Implantable pressure transducer
First Claim
1. In a transducer adapted for implantation beneath the skin and having a resonant L-C circuit with capacitor and inductor elements, one of the elements being variable and driven by a mechanical force sensor whereby the circuit has a variable resonant frequency which is related to the magnitude of force sensed by the sensor, and the frequency can be determined without wired connection by a remote circuit, the transducer including a housing for supporting the circuit elements and force sensor, the housing having an end adapted to be positioned closer to the skin than the inductor element when the transducer is implanted;
- the improvement comprising a coupling coil positioned adjacent and inductively coupled to the inductor element, and an antenna coil connected across and spaced from the coupling coil, the antenna coil being positioned adjacent said housing end to be closer to the skin than the inductor element to enable enhanced transmission of electromagnetic energy between the remote circuit and the resonant L-C circuit through the antenna coil.
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Accused Products
Abstract
A wireless, surgically implantable pressure transducer for measuring pressure of fluid or tissue in a body chamber such as a brain ventricle of a patient suffering hydrocephalus or a head injury. The transducer includes an inductor and a capacitor connected in parallel to form a resonant L-C circuit. One of these reactive components is variable, and a bellows (or similar pressure-sensitive force-summing device) is mechanically connected to the variable component to vary the value of capacitance or inductance and hence the resonant frequency of the L-C circuit in response to pressure changes of the fluid in which the bellows is immersed. The transducer is electromagnetically coupled to an external source of variable-frequency energy such as a grid-dip oscillator, enabling external detection of the transducer resonant frequency which is a measure of the fluid pressure being sensed. An antenna coil is inductively coupled to the transducer inductor, and is positioned in the transducer to be just beneath the skin when the housing is implanted to provide efficient coupling of the external oscillator and internal resonant circuit. A second bellows or analogous device may be coupled to a reference-pressure side of the transducer to provide improved compensation of variations in ambient temperature and atmospheric pressure.
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Citations
13 Claims
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1. In a transducer adapted for implantation beneath the skin and having a resonant L-C circuit with capacitor and inductor elements, one of the elements being variable and driven by a mechanical force sensor whereby the circuit has a variable resonant frequency which is related to the magnitude of force sensed by the sensor, and the frequency can be determined without wired connection by a remote circuit, the transducer including a housing for supporting the circuit elements and force sensor, the housing having an end adapted to be positioned closer to the skin than the inductor element when the transducer is implanted;
- the improvement comprising a coupling coil positioned adjacent and inductively coupled to the inductor element, and an antenna coil connected across and spaced from the coupling coil, the antenna coil being positioned adjacent said housing end to be closer to the skin than the inductor element to enable enhanced transmission of electromagnetic energy between the remote circuit and the resonant L-C circuit through the antenna coil.
- View Dependent Claims (2, 3)
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4. A wireless pressure transducer for implantation beneath the skin, comprising:
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an implantable housing; a resonant circuit mounted in the housing, and including capacitor and inductor elements, one of the elements being variable whereby the circuit has a variable resonant frequency, the housing having an end adapted to be positioned closer to the skin than the inductor element when the housing is implanted; pressure-sensing means secured to the housing and mechanically connected to said variable element to vary the resonant frequency of the L-C circuit responsive to pressure changes; a coupling coil positioned adjacent and inductively coupled to said inductor element; and an antenna coil electrically connected across and spaced from said coupling coil to be positioned adjacent said housing end and close to the skin for enhanced inductive coupling of the resonant circuit to an external transmitting coil of a variable-frequency oscillator. - View Dependent Claims (5, 6, 7, 8, 9, 10, 11, 12, 13)
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Specification