Patent Description:
Emergency rescue equipment having harmonic radars have been used for a long time in search and rescue operations throughout the world. In a typical avalanche scenario, a skier is lost in an avalanche and a rescue team arrives shortly thereafter, the skier is equipped with an emergency rescue equipment having a reflector. The rescue team is equipped with a detector that transmits a signal with a transmit frequency. When the reflector on the skier receives this signal, the reflector converts the frequency of the signal to a multiple thereof and transmit the converted signal back to the detector. This means that the detector transmits on a first frequency and receives on a multiple of the first frequency, this information is then used to determine the position of the skier.

However, the tuning of the reflector in the emergency rescue equipment involves tuning the antenna for receiving on the first frequency and transmitting on a multiple of the first frequency. Furthermore, a conventional reflector uses a non-linear element such as a diode for resonance and the antenna needs to be matched to this element in order to provide sufficient power for the frequency conversion and retransmission of the converted signal. An example of a harmonic reflector is provided in <CIT>. This patent provides a guideline for matching of the components of a harmonic reflector by means of transmission line sections.

According to prior art, such as disclosed above, the skilled person is mainly focused on providing a good efficiency in terms of reflected power at a single frequency.

If a conventional reflector is placed in emergency rescue equipment with different properties, a compromise must be made in order to minimize the impact of the object on the reflector. The conventional reflector is designed for a typical electromagnetic surrounding of the object. Therefore, a conventional reflector is designed to be mounted on objects with similar properties such as ski-boots or ski-helmets.

According to prior-art, such as <CIT>, the antenna is encapsulated in a dielectric, which solves the problem if a reflector is mounted inside a ski-boot or attached to the outside of the ski-boot.

However, the known solutions exhibit problems related to detection of objects with large differences in size and properties, due to the objects electromagnetic interaction with the reflector.

The present invention aims at solving that problem.

The above-mentioned problem is solved by means of an emergency rescue equipment having a harmonic reflector circuit according to claim <NUM>, which reflects an incoming signal at a receive frequency at a transmit frequency being a multiple of the receive frequency, wherein the harmonic radar reflector is designed for a broadband response.

Prior-art harmonic reflectors provide narrow band response, this is due to the fact that prior-art harmonic reflectors are mainly tuned to minimize return-loss at the specific receive frequency which means that a large amount of incoming energy to the harmonic radar is transferred to the non-linear element. The harmonic reflector may be tuned for a narrow band response; this further implies that the prior-art harmonic reflector is sensitive for electromagnetic interaction with the object it is attached to.

Prior-art harmonic reflectors are designed to maximize performance for a single constant environment. When the reflector is placed in an environment with different properties the performance will be degrade. This is mainly due to that the change in the electromagnetic properties result in different antenna impedance, resulting in a poor impedance match between the reflector antenna and the non-linear element.

The present invention provides an emergency rescue equipment having a harmonic reflector circuit comprising an antenna connected to a non-linear circuit via a matching circuit and a casing that full or in part encloses the harmonic reflector circuit, wherein the harmonic reflector circuit is configured to receive a signal at a receive frequency (fRX), and configured to re-transmit said received signal at a transmit frequency (fTX), where the transmit frequency is a multiple of the receive frequency, wherein the receive frequency (fRX) is in an interval from a first frequency to a second frequency, where: the first frequency is at least <NUM>; and the second frequency is at least <NUM> higher than the first frequency; the received signal is transmitted at the transmit frequency (fTX) with an output power (Pout) of at least <NUM>% of the maximum available output power (Pmax) for a frequency in the transmit frequency range from the multiple of the first frequency to the same multiple of the second frequency. This allows detection of objects with large differences in material and size, due to the broadband behaviour of the harmonic reflector circuit. Using an emergency rescue equipment in an environment with varied electromagnetic properties may degrades the performance. This degradation is due to the change in the electromagnetic properties result in different antenna impedance, resulting in a poor impedance match between the reflector antenna and the non-linear element. For example, such varied electromagnetic properties may for example be by enclosing the harmonic reflector circuit in casings of different materials, by having different material between the harmonic reflector circuit and the signal that is transmitted by the rescue team or by different humidity's. By utilizing a harmonic reflector circuit with a broadband behaviour, the emergency rescue equipment may be detected in in a wide span of surroundings where prior art equipment tuned for a specific receive frequencies would be vulnerable. For example, by utilizing a harmonic reflector circuit with a broadband behaviour, the emergency rescue equipment would be more robust and be functional in more numerous types of casings and situations. Thereby the safety of the user can be increased.

According to an aspect, the first frequency is <NUM> and the second frequency may be <NUM>.

According to an aspect, the maximum available output power (Pmax) may be at least <NUM>% of the incoming radiated power at the antenna.

