MICROWAVE RADIOMETER

Abstract

Radiometer for non-invasive measurement of internal tissue temperature of biological objects. The radiometer comprises, connected in series, antenna, SPDT switch, circulator, receiver including amplifier with bandpass filters, amplitude detector, narrowband low-frequency amplifier and synchronous detector, integrator, direct current power amplifier, reference voltage generator connected to the SPDT switch and synchronous detector. A Peltier element is connected to the receiver output. First and second microwave loads are installed on the Peltier element and have thermal contact with it. There is at least one temperature sensor for measuring the temperature of microwave loads. The first microwave load is adapted for connection to the SPDT switch. The SPDT switch is adapted to connect either, to a first arm of the circulator, the antenna, or the first microwave load. A second arm of the circulator is connected to the receiver, and a third arm of the circulator is connected to the second microwave load.

Claims

1. A radiometer comprising connected in series an antenna for contact with a biological subject, a SPDT switch, a circulator, a receiver including: an amplifier with bandpass filters, an amplitude detector, a narrowband low-frequency amplifier an synchronous detector, an integrator, a direct current (dc) power amplifier, and a reference voltage generator which is connected to the SPDT switch and to the synchronous detector, a Peltier element, which is connected to an output of the receiver a first microwave load and a second microwave load mounted on the Peltier element and in thermal contact therewith, at least one temperature sensor for measuring the temperature of said microwave loads, wherein the first microwave load is adapted for connection to the SPDT switch, the SPDT switch is adapted to connect either the antenna or the first microwave load to a first arm of the circulator, a second arm of the circulator is connected to the receiver, and a third arm of the circulator is connected to the second microwave load.

2. The radiometer according to claim 1, further comprising an attenuator which is mounted between an output of the first microwave load and the SPDT switch.

3. The radiometer according to claim 1, wherein the temperature sensor is mounted on the Peltier element and/or on the microwave load.

4. The radiometer according to claim 1, wherein the temperature sensor is an infrared sensor for remote temperature measurement.

5. The radiometer according to claim 1 further comprising an integrator which is connected to an output of the temperature sensor.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0034] FIG. 1 is a block diagram of the known from the prior art, null balancing radiometer according to RU Pat. No. 2082118.

[0035] FIG. 2 is a block diagram of the known from the prior art, null balancing radiometer according to the closest analogue (prototype) of the present technology, which has two nonreciprocal elements and in which the resistor is accommodated on a Peltier element.

[0036] FIG. 3 is a block diagram of an embodiment of a radiometer, according to the present technology, which has a SPDT switch and two microwave loads installed on a Peltier element and connected, correspondingly, to the circulator and SPDT switch.

[0037] FIG. 4 is a block diagram of another embodiment of the radiometer, according to the present technology, with a SPDT switch and two microwave loads installed on a Peltier element, wherein an attenuator is mounted between the first microwave load and the SPDT switch.

DETAILED DESCRIPTION OF THE NON-LIMITING EMBODIMENTS

[0038] FIG. 1 shows a block diagram of a null balancing radiometer known from the prior art, (RU Pat. No. 2082118), in which the block diagram has been adapted and is presented similarly to the present technology. This known null balancing radiometer consists of an antenna (1) for contact with a biological object and receive a noise signal coming from the biological object. From the antenna output, the microwave noise signal enters the input of an electronic modulator (2). In the modulator (2) of the radiometer according to RU Pat. No. 2082118, a SPST switch (2) is used, which closes and opens the connection of a circulator with the antenna.

[0039] The modulator is controlled by a reference voltage generator with a clock frequency of 1 kHz. When the SPST switch (2) of the modulator is ON, the noise signal from the antenna output enters a circulator (4) and then enters the input of a receiver (5). When the SPST switch (2) of the modulator is off, the noise signal from a heated resistor accommodated on the third arm of the circulator (4) is reflected from the OFF switch of the modulator and enters the input of the circulator and then the input of the receiver (5).

[0040] The receiver contains a low-noise amplifier with bandpass filters (7), an amplitude detector (8), a narrowband low-frequency amplifier (9), a synchronous detector (10), an integrator (11), a direct current amplifier (12).

[0041] At the receiver output, voltage is formed that is proportional to the difference of the heated resistor noise temperature Tr and the temperature Ta of noise coming from the antenna output

U=k(T.sub.aT.sub.r), where [0042] k is the gain of the radiometer receiver. [0043] Ta is the noise temperature from the antenna output, [0044] Tr is the noise temperature of the resistor.

