Systems and methods for wireless transmission of biopotentials

Abstract

The invention relates to wireless biotelemetry of low level bioelectric and biosensor signals by directly modulating the backscatter of a resonant circuit. Low level electrical analog or digital signals are directly applied to a resonant circuit containing a voltage-variable capacitor such as a varactor diode, that proportionally shifts the resonant frequency and so amplitude of radiofrequency backscatter in a way that represents analog bioelectric or biosensor waveform data. By strongly driving the resonant circuit with a radiofrequency source, a voltage variable capacitance can be caused to amplify the bio-signal level by a parametric process and so provide sufficient sensitivity to telemeter for low millivolt and microvolt level signals without additional amplification. A feature of the device is its simplicity and that it accomplishes both modulation and preamplification of low level sensor signals by the same variable capacitance circuit which reduces the device size and power consumption.

1 . An apparatus comprising:
 an electronic circuit configured to provide an inductance and a variable capacitance, wherein:
 the electronic circuit is configured to receive an excitation signal and an analog sensor signal; 
 the electronic circuit has a resonant frequency that varies in response to a biosignal; 
 the electronic circuit is configured to transmit a response signal when the electronic circuit receives the excitation signal and the biosignal; and 
 a characteristic of the analog signal can be determined by measuring the response signal. 
   
     
     
         2 . The apparatus of  claim 1 , wherein the biosignal is generated by a sensor selected from the group consisting of: a chemical, biochemical, magnetic, electromagnetic, physiological, and mechanical sensor. 
     
     
         3 . The apparatus of  claim 1 , wherein the electronic circuit is configured to transmit the response signal wirelessly. 
     
     
         4 . The apparatus of  claim 1 , wherein the characteristic of the analog signal is an amplitude of the analog signal. 
     
     
         5 . The apparatus of  claim 1 , wherein the characteristic of the analog signal is a frequency of the analog signal. 
     
     
         6 . The apparatus of  claim 1 , wherein the biosignal is generated by a biopotential. 
     
     
         7 . The apparatus of  claim 1 , wherein the excitation signal is a radio frequency signal. 
     
     
         8 . The apparatus of  claim 1 , wherein the excitation signal is a digital logic signal. 
     
     
         9 . The apparatus of  claim 1 , wherein the electronic circuit further comprises an isolating resistor. 
     
     
         10 . The apparatus of  claim 1 , wherein the electronic circuit is configured to receive the biosignal in vivo. 
     
     
         11 . The apparatus of  claim 10 , wherein the electronic circuit is configured to be implanted sub-cutaneously in a test subject. 
     
     
         12 . The apparatus of  claim 11 , wherein the electronic circuit is configured to be inserted with a needle into the test subject. 
     
     
         13 . The apparatus of  claim 11 , wherein the electronic circuit is configured to pass through the lumen of a 1 millimeter syringe needle. 
     
     
         14 . The apparatus of  claim 10 , wherein the electronic circuit is configured to be placed on the skin surface of a test subject. 
     
     
         15 . The apparatus of  claim 1 , wherein the electronic circuit comprises a pair of varactor diodes coupled back-to-back to form an equivalent series capacitance. 
     
     
         16 . The apparatus of  claim 1 , further comprising a remote exciter configured to emit the excitation signal at a frequency equivalent to the resonant frequency of the electronic circuit when an analog sensor signal is not being applied to the electronic circuit. 
     
     
         17 . The apparatus of  claim 1 , wherein the excitation signal has a frequency between 30 MHz and 10 GHz. 
     
     
         18 . The apparatus of  claim 1 , wherein the excitation signal has a frequency between 100 MHz and 3 GHz. 
     
     
         19 . The apparatus of  claim 1 , wherein the excitation signal induces a voltage between 0.5 and 5.0 volts in the electronic circuit. 
     
     
         20 . A method of measuring a biocharacteristic, the method comprising:
 providing an electronic circuit configured to measure a biopotential;   providing an excitation signal to the electronic circuit;   generating a biosignal with the biopotential and transmitting the biosignal to the electronic circuit;   transmitting a response signal from the electronic circuit; and   measuring the response signal to determine a characteristic of the biosignal.   
     
     
         21 . The method of  claim 20 , wherein electronic circuit comprises a resonant frequency that is variable. 
     
     
         22 . The method of  claim 20 , wherein the electronic circuit is configured to provide an inductance and a variable capacitance. 
     
     
         23 . The method of  claim 20 , wherein electronic circuit comprises a base resonant frequency when a biosignal is not transmitted to the electronic circuit, and wherein the excitation signal is provided at the base resonant frequency. 
     
     
         24 . The method of  claim 20 , wherein the biosignal is generated by a sensor selected from the group consisting of: a chemical, biochemical, magnetic, electromagnetic, physiological, and mechanical sensor. 
     