According to an aspect, the transmit frequency fTX may be the double receive frequency fRX.

According to an aspect, the harmonic reflector may comprise a substrate with a metal film.

According to an aspect, the harmonic reflector may comprise a flexible substrate with a metal film.

According to an aspect, the antenna and parts of the matching circuit may be formed in the metal film.

According to an aspect, the harmonic reflector may comprise a diode as the non-linear element.

According to an aspect, the casing may comprise a material having a dielectric constant in the range of <NUM> and <NUM>.

According to an aspect, the casing may comprise a material having a dielectric constant in the range of <NUM> and <NUM>. This may for example be different plastic materials, such as polyurethane foam, PVC, Bakelite, polystyrene, polyvinyl, nylon and/or rubber.

According to an aspect, the casing may comprise a material having a dielectric constant in the range of <NUM> and <NUM>. This may for example be different glass materials, such as silicate glass, fused quartz, soda-lime-silica glass, sodium borosilicate glass, lead oxide glass, aluminosilicate glass and/or germanium oxide glass.

According to an aspect, the casing may comprise a material having a dielectric constant in the range of <NUM> and <NUM>. This may for example be water in different states and with different additives.

According to an aspect, the casing may comprise a material having a dielectric constant in the range of <NUM> and <NUM>. This may for example be vacuum or air in different states or pressures and with different additives.

According to an aspect, the casing may comprise a material that shifts the operating frequency range of the harmonic reflector circuit.

According to an aspect, the operating frequency range of the harmonic reflector may be between the first frequency and the second frequency.

According to an aspect, the operating frequency range of the harmonic reflector may be the span of frequencies between the first frequency and the second frequency.

According to an aspect, the operating frequency range may be shifted by at least partially covering the emergency rescue equipment in a liquid.

According to an aspect, the casing may have a first and a second state, in which the operating frequency range is shifted in the second state in comparison to the first state.

According to an aspect, the casing may comprise a material having a first dielectric constant in a first state and a second dielectric constant in a second state, in which the operating frequency range is shifted in the second state in comparison to the first state; wherein the first state is being dry and the second state is being wet.

According to an aspect, the casing may be made of leather. For example, the casing may be or be a part of a wearable, clothing or a tag. For example, the casing may be a belt, boots, shoes, a bracelet, other wearables, a pendant or similar.

According to an aspect, the casing may be made of fabric. For example, the casing may be or be a part of a wearable, clothing or a tag. For example a jacket, a ski jacket a wind jacket, trousers, a backpack or similar.

According to an aspect, the casing may be made of plastic. For example, the casing may be or be a part of a wearable, clothing or a tag.

According to an aspect, the casing may be a shoe. The harmonic reflector circuit may for example be mounted on the outside of the shoe or in an internal compartment. The harmonic reflector circuit may also be cast solid as a part of the shoe. The shoe may for example be a boot, a hiking shoe, a ski boot and/or an ordinary shoe.

According to an aspect, the casing may be a life jacket. The harmonic reflector circuit may for example be mounted on the outside of the life jacket or in an internal compartment. The harmonic reflector circuit may also be cast solid as a part of the life jacket. The life jacket may be inflatable or solid.

According to an aspect, the casing may be a bracelet. The harmonic reflector circuit may for example be mounted on the outside of the bracelet or in an internal compartment.

Further features and advantages of the present invention will be presented in the following detailed description of exemplifying embodiments of the invention with reference to the annexed drawing.

<FIG> shows a harmonic reflector circuit, generally designated <NUM>, and a detector, generally designated <NUM>.

The detector <NUM> transmits a signal S1 at a frequency fRX this signal S1 is received by the harmonic reflector circuit <NUM> and converted and transmitted as a second signal S2 at a frequency fTX by the harmonic reflector circuit <NUM>. The harmonic reflector circuit <NUM> receives the incoming signal S1 by means of an antenna <NUM>. The antenna <NUM> is connected to a matching circuit <NUM> which provides an impedance match between the antenna <NUM> and the non-linear circuit <NUM> for both the frequency fRX and the frequency fTX. The impedance matching is crucial for a conversion with low losses from the first signal S1 to the second signal S2, at their frequency fRX and fTX, respectively.

In <FIG> a typical response from the harmonic reflector <NUM> is disclosed. A first curve <NUM> shows the reflected power P from a signal transmitted at frequency fc, the bandwidth of the curve <NUM> depends on the impedance matching between the non-linear circuit <NUM> and the antenna <NUM>, and of course the bandwidth of the antenna <NUM> and the non-linear circuit <NUM>, themselves.

