially provides water companies and/or government bodies with an opportunity to levy a waste water charge that is proportionate with the level of pollution that is being caused by the owners/tenants of a particular property. It also enables illegal discharge (such as hydrocarbons and metals) to be identified.

p-0082References to ‘computer-readable storage medium’, ‘computer program product’, ‘tangibly embodied computer program’ etc. or a ‘computer’, ‘processor’ etc. should be understood to encompass not only computers having different architectures such as single/multi-processor architectures and sequential (Von Neumann)/parallel architectures but also specialized circuits such as field-programmable gate arrays (FPGA), application specific circuits (ASIC), signal processing devices and other devices. References to computer program, instructions, code etc. should be understood to encompass software for a programmable processor or firmware such as, for example, the programmable content of a hardware device whether instructions for a processor, or configuration settings for a fixed-function device, gate array or programmable logic device etc.

p-0083The blocks illustrated in <figref idrefs="DRAWINGS">FIG. 4</figref> may represent steps in a method and/or sections of code in the computer program <b>20</b>. The illustration of a particular order to the blocks does not necessarily imply that there is a required or preferred order for the blocks and the order and arrangement of the block may be varied. Furthermore, it may be possible for some steps to be omitted.

p-0084Although embodiments of the present invention have been described in the preceding paragraphs with reference to various examples, it should be appreciated that modifications to the examples given can be made without departing from the scope of the invention as claimed. For example, in the exemplary embodiments of the invention described above, the conduit <b>90</b> is described as being made from clay or a plastics material. In practice, the conduit <b>90</b> may be made from metal. If so, an aperture may be created in the conduit <b>90</b> to prevent transmitted microwaves from being reflected from the outside of the conduit <b>90</b>.

p-0085UWB signals are considered to be particularly suitable for use in embodiments of the invention because they provide a fine spatial resolution, enable relatively easy extraction of target features from a reflected signal, are difficult to reproduce to the required degree of accuracy for the purpose of cheating the apparatus <b>10</b> and are unlikely to cause interference to nearby electronics. However, it will be appreciated by those skilled in the art that other forms of signal could be used.

p-0086Features described in the preceding description may be used in combinations other than the combinations explicitly described.

p-0087Although functions have been described with reference to certain features, those functions may be performable by other features whether described or not.

p-0088Although features have been described with reference to certain embodiments, those features may also be present in other embodiments whether described or not.

p-0089Whilst endeavoring in the foregoing specification to draw attention to those features of the invention believed to be of particular importance it should be understood that the Applicant claims protection in respect of any patentable feature or combination of features hereinbefore referred to and/or shown in the drawings whether or not particular emphasis has been placed thereon.