[0045] This signal is amplified and comes onto the heated resistor (6), resulting in a change of its thermodynamic temperature and, consequently, the resistor noise temperature Tr. Cooling of the heated resistor was achieved by way of natural air cooling.

[0046] Due to negative feedback, voltage at the synchronous detector outlet tends toward zero, and the noise temperature of the heated resistor T.sub.r tends toward the noise temperature Ta coming from the antenna output.

[0047] As at the synchronous detector output, voltage is close to zero, the noise temperature coming from the antenna output is equal to the noise temperature of the heated resistor.

[0048] In the absence of reflections, the noise temperature Tr of the heated resistor coincides with the thermodynamic temperature measured with the help of a temperature sensor mounted on the heated resistor. To reduce the fluctuation error, voltage coming from the temperature sensor output is averaged in the integrator (14) and amplified.

[0049] FIG. 2 shows, in a presentation form similar to the present technology, a block diagram of a commercial radiometerprototype described by Vaisblat A. V. in paper Medial Radiometer RTM-01-RES, Biomedical Technologies and Radio Electronics, No. 8, 2001, P. 11-23. That prototype radiometer consists of an antenna (1), a modulator (2), a circulator (3), an isolator (15), a receiver (5), a Peltier element (16), a microwave load (6), mounted on a Peltier element (16), a temperature sensor (13) measuring the temperature of microwave load (6), an integrator (14), a reference voltage generator (3) controlling the modulator (2). Wherein, similarly to the radiometer of RU Pat. No. 2082118, the Vaisblat prototype modulator (2) includes a SPST switch (2), which can only close and open the connection between the circulator and antenna.

[0050] The receiver in the prototype consists of a low-noise amplifier with bandpass filters (7), an amplitude detector (8), a narrowband low-frequency amplifier (9), and a synchronous detector (10), and integrator (11), direct current amplifier (12).

[0051] In the prototype radiometer shown in FIG. 2, in contrast to the block diagram shown in FIG. 1, the load temperature is controlled with the help of Peltier element (16). This allows implementing both heating and cooling of the load. To increase isolation between the receiver and antenna, in the prototype radiometer a second nonreciprocal elementisolator (15)is mounted. This allows increasing isolation between the SPST switch (2) and receiver to 34 dB in the frequency spectrum of 500 MHz and reduce the level of noise coming on to the modulator (2) from the receiver (5), but enlarges outer dimensions of the device.

[0052] Thus, the prototype radiometer does not provide the required accuracy of measurement because compensation of reflections from the antenna is still insufficient, besides, the radiometer has large outer dimensions due to use of nonreciprocal elements, for example, the isolator (15), which makes it inconvenient in use.

[0053] The design of the presently claimed radiometer is explained in detail with a reference to FIGS. 3 and 4. FIG. 3 shows the first embodiment of the radiometer according to the present technology, which additionally has a second microwave load (a second resistor) installed on the Peltier element, and the modulator has a SPDT switch (2) rather than a SPST switch, which connects to the first arm of the circulator either the antenna (1) or the first load (6) (the first resistor). The SPDT switch (2) is controlled by a reference voltage generator, for example, having 1 kHz frequency. The noise signal from the output of SPDT switch (2) passes through a circulator (4) and enters a receiver (5).

[0054] The receiver (5) contains a low-noise amplifier with bandpass filters (7), an amplitude detector (8), a narrowband low-frequency amplifier (9), a synchronous detector (10), an integrator (11), a direct current amplifier (12).

[0055] During operation of the present radiometer, voltage U is formed at the receiver output, which is proportional to the difference of the noise temperature coming from the antenna and temperature Tr.sub.1 of the first heated resistor:

U=k(T.sub.aT.sub.r1), where [0056] k is the gain of the radiometer receiver, [0057] Ta is the noise temperature from the antenna output, [0058] Tr.sub.1 is the noise temperature of the first microwave load (the first resistor).

[0059] This voltage is amplified and comes on the Peltier element (16). In contrast to the block diagrams of the prior art devices shown in FIG. 1 and FIG. 2, in the present technology, two microwave loads (6) and (17) are used, that is two resistors installed on the Peltier element and having good thermal contact with the Peltier element. The first microwave load (6) is connected to the input of SPDT switch (2) of the modulator (2). The second microwave load (17) is connected to the third arm of the circulator (4).