In <FIG> the harmonic reflector circuit <NUM> is shown together with a ground plane <NUM>. The ground plane <NUM> may be a physical object, such as a helmet or a human. The ground plane <NUM> causes a dielectric coupling to the harmonic reflector circuit <NUM> which changes the properties of the matching circuit <NUM>. This means that the reflected power at frequency fc decreases from P to P' on corresponding curve <NUM>. In a prior-art harmonic reflector circuit <NUM> the matching circuit is configured to provide matching for a predetermined ground plane at a predetermined distance and a predetermined dielectric environment. For example the harmonic reflector circuit <NUM> is dimensioned for mounting on a ski boot or a helmet i.e. ground planes of the same order of magnitude and similar dielectric properties. This means that a conventional harmonic reflector circuit <NUM> mounted on a pair of glasses or mounted on a container will provide very different responses in terms of reflected power P, partly due to the large differences of the ground planes and dielectric properties of the surroundings.

The present inventors have realized that the problem of varying properties of the ground plane and dielectric properties are main contributors related to the problem of detecting harmonic radar reflections from objects of various properties.

The present inventors have realized that a solution to the above problem related to harmonic radar reflections from objects of varying properties, is provided by increasing the bandwidth of the harmonic reflector circuit <NUM>. This can be understood by studying <FIG> in which the reflected harmonic power P is shown as a function of frequency f. The first curve <NUM> illustrates the reflected harmonic power around the center frequency fc, this first curve provides a larger bandwidth compared to the prior-art curve <NUM>. Assume that a ground plane <NUM> is placed such that the coupling from the ground plane to the harmonic reflector circuit <NUM> causes a shift of the first curve <NUM> to a second curve <NUM> with a center frequency fc'. The y-axis of <FIG> discloses the reflected power at a multiple of the frequency fRX, which is the frequency fTX. The x-axis shows the receive frequency fRX. The reflected power P decreases to P', which is much less than the decrease shown in <FIG>. This means that the reflected power P is not significantly affected by the ground plane <NUM>.

In <FIG> the reflected power P at the transmit frequency fTX is shown as a function of the receive frequency fRX from a harmonic reflector circuit <NUM> according to the present invention. The receive frequency (fRX) is in an interval from a first frequency f1 to a second frequency f2, where the first frequency f1 is at least <NUM>. The second frequency f2 is at least <NUM> larger than the first frequency. The received signal is transmitted at the transmit frequency (fTX) with an output power (Pout) of at least <NUM>% of the maximum available output power (Pmax) for a defined electromagnetic environment.

In one embodiment, the first frequency is <NUM> and the second frequency is <NUM>.

In <FIG> an embodiment of a harmonic reflector circuit, generally designated <NUM>, is drawn to scale in a top view. This harmonic reflector circuit <NUM> comprises a non-linear circuit which in this embodiment is a surface mounted diode <NUM> soldered to a metal film <NUM> of a substrate. The antenna and the matching circuit are integrally formed in the metal film <NUM> of the substrate. The harmonic reflector circuit <NUM> is drawn to scale, which means that by measuring and scaling the drawing a broadband harmonic reflector circuit <NUM> is achieved.

In <FIG> an embodiment of an emergency rescue equipment having a harmonic reflector circuit is shown. In the illustrated embodiment, the emergency rescue equipment <NUM> has two harmonic reflector circuits <NUM> and <NUM> that is enclosed by a casing <NUM> that is in the shape of a hiking boot. The emergency rescue equipment <NUM> may alternatively have a single harmonic reflector circuit or multiple harmonic reflector units. The harmonic reflector units may for example be located in the tongue of the hiking boot as the harmonic reflector unit <NUM> and/or in the quarter of the hiking boot as the harmonic reflector unit <NUM>. The harmonic reflector unit may also be located in other parts of the hiking boot or a shoe, such as the lining, the backstay, the heel, the sole, the vamp, the toe box, the counter and/or similar.

Claim 1:
An emergency rescue equipment (<NUM>; <NUM>) comprising a harmonic reflector circuit (<NUM>; <NUM>, <NUM>; <NUM>), having an antenna connected to a non-linear circuit via a matching circuit and a casing (<NUM>; <NUM>) that in full or in part encloses the harmonic reflector circuit, wherein the harmonic reflector circuit is configured to receive a signal at a receive frequency (fRX), and configured to re-transmit said received signal at a transmit frequency (fTX), wherein the transmit frequency is a multiple of the receive frequency, the harmonic reflector circuit (<NUM>; <NUM>, <NUM>; <NUM>) is characterized in that:
its bandwidth is increased such that the receive frequency (fRX) is in an interval from a first frequency to a second frequency, where:
the first frequency is at least <NUM>; and
the second frequency is at least <NUM> higher than the first frequency;
the received signal is re-transmitted at the transmit frequency (fTX) with an output power (Pout) of at least <NUM>% of a maximum available output power (Pmax).