     
         25 . The method of  claim 20 , wherein the characteristic of the biosignal is an amplitude of the biosignal. 
     
     
         26 . The method of  claim 20 , wherein the characteristic of the biosignal is a frequency of the biosignal. 
     
     
         27 . The method of  claim 20 , wherein the electronic circuit transmits the response signal wirelessly. 
     
     
         28 . The method of  claim 20 , wherein the excitation signal is a radio frequency signal. 
     
     
         29 . The method of  claim 20 , wherein the electronic circuit further comprises an isolating resistor. 
     
     
         30 . The method of  claim 20 , wherein the electronic circuit receives the biosignal in vivo. 
     
     
         31 . The method of  claim 30 , further comprising implanting the electronic circuit sub-cutaneously in a test subject. 
     
     
         32 . The method of  claim 31 , further comprising implanting the electronic circuit in a test subject with a needle. 
     
     
         33 . The method of  claim 32 , wherein the needle is a hollow needle. 
     
     
         34 . The method of  claim 31 , wherein the electronic circuit is configured to pass through the lumen of a 1 millimeter syringe needle. 
     
     
         35 . The method of  claim 30 , further comprising placing the electronic circuit on the skin surface of a test subject. 
     
     
         36 . The method of  claim 20 , wherein the electronic circuit comprises a pair of varactor diodes coupled back-to-back to form an equivalent series capacitance. 
     
     
         37 . The method of  claim 20 , further comprising using a remote exciter to emit the excitation signal at a frequency equivalent to the resonant frequency of the electronic circuit when an analog sensor signal is not being applied to the electronic circuit. 
     
     
         38 . The method of  claim 20 , wherein the excitation signal has a frequency between 30 MHz and 10 GHz. 
     
     
         39 . The method of  claim 20 , wherein the excitation signal has a frequency between 100 MHz and 3 GHz. 
     
     
         40 . The method of  claim 20 , wherein the excitation signal induces a voltage between 0.5 and 5.0 volts in the electronic circuit. 
     
     
         41 . An apparatus of electronic components constituting a device such that a voltage variable capacitive reactance is coupled to an inductance forming a resonant circuit, wherein low level analog electrical potentials from high impedance bioelectrical or biosensor sources applied to this circuit will vary the said capacitive reactance and so change the resonance of said circuit in proportion to the amplitude of the analog waveform envelope. 
     
     
         42 . The device of  claim 41 , wherein the capacitive reactance is provided by at least one electronic component. 
     
     
         43 . The device of  claim 42 , wherein the electronic component is a varactor diode. 
     
     
         44 . The device of  claim 41 , wherein the capacitive reactance is provided by p-n junction capacitance. 
     
     
         45 . The device of  claim 41 , further defined as comprising a remote radio exciter tuned to the resonant frequency of the system of components such that sufficient signal is induced in the said inductance that the assembly will detectably backscatter the radio exciter signal as well as generate remotely detectable radio harmonics of said radio exciter. 
     
     
         46 . The device of  claim 45 , further defined as comprising a radio receiver that detects and demodulates the backscattered signals, the demodulation process following those techniques, wherein such methods may include direct conversion demodulation, AM, FM, or phase demodulation so as to reproduce the original modulation signal. 
     
     
         47 . A method of using the device of  claim 45 , wherein the voltage variable capacitive reactance is electrically driven by an applied radio exciter signal known as a pump signal, of sufficient amplitude such that a device having time varying capacitance reactance in combination with the inductance forming a resonant circuit results in a parametric amplification of the electrical signal modulation according to principles of parametric amplification, the amplification process then substantially improving the sensitivity of the device to modulating signals. 
     
     
         48 . A method of generating a bias voltage needed for the proper electrical operating point of the variable capacitance by a method of summing the bioelectrical or biosensor input signal with an electrical offset potential, wherein the offset potential may be generated by a small conventional on-device battery generated by dissimilar metals constituting the two biopotential electrodes used to detect the bioelectrical signal, the said bias voltage naturally resulting from the use of electrode metals having dissimilar half-cell potentials. 
     
     
         49 . The method of  claim 48 , wherein the device is implanted within the human body and connected to biopotential electrodes to telemeter bioelectrical signals originating from the heart, brain, and nervous system. 
     
     
         50 . The method of  claim 48 , wherein the device is connected to a biochemical or physical sensor wherein signals from the sensor are wirelessly transmitted to a base station. 
     
     
         51 . The method of  claim 48 , wherein the device is used to monitor the functions of brain electrical activity for the purposes of diagnosis and detection of neurological disorders of a bioelectrical nature such as epilepsy. 
     
     
         52 . The method of  claim 48 , wherein the device is placed in or on the heart to monitor the bioelectrical activity of the heart for purposes of control of devices which control the heart rhythm and electrical functionality.