[0060] The temperature of microwave loads is measured with the help of a temperature sensor (13), which may be mounted on the Peltier element or at least on one of the loads and has a good thermal contact with them, then the measurement signal from the temperature sensor is integrated in an additional integrator (14) connected with the temperature sensor (13), is amplified and comes onto an indicator or into a computer (19), performing the functions of a data processing unit and a control unit.

[0061] In contrast with the prior art block diagrams of FIG. 1 and FIG. 2, in the present technology, instead of the SPST switch (2), which is contained in the modulator and either connects the antenna output with the circulator or breaks the connection, a SPDT switch (2) is used, which connects either the antenna or the first microwave load to the first arm of the circulator. In this instance, at the input of the receiver (5), comparison of signals coming from the antenna (1) and from the first microwave load (6) takes place.

[0062] In some prior art solutions, attempts have also been made to use SPDT switch in radiometer designs, for example, in the design of the radiometer according to RU Pat. 2485462 published 20 Jun. 2013, between a modulator and a circulator, a directional coupler is installed, to which a two-pole switch having three inputs and two outputs is installed. In this design, three matched loads are used, wherein the first matched load is connected to a circulator, and the second and third matched loads may be commutated to the SPDT switch, and the SPDT switch in RU patent 2485462 is made with the faculty of either connecting the first output of the SPDT switch to a noise generator and the second output to the second matched load, or connecting the first output of the SPDT switch of the third matched load and the second output to the noise generator. Whereas, the modulator, directional coupler, circulator, SPDT switch, noise generator and source of current for it, as well as the first, second and third matched loads are mounted on a thermostat plate and have an equal temperature, but there is not Peltier element in this design.

[0063] Thus, the radiometer schematic according to the present technology has a simpler design, contains only two matched microwave loads, which have other connections to other elements of the design. Besides, in the presently claimed radiometer, both loads are mounted on a Peltier element, which can both heat loads and cool them, hence, loads have an equal regulated temperature that is different from the temperature of other elements of the schematic. This provides a higher accuracy of brightness temperature measurement at a minimal number of nonreciprocal elements, which reduces the outer dimensions of the design and improves convenience of its use during measurement of the internal temperature in many points of a biological object.

[0064] During radiometer operation, due to negative feedback, voltage at the synchronous detector outlet tends toward zero and noise temperature T.sub.r1 of the first load (6) comes close to the temperature of noise T.sub.a coming from the antenna output.

[0065] Due to an imperfect isolation of the circulator, a part of the receiver noise passes through the circulator (4) and enters the SPST switch (2). In the prior art prototype radiometer, which block diagram is shown in FIG. 2, noise was reflected from the open arm of SPST switch (2) and entered the receiver input. In contrast to the prior art prototype device shown in FIG. 2, in the present technology this noise is absorbed in the first load (6) and does not get to the input of receiver (5). Thanks to this, in the embodiment of the radiometer, there are lower requirement to circulator isolation and it is not necessary to install additionally an isolator as it was made in the prior art prototype (see FIG. 2). This allows almost a double decrease in the sizes of frontend of the radiometer, that is reducing the radiometer dimensions in general, which significantly simplifies radiometer manipulation during an examination, improves convenience of its use, and reduces the time required for an examination in multiple points as is the case, for example, during a breast examination.

[0066] Improvement of the measurement accuracy by compensating reflections from the input of antenna (1) in the embodiment of the radiometer is also achieved thanks to receipt in the antenna output of a noise signal from the second load (17). As it has a good thermal contact with the first load (6) through accommodation on one Peltier element, their temperatures are equal Tr.sub.1=Tr.sub.2. But since the noise temperature of the first load Tr.sub.1 is close to the temperature Ta of the noise coming from the antenna output, then the temperature Tr.sub.2 of the second load is close to the temperature of noise Ta at the antenna output. Thanks to this, a fuller compensation of the reflected noise power from the antenna is achieved and the accuracy of measuring the temperature of a biological object is improved.

[0067] It should be noted that due to losses in the circulator (4) and SPDT switch (2), the power of noise coming from the side of the second load (17) onto the antenna outlet will differ from the power of noise coming from the antenna output, therefore, a still fuller compensation of the reflected power is provided by the radiometer embodiment shown in FIG. 4.

[0068] In the radiometer embodiment shown in FIG. 4, the noise power from the output of the first microwave load (6) comes on an attenuator (18) connected between the output of the first microwave load (6) and the SPDT switch (2) and having the temperature radiometer frontend. The noise temperature T.sub.ra at the attenuator output is equal to

T.sub.ra=T.sub.r1*k.sub.ra+(1k.sub.ra)*T.sub.amb, where [0069] k.sub.ra is the transmission coefficient, [0070] T.sub.amb is the noise temperature of the radiometer frontend, [0071] Tr.sub.1 is the noise temperature of the first heated resistor (the first microwave load).

[0072] The radiometer functions so that the SPDT switch (2) connects to the first arm of the circulator either the noise signal from the output of antenna (1), the power of which is proportional to the temperature of internal tissues of a biological object, or the noise signal from the output of attenuator (18). The SPDT switch (2) is controlled by the reference voltage generator (3) having 1 kHz frequency. The noise signal from the output of SPDT switch (2) passes through the circulator (4) and enters the receiver (5).

[0073] The receiver, in the radiometer embodiment shown in FIG. 4, also consists of a low-noise amplifier with bandpass filters (7), an amplitude detector (8), a narrowband low-frequency amplifier (9), and a synchronous detector (10), an integrator (11), a direct current amplifier (12).

[0074] At the receiver output, voltage is formed that is proportional to the difference of the noise temperature Ta from the antenna output and the noise temperature T.sub.ra from the attenuator output:

U=k(T.sub.aT.sub.ra), where [0075] k is the transmission coefficient of the radiometer [0076] Ta is the noise temperature from the antenna output, [0077] Tra is the noise temperature from the attenuator output.

[0078] This voltage is amplified and comes onto the Peltier element (16). Same as in the first embodiment of the present technology shown in FIG. 3, two loads are installed on the Peltier element, which have a good thermal contact with the Peltier element. However, the first load (6) is connected to the input of attenuator (18), which is connected to the SPDT switch, while the second load is connected to the third arm of circulator (4).

[0079] The temperature of loads is measured with the help of a temperature sensor (7), which can be installed on the Peltier element and/or at least on one of the loads and has a good thermal contact with them.

[0080] Due to negative feedback, voltage at the synchronous detector outlet tends toward zero while noise temperature Tr.sub.1 of the first load comes close to the noise temperature Ta from the antenna output. Due to dissipation losses in the attenuator (18), the temperature of the first and second loads differs from the temperature Ta of noise coming from the antenna output.

[00002]$\mathrm{Tr}.Math..Math.1=\mathrm{Tr}.Math..Math.2=\frac{\mathrm{Ta}}{\mathrm{kra}}-\left(1-k_{\mathrm{ra}}\right).Math.\frac{\mathrm{Tamb}}{\mathrm{kra}},$

where [0081] k.sub.ra is the transmission coefficient of the attenuator, [0082] Tr.sub.1 is the noise temperature of the first load, [0083] Tr.sub.2 is the noise temperature of the second load, [0084] Ta is the noise temperature from the antenna output, [0085] T amb is the noise temperature of the radiometer frontend.

[0086] The power of noise coming on the antenna output on the side of the second load (17) is equal to:

Tra=Tr2*k.sub.sk.sub.cir+(1k.sub.sk.sub.cir)*Tamb, where [0087] k.sub.s is the transmission coefficient of the switch, [0088] k.sub.cir is the transmission coefficient of the circulator, [0089] Tra is the noise temperature of the attenuator, [0090] Tr.sub.2 is the noise temperature of the second load, [0091] Tamb is the noise temperature of the radiometer frontend.

[0092] If the transmission coefficient k of the attenuator coincides with the transmission coefficient of the cascade connection of the circulator and switch k.sub.sk.sub.cir, then

Tra=Ta, [0093] that is compensation of the noise reflected from the antenna input occurs.

[0094] So, in the design of radiometer according to the present technology, in the modulator a SPDT switch is used instead of a SPST switch, and two microwave loads. Wherein, the first microwave load can be connected to the SPDT switch, the second microwave load is connected to the third arm of the circulator, and the SPDT switch is made with the faculty of connecting to the first arm of the circulator either the antenna or the first microwave load. Besides, between the output of the first microwave load and the SPDT switch, the attenuator (18) is preferably installed, and in such case, the SPDT switch connects to the first arm of the circulator either the antenna (1) or the attenuator.

[0095] Such modification of the design of radiometer according to the present technology provides a higher accuracy of the non-invasive measurement of temperature of the inner tissues of biological objects with use for early diagnosis of oncological diseases, also provides reduced dimensions of the instrument, improved convenience of its use, and lower cost of its manufacture.

[0096] It should be appreciated that the technology is not limited to the particular embodiments described and illustrated herein but includes all modifications and variations falling within the scope of the invention as defined in the appended claims.